Merge pull request #174 from benbjohnson/fix-snapshot-only-restore

Fix snapshot-only restore

.github/pull_request_template.md

@@ -0,0 +1,7 @@
+Litestream is not accepting code contributions at this time. You can find a summary of why on the project's GitHub README:
+
+https://github.com/benbjohnson/litestream#open-source-not-open-contribution
+
+Web site & Documentation changes, however, are welcome. You can find that repository here:
+
+https://github.com/benbjohnson/litestream.io

.github/workflows/release.linux.yml

@@ -3,10 +3,30 @@ on:
     types:
       - created
 
-name: release
+name: release (linux)
 jobs:
-  linux:
+  build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - arch: amd64
+            cc:   gcc
+          - arch: arm64
+            cc:   aarch64-linux-gnu-gcc
+          - arch: arm
+            arm:  6
+            cc:   arm-linux-gnueabi-gcc
+          - arch: arm
+            arm:  7
+            cc:   arm-linux-gnueabihf-gcc
+
+    env:
+      GOOS:   linux
+      GOARCH: ${{ matrix.arch }}
+      GOARM:  ${{ matrix.arm }}
+      CC:     ${{ matrix.cc }}
+
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-go@v2
@@ -16,6 +36,11 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ github.token }}
 
+      - name: Install cross-compilers
+        run: |
+          sudo apt-get update 
+          sudo apt-get install -y gcc-aarch64-linux-gnu gcc-arm-linux-gnueabihf gcc-arm-linux-gnueabi
+
       - name: Install nfpm
         run: |
           wget https://github.com/goreleaser/nfpm/releases/download/v2.2.3/nfpm_2.2.3_Linux_x86_64.tar.gz
@@ -23,23 +48,24 @@ jobs:
 
       - name: Build litestream
         run: |
+          rm -rf dist
           mkdir -p dist
           cp etc/litestream.yml etc/litestream.service dist
           cat etc/nfpm.yml | LITESTREAM_VERSION=${{ steps.release.outputs.tag_name }} envsubst > dist/nfpm.yml
-          go build -ldflags "-X 'main.Version=${{ steps.release.outputs.tag_name }}'" -o dist/litestream ./cmd/litestream
+          CGO_ENABLED=1 go build -ldflags "-s -w -X 'main.Version=${{ steps.release.outputs.tag_name }}'" -o dist/litestream ./cmd/litestream
           
           cd dist
-          tar -czvf litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.tar.gz litestream
+          tar -czvf litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.tar.gz litestream
-          ../nfpm pkg --config nfpm.yml --packager deb --target litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.deb 
+          ../nfpm pkg --config nfpm.yml --packager deb --target litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.deb 
 
-      - name: Upload release binary
+      - name: Upload release tarball
         uses: actions/upload-release-asset@v1.0.2
         env:
           GITHUB_TOKEN: ${{ github.token }}
         with:
           upload_url: ${{ steps.release.outputs.upload_url }}
-          asset_path: ./dist/litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.tar.gz
+          asset_path: ./dist/litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.tar.gz
-          asset_name: litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.tar.gz
+          asset_name: litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.tar.gz
           asset_content_type: application/gzip
 
       - name: Upload debian package
@@ -48,6 +74,6 @@ jobs:
           GITHUB_TOKEN: ${{ github.token }}
         with:
           upload_url: ${{ steps.release.outputs.upload_url }}
-          asset_path: ./dist/litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.deb
+          asset_path: ./dist/litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.deb
-          asset_name: litestream-${{ steps.release.outputs.tag_name }}-linux-amd64.deb
+          asset_name: litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}.deb
           asset_content_type: application/octet-stream

.github/workflows/release.linux_static.yml

@@ -0,0 +1,60 @@
+on:
+  release:
+    types:
+      - created
+
+name: release (linux/static)
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - arch: amd64
+            cc:   gcc
+          - arch: arm64
+            cc:   aarch64-linux-gnu-gcc
+          - arch: arm
+            arm:  6
+            cc:   arm-linux-gnueabi-gcc
+          - arch: arm
+            arm:  7
+            cc:   arm-linux-gnueabihf-gcc
+
+    env:
+      GOOS:   linux
+      GOARCH: ${{ matrix.arch }}
+      GOARM:  ${{ matrix.arm }}
+      CC:     ${{ matrix.cc }}
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-go@v2
+
+      - id: release
+        uses: bruceadams/get-release@v1.2.2
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+
+      - name: Install cross-compilers
+        run: |
+          sudo apt-get update 
+          sudo apt-get install -y gcc-aarch64-linux-gnu gcc-arm-linux-gnueabihf gcc-arm-linux-gnueabi
+
+      - name: Build litestream
+        run: |
+          rm -rf dist
+          mkdir -p dist
+          CGO_ENABLED=1 go build -ldflags "-s -w -extldflags "-static" -X 'main.Version=${{ steps.release.outputs.tag_name }}'" -tags osusergo,netgo,sqlite_omit_load_extension -o dist/litestream ./cmd/litestream
+          cd dist
+          tar -czvf litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}-static.tar.gz litestream
+
+      - name: Upload release tarball
+        uses: actions/upload-release-asset@v1.0.2
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        with:
+          upload_url: ${{ steps.release.outputs.upload_url }}
+          asset_path: ./dist/litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}-static.tar.gz
+          asset_name: litestream-${{ steps.release.outputs.tag_name }}-${{ env.GOOS }}-${{ env.GOARCH }}${{ env.GOARM }}-static.tar.gz
+          asset_content_type: application/gzip

Dockerfile

@@ -0,0 +1,11 @@
+FROM golang:1.16 as builder
+WORKDIR /src/litestream
+COPY . .
+RUN --mount=type=cache,target=/root/.cache/go-build \
+	--mount=type=cache,target=/go/pkg \
+	go build -ldflags '-s -w -extldflags "-static"' -tags osusergo,netgo,sqlite_omit_load_extension -o /usr/local/bin/litestream ./cmd/litestream
+
+FROM alpine
+COPY --from=builder /usr/local/bin/litestream /usr/local/bin/litestream
+ENTRYPOINT ["/usr/local/bin/litestream"]
+CMD []

LICENSE

@@ -1,674 +1,202 @@
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-            How to Apply These Terms to Your New Programs
+   APPENDIX: How to apply the Apache License to your work.
 
-  If you develop a new program, and you want it to be of the greatest
+      To apply the Apache License to your work, attach the following
-possible use to the public, the best way to achieve this is to make it
+      boilerplate notice, with the fields enclosed by brackets "[]"
-free software which everyone can redistribute and change under these terms.
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
 
-  To do so, attach the following notices to the program.  It is safest
+   Copyright [yyyy] [name of copyright owner]
-to attach them to the start of each source file to most effectively
-state the exclusion of warranty; and each file should have at least
-the "copyright" line and a pointer to where the full notice is found.
 
-    <one line to give the program's name and a brief idea of what it does.>
+   Licensed under the Apache License, Version 2.0 (the "License");
-    Copyright (C) <year>  <name of author>
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
 
-    This program is free software: you can redistribute it and/or modify
+       http://www.apache.org/licenses/LICENSE-2.0
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
 
-    This program is distributed in the hope that it will be useful,
+   Unless required by applicable law or agreed to in writing, software
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
+   distributed under the License is distributed on an "AS IS" BASIS,
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-    GNU General Public License for more details.
+   See the License for the specific language governing permissions and
-
+   limitations under the License.
-    You should have received a copy of the GNU General Public License
-    along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
-Also add information on how to contact you by electronic and paper mail.
-
-  If the program does terminal interaction, make it output a short
-notice like this when it starts in an interactive mode:
-
-    <program>  Copyright (C) <year>  <name of author>
-    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
-    This is free software, and you are welcome to redistribute it
-    under certain conditions; type `show c' for details.
-
-The hypothetical commands `show w' and `show c' should show the appropriate
-parts of the General Public License.  Of course, your program's commands
-might be different; for a GUI interface, you would use an "about box".
-
-  You should also get your employer (if you work as a programmer) or school,
-if any, to sign a "copyright disclaimer" for the program, if necessary.
-For more information on this, and how to apply and follow the GNU GPL, see
-<https://www.gnu.org/licenses/>.
-
-  The GNU General Public License does not permit incorporating your program
-into proprietary programs.  If your program is a subroutine library, you
-may consider it more useful to permit linking proprietary applications with
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-Public License instead of this License.  But first, please read
-<https://www.gnu.org/licenses/why-not-lgpl.html>.

Makefile

@@ -1,17 +1,26 @@
 default:
 
+docker:
+	docker build -t litestream .
+
 dist-linux:
 	mkdir -p dist
 	cp etc/litestream.yml dist/litestream.yml
-	docker run --rm -v "${PWD}":/usr/src/litestream -w /usr/src/litestream -e GOOS=linux -e GOARCH=amd64 golang:1.15 go build -v -o dist/litestream ./cmd/litestream
+	docker run --rm -v "${PWD}":/usr/src/litestream -w /usr/src/litestream -e GOOS=linux -e GOARCH=amd64 golang:1.16 go build -v -ldflags "-s -w" -o dist/litestream ./cmd/litestream
 	tar -cz -f dist/litestream-linux-amd64.tar.gz -C dist litestream
 
+dist-linux-arm:
+	docker run --rm -v "${PWD}":/usr/src/litestream -w /usr/src/litestream -e CGO_ENABLED=1 -e CC=arm-linux-gnueabihf-gcc -e GOOS=linux -e GOARCH=arm golang-xc:1.16 go build -v -o dist/litestream-linux-arm ./cmd/litestream
+
+dist-linux-arm64:
+	docker run --rm -v "${PWD}":/usr/src/litestream -w /usr/src/litestream -e CGO_ENABLED=1 -e CC=aarch64-linux-gnu-gcc -e GOOS=linux -e GOARCH=arm64 golang-xc:1.16 go build -v -o dist/litestream-linux-arm64 ./cmd/litestream
+
 dist-macos:
 ifndef LITESTREAM_VERSION
 	$(error LITESTREAM_VERSION is undefined)
 endif
 	mkdir -p dist
-	go build -v -ldflags "-X 'main.Version=${LITESTREAM_VERSION}'"  -o dist/litestream ./cmd/litestream
+	go build -v -ldflags "-s -w -X 'main.Version=${LITESTREAM_VERSION}'"  -o dist/litestream ./cmd/litestream
 	gon etc/gon.hcl
 	mv dist/litestream.zip dist/litestream-${LITESTREAM_VERSION}-darwin-amd64.zip
 	openssl dgst -sha256 dist/litestream-${LITESTREAM_VERSION}-darwin-amd64.zip

README.md

@@ -2,6 +2,7 @@ Litestream
 ![GitHub release (latest by date)](https://img.shields.io/github/v/release/benbjohnson/litestream)
 ![Status](https://img.shields.io/badge/status-beta-blue)
 ![GitHub](https://img.shields.io/github/license/benbjohnson/litestream)
+[![Docker Pulls](https://img.shields.io/docker/pulls/litestream/litestream.svg?maxAge=604800)](https://hub.docker.com/r/litestream/litestream/)
 ![test](https://github.com/benbjohnson/litestream/workflows/test/badge.svg)
 ==========
 
@@ -10,275 +11,35 @@ background process and safely replicates changes incrementally to another file
 or S3. Litestream only communicates with SQLite through the SQLite API so it
 will not corrupt your database.
 
-If you need support or have ideas for improving Litestream, please visit the
+If you need support or have ideas for improving Litestream, please join the
-[GitHub Discussions](https://github.com/benbjohnson/litestream/discussions) to
+[Litestream Slack][slack] or visit the [GitHub Discussions](https://github.com/benbjohnson/litestream/discussions).
-chat. 
+Please visit the [Litestream web site](https://litestream.io) for installation
+instructions and documentation.
 
 If you find this project interesting, please consider starring the project on
 GitHub.
 
+[slack]: https://join.slack.com/t/litestream/shared_invite/zt-n0j4s3ci-lx1JziR3bV6L2NMF723H3Q
 
-## Installation
 
-### Mac OS (Homebrew)
+## Acknowledgements
 
-To install from homebrew, run the following command:
+While the Litestream project does not accept external code patches, many
-
+of the most valuable contributions are in the forms of testing, feedback, and
-```sh
+documentation. These help harden software and streamline usage for other users.
-$ brew install benbjohnson/litestream/litestream
-```
-
-
-### Linux (Debian)
-
-You can download the `.deb` file from the [Releases page][releases] page and
-then run the following:
-
-```sh
-$ sudo dpkg -i litestream-v0.3.0-linux-amd64.deb
-```
-
-Once installed, you'll need to enable & start the service:
-
-```sh
-$ sudo systemctl enable litestream
-$ sudo systemctl start litestream
-```
-
-
-### Release binaries
-
-You can also download the release binary for your system from the
-[releases page][releases] and run it as a standalone application.
-
-
-### Building from source
-
-Download and install the [Go toolchain](https://golang.org/) and then run:
-
-```sh
-$ go install ./cmd/litestream
-```
-
-The `litestream` binary should be in your `$GOPATH/bin` folder.
-
-
-## Quick Start
-
-Litestream provides a configuration file that can be used for production
-deployments but you can also specify a single database and replica on the
-command line when trying it out.
-
-First, you'll need to create an S3 bucket that we'll call `"mybkt"` in this
-example. You'll also need to set your AWS credentials:
-
-```sh
-$ export AWS_ACCESS_KEY_ID=AKIAxxxxxxxxxxxxxxxx
-$ export AWS_SECRET_ACCESS_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/xxxxxxxxx
-```
-
-Next, you can run the `litestream replicate` command with the path to the
-database you want to backup and the URL of your replica destination:
-
-```sh
-$ litestream replicate /path/to/db s3://mybkt/db
-```
-
-If you make changes to your local database, those changes will be replicated
-to S3 every 10 seconds. From another terminal window, you can restore your
-database from your S3 replica:
-
-```
-$ litestream restore -o /path/to/restored/db s3://mybkt/db
-```
-
-Voila! 🎉
-
-Your database should be restored to the last replicated state that
-was sent to S3. You can adjust your replication frequency and other options by
-using a configuration-based approach specified below.
-
-
-## Configuration
-
-A configuration-based install gives you more replication options. By default,
-the config file lives at `/etc/litestream.yml` but you can pass in a different
-path to any `litestream` command using the `-config PATH` flag. You can also 
-set the `LITESTREAM_CONFIG` environment variable to specify a new path.
-
-The configuration specifies one or more `dbs` and a list of one or more replica
-locations for each db. Below are some common configurations:
-
-### Replicate to S3
-
-This will replicate the database at `/path/to/db` to the `"/db"` path inside
-the S3 bucket named `"mybkt"`.
-
-```yaml
-access-key-id:     AKIAxxxxxxxxxxxxxxxx
-secret-access-key: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/xxxxxxxxx
-
-dbs:
-  - path: /path/to/db
-    replicas:
-      - url: s3://mybkt/db
-```
-
-### Replicate to another file path
-
-This will replicate the database at `/path/to/db` to a directory named
-`/path/to/replica`.
-
-```yaml
-dbs:
-  - path: /path/to/db
-    replicas:
-      - path: /path/to/replica
-```
-
-### Retention period
-
-By default, replicas will retain a snapshot & subsequent WAL changes for 24
-hours. When the snapshot age exceeds the retention threshold, a new snapshot
-is taken and uploaded and the previous snapshot and WAL files are removed.
-
-You can configure this setting per-replica. Times are parsed using [Go's
-duration](https://golang.org/pkg/time/#ParseDuration) so time units of hours
-(`h`), minutes (`m`), and seconds (`s`) are allowed but days, weeks, months, and
-years are not.
-
-
-```yaml
-db:
-  - path: /path/to/db
-    replicas:
-      - url: s3://mybkt/db
-        retention: 1h          # 1 hour retention
-```
-
-
-### Monitoring replication
-
-You can also enable a Prometheus metrics endpoint to monitor replication by
-specifying a bind address with the `addr` field:
-
-```yml
-addr: ":9090"
-```
-
-This will make metrics available at: http://localhost:9090/metrics
-
-
-### Other configuration options
-
-These are some additional configuration options available on replicas:
-
-- `type`—Specify the type of replica (`"file"` or `"s3"`). Derived from `"path"`.
-- `name`—Specify an optional name for the replica if you are using multiple replicas.
-- `path`—File path to the replica location.
-- `url`—URL to the replica location.
-- `retention-check-interval`—Time between retention enforcement checks. Defaults to `1h`.
-- `validation-interval`—Interval between periodic checks to ensure restored backup matches current database. Disabled by default.
-
-These replica options are only available for S3 replicas:
-
-- `bucket`—S3 bucket name. Derived from `"path"`.
-- `region`—S3 bucket region. Looked up on startup if unspecified.
-- `sync-interval`—Replication sync frequency.
-
-
-
-## Usage
-
-### Replication
-
-Once your configuration is saved, you'll need to begin replication. If you
-installed the `.deb` file then run:
-
-```sh
-$ sudo systemctl restart litestream
-```
-
-To run litestream on its own, run:
-
-```sh
-# Replicate using the /etc/litestream.yml configuration.
-$ litestream replicate
-
-# Replicate using a different configuration path.
-$ litestream replicate -config /path/to/litestream.yml
-```
-
-The `litestream` command will initialize and then wait indefinitely for changes.
-You should see your destination replica path is now populated with a
-`generations` directory. Inside there should be a 16-character hex generation
-directory and inside there should be snapshots & WAL files. As you make changes
-to your source database, changes will be copied over to your replica incrementally.
-
-
-### Restoring a backup
-
-Litestream can restore a previous snapshot and replay all replicated WAL files.
-By default, it will restore up to the latest WAL file but you can also perform
-point-in-time restores.
-
-A database can only be restored to a path that does not exist so you don't need
-to worry about accidentally overwriting your current database.
-
-```sh
-# Restore database to original path.
-$ litestream restore /path/to/db
-
-# Restore database to a new location.
-$ litestream restore -o /path/to/restored/db /path/to/db
-
-# Restore from a replica URL.
-$ litestream restore -o /path/to/restored/db s3://mybkt/db
-
-# Restore database to a specific point-in-time.
-$ litestream restore -timestamp 2020-01-01T00:00:00Z /path/to/db
-```
-
-Point-in-time restores only have the resolution of the timestamp of the WAL file
-itself. By default, Litestream will start a new WAL file every minute so
-point-in-time restores are only accurate to the minute.
-
-
-
-## How it works
-
-SQLite provides a WAL (write-ahead log) journaling mode which writes pages to
-a `-wal` file before eventually being copied over to the original database file.
-This copying process is known as checkpointing. The WAL file works as a circular
-buffer so when the WAL reaches a certain size then it restarts from the beginning.
-
-Litestream works by taking over the checkpointing process and controlling when
-it is restarted to ensure that it copies every new page. Checkpointing is only
-allowed when there are no read transactions so Litestream maintains a
-long-running read transaction against each database until it is ready to
-checkpoint.
-
-The SQLite WAL file is copied to a separate location called the shadow WAL which
-ensures that it will not be overwritten by SQLite. This shadow WAL acts as a
-temporary buffer so that replicas can replicate to their destination (e.g.
-another file path or to S3). The shadow WAL files are removed once they have
-been fully replicated. You can find the shadow directory as a hidden directory
-next to your database file. If you database file is named `/var/lib/my.db` then
-the shadow directory will be `/var/lib/.my.db-litestream`.
-
-Litestream groups a snapshot and all subsequent WAL changes into "generations".
-A generation is started on initial replication of a database and a new
-generation will be started if litestream detects that the WAL replication is
-no longer contiguous. This can occur if the `litestream` process is stopped and
-another process is allowed to checkpoint the WAL.
 
