1 files changed, 211 insertions, 0 deletions
diff --git a/format/pack/ingest/thin_fix.go b/format/pack/ingest/thin_fix.go
new file mode 100644
index 00000000..e605c3f2
--- /dev/null
+++ b/format/pack/ingest/thin_fix.go
@@ -0,0 +1,211 @@
+package ingest
+
+import (
+	"encoding/binary"
+	"fmt"
+	"hash/crc32"
+	"io"
+	"os"
+
+	"codeberg.org/lindenii/furgit/internal/compress/zlib"
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// maybeFixThin appends missing bases and rewrites pack header/trailer when needed.
+func maybeFixThin(state *ingestState) error {
+	if len(state.unresolvedRefDeltas) == 0 {
+		return nil
+	}
+	if !state.fixThin {
+		return &ErrThinPackUnresolved{Count: len(state.unresolvedRefDeltas)}
+	}
+	if state.base == nil {
+		return &ErrThinPackUnresolved{Count: len(state.unresolvedRefDeltas)}
+	}
+
+	hashSize := int64(state.algo.Size())
+	info, err := state.packFile.Stat()
+	if err != nil {
+		return err
+	}
+	size := info.Size()
+	if size < hashSize {
+		return fmt.Errorf("format/pack/ingest: pack too short to trim trailer")
+	}
+	newEnd := size - hashSize
+	if err := state.packFile.Truncate(newEnd); err != nil {
+		return err
+	}
+	state.stream.offset = uint64(newEnd)
+
+	baseIDs := unresolvedThinBaseIDs(state)
+	for _, id := range baseIDs {
+		ty, content, err := state.base.ReadBytesContent(id)
+		if err != nil {
+			continue
+		}
+		if _, err := appendBaseObject(state, id, ty, content); err != nil {
+			return err
+		}
+		state.thinFixed = true
+	}
+
+	if err := rewritePackHeaderAndTrailer(state); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// appendBaseObject appends one base object as a new packed non-delta entry.
+func appendBaseObject(state *ingestState, id objectid.ObjectID, realType objecttype.Type, content []byte) (int, error) {
+	start := state.stream.offset
+	header := encodePackEntryHeader(realType, int64(len(content)))
+	if _, err := state.packFile.WriteAt(header, int64(start)); err != nil {
+		return 0, err
+	}
+
+	section := &fileSectionWriter{file: state.packFile, off: int64(start) + int64(len(header))}
+	crc := crc32.NewIEEE()
+	_, _ = crc.Write(header)
+	counting := &countingWriter{dst: section}
+	zw := zlib.NewWriter(io.MultiWriter(counting, crc))
+	if _, err := zw.Write(content); err != nil {
+		return 0, err
+	}
+	if err := zw.Close(); err != nil {
+		return 0, err
+	}
+
+	packedLen := uint64(len(header)) + uint64(counting.n)
+	end := start + packedLen
+	state.stream.offset = end
+
+	record := objectRecord{
+		offset:       start,
+		headerLen:    uint32(len(header)),
+		packedLen:    packedLen,
+		crc32:        crc.Sum32(),
+		packedType:   realType,
+		realType:     realType,
+		declaredSize: int64(len(content)),
+		dataOffset:   start + uint64(len(header)),
+		objectID:     id,
+		resolved:     true,
+	}
+
+	recordIdx := len(state.records)
+	state.records = append(state.records, record)
+	state.offsetToRecord[start] = recordIdx
+	state.objectToRecord[id.String()] = recordIdx
+	state.baseCache.add(recordIdx, realType, content)
+
+	return recordIdx, nil
+}
+
+// fileSectionWriter writes sequentially to file via WriteAt at one base offset.
+type fileSectionWriter struct {
+	file *os.File
+	off  int64
+	pos  int64
+}
+
+// Write writes src at current section position.
+func (writer *fileSectionWriter) Write(src []byte) (int, error) {
+	if len(src) == 0 {
+		return 0, nil
+	}
+	n, err := writer.file.WriteAt(src, writer.off+writer.pos)
+	writer.pos += int64(n)
+
+	return n, err
+}
+
+// countingWriter counts bytes written to dst.
+type countingWriter struct {
+	dst io.Writer
+	n   int
+}
+
+// Write writes src to dst and tracks output byte count.
+func (writer *countingWriter) Write(src []byte) (int, error) {
+	n, err := writer.dst.Write(src)
+	writer.n += n
+
+	return n, err
+}
+
+// rewritePackHeaderAndTrailer rewrites object count and trailer hash using ReadAt/WriteAt.
+func rewritePackHeaderAndTrailer(state *ingestState) error {
+	var countRaw [4]byte
+	binary.BigEndian.PutUint32(countRaw[:], uint32(len(state.records)))
+	if _, err := state.packFile.WriteAt(countRaw[:], 8); err != nil {
+		return err
+	}
+
+	info, err := state.packFile.Stat()
+	if err != nil {
+		return err
+	}
+	endWithoutTrailer := info.Size()
+
+	hashImpl, err := state.algo.New()
+	if err != nil {
+		return err
+	}
+	var (
+		buf [128 << 10]byte
+		pos int64
+	)
+	for pos < endWithoutTrailer {
+		want := int64(len(buf))
+		remaining := endWithoutTrailer - pos
+		if remaining < want {
+			want = remaining
+		}
+		n, err := state.packFile.ReadAt(buf[:want], pos)
+		if err != nil && err != io.EOF {
+			return err
+		}
+		if n == 0 {
+			return io.ErrUnexpectedEOF
+		}
+		_, _ = hashImpl.Write(buf[:n])
+		pos += int64(n)
+	}
+
+	sum := hashImpl.Sum(nil)
+	if _, err := state.packFile.WriteAt(sum, endWithoutTrailer); err != nil {
+		return err
+	}
+
+	packHash, err := objectid.FromBytes(state.algo, sum)
+	if err != nil {
+		return err
+	}
+	state.packHash = packHash
+	state.objectCountHeader = uint32(len(state.records))
+	state.stream.offset = uint64(endWithoutTrailer + int64(len(sum)))
+
+	return nil
+}
+
+// encodePackEntryHeader encodes one non-delta packed entry header.
+func encodePackEntryHeader(ty objecttype.Type, size int64) []byte {
+	var out [16]byte
+	n := 0
+	s := uint64(size)
+	c := byte((uint8(ty) << 4) | byte(s&0x0f))
+	s >>= 4
+	for s != 0 {
+		out[n] = c | 0x80
+		n++
+		c = byte(s & 0x7f)
+		s >>= 7
+	}
+	out[n] = c
+	n++
+
+	return append([]byte(nil), out[:n]...)
+}