From 4349398ff56384651fe08feab857e99c71af8607 Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Mon, 31 Jan 2022 15:56:42 -0700
Subject: [PATCH] Remove shadow WAL iterator

This commit removes the shadow WAL iterator and replaces it with a
fileWalSegmentIterator instead. This works since the shadow WAL now
has the same structure as the replica WAL. This reduces duplicate
code and will make it so read replication can be daisy chained in
the future.
---
 db.go | 98 +----------------------------------------------------------
 1 file changed, 1 insertion(+), 97 deletions(-)

diff --git a/db.go b/db.go
index 74f9391..f73cf0e 100644
--- a/db.go
+++ b/db.go
@@ -1236,103 +1236,7 @@ func (db *DB) WALSegments(ctx context.Context, generation string) (WALSegmentIte
 
 	sort.Ints(indexes)
 
-	return newShadowWALSegmentIterator(db, generation, indexes), nil
-}
-
-type shadowWALSegmentIterator struct {
-	db         *DB
-	generation string
-	indexes    []int
-
-	infos []WALSegmentInfo
-	err   error
-}
-
-func newShadowWALSegmentIterator(db *DB, generation string, indexes []int) *shadowWALSegmentIterator {
-	return &shadowWALSegmentIterator{
-		db:         db,
-		generation: generation,
-		indexes:    indexes,
-	}
-}
-
-func (itr *shadowWALSegmentIterator) Close() (err error) {
-	return itr.err
-}
-
-func (itr *shadowWALSegmentIterator) Next() bool {
-	// Exit if an error has already occurred.
-	if itr.err != nil {
-		return false
-	}
-
-	for {
-		// Move to the next segment in cache, if available.
-		if len(itr.infos) > 1 {
-			itr.infos = itr.infos[1:]
-			return true
-		}
-		itr.infos = itr.infos[:0] // otherwise clear infos
-
-		// If no indexes remain, stop iteration.
-		if len(itr.indexes) == 0 {
-			return false
-		}
-
-		// Read segments into a cache for the current index.
-		index := itr.indexes[0]
-		itr.indexes = itr.indexes[1:]
-		f, err := os.Open(filepath.Join(itr.db.ShadowWALDir(itr.generation), FormatIndex(index)))
-		if err != nil {
-			itr.err = err
-			return false
-		}
-		defer func() { _ = f.Close() }()
-
-		fis, err := f.Readdir(-1)
-		if err != nil {
-			itr.err = err
-			return false
-		} else if err := f.Close(); err != nil {
-			itr.err = err
-			return false
-		}
-		for _, fi := range fis {
-			filename := filepath.Base(fi.Name())
-			if fi.IsDir() {
-				continue
-			}
-
-			offset, err := ParseOffset(strings.TrimSuffix(filename, ".wal.lz4"))
-			if err != nil {
-				continue
-			}
-
-			itr.infos = append(itr.infos, WALSegmentInfo{
-				Generation: itr.generation,
-				Index:      index,
-				Offset:     offset,
-				Size:       fi.Size(),
-				CreatedAt:  fi.ModTime().UTC(),
-			})
-		}
-
-		// Ensure segments are sorted within index.
-		sort.Sort(WALSegmentInfoSlice(itr.infos))
-
-		if len(itr.infos) > 0 {
-			return true
-		}
-	}
-}
-
-func (itr *shadowWALSegmentIterator) Err() error { return itr.err }
-
-func (itr *shadowWALSegmentIterator) WALSegment() WALSegmentInfo {
-	if len(itr.infos) == 0 {
-		return WALSegmentInfo{}
-	}
-	return itr.infos[0]
+	return newFileWALSegmentIterator(db.ShadowWALDir(generation), generation, indexes), nil
 }
 
 // SQLite WAL constants