a090706421
This commit adds an http server and client for streaming snapshots and WAL pages from an upstream Litestream primary to a read-only replica.
104 lines
2.8 KiB
Go
104 lines
2.8 KiB
Go
package litestream
|
|
|
|
import (
|
|
"encoding/binary"
|
|
"fmt"
|
|
"os"
|
|
)
|
|
|
|
// WALWriter represents a writer to a SQLite WAL file.
|
|
type WALWriter struct {
|
|
path string
|
|
mode os.FileMode
|
|
pageSize int
|
|
|
|
f *os.File // WAL file handle
|
|
buf []byte // frame buffer
|
|
|
|
chksum0, chksum1 uint32 // ongoing checksum
|
|
|
|
Salt0, Salt1 uint32
|
|
}
|
|
|
|
// NewWALWriter returns a new instance of WALWriter.
|
|
func NewWALWriter(path string, mode os.FileMode, pageSize int) *WALWriter {
|
|
return &WALWriter{
|
|
path: path,
|
|
mode: mode,
|
|
pageSize: pageSize,
|
|
|
|
buf: make([]byte, WALFrameHeaderSize+pageSize),
|
|
}
|
|
}
|
|
|
|
// Open opens the file handle to the WAL file.
|
|
func (w *WALWriter) Open() (err error) {
|
|
w.f, err = os.OpenFile(w.path, os.O_WRONLY|os.O_TRUNC, w.mode)
|
|
return err
|
|
}
|
|
|
|
// Close closes the file handle to the WAL file.
|
|
func (w *WALWriter) Close() error {
|
|
if w.f == nil {
|
|
return nil
|
|
}
|
|
return w.f.Close()
|
|
}
|
|
|
|
// WriteHeader writes the WAL header to the beginning of the file.
|
|
func (w *WALWriter) WriteHeader() error {
|
|
// Build WAL header byte slice. Page size and checksum set afterward.
|
|
hdr := []byte{
|
|
0x37, 0x7f, 0x06, 0x82, // magic (little-endian)
|
|
0x00, 0x2d, 0xe2, 0x18, // file format version (3007000)
|
|
0x00, 0x00, 0x00, 0x00, // page size
|
|
0x00, 0x00, 0x00, 0x00, // checkpoint sequence number
|
|
0x00, 0x00, 0x00, 0x00, // salt
|
|
0x00, 0x00, 0x00, 0x00,
|
|
0x00, 0x00, 0x00, 0x00, // checksum
|
|
0x00, 0x00, 0x00, 0x00,
|
|
}
|
|
|
|
// Set page size on header
|
|
binary.BigEndian.PutUint32(hdr[8:], uint32(w.pageSize))
|
|
|
|
// Set salt
|
|
binary.BigEndian.PutUint32(hdr[16:], w.Salt0)
|
|
binary.BigEndian.PutUint32(hdr[20:], w.Salt1)
|
|
|
|
// Compute header checksum.
|
|
w.chksum0, w.chksum1 = Checksum(binary.LittleEndian, w.chksum0, w.chksum1, hdr[:24])
|
|
binary.BigEndian.PutUint32(hdr[24:], w.chksum0)
|
|
binary.BigEndian.PutUint32(hdr[28:], w.chksum1)
|
|
|
|
// Write header to WAL.
|
|
_, err := w.f.Write(hdr)
|
|
return err
|
|
}
|
|
|
|
func (w *WALWriter) WriteFrame(pgno, commit uint32, data []byte) error {
|
|
// Ensure data matches page size.
|
|
if len(data) != w.pageSize {
|
|
return fmt.Errorf("data size %d must match page size %d", len(data), w.pageSize)
|
|
}
|
|
|
|
// Write frame header.
|
|
binary.BigEndian.PutUint32(w.buf[0:], pgno) // page number
|
|
binary.BigEndian.PutUint32(w.buf[4:], commit) // commit record (page count)
|
|
binary.BigEndian.PutUint32(w.buf[8:], w.Salt0) // salt
|
|
binary.BigEndian.PutUint32(w.buf[12:], w.Salt1)
|
|
|
|
// Copy data to frame.
|
|
copy(w.buf[WALFrameHeaderSize:], data)
|
|
|
|
// Compute checksum for frame.
|
|
w.chksum0, w.chksum1 = Checksum(binary.LittleEndian, w.chksum0, w.chksum1, w.buf[:8])
|
|
w.chksum0, w.chksum1 = Checksum(binary.LittleEndian, w.chksum0, w.chksum1, w.buf[24:])
|
|
binary.BigEndian.PutUint32(w.buf[16:], w.chksum0)
|
|
binary.BigEndian.PutUint32(w.buf[20:], w.chksum1)
|
|
|
|
// Write to local WAL
|
|
_, err := w.f.Write(w.buf)
|
|
return err
|
|
}
|