+I want to give special thanks to individuals who invest much of their time and 
+energy into the project to help make it better. Shout out to [Michael
+Lynch](https://github.com/mtlynch) for digging into issues and contributing to
+the documentation.
 
 
 ## Open-source, not open-contribution
 
 [Similar to SQLite](https://www.sqlite.org/copyright.html), Litestream is open
-source but closed to contributions. This keeps the code base free of proprietary
+source but closed to code contributions. This keeps the code base free of
-or licensed code but it also helps me continue to maintain and build Litestream.
+proprietary or licensed code but it also helps me continue to maintain and build
+Litestream.
 
 As the author of [BoltDB](https://github.com/boltdb/bolt), I found that
 accepting and maintaining third party patches contributed to my burn out and
@@ -292,5 +53,8 @@ not wish to come off as anything but welcoming, however, I've
 made the decision to keep this project closed to contributions for my own
 mental health and long term viability of the project.
 
+The [documentation repository][docs] is MIT licensed and pull requests are welcome there.
 
 [releases]: https://github.com/benbjohnson/litestream/releases
+[docs]: https://github.com/benbjohnson/litestream.io
+

cmd/litestream/databases.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -15,21 +14,20 @@ type DatabasesCommand struct{}
 
 // Run executes the command.
 func (c *DatabasesCommand) Run(ctx context.Context, args []string) (err error) {
-	var configPath string
 	fs := flag.NewFlagSet("litestream-databases", flag.ContinueOnError)
-	registerConfigFlag(fs, &configPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	fs.Usage = c.Usage
 	if err := fs.Parse(args); err != nil {
 		return err
 	} else if fs.NArg() != 0 {
-		return fmt.Errorf("too many argument")
+		return fmt.Errorf("too many arguments")
 	}
 
 	// Load configuration.
-	if configPath == "" {
+	if *configPath == "" {
-		return errors.New("-config required")
+		*configPath = DefaultConfigPath()
 	}
-	config, err := ReadConfigFile(configPath)
+	config, err := ReadConfigFile(*configPath, !*noExpandEnv)
 	if err != nil {
 		return err
 	}
@@ -40,7 +38,7 @@ func (c *DatabasesCommand) Run(ctx context.Context, args []string) (err error) {
 
 	fmt.Fprintln(w, "path\treplicas")
 	for _, dbConfig := range config.DBs {
-		db, err := newDBFromConfig(&config, dbConfig)
+		db, err := NewDBFromConfig(dbConfig)
 		if err != nil {
 			return err
 		}
@@ -74,6 +72,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 `[1:],
 		DefaultConfigPath(),
 	)

cmd/litestream/generations.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -18,9 +17,8 @@ type GenerationsCommand struct{}
 
 // Run executes the command.
 func (c *GenerationsCommand) Run(ctx context.Context, args []string) (err error) {
-	var configPath string
 	fs := flag.NewFlagSet("litestream-generations", flag.ContinueOnError)
-	registerConfigFlag(fs, &configPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	replicaName := fs.String("replica", "", "replica name")
 	fs.Usage = c.Usage
 	if err := fs.Parse(args); err != nil {
@@ -35,12 +33,19 @@ func (c *GenerationsCommand) Run(ctx context.Context, args []string) (err error)
 	var r litestream.Replica
 	updatedAt := time.Now()
 	if isURL(fs.Arg(0)) {
-		if r, err = NewReplicaFromURL(fs.Arg(0)); err != nil {
+		if *configPath != "" {
+			return fmt.Errorf("cannot specify a replica URL and the -config flag")
+		}
+		if r, err = NewReplicaFromConfig(&ReplicaConfig{URL: fs.Arg(0)}, nil); err != nil {
 			return err
 		}
-	} else if configPath != "" {
+	} else {
+		if *configPath == "" {
+			*configPath = DefaultConfigPath()
+		}
+
 		// Load configuration.
-		config, err := ReadConfigFile(configPath)
+		config, err := ReadConfigFile(*configPath, !*noExpandEnv)
 		if err != nil {
 			return err
 		}
@@ -50,7 +55,7 @@ func (c *GenerationsCommand) Run(ctx context.Context, args []string) (err error)
 			return err
 		} else if dbc := config.DBConfig(path); dbc == nil {
 			return fmt.Errorf("database not found in config: %s", path)
-		} else if db, err = newDBFromConfig(&config, dbc); err != nil {
+		} else if db, err = NewDBFromConfig(dbc); err != nil {
 			return err
 		}
 
@@ -65,8 +70,6 @@ func (c *GenerationsCommand) Run(ctx context.Context, args []string) (err error)
 		if updatedAt, err = db.UpdatedAt(); err != nil {
 			return err
 		}
-	} else {
-		return errors.New("config path or replica URL required")
 	}
 
 	var replicas []litestream.Replica
@@ -128,6 +131,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 	-replica NAME
 	    Optional, filters by replica.
 

cmd/litestream/main.go

@@ -2,15 +2,19 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
 	"net/url"
 	"os"
+	"os/signal"
 	"os/user"
 	"path"
 	"path/filepath"
+	"regexp"
+	"strconv"
 	"strings"
 	"time"
 
@@ -25,14 +29,17 @@ var (
 	Version = "(development build)"
 )
 
+// errStop is a terminal error for indicating program should quit.
+var errStop = errors.New("stop")
+
 func main() {
 	log.SetFlags(0)
 
 	m := NewMain()
-	if err := m.Run(context.Background(), os.Args[1:]); err == flag.ErrHelp {
+	if err := m.Run(context.Background(), os.Args[1:]); err == flag.ErrHelp || err == errStop {
 		os.Exit(1)
 	} else if err != nil {
-		fmt.Fprintln(os.Stderr, err)
+		log.Println(err)
 		os.Exit(1)
 	}
 }
@@ -47,6 +54,17 @@ func NewMain() *Main {
 
 // Run executes the program.
 func (m *Main) Run(ctx context.Context, args []string) (err error) {
+	// Execute replication command if running as a Windows service.
+	if isService, err := isWindowsService(); err != nil {
+		return err
+	} else if isService {
+		return runWindowsService(ctx)
+	}
+
+	// Copy "LITESTEAM" environment credentials.
+	applyLitestreamEnv()
+
+	// Extract command name.
 	var cmd string
 	if len(args) > 0 {
 		cmd, args = args[0], args[1:]
@@ -58,7 +76,32 @@ func (m *Main) Run(ctx context.Context, args []string) (err error) {
 	case "generations":
 		return (&GenerationsCommand{}).Run(ctx, args)
 	case "replicate":
-		return (&ReplicateCommand{}).Run(ctx, args)
+		c := NewReplicateCommand()
+		if err := c.ParseFlags(ctx, args); err != nil {
+			return err
+		}
+
+		// Setup signal handler.
+		ctx, cancel := context.WithCancel(ctx)
+		ch := signalChan()
+		go func() { <-ch; cancel() }()
+
+		if err := c.Run(ctx); err != nil {
+			return err
+		}
+
+		// Wait for signal to stop program.
+		<-ctx.Done()
+		signal.Reset()
+		fmt.Println("signal received, litestream shutting down")
+
+		// Gracefully close.
+		if err := c.Close(); err != nil {
+			return err
+		}
+		fmt.Println("litestream shut down")
+		return nil
+
 	case "restore":
 		return (&RestoreCommand{}).Run(ctx, args)
 	case "snapshots":
@@ -108,8 +151,20 @@ type Config struct {
 	// Global S3 settings
 	AccessKeyID     string `yaml:"access-key-id"`
 	SecretAccessKey string `yaml:"secret-access-key"`
-	Region          string `yaml:"region"`
+}
-	Bucket          string `yaml:"bucket"`
+
+// propagateGlobalSettings copies global S3 settings to replica configs.
+func (c *Config) propagateGlobalSettings() {
+	for _, dbc := range c.DBs {
+		for _, rc := range dbc.Replicas {
+			if rc.AccessKeyID == "" {
+				rc.AccessKeyID = c.AccessKeyID
+			}
+			if rc.SecretAccessKey == "" {
+				rc.SecretAccessKey = c.SecretAccessKey
+			}
+		}
+	}
 }
 
 // DefaultConfig returns a new instance of Config with defaults set.
@@ -128,7 +183,8 @@ func (c *Config) DBConfig(path string) *DBConfig {
 }
 
 // ReadConfigFile unmarshals config from filename. Expands path if needed.
-func ReadConfigFile(filename string) (_ Config, err error) {
+// If expandEnv is true then environment variables are expanded in the config.
+func ReadConfigFile(filename string, expandEnv bool) (_ Config, err error) {
 	config := DefaultConfig()
 
 	// Expand filename, if necessary.
@@ -137,12 +193,20 @@ func ReadConfigFile(filename string) (_ Config, err error) {
 		return config, err
 	}
 
-	// Read & deserialize configuration.
+	// Read configuration.
-	if buf, err := ioutil.ReadFile(filename); os.IsNotExist(err) {
+	buf, err := ioutil.ReadFile(filename)
+	if os.IsNotExist(err) {
 		return config, fmt.Errorf("config file not found: %s", filename)
 	} else if err != nil {
 		return config, err
-	} else if err := yaml.Unmarshal(buf, &config); err != nil {
+	}
+
+	// Expand environment variables, if enabled.
+	if expandEnv {
+		buf = []byte(os.ExpandEnv(string(buf)))
+	}
+
+	if err := yaml.Unmarshal(buf, &config); err != nil {
 		return config, err
 	}
 
@@ -153,15 +217,59 @@ func ReadConfigFile(filename string) (_ Config, err error) {
 		}
 	}
 
+	// Propage settings from global config to replica configs.
+	config.propagateGlobalSettings()
+
 	return config, nil
 }
 
 // DBConfig represents the configuration for a single database.
 type DBConfig struct {
 	Path               string         `yaml:"path"`
+	MonitorInterval    *time.Duration `yaml:"monitor-interval"`
+	CheckpointInterval *time.Duration `yaml:"checkpoint-interval"`
+	MinCheckpointPageN *int           `yaml:"min-checkpoint-page-count"`
+	MaxCheckpointPageN *int           `yaml:"max-checkpoint-page-count"`
+
 	Replicas []*ReplicaConfig `yaml:"replicas"`
 }
 
+// NewDBFromConfig instantiates a DB based on a configuration.
+func NewDBFromConfig(dbc *DBConfig) (*litestream.DB, error) {
+	path, err := expand(dbc.Path)
+	if err != nil {
+		return nil, err
+	}
+
+	// Initialize database with given path.
+	db := litestream.NewDB(path)
+
+	// Override default database settings if specified in configuration.
+	if dbc.MonitorInterval != nil {
+		db.MonitorInterval = *dbc.MonitorInterval
+	}
+	if dbc.CheckpointInterval != nil {
+		db.CheckpointInterval = *dbc.CheckpointInterval
+	}
+	if dbc.MinCheckpointPageN != nil {
+		db.MinCheckpointPageN = *dbc.MinCheckpointPageN
+	}
+	if dbc.MaxCheckpointPageN != nil {
+		db.MaxCheckpointPageN = *dbc.MaxCheckpointPageN
+	}
+
+	// Instantiate and attach replicas.
+	for _, rc := range dbc.Replicas {
+		r, err := NewReplicaFromConfig(rc, db)
+		if err != nil {
+			return nil, err
+		}
+		db.Replicas = append(db.Replicas, r)
+	}
+
+	return db, nil
+}
+
 // ReplicaConfig represents the configuration for a single replica in a database.
 type ReplicaConfig struct {
 	Type                   string        `yaml:"type"` // "file", "s3"
@@ -171,6 +279,7 @@ type ReplicaConfig struct {
 	Retention              time.Duration `yaml:"retention"`
 	RetentionCheckInterval time.Duration `yaml:"retention-check-interval"`
 	SyncInterval           time.Duration `yaml:"sync-interval"` // s3 only
+	SnapshotInterval       time.Duration `yaml:"snapshot-interval"`
 	ValidationInterval     time.Duration `yaml:"validation-interval"`
 
 	// S3 settings
@@ -178,25 +287,162 @@ type ReplicaConfig struct {
 	SecretAccessKey string `yaml:"secret-access-key"`
 	Region          string `yaml:"region"`
 	Bucket          string `yaml:"bucket"`
+	Endpoint        string `yaml:"endpoint"`
+	ForcePathStyle  *bool  `yaml:"force-path-style"`
+	SkipVerify      bool   `yaml:"skip-verify"`
 }
 
-// NewReplicaFromURL returns a new Replica instance configured from a URL.
+// NewReplicaFromConfig instantiates a replica for a DB based on a config.
-// The replica's database is not set.
+func NewReplicaFromConfig(c *ReplicaConfig, db *litestream.DB) (litestream.Replica, error) {
-func NewReplicaFromURL(s string) (litestream.Replica, error) {
+	// Ensure user did not specify URL in path.
-	scheme, host, path, err := ParseReplicaURL(s)
+	if isURL(c.Path) {
-	if err != nil {
+		return nil, fmt.Errorf("replica path cannot be a url, please use the 'url' field instead: %s", c.Path)
+	}
+
+	switch c.ReplicaType() {
+	case "file":
+		return newFileReplicaFromConfig(c, db)
+	case "s3":
+		return newS3ReplicaFromConfig(c, db)
+	default:
+		return nil, fmt.Errorf("unknown replica type in config: %q", c.Type)
+	}
+}
+
+// newFileReplicaFromConfig returns a new instance of FileReplica build from config.
+func newFileReplicaFromConfig(c *ReplicaConfig, db *litestream.DB) (_ *litestream.FileReplica, err error) {
+	// Ensure URL & path are not both specified.
+	if c.URL != "" && c.Path != "" {
+		return nil, fmt.Errorf("cannot specify url & path for file replica")
+	}
+
+	// Parse path from URL, if specified.
+	path := c.Path
+	if c.URL != "" {
+		if _, _, path, err = ParseReplicaURL(c.URL); err != nil {
+			return nil, err
+		}
+	}
+
+	// Ensure path is set explicitly or derived from URL field.
+	if path == "" {
+		return nil, fmt.Errorf("file replica path required")
+	}
+
+	// Expand home prefix and return absolute path.
+	if path, err = expand(path); err != nil {
 		return nil, err
 	}
 
