1 files changed, 97 insertions, 0 deletions
diff --git a/format/pack/ingest/stream.go b/format/pack/ingest/stream.go
new file mode 100644
index 00000000..17a19d8d
--- /dev/null
+++ b/format/pack/ingest/stream.go
@@ -0,0 +1,97 @@
+package ingest
+
+import (
+	"bufio"
+	"fmt"
+	"hash"
+	"hash/crc32"
+	"io"
+	"os"
+)
+
+// streamCopier reads bytes from src, writes them to packFile, and updates
+// trailer verification state.
+type streamCopier struct {
+	reader   *bufio.Reader
+	packFile *os.File
+	verifier *trailerVerifier
+	offset   uint64
+	entryCRC hash.Hash32
+}
+
+// newStreamCopier constructs one stream copier.
+func newStreamCopier(src io.Reader, packFile *os.File, verifier *trailerVerifier) *streamCopier {
+	return &streamCopier{
+		reader:   bufio.NewReaderSize(src, 64<<10),
+		packFile: packFile,
+		verifier: verifier,
+	}
+}
+
+// Read implements io.Reader.
+func (stream *streamCopier) Read(dst []byte) (int, error) {
+	n, err := stream.reader.Read(dst)
+	if n > 0 {
+		if writeErr := stream.writeChunk(dst[:n]); writeErr != nil {
+			return 0, writeErr
+		}
+	}
+
+	return n, err
+}
+
+// ReadByte implements io.ByteReader.
+func (stream *streamCopier) ReadByte() (byte, error) {
+	b, err := stream.reader.ReadByte()
+	if err != nil {
+		return 0, err
+	}
+
+	if writeErr := stream.writeChunk([]byte{b}); writeErr != nil {
+		return 0, writeErr
+	}
+
+	return b, nil
+}
+
+// readFull reads exactly len(dst) bytes through stream.
+func (stream *streamCopier) readFull(dst []byte) error {
+	_, err := io.ReadFull(stream, dst)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// writeChunk mirrors src bytes to destination artifacts and accounting.
+func (stream *streamCopier) writeChunk(src []byte) error {
+	_, err := stream.packFile.WriteAt(src, int64(stream.offset))
+	if err != nil {
+		return &ErrDestinationWrite{Op: fmt.Sprintf("write pack: %v", err)}
+	}
+
+	if stream.entryCRC != nil {
+		_, _ = stream.entryCRC.Write(src)
+	}
+	stream.verifier.write(src)
+	stream.offset += uint64(len(src))
+
+	return nil
+}
+
+// beginEntryCRC starts inline CRC accumulation for one packed entry.
+func (stream *streamCopier) beginEntryCRC() {
+	stream.entryCRC = crc32.NewIEEE()
+}
+
+// endEntryCRC finishes inline CRC accumulation for one packed entry.
+func (stream *streamCopier) endEntryCRC() (uint32, error) {
+	if stream.entryCRC == nil {
+		return 0, fmt.Errorf("format/pack/ingest: entry CRC not started")
+	}
+	crc := stream.entryCRC.Sum32()
+	stream.entryCRC = nil
+
+	return crc, nil
+}