-	switch scheme {
+	// Instantiate replica and apply time fields, if set.
-	case "file":
+	r := litestream.NewFileReplica(db, c.Name, path)
-		return litestream.NewFileReplica(nil, "", path), nil
+	if v := c.Retention; v > 0 {
-	case "s3":
+		r.Retention = v
-		r := s3.NewReplica(nil, "")
+	}
-		r.Bucket, r.Path = host, path
+	if v := c.RetentionCheckInterval; v > 0 {
+		r.RetentionCheckInterval = v
+	}
+	if v := c.SnapshotInterval; v > 0 {
+		r.SnapshotInterval = v
+	}
+	if v := c.ValidationInterval; v > 0 {
+		r.ValidationInterval = v
+	}
 	return r, nil
-	default:
+}
-		return nil, fmt.Errorf("invalid replica url type: %s", s)
+
+// newS3ReplicaFromConfig returns a new instance of S3Replica build from config.
+func newS3ReplicaFromConfig(c *ReplicaConfig, db *litestream.DB) (_ *s3.Replica, err error) {
+	// Ensure URL & constituent parts are not both specified.
+	if c.URL != "" && c.Path != "" {
+		return nil, fmt.Errorf("cannot specify url & path for s3 replica")
+	} else if c.URL != "" && c.Bucket != "" {
+		return nil, fmt.Errorf("cannot specify url & bucket for s3 replica")
+	}
+
+	bucket, path := c.Bucket, c.Path
+	region, endpoint, skipVerify := c.Region, c.Endpoint, c.SkipVerify
+
+	// Use path style if an endpoint is explicitly set. This works because the
+	// only service to not use path style is AWS which does not use an endpoint.
+	forcePathStyle := (endpoint != "")
+	if v := c.ForcePathStyle; v != nil {
+		forcePathStyle = *v
+	}
+
+	// Apply settings from URL, if specified.
+	if c.URL != "" {
+		_, host, upath, err := ParseReplicaURL(c.URL)
+		if err != nil {
+			return nil, err
+		}
+		ubucket, uregion, uendpoint, uforcePathStyle := s3.ParseHost(host)
+
+		// Only apply URL parts to field that have not been overridden.
+		if path == "" {
+			path = upath
+		}
+		if bucket == "" {
+			bucket = ubucket
+		}
+		if region == "" {
+			region = uregion
+		}
+		if endpoint == "" {
+			endpoint = uendpoint
+		}
+		if !forcePathStyle {
+			forcePathStyle = uforcePathStyle
+		}
+	}
+
+	// Ensure required settings are set.
+	if bucket == "" {
+		return nil, fmt.Errorf("bucket required for s3 replica")
+	}
+
+	// Build replica.
+	r := s3.NewReplica(db, c.Name)
+	r.AccessKeyID = c.AccessKeyID
+	r.SecretAccessKey = c.SecretAccessKey
+	r.Bucket = bucket
+	r.Path = path
+	r.Region = region
+	r.Endpoint = endpoint
+	r.ForcePathStyle = forcePathStyle
+	r.SkipVerify = skipVerify
+
+	if v := c.Retention; v > 0 {
+		r.Retention = v
+	}
+	if v := c.RetentionCheckInterval; v > 0 {
+		r.RetentionCheckInterval = v
+	}
+	if v := c.SyncInterval; v > 0 {
+		r.SyncInterval = v
+	}
+	if v := c.SnapshotInterval; v > 0 {
+		r.SnapshotInterval = v
+	}
+	if v := c.ValidationInterval; v > 0 {
+		r.ValidationInterval = v
+	}
+	return r, nil
+}
+
+// applyLitestreamEnv copies "LITESTREAM" prefixed environment variables to
+// their AWS counterparts as the "AWS" prefix can be confusing when using a
+// non-AWS S3-compatible service.
+func applyLitestreamEnv() {
+	if v, ok := os.LookupEnv("LITESTREAM_ACCESS_KEY_ID"); ok {
+		if _, ok := os.LookupEnv("AWS_ACCESS_KEY_ID"); !ok {
+			os.Setenv("AWS_ACCESS_KEY_ID", v)
+		}
+	}
+	if v, ok := os.LookupEnv("LITESTREAM_SECRET_ACCESS_KEY"); ok {
+		if _, ok := os.LookupEnv("AWS_SECRET_ACCESS_KEY"); !ok {
+			os.Setenv("AWS_SECRET_ACCESS_KEY", v)
+		}
 	}
 }
 
@@ -222,15 +468,14 @@ func ParseReplicaURL(s string) (scheme, host, urlpath string, err error) {
 
 // isURL returns true if s can be parsed and has a scheme.
 func isURL(s string) bool {
-	u, err := url.Parse(s)
+	return regexp.MustCompile(`^\w+:\/\/`).MatchString(s)
-	return err == nil && u.Scheme != ""
 }
 
 // ReplicaType returns the type based on the type field or extracted from the URL.
 func (c *ReplicaConfig) ReplicaType() string {
-	typ, _, _, _ := ParseReplicaURL(c.URL)
+	scheme, _, _, _ := ParseReplicaURL(c.URL)
-	if typ != "" {
+	if scheme != "" {
-		return typ
+		return scheme
 	} else if c.Type != "" {
 		return c.Type
 	}
@@ -242,138 +487,12 @@ func DefaultConfigPath() string {
 	if v := os.Getenv("LITESTREAM_CONFIG"); v != "" {
 		return v
 	}
-	return "/etc/litestream.yml"
+	return defaultConfigPath
 }
 
-func registerConfigFlag(fs *flag.FlagSet, p *string) {
+func registerConfigFlag(fs *flag.FlagSet) (configPath *string, noExpandEnv *bool) {
-	fs.StringVar(p, "config", DefaultConfigPath(), "config path")
+	return fs.String("config", "", "config path"),
-}
+		fs.Bool("no-expand-env", false, "do not expand env vars in config")
-
-// newDBFromConfig instantiates a DB based on a configuration.
-func newDBFromConfig(c *Config, dbc *DBConfig) (*litestream.DB, error) {
-	path, err := expand(dbc.Path)
-	if err != nil {
-		return nil, err
-	}
-
-	// Initialize database with given path.
-	db := litestream.NewDB(path)
-
-	// Instantiate and attach replicas.
-	for _, rc := range dbc.Replicas {
-		r, err := newReplicaFromConfig(db, c, dbc, rc)
-		if err != nil {
-			return nil, err
-		}
-		db.Replicas = append(db.Replicas, r)
-	}
-
-	return db, nil
-}
-
-// newReplicaFromConfig instantiates a replica for a DB based on a config.
-func newReplicaFromConfig(db *litestream.DB, c *Config, dbc *DBConfig, rc *ReplicaConfig) (litestream.Replica, error) {
-	// Ensure user did not specify URL in path.
-	if isURL(rc.Path) {
-		return nil, fmt.Errorf("replica path cannot be a url, please use the 'url' field instead: %s", rc.Path)
-	}
-
-	switch rc.ReplicaType() {
-	case "file":
-		return newFileReplicaFromConfig(db, c, dbc, rc)
-	case "s3":
-		return newS3ReplicaFromConfig(db, c, dbc, rc)
-	default:
-		return nil, fmt.Errorf("unknown replica type in config: %q", rc.Type)
-	}
-}
-
-// newFileReplicaFromConfig returns a new instance of FileReplica build from config.
-func newFileReplicaFromConfig(db *litestream.DB, c *Config, dbc *DBConfig, rc *ReplicaConfig) (_ *litestream.FileReplica, err error) {
-	path := rc.Path
-	if rc.URL != "" {
-		_, _, path, err = ParseReplicaURL(rc.URL)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	if path == "" {
-		return nil, fmt.Errorf("%s: file replica path required", db.Path())
-	}
-
-	if path, err = expand(path); err != nil {
-		return nil, err
-	}
-
-	r := litestream.NewFileReplica(db, rc.Name, path)
-	if v := rc.Retention; v > 0 {
-		r.Retention = v
-	}
-	if v := rc.RetentionCheckInterval; v > 0 {
-		r.RetentionCheckInterval = v
-	}
-	if v := rc.ValidationInterval; v > 0 {
-		r.ValidationInterval = v
-	}
-	return r, nil
-}
-
-// newS3ReplicaFromConfig returns a new instance of S3Replica build from config.
-func newS3ReplicaFromConfig(db *litestream.DB, c *Config, dbc *DBConfig, rc *ReplicaConfig) (_ *s3.Replica, err error) {
-	bucket := c.Bucket
-	if v := rc.Bucket; v != "" {
-		bucket = v
-	}
-
-	path := rc.Path
-	if rc.URL != "" {
-		_, bucket, path, err = ParseReplicaURL(rc.URL)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	// Use global or replica-specific S3 settings.
-	accessKeyID := c.AccessKeyID
-	if v := rc.AccessKeyID; v != "" {
-		accessKeyID = v
-	}
-	secretAccessKey := c.SecretAccessKey
-	if v := rc.SecretAccessKey; v != "" {
-		secretAccessKey = v
-	}
-	region := c.Region
-	if v := rc.Region; v != "" {
-		region = v
-	}
-
-	// Ensure required settings are set.
-	if bucket == "" {
-		return nil, fmt.Errorf("%s: s3 bucket required", db.Path())
-	}
-
-	// Build replica.
-	r := s3.NewReplica(db, rc.Name)
-	r.AccessKeyID = accessKeyID
-	r.SecretAccessKey = secretAccessKey
-	r.Region = region
-	r.Bucket = bucket
-	r.Path = path
-
-	if v := rc.Retention; v > 0 {
-		r.Retention = v
-	}
-	if v := rc.RetentionCheckInterval; v > 0 {
-		r.RetentionCheckInterval = v
-	}
-	if v := rc.SyncInterval; v > 0 {
-		r.SyncInterval = v
-	}
-	if v := rc.ValidationInterval; v > 0 {
-		r.ValidationInterval = v
-	}
-	return r, nil
 }
 
 // expand returns an absolute path for s.
@@ -398,3 +517,24 @@ func expand(s string) (string, error) {
 	}
 	return filepath.Join(u.HomeDir, strings.TrimPrefix(s, prefix)), nil
 }
+
+// indexVar allows the flag package to parse index flags as 4-byte hexadecimal values.
+type indexVar int
+
+// Ensure type implements interface.
+var _ flag.Value = (*indexVar)(nil)
+
+// String returns an 8-character hexadecimal value.
+func (v *indexVar) String() string {
+	return fmt.Sprintf("%08x", int(*v))
+}
+
+// Set parses s into an integer from a hexadecimal value.
+func (v *indexVar) Set(s string) error {
+	i, err := strconv.ParseInt(s, 16, 32)
+	if err != nil {
+		return fmt.Errorf("invalid hexadecimal format")
+	}
+	*v = indexVar(i)
+	return nil
+}

cmd/litestream/main_notwindows.go

@@ -0,0 +1,26 @@
+// +build !windows
+
+package main
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+const defaultConfigPath = "/etc/litestream.yml"
+
+func isWindowsService() (bool, error) {
+	return false, nil
+}
+
+func runWindowsService(ctx context.Context) error {
+	panic("cannot run windows service as unix process")
+}
+
+func signalChan() <-chan os.Signal {
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM)
+	return ch
+}

cmd/litestream/main_test.go

@@ -0,0 +1,182 @@
+package main_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/benbjohnson/litestream"
+	main "github.com/benbjohnson/litestream/cmd/litestream"
+	"github.com/benbjohnson/litestream/s3"
+)
+
+func TestReadConfigFile(t *testing.T) {
+	// Ensure global AWS settings are propagated down to replica configurations.
+	t.Run("PropagateGlobalSettings", func(t *testing.T) {
+		filename := filepath.Join(t.TempDir(), "litestream.yml")
+		if err := ioutil.WriteFile(filename, []byte(`
+access-key-id: XXX
+secret-access-key: YYY
+
+dbs:
+  - path: /path/to/db
+    replicas:
+      - url: s3://foo/bar
+`[1:]), 0666); err != nil {
+			t.Fatal(err)
+		}
+
+		config, err := main.ReadConfigFile(filename, true)
+		if err != nil {
+			t.Fatal(err)
+		} else if got, want := config.AccessKeyID, `XXX`; got != want {
+			t.Fatalf("AccessKeyID=%v, want %v", got, want)
+		} else if got, want := config.SecretAccessKey, `YYY`; got != want {
+			t.Fatalf("SecretAccessKey=%v, want %v", got, want)
+		} else if got, want := config.DBs[0].Replicas[0].AccessKeyID, `XXX`; got != want {
+			t.Fatalf("Replica.AccessKeyID=%v, want %v", got, want)
+		} else if got, want := config.DBs[0].Replicas[0].SecretAccessKey, `YYY`; got != want {
+			t.Fatalf("Replica.SecretAccessKey=%v, want %v", got, want)
+		}
+	})
+
+	// Ensure environment variables are expanded.
+	t.Run("ExpandEnv", func(t *testing.T) {
+		os.Setenv("LITESTREAM_TEST_0129380", "/path/to/db")
+		os.Setenv("LITESTREAM_TEST_1872363", "s3://foo/bar")
+
+		filename := filepath.Join(t.TempDir(), "litestream.yml")
+		if err := ioutil.WriteFile(filename, []byte(`
+dbs:
+  - path: $LITESTREAM_TEST_0129380
+    replicas:
+      - url: ${LITESTREAM_TEST_1872363}
+      - url: ${LITESTREAM_TEST_NO_SUCH_ENV}
+`[1:]), 0666); err != nil {
+			t.Fatal(err)
+		}
+
+		config, err := main.ReadConfigFile(filename, true)
+		if err != nil {
+			t.Fatal(err)
+		} else if got, want := config.DBs[0].Path, `/path/to/db`; got != want {
+			t.Fatalf("DB.Path=%v, want %v", got, want)
+		} else if got, want := config.DBs[0].Replicas[0].URL, `s3://foo/bar`; got != want {
+			t.Fatalf("Replica[0].URL=%v, want %v", got, want)
+		} else if got, want := config.DBs[0].Replicas[1].URL, ``; got != want {
+			t.Fatalf("Replica[1].URL=%v, want %v", got, want)
+		}
+	})
+
+	// Ensure environment variables are not expanded.
+	t.Run("NoExpandEnv", func(t *testing.T) {
+		os.Setenv("LITESTREAM_TEST_9847533", "s3://foo/bar")
+
+		filename := filepath.Join(t.TempDir(), "litestream.yml")
+		if err := ioutil.WriteFile(filename, []byte(`
+dbs:
+  - path: /path/to/db
+    replicas:
+      - url: ${LITESTREAM_TEST_9847533}
+`[1:]), 0666); err != nil {
+			t.Fatal(err)
+		}
+
+		config, err := main.ReadConfigFile(filename, false)
+		if err != nil {
+			t.Fatal(err)
+		} else if got, want := config.DBs[0].Replicas[0].URL, `${LITESTREAM_TEST_9847533}`; got != want {
+			t.Fatalf("Replica.URL=%v, want %v", got, want)
+		}
+	})
+}
+
+func TestNewFileReplicaFromConfig(t *testing.T) {
+	r, err := main.NewReplicaFromConfig(&main.ReplicaConfig{Path: "/foo"}, nil)
+	if err != nil {
+		t.Fatal(err)
+	} else if r, ok := r.(*litestream.FileReplica); !ok {
+		t.Fatal("unexpected replica type")
+	} else if got, want := r.Path(), "/foo"; got != want {
+		t.Fatalf("Path=%s, want %s", got, want)
+	}
+}
+
+func TestNewS3ReplicaFromConfig(t *testing.T) {
+	t.Run("URL", func(t *testing.T) {
+		r, err := main.NewReplicaFromConfig(&main.ReplicaConfig{URL: "s3://foo/bar"}, nil)
+		if err != nil {
+			t.Fatal(err)
+		} else if r, ok := r.(*s3.Replica); !ok {
+			t.Fatal("unexpected replica type")
+		} else if got, want := r.Bucket, "foo"; got != want {
+			t.Fatalf("Bucket=%s, want %s", got, want)
+		} else if got, want := r.Path, "bar"; got != want {
+			t.Fatalf("Path=%s, want %s", got, want)
+		} else if got, want := r.Region, ""; got != want {
+			t.Fatalf("Region=%s, want %s", got, want)
+		} else if got, want := r.Endpoint, ""; got != want {
+			t.Fatalf("Endpoint=%s, want %s", got, want)
+		} else if got, want := r.ForcePathStyle, false; got != want {
+			t.Fatalf("ForcePathStyle=%v, want %v", got, want)
+		}
+	})
+
+	t.Run("MinIO", func(t *testing.T) {
+		r, err := main.NewReplicaFromConfig(&main.ReplicaConfig{URL: "s3://foo.localhost:9000/bar"}, nil)
+		if err != nil {
+			t.Fatal(err)
+		} else if r, ok := r.(*s3.Replica); !ok {
+			t.Fatal("unexpected replica type")
+		} else if got, want := r.Bucket, "foo"; got != want {
+			t.Fatalf("Bucket=%s, want %s", got, want)
+		} else if got, want := r.Path, "bar"; got != want {
+			t.Fatalf("Path=%s, want %s", got, want)
+		} else if got, want := r.Region, "us-east-1"; got != want {
+			t.Fatalf("Region=%s, want %s", got, want)
+		} else if got, want := r.Endpoint, "http://localhost:9000"; got != want {
+			t.Fatalf("Endpoint=%s, want %s", got, want)
+		} else if got, want := r.ForcePathStyle, true; got != want {
+			t.Fatalf("ForcePathStyle=%v, want %v", got, want)
+		}
+	})
+
+	t.Run("Backblaze", func(t *testing.T) {
+		r, err := main.NewReplicaFromConfig(&main.ReplicaConfig{URL: "s3://foo.s3.us-west-000.backblazeb2.com/bar"}, nil)
+		if err != nil {
+			t.Fatal(err)
+		} else if r, ok := r.(*s3.Replica); !ok {
+			t.Fatal("unexpected replica type")
+		} else if got, want := r.Bucket, "foo"; got != want {
+			t.Fatalf("Bucket=%s, want %s", got, want)
+		} else if got, want := r.Path, "bar"; got != want {
+			t.Fatalf("Path=%s, want %s", got, want)
+		} else if got, want := r.Region, "us-west-000"; got != want {
+			t.Fatalf("Region=%s, want %s", got, want)
+		} else if got, want := r.Endpoint, "https://s3.us-west-000.backblazeb2.com"; got != want {
+			t.Fatalf("Endpoint=%s, want %s", got, want)
+		} else if got, want := r.ForcePathStyle, true; got != want {
+			t.Fatalf("ForcePathStyle=%v, want %v", got, want)
+		}
+	})
+
+	t.Run("GCS", func(t *testing.T) {
+		r, err := main.NewReplicaFromConfig(&main.ReplicaConfig{URL: "s3://foo.storage.googleapis.com/bar"}, nil)
+		if err != nil {
+			t.Fatal(err)
+		} else if r, ok := r.(*s3.Replica); !ok {
+			t.Fatal("unexpected replica type")
+		} else if got, want := r.Bucket, "foo"; got != want {
+			t.Fatalf("Bucket=%s, want %s", got, want)
+		} else if got, want := r.Path, "bar"; got != want {
+			t.Fatalf("Path=%s, want %s", got, want)
+		} else if got, want := r.Region, "us-east-1"; got != want {
+			t.Fatalf("Region=%s, want %s", got, want)
+		} else if got, want := r.Endpoint, "https://storage.googleapis.com"; got != want {
+			t.Fatalf("Endpoint=%s, want %s", got, want)
+		} else if got, want := r.ForcePathStyle, true; got != want {
+			t.Fatalf("ForcePathStyle=%v, want %v", got, want)
+		}
+	})
+}

cmd/litestream/main_windows.go

@@ -0,0 +1,112 @@
+// +build windows
+
+package main
+
+import (
+	"context"
+	"io"
+	"log"
+	"os"
+	"os/signal"
+
+	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/svc"
+	"golang.org/x/sys/windows/svc/eventlog"
+)
+
+const defaultConfigPath = `C:\Litestream\litestream.yml`
+
+// serviceName is the Windows Service name.
+const serviceName = "Litestream"
+
+// isWindowsService returns true if currently executing within a Windows service.
+func isWindowsService() (bool, error) {
+	return svc.IsWindowsService()
+}
+
+func runWindowsService(ctx context.Context) error {
+	// Attempt to install new log service. This will fail if already installed.
+	// We don't log the error because we don't have anywhere to log until we open the log.
+	_ = eventlog.InstallAsEventCreate(serviceName, eventlog.Error|eventlog.Warning|eventlog.Info)
+
+	elog, err := eventlog.Open(serviceName)
+	if err != nil {
+		return err
+	}
+	defer elog.Close()
+
+	// Set eventlog as log writer while running.
+	log.SetOutput((*eventlogWriter)(elog))
+	defer log.SetOutput(os.Stderr)
+
+	log.Print("Litestream service starting")
+
+	if err := svc.Run(serviceName, &windowsService{ctx: ctx}); err != nil {
+		return errStop
+	}
+
+	log.Print("Litestream service stopped")
+	return nil
+}
+
+// windowsService is an interface adapter for svc.Handler.
+type windowsService struct {
+	ctx context.Context
+}
+
+func (s *windowsService) Execute(args []string, r <-chan svc.ChangeRequest, statusCh chan<- svc.Status) (svcSpecificEC bool, exitCode uint32) {
+	var err error
+
+	// Notify Windows that the service is starting up.
+	statusCh <- svc.Status{State: svc.StartPending}
+
+	// Instantiate replication command and load configuration.
+	c := NewReplicateCommand()
+	if c.Config, err = ReadConfigFile(DefaultConfigPath()); err != nil {
+		log.Printf("cannot load configuration: %s", err)
+		return true, 1
+	}
+
+	// Execute replication command.
+	if err := c.Run(s.ctx); err != nil {
+		log.Printf("cannot replicate: %s", err)
+		statusCh <- svc.Status{State: svc.StopPending}
+		return true, 2
+	}
+
+	// Notify Windows that the service is now running.
+	statusCh <- svc.Status{State: svc.Running, Accepts: svc.AcceptStop}
+
+	for {
+		select {
+		case req := <-r:
+			switch req.Cmd {
+			case svc.Stop:
+				c.Close()
+				statusCh <- svc.Status{State: svc.StopPending}
+				return false, windows.NO_ERROR
+			case svc.Interrogate:
+				statusCh <- req.CurrentStatus
+			default:
+				log.Printf("Litestream service received unexpected change request cmd: %d", req.Cmd)
+			}
+		}
+	}
+}
+
+// Ensure implementation implements io.Writer interface.
+var _ io.Writer = (*eventlogWriter)(nil)
+
+// eventlogWriter is an adapter for using eventlog.Log as an io.Writer.
+type eventlogWriter eventlog.Log
+
+func (w *eventlogWriter) Write(p []byte) (n int, err error) {
+	elog := (*eventlog.Log)(w)
+	return 0, elog.Info(1, string(p))
+}
+
+func signalChan() <-chan os.Signal {
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, os.Interrupt)
+	return ch
+}

cmd/litestream/replicate.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -10,7 +9,6 @@ import (
 	"net/http"
 	_ "net/http/pprof"
 	"os"
-	"os/signal"
 	"time"
 
 	"github.com/benbjohnson/litestream"
@@ -20,28 +18,34 @@ import (
 
 // ReplicateCommand represents a command that continuously replicates SQLite databases.
 type ReplicateCommand struct {
-	ConfigPath string
 	Config Config
 
 	// List of managed databases specified in the config.
 	DBs []*litestream.DB
 }
 
-// Run loads all databases specified in the configuration.
+func NewReplicateCommand() *ReplicateCommand {
-func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
+	return &ReplicateCommand{}
+}
+
+// ParseFlags parses the CLI flags and loads the configuration file.
+func (c *ReplicateCommand) ParseFlags(ctx context.Context, args []string) (err error) {
 	fs := flag.NewFlagSet("litestream-replicate", flag.ContinueOnError)
 	tracePath := fs.String("trace", "", "trace path")
-	registerConfigFlag(fs, &c.ConfigPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	fs.Usage = c.Usage
 	if err := fs.Parse(args); err != nil {
 		return err
 	}
 
 	// Load configuration or use CLI args to build db/replica.
-	var config Config
 	if fs.NArg() == 1 {
 		return fmt.Errorf("must specify at least one replica URL for %s", fs.Arg(0))
 	} else if fs.NArg() > 1 {
+		if *configPath != "" {
+			return fmt.Errorf("cannot specify a replica URL and the -config flag")
+		}
+
 		dbConfig := &DBConfig{Path: fs.Arg(0)}
 		for _, u := range fs.Args()[1:] {
 			dbConfig.Replicas = append(dbConfig.Replicas, &ReplicaConfig{
@@ -49,14 +53,14 @@ func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
 				SyncInterval: 1 * time.Second,
 			})
 		}
-		config.DBs = []*DBConfig{dbConfig}
+		c.Config.DBs = []*DBConfig{dbConfig}
-	} else if c.ConfigPath != "" {
+	} else {
-		config, err = ReadConfigFile(c.ConfigPath)
+		if *configPath == "" {
-		if err != nil {
+			*configPath = DefaultConfigPath()
+		}
+		if c.Config, err = ReadConfigFile(*configPath, !*noExpandEnv); err != nil {
 			return err
 		}
-	} else {
-		return errors.New("-config flag or database/replica arguments required")
 	}
 
 	// Enable trace logging.
@@ -66,24 +70,23 @@ func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
 			return err
 		}
 		defer f.Close()
-		litestream.Tracef = log.New(f, "", log.LstdFlags|log.LUTC|log.Lshortfile).Printf
+		litestream.Tracef = log.New(f, "", log.LstdFlags|log.Lmicroseconds|log.LUTC|log.Lshortfile).Printf
 	}
 
-	// Setup signal handler.
+	return nil
-	ctx, cancel := context.WithCancel(ctx)
+}
-	ch := make(chan os.Signal, 1)
-	signal.Notify(ch, os.Interrupt)
-	go func() { <-ch; cancel() }()
 
+// Run loads all databases specified in the configuration.
+func (c *ReplicateCommand) Run(ctx context.Context) (err error) {
 	// Display version information.
-	fmt.Printf("litestream %s\n", Version)
+	log.Printf("litestream %s", Version)
 
-	if len(config.DBs) == 0 {
+	if len(c.Config.DBs) == 0 {
-		fmt.Println("no databases specified in configuration")
+		log.Println("no databases specified in configuration")
 	}
 
-	for _, dbConfig := range config.DBs {
+	for _, dbConfig := range c.Config.DBs {
-		db, err := newDBFromConfig(&config, dbConfig)
+		db, err := NewDBFromConfig(dbConfig)
 		if err != nil {
 			return err
 		}
@@ -97,41 +100,37 @@ func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
 
 	// Notify user that initialization is done.
 	for _, db := range c.DBs {
-		fmt.Printf("initialized db: %s\n", db.Path())
+		log.Printf("initialized db: %s", db.Path())
 		for _, r := range db.Replicas {
 			switch r := r.(type) {
 			case *litestream.FileReplica:
-				fmt.Printf("replicating to: name=%q type=%q path=%q\n", r.Name(), r.Type(), r.Path())
+				log.Printf("replicating to: name=%q type=%q path=%q", r.Name(), r.Type(), r.Path())
 			case *s3.Replica:
-				fmt.Printf("replicating to: name=%q type=%q bucket=%q path=%q region=%q\n", r.Name(), r.Type(), r.Bucket, r.Path, r.Region)
+				log.Printf("replicating to: name=%q type=%q bucket=%q path=%q region=%q endpoint=%q sync-interval=%s", r.Name(), r.Type(), r.Bucket, r.Path, r.Region, r.Endpoint, r.SyncInterval)
 			default:
-				fmt.Printf("replicating to: name=%q type=%q\n", r.Name(), r.Type())
+				log.Printf("replicating to: name=%q type=%q", r.Name(), r.Type())
 			}
 		}
 	}
 
 	// Serve metrics over HTTP if enabled.
-	if config.Addr != "" {
+	if c.Config.Addr != "" {
-		_, port, _ := net.SplitHostPort(config.Addr)
+		hostport := c.Config.Addr
-		fmt.Printf("serving metrics on http://localhost:%s/metrics\n", port)
+		if host, port, _ := net.SplitHostPort(c.Config.Addr); port == "" {
+			return fmt.Errorf("must specify port for bind address: %q", c.Config.Addr)
+		} else if host == "" {
+			hostport = net.JoinHostPort("localhost", port)
+		}
+
+		log.Printf("serving metrics on http://%s/metrics", hostport)
 		go func() {
 			http.Handle("/metrics", promhttp.Handler())
-			if err := http.ListenAndServe(config.Addr, nil); err != nil {
+			if err := http.ListenAndServe(c.Config.Addr, nil); err != nil {
 				log.Printf("cannot start metrics server: %s", err)
 			}
 		}()
 	}
 
-	// Wait for signal to stop program.
-	<-ctx.Done()
-	signal.Reset()
-
-	// Gracefully close
-	if err := c.Close(); err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
-	}
-
 	return nil
 }
 
@@ -139,12 +138,13 @@ func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
 func (c *ReplicateCommand) Close() (err error) {
 	for _, db := range c.DBs {
 		if e := db.SoftClose(); e != nil {
-			fmt.Printf("error closing db: path=%s err=%s\n", db.Path(), e)
+			log.Printf("error closing db: path=%s err=%s", db.Path(), e)
 			if err == nil {
 				err = e
 			}
 		}
 	}
+	// TODO(windows): Clear DBs
 	return err
 }
 
@@ -168,6 +168,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 	-trace PATH
 	    Write verbose trace logging to PATH.
 

cmd/litestream/restore.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"strconv"
 	"time"
 
 	"github.com/benbjohnson/litestream"
@@ -17,17 +18,17 @@ type RestoreCommand struct{}
 
 // Run executes the command.
 func (c *RestoreCommand) Run(ctx context.Context, args []string) (err error) {
-	var configPath string
 	opt := litestream.NewRestoreOptions()
 	opt.Verbose = true
 
 	fs := flag.NewFlagSet("litestream-restore", flag.ContinueOnError)
-	registerConfigFlag(fs, &configPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	fs.StringVar(&opt.OutputPath, "o", "", "output path")
 	fs.StringVar(&opt.ReplicaName, "replica", "", "replica name")
 	fs.StringVar(&opt.Generation, "generation", "", "generation name")
-	fs.IntVar(&opt.Index, "index", opt.Index, "wal index")
+	fs.Var((*indexVar)(&opt.Index), "index", "wal index")
-	fs.BoolVar(&opt.DryRun, "dry-run", false, "dry run")
+	fs.IntVar(&opt.Parallelism, "parallelism", opt.Parallelism, "parallelism")
+	ifReplicaExists := fs.Bool("if-replica-exists", false, "")
 	timestampStr := fs.String("timestamp", "", "timestamp")
 	verbose := fs.Bool("v", false, "verbose output")
 	fs.Usage = c.Usage
@@ -46,32 +47,36 @@ func (c *RestoreCommand) Run(ctx context.Context, args []string) (err error) {
 		}
 	}
 
-	// Verbose output is automatically enabled if dry run is specified.
-	if opt.DryRun {
-		*verbose = true
-	}
-
 	// Instantiate logger if verbose output is enabled.
 	if *verbose {
-		opt.Logger = log.New(os.Stderr, "", log.LstdFlags)
+		opt.Logger = log.New(os.Stderr, "", log.LstdFlags|log.Lmicroseconds)
 	}
 
 	// Determine replica & generation to restore from.
 	var r litestream.Replica
 	if isURL(fs.Arg(0)) {
+		if *configPath != "" {
+			return fmt.Errorf("cannot specify a replica URL and the -config flag")
+		}
 		if r, err = c.loadFromURL(ctx, fs.Arg(0), &opt); err != nil {
 			return err
 		}
-	} else if configPath != "" {
+	} else {
-		if r, err = c.loadFromConfig(ctx, fs.Arg(0), configPath, &opt); err != nil {
+		if *configPath == "" {
+			*configPath = DefaultConfigPath()
+		}
+		if r, err = c.loadFromConfig(ctx, fs.Arg(0), *configPath, !*noExpandEnv, &opt); err != nil {
 			return err
 		}
-	} else {
-		return errors.New("config path or replica URL required")
 	}
 
 	// Return an error if no matching targets found.
+	// If optional flag set, return success. Useful for automated recovery.
 	if opt.Generation == "" {
+		if *ifReplicaExists {
+			fmt.Println("no matching backups found")
+			return nil
+		}
 		return fmt.Errorf("no matching backups found")
 	}
 
@@ -80,7 +85,7 @@ func (c *RestoreCommand) Run(ctx context.Context, args []string) (err error) {
 
 // loadFromURL creates a replica & updates the restore options from a replica URL.
 func (c *RestoreCommand) loadFromURL(ctx context.Context, replicaURL string, opt *litestream.RestoreOptions) (litestream.Replica, error) {
-	r, err := NewReplicaFromURL(replicaURL)
+	r, err := NewReplicaFromConfig(&ReplicaConfig{URL: replicaURL}, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -89,9 +94,9 @@ func (c *RestoreCommand) loadFromURL(ctx context.Context, replicaURL string, opt
 }
 
 // loadFromConfig returns a replica & updates the restore options from a DB reference.
-func (c *RestoreCommand) loadFromConfig(ctx context.Context, dbPath, configPath string, opt *litestream.RestoreOptions) (litestream.Replica, error) {
+func (c *RestoreCommand) loadFromConfig(ctx context.Context, dbPath, configPath string, expandEnv bool, opt *litestream.RestoreOptions) (litestream.Replica, error) {
 	// Load configuration.
-	config, err := ReadConfigFile(configPath)
+	config, err := ReadConfigFile(configPath, expandEnv)
 	if err != nil {
 		return nil, err
 	}
@@ -104,7 +109,7 @@ func (c *RestoreCommand) loadFromConfig(ctx context.Context, dbPath, configPath
 	if dbConfig == nil {
 		return nil, fmt.Errorf("database not found in config: %s", dbPath)
 	}
-	db, err := newDBFromConfig(&config, dbConfig)
+	db, err := NewDBFromConfig(dbConfig)
 	if err != nil {
 		return nil, err
 	}
@@ -141,6 +146,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 	-replica NAME
 	    Restore from a specific replica.
 	    Defaults to replica with latest data.
@@ -150,7 +158,7 @@ Arguments:
 	    Defaults to generation with latest data.
 
 	-index NUM
-	    Restore up to a specific WAL index (inclusive).
+	    Restore up to a specific hex-encoded WAL index (inclusive).
 	    Defaults to use the highest available index.
 
 	-timestamp TIMESTAMP
@@ -161,9 +169,12 @@ Arguments:
 	    Output path of the restored database.
 	    Defaults to original DB path.
 
-	-dry-run
+	-if-replica-exists
-	    Prints all log output as if it were running but does
+	    Returns exit code of 0 if no backups found.
-	    not perform actual restore.
+
+	-parallelism NUM
+	    Determines the number of WAL files downloaded in parallel.
+	    Defaults to `+strconv.Itoa(litestream.DefaultRestoreParallelism)+`.
 
 	-v
 	    Verbose output.

cmd/litestream/snapshots.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -17,9 +16,8 @@ type SnapshotsCommand struct{}
 
 // Run executes the command.
 func (c *SnapshotsCommand) Run(ctx context.Context, args []string) (err error) {
-	var configPath string
 	fs := flag.NewFlagSet("litestream-snapshots", flag.ContinueOnError)
-	registerConfigFlag(fs, &configPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	replicaName := fs.String("replica", "", "replica name")
 	fs.Usage = c.Usage
 	if err := fs.Parse(args); err != nil {
@@ -33,12 +31,19 @@ func (c *SnapshotsCommand) Run(ctx context.Context, args []string) (err error) {
 	var db *litestream.DB
 	var r litestream.Replica
 	if isURL(fs.Arg(0)) {
-		if r, err = NewReplicaFromURL(fs.Arg(0)); err != nil {
+		if *configPath != "" {
+			return fmt.Errorf("cannot specify a replica URL and the -config flag")
+		}
+		if r, err = NewReplicaFromConfig(&ReplicaConfig{URL: fs.Arg(0)}, nil); err != nil {
 			return err
 		}
-	} else if configPath != "" {
+	} else {
+		if *configPath == "" {
+			*configPath = DefaultConfigPath()
+		}
+
 		// Load configuration.
-		config, err := ReadConfigFile(configPath)
+		config, err := ReadConfigFile(*configPath, !*noExpandEnv)
 		if err != nil {
 			return err
 		}
@@ -48,7 +53,7 @@ func (c *SnapshotsCommand) Run(ctx context.Context, args []string) (err error) {
 			return err
 		} else if dbc := config.DBConfig(path); dbc == nil {
 			return fmt.Errorf("database not found in config: %s", path)
-		} else if db, err = newDBFromConfig(&config, dbc); err != nil {
+		} else if db, err = NewDBFromConfig(dbc); err != nil {
 			return err
 		}
 
@@ -58,8 +63,6 @@ func (c *SnapshotsCommand) Run(ctx context.Context, args []string) (err error) {
 				return fmt.Errorf("replica %q not found for database %q", *replicaName, db.Path())
 			}
 		}
-	} else {
-		return errors.New("config path or replica URL required")
 	}
 
 	// Find snapshots by db or replica.
@@ -109,6 +112,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 	-replica NAME
 	    Optional, filter by a specific replica.
 

cmd/litestream/wal.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -17,9 +16,8 @@ type WALCommand struct{}
 
 // Run executes the command.
 func (c *WALCommand) Run(ctx context.Context, args []string) (err error) {
-	var configPath string
 	fs := flag.NewFlagSet("litestream-wal", flag.ContinueOnError)
-	registerConfigFlag(fs, &configPath)
+	configPath, noExpandEnv := registerConfigFlag(fs)
 	replicaName := fs.String("replica", "", "replica name")
 	generation := fs.String("generation", "", "generation name")
 	fs.Usage = c.Usage
@@ -34,12 +32,19 @@ func (c *WALCommand) Run(ctx context.Context, args []string) (err error) {
 	var db *litestream.DB
 	var r litestream.Replica
 	if isURL(fs.Arg(0)) {
-		if r, err = NewReplicaFromURL(fs.Arg(0)); err != nil {
+		if *configPath != "" {
+			return fmt.Errorf("cannot specify a replica URL and the -config flag")
+		}
+		if r, err = NewReplicaFromConfig(&ReplicaConfig{URL: fs.Arg(0)}, nil); err != nil {
 			return err
 		}
-	} else if configPath != "" {
+	} else {
+		if *configPath == "" {
+			*configPath = DefaultConfigPath()
+		}
+
 		// Load configuration.
-		config, err := ReadConfigFile(configPath)
+		config, err := ReadConfigFile(*configPath, !*noExpandEnv)
 		if err != nil {
 			return err
 		}
@@ -49,7 +54,7 @@ func (c *WALCommand) Run(ctx context.Context, args []string) (err error) {
 			return err
 		} else if dbc := config.DBConfig(path); dbc == nil {
 			return fmt.Errorf("database not found in config: %s", path)
-		} else if db, err = newDBFromConfig(&config, dbc); err != nil {
+		} else if db, err = NewDBFromConfig(dbc); err != nil {
 			return err
 		}
 
@@ -59,8 +64,6 @@ func (c *WALCommand) Run(ctx context.Context, args []string) (err error) {
 				return fmt.Errorf("replica %q not found for database %q", *replicaName, db.Path())
 			}
 		}
-	} else {
-		return errors.New("config path or replica URL required")
 	}
 
 	// Find WAL files by db or replica.
@@ -115,6 +118,9 @@ Arguments:
 	    Specifies the configuration file.
 	    Defaults to %s
 
+	-no-expand-env
+	    Disables environment variable expansion in configuration file.
+
 	-replica NAME
 	    Optional, filter by a specific replica.
 

db.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
+	"golang.org/x/sync/errgroup"
 )
 
 // Default DB settings.
@@ -45,6 +46,7 @@ type DB struct {
 	mu       sync.RWMutex
 	path     string        // part to database
 	db       *sql.DB       // target database
+	f        *os.File      // long-running db file descriptor
 	rtx      *sql.Tx       // long running read transaction
 	pageSize int           // page size, in bytes
 	notify   chan struct{} // closes on WAL change
@@ -259,6 +261,11 @@ func (db *DB) PageSize() int {
 
 // Open initializes the background monitoring goroutine.
 func (db *DB) Open() (err error) {
+	// Validate fields on database.
+	if db.MinCheckpointPageN <= 0 {
+		return fmt.Errorf("minimum checkpoint page count required")
+	}
+
 	// Validate that all replica names are unique.
 	m := make(map[string]struct{})
 	for _, r := range db.Replicas {
@@ -285,15 +292,55 @@ func (db *DB) Open() (err error) {
 // Close releases the read lock & closes the database. This method should only
 // be called by tests as it causes the underlying database to be checkpointed.
 func (db *DB) Close() (err error) {
-	if e := db.SoftClose(); e != nil && err == nil {
+	return db.close(false)
+}
+
+// SoftClose closes everything but the underlying db connection. This method
+// is available because the binary needs to avoid closing the database on exit
+// to prevent autocheckpointing.
+func (db *DB) SoftClose() (err error) {
+	return db.close(true)
+}
+
+func (db *DB) close(soft bool) (err error) {
+	db.cancel()
+	db.wg.Wait()
+
+	// Start a new context for shutdown since we canceled the DB context.
+	ctx := context.Background()
+
+	// Perform a final db sync, if initialized.
+	if db.db != nil {
+		if e := db.Sync(ctx); e != nil && err == nil {
 			err = e
 		}
+	}
 
+	// Ensure replicas perform a final sync and stop replicating.
+	for _, r := range db.Replicas {
 		if db.db != nil {
+			if e := r.Sync(ctx); e != nil && err == nil {
+				err = e
+			}
+		}
+		r.Stop(!soft)
+	}
+
+	// Release the read lock to allow other applications to handle checkpointing.
+	if db.rtx != nil {
+		if e := db.releaseReadLock(); e != nil && err == nil {
+			err = e
+		}
+	}
+
+	// Only perform full close if this is not a soft close.
+	// This closes the underlying database connection which can clean up the WAL.
+	if !soft && db.db != nil {
 		if e := db.db.Close(); e != nil && err == nil {
 			err = e
 		}
 	}
+
 	return err
 }
 
@@ -381,11 +428,34 @@ func (db *DB) init() (err error) {
 	dsn := db.path
 	dsn += fmt.Sprintf("?_busy_timeout=%d", BusyTimeout.Milliseconds())
 
-	// Connect to SQLite database & enable WAL.
+	// Connect to SQLite database.
 	if db.db, err = sql.Open("sqlite3", dsn); err != nil {
 		return err
-	} else if _, err := db.db.Exec(`PRAGMA journal_mode = wal;`); err != nil {
+	}
-		return fmt.Errorf("enable wal: %w", err)
+
+	// Open long-running database file descriptor. Required for non-OFD locks.
+	if db.f, err = os.Open(db.path); err != nil {
+		return fmt.Errorf("open db file descriptor: %w", err)
+	}
+
+	// Ensure database is closed if init fails.
+	// Initialization can retry on next sync.
+	defer func() {
+		if err != nil {
+			_ = db.releaseReadLock()
+			db.db.Close()
+			db.f.Close()
+			db.db, db.f = nil, nil
+		}
+	}()
+
+	// Enable WAL and ensure it is set. New mode should be returned on success:
+	// https://www.sqlite.org/pragma.html#pragma_journal_mode
+	var mode string
+	if err := db.db.QueryRow(`PRAGMA journal_mode = wal;`).Scan(&mode); err != nil {
+		return err
+	} else if mode != "wal" {
+		return fmt.Errorf("enable wal failed, mode=%q", mode)
 	}
 
 	// Disable autocheckpoint for litestream's connection.
@@ -425,7 +495,7 @@ func (db *DB) init() (err error) {
 
 	// If we have an existing shadow WAL, ensure the headers match.
 	if err := db.verifyHeadersMatch(); err != nil {
-		log.Printf("%s: init: cannot determine last wal position, clearing generation (%s)", db.path, err)
+		log.Printf("%s: init: cannot determine last wal position, clearing generation; %s", db.path, err)
 		if err := os.Remove(db.GenerationNamePath()); err != nil && !os.IsNotExist(err) {
 			return fmt.Errorf("remove generation name: %w", err)
 		}
@@ -475,7 +545,7 @@ func (db *DB) verifyHeadersMatch() error {
 	}
 
 	if !bytes.Equal(hdr0, hdr1) {
-		return fmt.Errorf("wal header mismatch")
+		return fmt.Errorf("wal header mismatch %x <> %x on %s", hdr0, hdr1, shadowWALPath)
 	}
 	return nil
 }
@@ -560,26 +630,6 @@ func (db *DB) cleanWAL() error {
 	return nil
 }
 
-// SoftClose closes everything but the underlying db connection. This method
-// is available because the binary needs to avoid closing the database on exit
-// to prevent autocheckpointing.
-func (db *DB) SoftClose() (err error) {
-	db.cancel()
-	db.wg.Wait()
-
-	// Ensure replicas all stop replicating.
-	for _, r := range db.Replicas {
-		r.Stop()
-	}
-
-	if db.rtx != nil {
-		if e := db.releaseReadLock(); e != nil && err == nil {
-			err = e
-		}
-	}
-	return err
-}
-
 // acquireReadLock begins a read transaction on the database to prevent checkpointing.
 func (db *DB) acquireReadLock() error {
 	if db.rtx != nil {
@@ -674,7 +724,7 @@ func (db *DB) createGeneration() (string, error) {
 }
 
 // Sync copies pending data from the WAL to the shadow WAL.
-func (db *DB) Sync() (err error) {
+func (db *DB) Sync(ctx context.Context) (err error) {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
@@ -701,27 +751,6 @@ func (db *DB) Sync() (err error) {
 		return fmt.Errorf("ensure wal exists: %w", err)
 	}
 
-	// Start a transaction. This will be promoted immediately after.
-	tx, err := db.db.Begin()
-	if err != nil {
-		return fmt.Errorf("begin: %w", err)
-	}
-
-	// Ensure write transaction rolls back before returning.
-	defer func() {
-		if e := rollback(tx); e != nil && err == nil {
-			err = e
-		}
-	}()
-
-	// Insert into the lock table to promote to a write tx. The lock table
-	// insert will never actually occur because our tx will be rolled back,
-	// however, it will ensure our tx grabs the write lock. Unfortunately,
-	// we can't call "BEGIN IMMEDIATE" as we are already in a transaction.
-	if _, err := tx.ExecContext(db.ctx, `INSERT INTO _litestream_lock (id) VALUES (1);`); err != nil {
-		return fmt.Errorf("_litestream_lock: %w", err)
-	}
-
 	// Verify our last sync matches the current state of the WAL.
 	// This ensures that we have an existing generation & that the last sync
 	// position of the real WAL hasn't been overwritten by another process.
@@ -768,16 +797,11 @@ func (db *DB) Sync() (err error) {
 		checkpoint = true
 	}
 
-	// Release write lock before checkpointing & exiting.
-	if err := tx.Rollback(); err != nil {
-		return fmt.Errorf("rollback write tx: %w", err)
-	}
-
 	// Issue the checkpoint.
 	if checkpoint {
 		changed = true
 
-		if err := db.checkpointAndInit(info.generation, checkpointMode); err != nil {
+		if err := db.checkpointAndInit(ctx, info.generation, checkpointMode); err != nil {
 			return fmt.Errorf("checkpoint: mode=%v err=%w", checkpointMode, err)
 		}
 	}
@@ -843,7 +867,7 @@ func (db *DB) verify() (info syncInfo, err error) {
 	if err != nil {
 		return info, err
 	}
-	info.walSize = fi.Size()
+	info.walSize = frameAlign(fi.Size(), db.pageSize)
 	info.walModTime = fi.ModTime()
 	db.walSizeGauge.Set(float64(fi.Size()))
 
@@ -867,7 +891,6 @@ func (db *DB) verify() (info syncInfo, err error) {
 	}
 	info.shadowWALSize = frameAlign(fi.Size(), db.pageSize)
 
-	// Truncate shadow WAL if there is a partial page.
 	// Exit if shadow WAL does not contain a full header.
 	if info.shadowWALSize < WALHeaderSize {
 		info.reason = "short shadow wal"
@@ -900,9 +923,9 @@ func (db *DB) verify() (info syncInfo, err error) {
 	// Verify last page synced still matches.
 	if info.shadowWALSize > WALHeaderSize {
 		offset := info.shadowWALSize - int64(db.pageSize+WALFrameHeaderSize)
-		if buf0, err := readFileAt(db.WALPath(), offset, int64(db.pageSize+WALFrameHeaderSize)); err != nil {
+		if buf0, err := readWALFileAt(db.WALPath(), offset, int64(db.pageSize+WALFrameHeaderSize)); err != nil {
 			return info, fmt.Errorf("cannot read last synced wal page: %w", err)
-		} else if buf1, err := readFileAt(info.shadowWALPath, offset, int64(db.pageSize+WALFrameHeaderSize)); err != nil {
+		} else if buf1, err := readWALFileAt(info.shadowWALPath, offset, int64(db.pageSize+WALFrameHeaderSize)); err != nil {
 			return info, fmt.Errorf("cannot read last synced shadow wal page: %w", err)
 		} else if !bytes.Equal(buf0, buf1) {
 			info.reason = "wal overwritten by another process"
@@ -1289,7 +1312,7 @@ func (db *DB) checkpoint(mode string) (err error) {
 
 // checkpointAndInit performs a checkpoint on the WAL file and initializes a
 // new shadow WAL file.
-func (db *DB) checkpointAndInit(generation, mode string) error {
+func (db *DB) checkpointAndInit(ctx context.Context, generation, mode string) error {
 	shadowWALPath, err := db.CurrentShadowWALPath(generation)
 	if err != nil {
 		return err
@@ -1321,6 +1344,21 @@ func (db *DB) checkpointAndInit(generation, mode string) error {
 		return nil
 	}
 
+	// Start a transaction. This will be promoted immediately after.
+	tx, err := db.db.Begin()
+	if err != nil {
+		return fmt.Errorf("begin: %w", err)
+	}
+	defer func() { _ = rollback(tx) }()
+
+	// Insert into the lock table to promote to a write tx. The lock table
+	// insert will never actually occur because our tx will be rolled back,
+	// however, it will ensure our tx grabs the write lock. Unfortunately,
+	// we can't call "BEGIN IMMEDIATE" as we are already in a transaction.
+	if _, err := tx.ExecContext(ctx, `INSERT INTO _litestream_lock (id) VALUES (1);`); err != nil {
+		return fmt.Errorf("_litestream_lock: %w", err)
+	}
+
 	// Copy the end of the previous WAL before starting a new shadow WAL.
 	if _, err := db.copyToShadowWAL(shadowWALPath); err != nil {
 		return fmt.Errorf("cannot copy to end of shadow wal: %w", err)
@@ -1338,6 +1376,10 @@ func (db *DB) checkpointAndInit(generation, mode string) error {
 		return fmt.Errorf("cannot init shadow wal file: name=%s err=%w", newShadowWALPath, err)
 	}
 
+	// Release write lock before checkpointing & exiting.
+	if err := tx.Rollback(); err != nil {
+		return fmt.Errorf("rollback post-checkpoint tx: %w", err)
+	}
 	return nil
 }
 
@@ -1355,7 +1397,7 @@ func (db *DB) monitor() {
 		}
 
 		// Sync the database to the shadow WAL.
-		if err := db.Sync(); err != nil && !errors.Is(err, context.Canceled) {
+		if err := db.Sync(db.ctx); err != nil && !errors.Is(err, context.Canceled) {
 			log.Printf("%s: sync error: %s", db.path, err)
 		}
 	}
@@ -1367,13 +1409,13 @@ func (db *DB) monitor() {
 // replica or generation or it will automatically choose the best one. Finally,
 // a timestamp can be specified to restore the database to a specific
 // point-in-time.
-func RestoreReplica(ctx context.Context, r Replica, opt RestoreOptions) error {
+func RestoreReplica(ctx context.Context, r Replica, opt RestoreOptions) (err error) {
 	// Validate options.
 	if opt.OutputPath == "" {
 		return fmt.Errorf("output path required")
-	} else if opt.Generation == "" && opt.Index != math.MaxInt64 {
+	} else if opt.Generation == "" && opt.Index != math.MaxInt32 {
 		return fmt.Errorf("must specify generation when restoring to index")
-	} else if opt.Index != math.MaxInt64 && !opt.Timestamp.IsZero() {
+	} else if opt.Index != math.MaxInt32 && !opt.Timestamp.IsZero() {
 		return fmt.Errorf("cannot specify index & timestamp to restore")
 	}
 
@@ -1388,19 +1430,23 @@ func RestoreReplica(ctx context.Context, r Replica, opt RestoreOptions) error {
 		logPrefix = fmt.Sprintf("%s(%s)", db.Path(), r.Name())
 	}
 
-	// Ensure output path does not already exist (unless this is a dry run).
+	// Ensure output path does not already exist.
-	if !opt.DryRun {
 	if _, err := os.Stat(opt.OutputPath); err == nil {
 		return fmt.Errorf("cannot restore, output path already exists: %s", opt.OutputPath)
 	} else if err != nil && !os.IsNotExist(err) {
 		return err
 	}
-	}
 
-	// Find lastest snapshot that occurs before timestamp.
+	// Find lastest snapshot that occurs before timestamp or index.
-	minWALIndex, err := SnapshotIndexAt(ctx, r, opt.Generation, opt.Timestamp)
+	var minWALIndex int
-	if err != nil {
+	if opt.Index < math.MaxInt32 {
-		return fmt.Errorf("cannot find snapshot index for restore: %w", err)
+		if minWALIndex, err = SnapshotIndexByIndex(ctx, r, opt.Generation, opt.Index); err != nil {
+			return fmt.Errorf("cannot find snapshot index: %w", err)
+		}
+	} else {
+		if minWALIndex, err = SnapshotIndexAt(ctx, r, opt.Generation, opt.Timestamp); err != nil {
+			return fmt.Errorf("cannot find snapshot index by timestamp: %w", err)
+		}
 	}
 
 	// Find the maximum WAL index that occurs before timestamp.
@@ -1408,7 +1454,7 @@ func RestoreReplica(ctx context.Context, r Replica, opt RestoreOptions) error {
 	if err != nil {
 		return fmt.Errorf("cannot find max wal index for restore: %w", err)
 	}
-	logger.Printf("%s: starting restore: generation %s, index %08x-%08x", logPrefix, opt.Generation, minWALIndex, maxWALIndex)
+	snapshotOnly := maxWALIndex == -1
 
 	// Initialize starting position.
 	pos := Pos{Generation: opt.Generation, Index: minWALIndex}
@@ -1416,51 +1462,122 @@ func RestoreReplica(ctx context.Context, r Replica, opt RestoreOptions) error {
 
 	// Copy snapshot to output path.
 	logger.Printf("%s: restoring snapshot %s/%08x to %s", logPrefix, opt.Generation, minWALIndex, tmpPath)
-	if !opt.DryRun {
 	if err := restoreSnapshot(ctx, r, pos.Generation, pos.Index, tmpPath); err != nil {
 		return fmt.Errorf("cannot restore snapshot: %w", err)
 	}
+
+	// If no WAL files available, move snapshot to final path & exit early.
+	if snapshotOnly {
+		logger.Printf("%s: snapshot only, finalizing database", logPrefix)
+		return os.Rename(tmpPath, opt.OutputPath)
 	}
 
-	// Restore each WAL file until we reach our maximum index.
+	// Begin processing WAL files.
+	logger.Printf("%s: restoring wal files: generation=%s index=[%08x,%08x]", logPrefix, opt.Generation, minWALIndex, maxWALIndex)
+
+	// Fill input channel with all WAL indexes to be loaded in order.
+	ch := make(chan int, maxWALIndex-minWALIndex+1)
 	for index := minWALIndex; index <= maxWALIndex; index++ {
-		if !opt.DryRun {
+		ch <- index
-			if err = restoreWAL(ctx, r, opt.Generation, index, tmpPath); os.IsNotExist(err) && index == minWALIndex && index == maxWALIndex {
-				logger.Printf("%s: no wal available, snapshot only", logPrefix)
-				break // snapshot file only, ignore error
-			} else if err != nil {
-				return fmt.Errorf("cannot restore wal: %w", err)
 	}
+	close(ch)
+
+	// Track load state for each WAL.
+	var mu sync.Mutex
+	cond := sync.NewCond(&mu)
+	walStates := make([]walRestoreState, maxWALIndex-minWALIndex+1)
+
+	parallelism := opt.Parallelism
+	if parallelism < 1 {
+		parallelism = 1
 	}
 
-		if opt.Verbose {
+	// Download WAL files to disk in parallel.
-			logger.Printf("%s: restored wal %s/%08x", logPrefix, opt.Generation, index)
+	g, ctx := errgroup.WithContext(ctx)
+	for i := 0; i < parallelism; i++ {
+		g.Go(func() error {
+			for {
+				select {
+				case <-ctx.Done():
+					cond.Broadcast()
+					return err
+				case index, ok := <-ch:
+					if !ok {
+						cond.Broadcast()
+						return nil
 					}
+
+					startTime := time.Now()
+
+					err := downloadWAL(ctx, r, opt.Generation, index, tmpPath)
+					if err != nil {
+						err = fmt.Errorf("cannot download wal %s/%08x: %w", opt.Generation, index, err)
+					}
+
+					// Mark index as ready-to-apply and notify applying code.
+					mu.Lock()
+					walStates[index-minWALIndex] = walRestoreState{ready: true, err: err}
+					mu.Unlock()
+					cond.Broadcast()
+
+					// Returning the error here will cancel the other goroutines.
+					if err != nil {
+						return err
+					}
+
+					logger.Printf("%s: downloaded wal %s/%08x elapsed=%s",
+						logPrefix, opt.Generation, index,
+						time.Since(startTime).String(),
+					)
+				}
+			}
+		})
+	}
+
+	// Apply WAL files in order as they are ready.
+	for index := minWALIndex; index <= maxWALIndex; index++ {
+		// Wait until next WAL file is ready to apply.
+		mu.Lock()
+		for !walStates[index-minWALIndex].ready {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+			cond.Wait()
+		}
+		if err := walStates[index-minWALIndex].err; err != nil {
+			return err
+		}
+		mu.Unlock()
+
+		// Apply WAL to database file.
+		startTime := time.Now()
+		if err = applyWAL(ctx, index, tmpPath); err != nil {
+			return fmt.Errorf("cannot apply wal: %w", err)
+		}
+		logger.Printf("%s: applied wal %s/%08x elapsed=%s",
+			logPrefix, opt.Generation, index,
+			time.Since(startTime).String(),
+		)
+	}
+
+	// Ensure all goroutines finish. All errors should have been handled during
+	// the processing of WAL files but this ensures that all processing is done.
+	if err := g.Wait(); err != nil {
+		return err
 	}
 
 	// Copy file to final location.
 	logger.Printf("%s: renaming database from temporary location", logPrefix)
-	if !opt.DryRun {
 	if err := os.Rename(tmpPath, opt.OutputPath); err != nil {
 		return err
 	}
-	}
 
 	return nil
 }
 
-func checksumFile(filename string) (uint64, error) {
+type walRestoreState struct {
-	f, err := os.Open(filename)
+	ready bool
-	if err != nil {
+	err   error
-		return 0, err
-	}
-	defer f.Close()
-
-	h := crc64.New(crc64.MakeTable(crc64.ISO))
-	if _, err := io.Copy(h, f); err != nil {
-		return 0, err
-	}
-	return h.Sum64(), nil
 }
 
 // CalcRestoreTarget returns a replica & generation to restore from based on opt criteria.
@@ -1572,8 +1689,10 @@ func restoreSnapshot(ctx context.Context, r Replica, generation string, index in
 	return f.Close()
 }
 
-// restoreWAL copies a WAL file from the replica to the local WAL and forces checkpoint.
+// downloadWAL copies a WAL file from the replica to a local copy next to the DB.
-func restoreWAL(ctx context.Context, r Replica, generation string, index int, dbPath string) error {
+// The WAL is later applied by applyWAL(). This function can be run in parallel
+// to download multiple WAL files simultaneously.
+func downloadWAL(ctx context.Context, r Replica, generation string, index int, dbPath string) error {
 	// Determine the user/group & mode based on the DB, if available.
 	uid, gid, mode := -1, -1, os.FileMode(0600)
 	if db := r.DB(); db != nil {
@@ -1588,7 +1707,7 @@ func restoreWAL(ctx context.Context, r Replica, generation string, index int, db
 	defer rd.Close()
 
 	// Open handle to destination WAL path.
-	f, err := createFile(dbPath+"-wal", mode, uid, gid)
+	f, err := createFile(fmt.Sprintf("%s-%08x-wal", dbPath, index), mode, uid, gid)
 	if err != nil {
 		return err
 	}
@@ -1600,6 +1719,15 @@ func restoreWAL(ctx context.Context, r Replica, generation string, index int, db
 	} else if err := f.Close(); err != nil {
 		return err
 	}
+	return nil
+}
+
+// applyWAL performs a truncating checkpoint on the given database.
+func applyWAL(ctx context.Context, index int, dbPath string) error {
+	// Copy WAL file from it's staging path to the correct "-wal" location.
+	if err := os.Rename(fmt.Sprintf("%s-%08x-wal", dbPath, index), dbPath+"-wal"); err != nil {
+		return err
+	}
 
 	// Open SQLite database and force a truncating checkpoint.
 	d, err := sql.Open("sqlite3", dbPath)
@@ -1614,7 +1742,6 @@ func restoreWAL(ctx context.Context, r Replica, generation string, index int, db
 	} else if row[0] != 0 {
 		return fmt.Errorf("truncation checkpoint failed during restore (%d,%d,%d)", row[0], row[1], row[2])
 	}
-
 	return d.Close()
 }
 
@@ -1625,7 +1752,7 @@ func restoreWAL(ctx context.Context, r Replica, generation string, index int, db
 // unable to checkpoint during this time.
 //
 // If dst is set, the database file is copied to that location before checksum.
-func (db *DB) CRC64() (uint64, Pos, error) {
+func (db *DB) CRC64(ctx context.Context) (uint64, Pos, error) {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
@@ -1643,7 +1770,7 @@ func (db *DB) CRC64() (uint64, Pos, error) {
 	}
 
 	// Force a RESTART checkpoint to ensure the database is at the start of the WAL.
-	if err := db.checkpointAndInit(generation, CheckpointModeRestart); err != nil {
+	if err := db.checkpointAndInit(ctx, generation, CheckpointModeRestart); err != nil {
 		return 0, Pos{}, err
 	}
 
@@ -1655,13 +1782,19 @@ func (db *DB) CRC64() (uint64, Pos, error) {
 	}
 	pos.Offset = 0
 
-	chksum, err := checksumFile(db.Path())
+	// Seek to the beginning of the db file descriptor and checksum whole file.
-	if err != nil {
+	h := crc64.New(crc64.MakeTable(crc64.ISO))
+	if _, err := db.f.Seek(0, io.SeekStart); err != nil {
+		return 0, pos, err
+	} else if _, err := io.Copy(h, db.f); err != nil {
 		return 0, pos, err
 	}
-	return chksum, pos, nil
+	return h.Sum64(), pos, nil
 }
 
+// DefaultRestoreParallelism is the default parallelism when downloading WAL files.
+const DefaultRestoreParallelism = 8
+
 // RestoreOptions represents options for DB.Restore().
 type RestoreOptions struct {
 	// Target path to restore into.
@@ -1677,16 +1810,15 @@ type RestoreOptions struct {
 	Generation string
 
 	// Specific index to restore from.
-	// Set to math.MaxInt64 to ignore index.
+	// Set to math.MaxInt32 to ignore index.
 	Index int
 
 	// Point-in-time to restore database.
 	// If zero, database restore to most recent state available.
 	Timestamp time.Time
 
-	// If true, no actual restore is performed.
+	// Specifies how many WAL files are downloaded in parallel during restore.
-	// Only equivalent log output for a regular restore.
+	Parallelism int
-	DryRun bool
 
 	// Logging settings.
 	Logger  *log.Logger
@@ -1696,7 +1828,8 @@ type RestoreOptions struct {
 // NewRestoreOptions returns a new instance of RestoreOptions with defaults.
 func NewRestoreOptions() RestoreOptions {
 	return RestoreOptions{
-		Index: math.MaxInt64,
+		Index:       math.MaxInt32,
+		Parallelism: DefaultRestoreParallelism,
 	}
 }
 
@@ -1791,24 +1924,3 @@ func headerByteOrder(hdr []byte) (binary.ByteOrder, error) {
 		return nil, fmt.Errorf("invalid wal header magic: %x", magic)
 	}
 }
-
-func copyFile(dst, src string) error {
-	r, err := os.Open(src)
-	if err != nil {
-		return err
-	}
-	defer r.Close()
-
-	w, err := os.Create(dst)
-	if err != nil {
-		return err
-	}
-	defer w.Close()
-
-	if _, err := io.Copy(w, r); err != nil {
-		return err
-	} else if err := w.Sync(); err != nil {
-		return err
-	}
-	return nil
-}

db_test.go

@@ -1,10 +1,12 @@
 package litestream_test
 
 import (
+	"context"
 	"database/sql"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
@@ -98,9 +100,12 @@ func TestDB_UpdatedAt(t *testing.T) {
 			t.Fatal(err)
 		}
 
+		sleepTime := 100 * time.Millisecond
 		if os.Getenv("CI") != "" {
-			time.Sleep(1 * time.Second)
+			sleepTime = 1 * time.Second
 		}
+		time.Sleep(sleepTime)
+
 		if _, err := sqldb.Exec(`CREATE TABLE t (id INT);`); err != nil {
 			t.Fatal(err)
 		}
@@ -118,7 +123,7 @@ func TestDB_CRC64(t *testing.T) {
 	t.Run("ErrNotExist", func(t *testing.T) {
 		db := MustOpenDB(t)
 		defer MustCloseDB(t, db)
-		if _, _, err := db.CRC64(); !os.IsNotExist(err) {
+		if _, _, err := db.CRC64(context.Background()); !os.IsNotExist(err) {
 			t.Fatalf("unexpected error: %#v", err)
 		}
 	})
@@ -127,11 +132,11 @@ func TestDB_CRC64(t *testing.T) {
 		db, sqldb := MustOpenDBs(t)
 		defer MustCloseDBs(t, db, sqldb)
 
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
-		chksum0, _, err := db.CRC64()
+		chksum0, _, err := db.CRC64(context.Background())
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -139,7 +144,7 @@ func TestDB_CRC64(t *testing.T) {
 		// Issue change that is applied to the WAL. Checksum should not change.
 		if _, err := sqldb.Exec(`CREATE TABLE t (id INT);`); err != nil {
 			t.Fatal(err)
-		} else if chksum1, _, err := db.CRC64(); err != nil {
+		} else if chksum1, _, err := db.CRC64(context.Background()); err != nil {
 			t.Fatal(err)
 		} else if chksum0 == chksum1 {
 			t.Fatal("expected different checksum event after WAL change")
@@ -150,7 +155,7 @@ func TestDB_CRC64(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		if chksum2, _, err := db.CRC64(); err != nil {
+		if chksum2, _, err := db.CRC64(context.Background()); err != nil {
 			t.Fatal(err)
 		} else if chksum0 == chksum2 {
 			t.Fatal("expected different checksums after checkpoint")
@@ -164,7 +169,7 @@ func TestDB_Sync(t *testing.T) {
 	t.Run("NoDB", func(t *testing.T) {
 		db := MustOpenDB(t)
 		defer MustCloseDB(t, db)
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 	})
@@ -174,7 +179,7 @@ func TestDB_Sync(t *testing.T) {
 		db, sqldb := MustOpenDBs(t)
 		defer MustCloseDBs(t, db, sqldb)
 
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -212,7 +217,7 @@ func TestDB_Sync(t *testing.T) {
 		}
 
 		// Perform initial sync & grab initial position.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -227,7 +232,7 @@ func TestDB_Sync(t *testing.T) {
 		}
 
 		// Sync to ensure position moves forward one page.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		} else if pos1, err := db.Pos(); err != nil {
 			t.Fatal(err)
@@ -246,7 +251,7 @@ func TestDB_Sync(t *testing.T) {
 		defer MustCloseDBs(t, db, sqldb)
 
 		// Issue initial sync and truncate WAL.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -275,7 +280,7 @@ func TestDB_Sync(t *testing.T) {
 		defer MustCloseDB(t, db)
 
 		// Re-sync and ensure new generation has been created.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -298,7 +303,7 @@ func TestDB_Sync(t *testing.T) {
 		}
 
 		// Issue initial sync and truncate WAL.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -334,7 +339,7 @@ func TestDB_Sync(t *testing.T) {
 		defer MustCloseDB(t, db)
 
 		// Re-sync and ensure new generation has been created.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -354,7 +359,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -378,7 +383,7 @@ func TestDB_Sync(t *testing.T) {
 		// Reopen managed database & ensure sync will still work.
 		db = MustOpenDBAt(t, db.Path())
 		defer MustCloseDB(t, db)
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -398,7 +403,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -417,7 +422,7 @@ func TestDB_Sync(t *testing.T) {
 		// Reopen managed database & ensure sync will still work.
 		db = MustOpenDBAt(t, db.Path())
 		defer MustCloseDB(t, db)
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -437,7 +442,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -462,7 +467,7 @@ func TestDB_Sync(t *testing.T) {
 		// Reopen managed database & ensure sync will still work.
 		db = MustOpenDBAt(t, db.Path())
 		defer MustCloseDB(t, db)
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -489,7 +494,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -508,7 +513,7 @@ func TestDB_Sync(t *testing.T) {
 		// Reopen managed database & ensure sync will still work.
 		db = MustOpenDBAt(t, db.Path())
 		defer MustCloseDB(t, db)
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -532,7 +537,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -544,7 +549,7 @@ func TestDB_Sync(t *testing.T) {
 		}
 
 		// Sync to shadow WAL.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -564,7 +569,7 @@ func TestDB_Sync(t *testing.T) {
 		// Execute a query to force a write to the WAL and then sync.
 		if _, err := sqldb.Exec(`CREATE TABLE foo (bar TEXT);`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -574,7 +579,7 @@ func TestDB_Sync(t *testing.T) {
 		// Write to WAL & sync.
 		if _, err := sqldb.Exec(`INSERT INTO foo (bar) VALUES ('baz');`); err != nil {
 			t.Fatal(err)
-		} else if err := db.Sync(); err != nil {
+		} else if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		}
 
@@ -589,12 +594,14 @@ func TestDB_Sync(t *testing.T) {
 
 // MustOpenDBs returns a new instance of a DB & associated SQL DB.
 func MustOpenDBs(tb testing.TB) (*litestream.DB, *sql.DB) {
+	tb.Helper()
 	db := MustOpenDB(tb)
 	return db, MustOpenSQLDB(tb, db.Path())
 }
 
 // MustCloseDBs closes db & sqldb and removes the parent directory.
 func MustCloseDBs(tb testing.TB, db *litestream.DB, sqldb *sql.DB) {
+	tb.Helper()
 	MustCloseDB(tb, db)
 	MustCloseSQLDB(tb, sqldb)
 }
@@ -619,7 +626,7 @@ func MustOpenDBAt(tb testing.TB, path string) *litestream.DB {
 // MustCloseDB closes db and removes its parent directory.
 func MustCloseDB(tb testing.TB, db *litestream.DB) {
 	tb.Helper()
-	if err := db.Close(); err != nil {
+	if err := db.Close(); err != nil && !strings.Contains(err.Error(), `database is closed`) {
 		tb.Fatal(err)
 	} else if err := os.RemoveAll(filepath.Dir(db.Path())); err != nil {
 		tb.Fatal(err)

etc/build.ps1

@@ -0,0 +1,17 @@
+[CmdletBinding()]
+Param (
+    [Parameter(Mandatory = $true)]
+    [String] $Version
+)
+$ErrorActionPreference = "Stop"
+
+# Update working directory.
+Push-Location $PSScriptRoot
+Trap {
+    Pop-Location
+}
+
+Invoke-Expression "candle.exe -nologo -arch x64 -ext WixUtilExtension -out litestream.wixobj -dVersion=`"$Version`" litestream.wxs"
+Invoke-Expression "light.exe  -nologo -spdb -ext WixUtilExtension -out `"litestream-${Version}.msi`" litestream.wixobj"
+
+Pop-Location

etc/litestream.wxs

@@ -0,0 +1,89 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Wix
+	xmlns="http://schemas.microsoft.com/wix/2006/wi"
+	xmlns:util="http://schemas.microsoft.com/wix/UtilExtension"
+>
+	<?if $(sys.BUILDARCH)=x64 ?>
+		<?define PlatformProgramFiles = "ProgramFiles64Folder" ?>
+	<?else ?>
+		<?define PlatformProgramFiles = "ProgramFilesFolder" ?>
+	<?endif ?>
+
+	<Product
+		Id="*"
+		UpgradeCode="5371367e-58b3-4e52-be0d-46945eb71ce6"
+		Name="Litestream"
+		Version="$(var.Version)"
+		Manufacturer="Litestream"
+		Language="1033"
+		Codepage="1252"
+	>
+		<Package
+			Id="*"
+			Manufacturer="Litestream"
+			InstallScope="perMachine"
+			InstallerVersion="500"
+			Description="Litestream $(var.Version) installer"
+			Compressed="yes"
+		/>
+		
+		<Media Id="1" Cabinet="litestream.cab" EmbedCab="yes"/>
+		
+		<MajorUpgrade
+			Schedule="afterInstallInitialize"
+			DowngradeErrorMessage="A later version of [ProductName] is already installed. Setup will now exit."
+		/>
+
+		<Directory Id="TARGETDIR" Name="SourceDir">
+			<Directory Id="$(var.PlatformProgramFiles)">
+				<Directory Id="APPLICATIONROOTDIRECTORY" Name="Litestream"/>
+			</Directory>
+		</Directory>
+
+		<ComponentGroup Id="Files">
+			<Component Directory="APPLICATIONROOTDIRECTORY">
+				<File
+					Id="litestream.exe"
+					Name="litestream.exe"
+					Source="litestream.exe"
+					KeyPath="yes"
+				/>
+
+				<ServiceInstall
+					Id="InstallService"
+					Name="Litestream"
+					DisplayName="Litestream"
+					Description="Replicates SQLite databases"
+					ErrorControl="normal"
+					Start="auto"
+					Type="ownProcess"
+				>
+					<util:ServiceConfig
+						FirstFailureActionType="restart"
+						SecondFailureActionType="restart"
+						ThirdFailureActionType="restart"
+						RestartServiceDelayInSeconds="60"
+					/>
+					<ServiceDependency Id="wmiApSrv" />
+				</ServiceInstall>
+
+				<ServiceControl
+					Id="ServiceStateControl"
+					Name="Litestream"
+					Remove="uninstall"
+					Start="install"
+					Stop="both"
+				/>
+				<util:EventSource
+					Log="Application"
+					Name="Litestream"
+					EventMessageFile="%SystemRoot%\System32\EventCreate.exe"
+				/>
+			</Component>
+		</ComponentGroup>
+
+		<Feature Id="DefaultFeature" Level="1">
+			<ComponentGroupRef Id="Files" />
+		</Feature>
+	</Product>
+</Wix>

etc/litestream.yml

@@ -6,5 +6,5 @@
 #  - path: /path/to/primary/db            # Database to replicate from
 #    replicas:
 #      - path: /path/to/replica           # File-based replication
-#      - path: s3://my.bucket.com/db      # S3-based replication
+#      - url:  s3://my.bucket.com/db      # S3-based replication
 

etc/nfpm.yml

@@ -1,13 +1,13 @@
 name: litestream
-arch: amd64
+arch: "${GOARCH}"
-platform: linux
+platform: "${GOOS}"
 version: "${LITESTREAM_VERSION}"
 section: "default"
 priority: "extra"
 maintainer: "Ben Johnson <benbjohnson@yahoo.com>"
 description: Litestream is a tool for real-time replication of SQLite databases.
 homepage: "https://github.com/benbjohnson/litestream"
-license: "GPLv3"
+license: "Apache 2"
 contents:
 - src: ./litestream
   dst: /usr/bin/litestream

go.mod

@@ -8,5 +8,7 @@ require (
 	github.com/mattn/go-sqlite3 v1.14.5
 	github.com/pierrec/lz4/v4 v4.1.3
 	github.com/prometheus/client_golang v1.9.0
+	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect
+	golang.org/x/sys v0.0.0-20201214210602-f9fddec55a1e
 	gopkg.in/yaml.v2 v2.4.0
 )

go.sum

@@ -316,6 +316,8 @@ golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c h1:5KslGYwFpkhGh+Q16bwMP3cOontH8FOep7tGV86Y7SQ=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180823144017-11551d06cbcc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

litestream.go

@@ -36,6 +36,7 @@ const (
 
 // Litestream errors.
 var (
+	ErrNoGeneration     = errors.New("no generation available")
 	ErrNoSnapshots      = errors.New("no snapshots available")
 	ErrChecksumMismatch = errors.New("invalid replica, checksum mismatch")
 )
@@ -151,8 +152,9 @@ func readWALHeader(filename string) ([]byte, error) {
 	return buf[:n], err
 }
 
-// readFileAt reads a slice from a file.
+// readWALFileAt reads a slice from a file. Do not use this with database files
-func readFileAt(filename string, offset, n int64) ([]byte, error) {
+// as it causes problems with non-OFD locks.
+func readWALFileAt(filename string, offset, n int64) ([]byte, error) {
 	f, err := os.Open(filename)
 	if err != nil {
 		return nil, err

replica.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"hash/crc64"
 	"io"
 	"io/ioutil"
 	"log"
@@ -31,10 +32,13 @@ type Replica interface {
 	DB() *DB
 
 	// Starts replicating in a background goroutine.
-	Start(ctx context.Context)
+	Start(ctx context.Context) error
 
 	// Stops all replication processing. Blocks until processing stopped.
-	Stop()
+	Stop(hard bool) error
+
+	// Performs a backup of outstanding WAL frames to the replica.
+	Sync(ctx context.Context) error
 
 	// Returns the last replication position.
 	LastPos() Pos
@@ -90,6 +94,9 @@ type FileReplica struct {
 	mu  sync.RWMutex
 	pos Pos // last position
 
+	muf sync.Mutex
+	f   *os.File // long-running file descriptor to avoid non-OFD lock issues
+
 	wg     sync.WaitGroup
 	cancel func()
 
@@ -98,8 +105,11 @@ type FileReplica struct {
 	walIndexGauge      prometheus.Gauge
 	walOffsetGauge     prometheus.Gauge
 
+	// Frequency to create new snapshots.
+	SnapshotInterval time.Duration
+
 	// Time to keep snapshots and related WAL files.
-	// Database is snapshotted after interval and older WAL files are discarded.
+	// Database is snapshotted after interval, if needed, and older WAL files are discarded.
 	Retention time.Duration
 
 	// Time between checks for retention.
@@ -389,29 +399,45 @@ func (r *FileReplica) WALs(ctx context.Context) ([]*WALInfo, error) {
 }
 
 // Start starts replication for a given generation.
-func (r *FileReplica) Start(ctx context.Context) {
+func (r *FileReplica) Start(ctx context.Context) (err error) {
 	// Ignore if replica is being used sychronously.
 	if !r.MonitorEnabled {
-		return
+		return nil
 	}
 
 	// Stop previous replication.
-	r.Stop()
+	r.Stop(false)
 
 	// Wrap context with cancelation.
 	ctx, r.cancel = context.WithCancel(ctx)
 
 	// Start goroutine to replicate data.
-	r.wg.Add(3)
+	r.wg.Add(4)
 	go func() { defer r.wg.Done(); r.monitor(ctx) }()
 	go func() { defer r.wg.Done(); r.retainer(ctx) }()
+	go func() { defer r.wg.Done(); r.snapshotter(ctx) }()
 	go func() { defer r.wg.Done(); r.validator(ctx) }()
+
+	return nil
 }
 
 // Stop cancels any outstanding replication and blocks until finished.
-func (r *FileReplica) Stop() {
+//
+// Performing a hard stop will close the DB file descriptor which could release
+// locks on per-process locks. Hard stops should only be performed when
+// stopping the entire process.
+func (r *FileReplica) Stop(hard bool) (err error) {
 	r.cancel()
 	r.wg.Wait()
+
+	r.muf.Lock()
+	defer r.muf.Unlock()
+	if hard && r.f != nil {
+		if e := r.f.Close(); e != nil && err == nil {
+			err = e
+		}
+	}
+	return err
 }
 
 // monitor runs in a separate goroutine and continuously replicates the DB.
@@ -446,7 +472,18 @@ func (r *FileReplica) monitor(ctx context.Context) {
 
 // retainer runs in a separate goroutine and handles retention.
 func (r *FileReplica) retainer(ctx context.Context) {
-	ticker := time.NewTicker(r.RetentionCheckInterval)
+	// Disable retention enforcement if retention period is non-positive.
+	if r.Retention <= 0 {
+		return
+	}
+
+	// Ensure check interval is not longer than retention period.
+	checkInterval := r.RetentionCheckInterval
+	if checkInterval > r.Retention {
+		checkInterval = r.Retention
+	}
+
+	ticker := time.NewTicker(checkInterval)
 	defer ticker.Stop()
 
 	for {
@@ -462,6 +499,28 @@ func (r *FileReplica) retainer(ctx context.Context) {
 	}
 }
 
+// snapshotter runs in a separate goroutine and handles snapshotting.
+func (r *FileReplica) snapshotter(ctx context.Context) {
+	if r.SnapshotInterval <= 0 {
+		return
+	}
+
+	ticker := time.NewTicker(r.SnapshotInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			if err := r.Snapshot(ctx); err != nil && err != ErrNoGeneration {
+				log.Printf("%s(%s): snapshotter error: %s", r.db.Path(), r.Name(), err)
+				continue
+			}
+		}
+	}
+}
+
 // validator runs in a separate goroutine and handles periodic validation.
 func (r *FileReplica) validator(ctx context.Context) {
 	// Initialize counters since validation occurs infrequently.
@@ -531,8 +590,28 @@ func (r *FileReplica) CalcPos(ctx context.Context, generation string) (pos Pos,
 	return pos, nil
 }
 
+// Snapshot copies the entire database to the replica path.
+func (r *FileReplica) Snapshot(ctx context.Context) error {
+	// Find current position of database.
+	pos, err := r.db.Pos()
+	if err != nil {
+		return fmt.Errorf("cannot determine current db generation: %w", err)
+	} else if pos.IsZero() {
+		return ErrNoGeneration
+	}
+	return r.snapshot(ctx, pos.Generation, pos.Index)
+}
+
 // snapshot copies the entire database to the replica path.
 func (r *FileReplica) snapshot(ctx context.Context, generation string, index int) error {
+	r.muf.Lock()
+	defer r.muf.Unlock()
+
+	// Issue a passive checkpoint to flush any pages to disk before snapshotting.
+	if _, err := r.db.db.ExecContext(ctx, `PRAGMA wal_checkpoint(PASSIVE);`); err != nil {
+		return fmt.Errorf("pre-snapshot checkpoint: %w", err)
+	}
+
 	// Acquire a read lock on the database during snapshot to prevent checkpoints.
 	tx, err := r.db.db.Begin()
 	if err != nil {
@@ -553,11 +632,50 @@ func (r *FileReplica) snapshot(ctx context.Context, generation string, index int
 
 	if err := mkdirAll(filepath.Dir(snapshotPath), r.db.dirmode, r.db.diruid, r.db.dirgid); err != nil {
 		return err
-	} else if err := compressFile(r.db.Path(), snapshotPath, r.db.uid, r.db.gid); err != nil {
+	}
+
+	// Open db file descriptor, if not already open.
+	if r.f == nil {
+		if r.f, err = os.Open(r.db.Path()); err != nil {
+			return err
+		}
+	}
+
+	if _, err := r.f.Seek(0, io.SeekStart); err != nil {
 		return err
 	}
 
-	log.Printf("%s(%s): snapshot: creating %s/%08x t=%s", r.db.Path(), r.Name(), generation, index, time.Since(startTime))
+	fi, err := r.f.Stat()
+	if err != nil {
+		return err
+	}
+
+	w, err := createFile(snapshotPath+".tmp", fi.Mode(), r.db.uid, r.db.gid)
+	if err != nil {
+		return err
+	}
+	defer w.Close()
+
+	zr := lz4.NewWriter(w)
+	defer zr.Close()
+
+	// Copy & compress file contents to temporary file.
+	if _, err := io.Copy(zr, r.f); err != nil {
+		return err
+	} else if err := zr.Close(); err != nil {
+		return err
+	} else if err := w.Sync(); err != nil {
+		return err
+	} else if err := w.Close(); err != nil {
+		return err
+	}
+
+	// Move compressed file to final location.
+	if err := os.Rename(snapshotPath+".tmp", snapshotPath); err != nil {
+		return err
+	}
+
+	log.Printf("%s(%s): snapshot: creating %s/%08x t=%s", r.db.Path(), r.Name(), generation, index, time.Since(startTime).Truncate(time.Millisecond))
 	return nil
 }
 
@@ -756,7 +874,7 @@ func (r *FileReplica) compress(ctx context.Context, generation string) error {
 		}
 
 		dst := filename + ".lz4"
-		if err := compressFile(filename, dst, r.db.uid, r.db.gid); err != nil {
+		if err := compressWALFile(filename, dst, r.db.uid, r.db.gid); err != nil {
 			return err
 		} else if err := os.Remove(filename); err != nil {
 			return err
@@ -951,34 +1069,65 @@ func SnapshotIndexAt(ctx context.Context, r Replica, generation string, timestam
 		return 0, ErrNoSnapshots
 	}
 
-	index := -1
+	snapshotIndex := -1
 	var max time.Time
 	for _, snapshot := range snapshots {
-		if !timestamp.IsZero() && snapshot.CreatedAt.After(timestamp) {
+		if snapshot.Generation != generation {
+			continue // generation mismatch, skip
+		} else if !timestamp.IsZero() && snapshot.CreatedAt.After(timestamp) {
 			continue // after timestamp, skip
 		}
 
 		// Use snapshot if it newer.
 		if max.IsZero() || snapshot.CreatedAt.After(max) {
-			index, max = snapshot.Index, snapshot.CreatedAt
+			snapshotIndex, max = snapshot.Index, snapshot.CreatedAt
 		}
 	}
 
-	if index == -1 {
+	if snapshotIndex == -1 {
 		return 0, ErrNoSnapshots
 	}
-	return index, nil
+	return snapshotIndex, nil
 }
 
-// WALIndexAt returns the highest index for a WAL file that occurs before maxIndex & timestamp.
+// SnapshotIndexbyIndex returns the highest index for a snapshot within a generation
-// If timestamp is zero, returns the highest WAL index.
+// that occurs before a given index. If index is MaxInt32, returns the latest snapshot.
+func SnapshotIndexByIndex(ctx context.Context, r Replica, generation string, index int) (int, error) {
+	snapshots, err := r.Snapshots(ctx)
+	if err != nil {
+		return 0, err
+	} else if len(snapshots) == 0 {
+		return 0, ErrNoSnapshots
+	}
+
+	snapshotIndex := -1
+	for _, snapshot := range snapshots {
+		if index < math.MaxInt32 && snapshot.Index > index {
+			continue // after index, skip
+		}
+
+		// Use snapshot if it newer.
+		if snapshotIndex == -1 || snapshotIndex >= snapshotIndex {
+			snapshotIndex = snapshot.Index
+		}
+	}
+
+	if snapshotIndex == -1 {
+		return 0, ErrNoSnapshots
+	}
+	return snapshotIndex, nil
+}
+
+// WALIndexAt returns the highest index for a WAL file that occurs before
+// maxIndex & timestamp. If timestamp is zero, returns the highest WAL index.
+// Returns -1 if no WAL found and MaxInt32 specified.
 func WALIndexAt(ctx context.Context, r Replica, generation string, maxIndex int, timestamp time.Time) (int, error) {
 	wals, err := r.WALs(ctx)
 	if err != nil {
 		return 0, err
 	}
 
-	var index int
+	index := -1
 	for _, wal := range wals {
 		if wal.Generation != generation {
 			continue
@@ -996,14 +1145,15 @@ func WALIndexAt(ctx context.Context, r Replica, generation string, maxIndex int,
 	}
 
 	// If max index is specified but not found, return an error.
-	if maxIndex != math.MaxInt64 && index != maxIndex {
+	if maxIndex != math.MaxInt32 && index != maxIndex {
 		return index, fmt.Errorf("unable to locate index %d in generation %q, highest index was %d", maxIndex, generation, index)
 	}
 	return index, nil
 }
 
-// compressFile compresses a file and replaces it with a new file with a .lz4 extension.
+// compressWALFile compresses a file and replaces it with a new file with a .lz4 extension.
-func compressFile(src, dst string, uid, gid int) error {
+// Do not use this on database files because of issues with non-OFD locks.
+func compressWALFile(src, dst string, uid, gid int) error {
 	r, err := os.Open(src)
 	if err != nil {
 		return err
@@ -1053,8 +1203,7 @@ func ValidateReplica(ctx context.Context, r Replica) error {
 
 	// Compute checksum of primary database under lock. This prevents a
 	// sync from occurring and the database will not be written.
-	primaryPath := filepath.Join(tmpdir, "primary")
+	chksum0, pos, err := db.CRC64(ctx)
-	chksum0, pos, err := db.CRC64()
 	if err != nil {
 		return fmt.Errorf("cannot compute checksum: %w", err)
 	}
@@ -1076,10 +1225,19 @@ func ValidateReplica(ctx context.Context, r Replica) error {
 	}
 
 	// Open file handle for restored database.
-	chksum1, err := checksumFile(restorePath)
+	// NOTE: This open is ok as the restored database is not managed by litestream.
+	f, err := os.Open(restorePath)
 	if err != nil {
 		return err
 	}
+	defer f.Close()
+
+	// Read entire file into checksum.
+	h := crc64.New(crc64.MakeTable(crc64.ISO))
+	if _, err := io.Copy(h, f); err != nil {
+		return err
+	}
+	chksum1 := h.Sum64()
 
 	status := "ok"
 	mismatch := chksum0 != chksum1
@@ -1091,15 +1249,6 @@ func ValidateReplica(ctx context.Context, r Replica) error {
 	// Validate checksums match.
 	if mismatch {
 		internal.ReplicaValidationTotalCounterVec.WithLabelValues(db.Path(), r.Name(), "error").Inc()
-
-		// Compress mismatched databases and report temporary path for investigation.
-		if err := compressFile(primaryPath, primaryPath+".lz4", db.uid, db.gid); err != nil {
-			return fmt.Errorf("cannot compress primary db: %w", err)
-		} else if err := compressFile(restorePath, restorePath+".lz4", db.uid, db.gid); err != nil {
-			return fmt.Errorf("cannot compress replica db: %w", err)
-		}
-		log.Printf("%s(%s): validator: mismatch files @ %s", db.Path(), r.Name(), tmpdir)
-
 		return ErrChecksumMismatch
 	}
 

replica_test.go

@@ -15,7 +15,7 @@ func TestFileReplica_Sync(t *testing.T) {
 		r := NewTestFileReplica(t, db)
 
 		// Sync database & then sync replica.
-		if err := db.Sync(); err != nil {
+		if err := db.Sync(context.Background()); err != nil {
 			t.Fatal(err)
 		} else if err := r.Sync(context.Background()); err != nil {
 			t.Fatal(err)
@@ -47,7 +47,7 @@ func TestFileReplica_Sync(t *testing.T) {
 
 			// Sync periodically.
 			if i%100 == 0 || i == n-1 {
-				if err := db.Sync(); err != nil {
+				if err := db.Sync(context.Background()); err != nil {
 					t.Fatal(err)
 				} else if err := r.Sync(context.Background()); err != nil {
 					t.Fatal(err)

s3/s3.go

@@ -3,12 +3,16 @@ package s3
 import (
 	"bytes"
 	"context"
+	"crypto/tls"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
+	"net"
+	"net/http"
 	"os"
 	"path"
+	"regexp"
 	"sync"
 	"time"
 
@@ -50,6 +54,9 @@ type Replica struct {
 	snapshotMu sync.Mutex
 	pos        litestream.Pos // last position
 
+	muf sync.Mutex
+	f   *os.File // long-lived read-only db file descriptor
+
 	wg     sync.WaitGroup
 	cancel func()
 
@@ -72,10 +79,16 @@ type Replica struct {
 	Region         string
 	Bucket         string
 	Path           string
+	Endpoint       string
+	ForcePathStyle bool
+	SkipVerify     bool
 
 	// Time between syncs with the shadow WAL.
 	SyncInterval time.Duration
 
+	// Frequency to create new snapshots.
+	SnapshotInterval time.Duration
+
 	// Time to keep snapshots and related WAL files.
 	// Database is snapshotted after interval and older WAL files are discarded.
 	Retention time.Duration
@@ -410,29 +423,47 @@ func (r *Replica) WALs(ctx context.Context) ([]*litestream.WALInfo, error) {
 }
 
 // Start starts replication for a given generation.
-func (r *Replica) Start(ctx context.Context) {
+func (r *Replica) Start(ctx context.Context) (err error) {
 	// Ignore if replica is being used sychronously.
 	if !r.MonitorEnabled {
-		return
+		return nil
 	}
 
 	// Stop previous replication.
-	r.Stop()
+	r.Stop(false)
 
 	// Wrap context with cancelation.
 	ctx, r.cancel = context.WithCancel(ctx)
 
 	// Start goroutines to manage replica data.
-	r.wg.Add(3)
+	r.wg.Add(4)
 	go func() { defer r.wg.Done(); r.monitor(ctx) }()
 	go func() { defer r.wg.Done(); r.retainer(ctx) }()
+	go func() { defer r.wg.Done(); r.snapshotter(ctx) }()
 	go func() { defer r.wg.Done(); r.validator(ctx) }()
+
+	return nil
 }
 
 // Stop cancels any outstanding replication and blocks until finished.
-func (r *Replica) Stop() {
+//
+// Performing a hard stop will close the DB file descriptor which could release
+// locks on per-process locks. Hard stops should only be performed when
+// stopping the entire process.
+func (r *Replica) Stop(hard bool) (err error) {
 	r.cancel()
 	r.wg.Wait()
+
+	r.muf.Lock()
+	defer r.muf.Unlock()
+
+	if hard && r.f != nil {
+		if e := r.f.Close(); e != nil && err == nil {
+			err = e
+		}
+	}
+
+	return err
 }
 
 // monitor runs in a separate goroutine and continuously replicates the DB.
@@ -475,7 +506,18 @@ func (r *Replica) monitor(ctx context.Context) {
 
 // retainer runs in a separate goroutine and handles retention.
 func (r *Replica) retainer(ctx context.Context) {
-	ticker := time.NewTicker(r.RetentionCheckInterval)
+	// Disable retention enforcement if retention period is non-positive.
+	if r.Retention <= 0 {
+		return
+	}
+
+	// Ensure check interval is not longer than retention period.
+	checkInterval := r.RetentionCheckInterval
+	if checkInterval > r.Retention {
+		checkInterval = r.Retention
+	}
+
+	ticker := time.NewTicker(checkInterval)
 	defer ticker.Stop()
 
 	for {
@@ -491,6 +533,28 @@ func (r *Replica) retainer(ctx context.Context) {
 	}
 }
 
+// snapshotter runs in a separate goroutine and handles snapshotting.
+func (r *Replica) snapshotter(ctx context.Context) {
+	if r.SnapshotInterval <= 0 {
+		return
+	}
+
+	ticker := time.NewTicker(r.SnapshotInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			if err := r.Snapshot(ctx); err != nil && err != litestream.ErrNoGeneration {
+				log.Printf("%s(%s): snapshotter error: %s", r.db.Path(), r.Name(), err)
+				continue
+			}
+		}
+	}
+}
+
 // validator runs in a separate goroutine and handles periodic validation.
 func (r *Replica) validator(ctx context.Context) {
 	// Initialize counters since validation occurs infrequently.
@@ -568,8 +632,28 @@ func (r *Replica) CalcPos(ctx context.Context, generation string) (pos litestrea
 	return pos, nil
 }
 
+// Snapshot copies the entire database to the replica path.
+func (r *Replica) Snapshot(ctx context.Context) error {
+	// Find current position of database.
+	pos, err := r.db.Pos()
+	if err != nil {
+		return fmt.Errorf("cannot determine current db generation: %w", err)
+	} else if pos.IsZero() {
+		return litestream.ErrNoGeneration
+	}
+	return r.snapshot(ctx, pos.Generation, pos.Index)
+}
+
 // snapshot copies the entire database to the replica path.
 func (r *Replica) snapshot(ctx context.Context, generation string, index int) error {
+	r.muf.Lock()
+	defer r.muf.Unlock()
+
+	// Issue a passive checkpoint to flush any pages to disk before snapshotting.
+	if _, err := r.db.SQLDB().ExecContext(ctx, `PRAGMA wal_checkpoint(PASSIVE);`); err != nil {
+		return fmt.Errorf("pre-snapshot checkpoint: %w", err)
+	}
+
 	// Acquire a read lock on the database during snapshot to prevent checkpoints.
 	tx, err := r.db.SQLDB().Begin()
 	if err != nil {
@@ -580,14 +664,21 @@ func (r *Replica) snapshot(ctx context.Context, generation string, index int) er
 	}
 	defer func() { _ = tx.Rollback() }()
 
-	// Open database file handle.
+	// Open long-lived file descriptor on database.
-	f, err := os.Open(r.db.Path())
+	if r.f == nil {
-	if err != nil {
+		if r.f, err = os.Open(r.db.Path()); err != nil {
 			return err
 		}
-	defer f.Close()
+	}
 
-	fi, err := f.Stat()
+	// Move the file descriptor to the beginning. We only use one long lived
+	// file descriptor because some operating systems will remove the database
+	// lock when closing a separate file descriptor on the DB.
+	if _, err := r.f.Seek(0, io.SeekStart); err != nil {
+		return err
+	}
+
+	fi, err := r.f.Stat()
 	if err != nil {
 		return err
 	}
@@ -595,7 +686,7 @@ func (r *Replica) snapshot(ctx context.Context, generation string, index int) er
 	pr, pw := io.Pipe()
 	zw := lz4.NewWriter(pw)
 	go func() {
-		if _, err := io.Copy(zw, f); err != nil {
+		if _, err := io.Copy(zw, r.f); err != nil {
 			_ = pw.CloseWithError(err)
 			return
 		}
@@ -616,8 +707,7 @@ func (r *Replica) snapshot(ctx context.Context, generation string, index int) er
 	r.putOperationTotalCounter.Inc()
 	r.putOperationBytesCounter.Add(float64(fi.Size()))
 
-	log.Printf("%s(%s): snapshot: creating %s/%08x t=%s", r.db.Path(), r.Name(), generation, index, time.Since(startTime))
+	log.Printf("%s(%s): snapshot: creating %s/%08x t=%s", r.db.Path(), r.Name(), generation, index, time.Since(startTime).Truncate(time.Millisecond))
-
 	return nil
 }
 
@@ -646,17 +736,25 @@ func (r *Replica) Init(ctx context.Context) (err error) {
 		return nil
 	}
 
-	// Look up region if not specified.
+	// Look up region if not specified and no endpoint is used.
+	// Endpoints are typically used for non-S3 object stores and do not
+	// necessarily require a region.
 	region := r.Region
 	if region == "" {
+		if r.Endpoint == "" {
 			if region, err = r.findBucketRegion(ctx, r.Bucket); err != nil {
 				return fmt.Errorf("cannot lookup bucket region: %w", err)
 			}
+		} else {
+			region = "us-east-1" // default for non-S3 object stores
+		}
 	}
 
 	// Create new AWS session.
 	config := r.config()
+	if region != "" {
 		config.Region = aws.String(region)
+	}
 	sess, err := session.NewSession(config)
 	if err != nil {
 		return fmt.Errorf("cannot create aws session: %w", err)
@@ -673,6 +771,18 @@ func (r *Replica) config() *aws.Config {
 	if r.AccessKeyID != "" || r.SecretAccessKey != "" {
 		config.Credentials = credentials.NewStaticCredentials(r.AccessKeyID, r.SecretAccessKey, "")
 	}
+	if r.Endpoint != "" {
+		config.Endpoint = aws.String(r.Endpoint)
+	}
+	if r.ForcePathStyle {
+		config.S3ForcePathStyle = aws.Bool(r.ForcePathStyle)
+	}
+	if r.SkipVerify {
+		config.HTTPClient = &http.Client{Transport: &http.Transport{
+			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
+		}}
+	}
+
 	return config
 }
 
@@ -1027,6 +1137,60 @@ func (r *Replica) deleteGenerationBefore(ctx context.Context, generation string,
 	return nil
 }
 
+// ParseHost extracts data from a hostname depending on the service provider.
+func ParseHost(s string) (bucket, region, endpoint string, forcePathStyle bool) {
+	// Extract port if one is specified.
+	host, port, err := net.SplitHostPort(s)
+	if err != nil {
+		host = s
+	}
+
+	// Default to path-based URLs, except for with AWS S3 itself.
+	forcePathStyle = true
+
+	// Extract fields from provider-specific host formats.
+	scheme := "https"
+	if a := localhostRegex.FindStringSubmatch(host); a != nil {
+		bucket, region = a[1], "us-east-1"
+		scheme, endpoint = "http", "localhost"
+	} else if a := gcsRegex.FindStringSubmatch(host); a != nil {
+		bucket, region = a[1], "us-east-1"
+		endpoint = "storage.googleapis.com"
+	} else if a := digitalOceanRegex.FindStringSubmatch(host); a != nil {
+		bucket, region = a[1], a[2]
+		endpoint = fmt.Sprintf("%s.digitaloceanspaces.com", region)
+	} else if a := linodeRegex.FindStringSubmatch(host); a != nil {
+		bucket, region = a[1], a[2]
+		endpoint = fmt.Sprintf("%s.linodeobjects.com", region)
+	} else if a := backblazeRegex.FindStringSubmatch(host); a != nil {
+		bucket, region = a[1], a[2]
+		endpoint = fmt.Sprintf("s3.%s.backblazeb2.com", region)
+	} else {
+		bucket = host
+		forcePathStyle = false
+	}
+
+	// Add port back to endpoint, if available.
+	if endpoint != "" && port != "" {
+		endpoint = net.JoinHostPort(endpoint, port)
+	}
+
+	// Prepend scheme to endpoint.
+	if endpoint != "" {
+		endpoint = scheme + "://" + endpoint
+	}
+
+	return bucket, region, endpoint, forcePathStyle
+}
+
+var (
+	localhostRegex    = regexp.MustCompile(`^(?:(.+)\.)?localhost$`)
+	digitalOceanRegex = regexp.MustCompile(`^(?:(.+)\.)?([^.]+)\.digitaloceanspaces.com$`)
+	linodeRegex       = regexp.MustCompile(`^(?:(.+)\.)?([^.]+)\.linodeobjects.com$`)
+	backblazeRegex    = regexp.MustCompile(`^(?:(.+)\.)?s3.([^.]+)\.backblazeb2.com$`)
+	gcsRegex          = regexp.MustCompile(`^(?:(.+)\.)?storage.googleapis.com$`)
+)
+
 // S3 metrics.
 var (
 	operationTotalCounterVec = promauto.NewCounterVec(prometheus.CounterOpts{

s3/s3_test.go

@@ -0,0 +1,80 @@
+package s3_test
+
+import (
+	"testing"
+
+	"github.com/benbjohnson/litestream/s3"
+)
+
+func TestParseHost(t *testing.T) {
+	// Ensure non-specific hosts return as buckets.
+	t.Run("S3", func(t *testing.T) {
+		bucket, region, endpoint, forcePathStyle := s3.ParseHost(`test.litestream.io`)
+		if got, want := bucket, `test.litestream.io`; got != want {
+			t.Fatalf("bucket=%q, want %q", got, want)
+		} else if got, want := region, ``; got != want {
+			t.Fatalf("region=%q, want %q", got, want)
+		} else if got, want := endpoint, ``; got != want {
+			t.Fatalf("endpoint=%q, want %q", got, want)
+		} else if got, want := forcePathStyle, false; got != want {
+			t.Fatalf("forcePathStyle=%v, want %v", got, want)
+		}
+	})
+
+	// Ensure localhosts use an HTTP endpoint and extract the bucket name.
+	t.Run("Localhost", func(t *testing.T) {
+		t.Run("WithPort", func(t *testing.T) {
+			bucket, region, endpoint, forcePathStyle := s3.ParseHost(`test.localhost:9000`)
+			if got, want := bucket, `test`; got != want {
+				t.Fatalf("bucket=%q, want %q", got, want)
+			} else if got, want := region, `us-east-1`; got != want {
+				t.Fatalf("region=%q, want %q", got, want)
+			} else if got, want := endpoint, `http://localhost:9000`; got != want {
+				t.Fatalf("endpoint=%q, want %q", got, want)
+			} else if got, want := forcePathStyle, true; got != want {
+				t.Fatalf("forcePathStyle=%v, want %v", got, want)
+			}
+		})
+
+		t.Run("WithoutPort", func(t *testing.T) {
+			bucket, region, endpoint, forcePathStyle := s3.ParseHost(`test.localhost`)
+			if got, want := bucket, `test`; got != want {
+				t.Fatalf("bucket=%q, want %q", got, want)
+			} else if got, want := region, `us-east-1`; got != want {
+				t.Fatalf("region=%q, want %q", got, want)
+			} else if got, want := endpoint, `http://localhost`; got != want {
+				t.Fatalf("endpoint=%q, want %q", got, want)
+			} else if got, want := forcePathStyle, true; got != want {
+				t.Fatalf("forcePathStyle=%v, want %v", got, want)
+			}
+		})
+	})
+
+	// Ensure backblaze B2 URLs extract bucket, region, & endpoint from host.
+	t.Run("Backblaze", func(t *testing.T) {
+		bucket, region, endpoint, forcePathStyle := s3.ParseHost(`test-123.s3.us-west-000.backblazeb2.com`)
+		if got, want := bucket, `test-123`; got != want {
+			t.Fatalf("bucket=%q, want %q", got, want)
+		} else if got, want := region, `us-west-000`; got != want {
+			t.Fatalf("region=%q, want %q", got, want)
+		} else if got, want := endpoint, `https://s3.us-west-000.backblazeb2.com`; got != want {
+			t.Fatalf("endpoint=%q, want %q", got, want)
+		} else if got, want := forcePathStyle, true; got != want {
+			t.Fatalf("forcePathStyle=%v, want %v", got, want)
+		}
+	})
+
+	// Ensure GCS URLs extract bucket & endpoint from host.
+	t.Run("GCS", func(t *testing.T) {
+		bucket, region, endpoint, forcePathStyle := s3.ParseHost(`litestream.io.storage.googleapis.com`)
+		if got, want := bucket, `litestream.io`; got != want {
+			t.Fatalf("bucket=%q, want %q", got, want)
+		} else if got, want := region, `us-east-1`; got != want {
+			t.Fatalf("region=%q, want %q", got, want)
+		} else if got, want := endpoint, `https://storage.googleapis.com`; got != want {
+			t.Fatalf("endpoint=%q, want %q", got, want)
+		} else if got, want := forcePathStyle, true; got != want {
+			t.Fatalf("forcePathStyle=%v, want %v", got, want)
+		}
+	})
+}