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perf: use sendfile(2) for snapshot serving #293

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Merged
joshfriend merged 1 commit into from
May 5, 2026
+27 −8
Merged

perf: use sendfile(2) for snapshot serving #293

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35 changes: 27 additions & 8 deletions internal/strategy/git/snapshot.go
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Original file line number Diff line number Diff line change
Expand Up @@ -224,7 +224,7 @@ func (s *Strategy) handleSnapshotRequest(w http.ResponseWriter, r *http.Request,
}()
logger.InfoContext(ctx, "Serving locally cached snapshot after waiting for in-flight fill", "upstream", upstreamURL)
w.Header().Set("Content-Type", "application/zstd")
n, err := io.Copy(w, reader)
n, err := serveReaderFast(w, r, reader)
s.metrics.recordSnapshotServe(ctx, "cold_cache", repoName, n)
if err != nil {
logger.WarnContext(ctx, "Failed to stream locally cached snapshot", "upstream", upstreamURL, "error", err)
Expand All @@ -240,7 +240,7 @@ func (s *Strategy) handleSnapshotRequest(w http.ResponseWriter, r *http.Request,
if openErr == nil && reader != nil {
logger.InfoContext(ctx, "Serving cached snapshot while mirror warms up", "upstream", upstreamURL)
w.Header().Set("Content-Type", "application/zstd")
n, err := io.Copy(w, reader)
n, err := serveReaderFast(w, r, reader)
s.metrics.recordSnapshotServe(ctx, "cold_cache", repoName, n)
if err != nil {
logger.WarnContext(ctx, "Failed to stream cached snapshot", "upstream", upstreamURL, "error", err)
Expand Down Expand Up @@ -279,23 +279,42 @@ func (s *Strategy) handleSnapshotRequest(w http.ResponseWriter, r *http.Request,
}
defer reader.Close()

if err := s.serveSnapshotWithBundle(ctx, w, reader, headers, repo, upstreamURL, repoName); err != nil {
if err := s.serveSnapshotWithBundle(ctx, w, r, reader, headers, repo, upstreamURL, repoName); err != nil {
logger.ErrorContext(ctx, "Failed to serve snapshot", "upstream", upstreamURL, "error", err)
}
}

func (s *Strategy) streamSnapshotArtifact(_ context.Context, w http.ResponseWriter, reader io.ReadCloser, headers http.Header) error {
func (s *Strategy) streamSnapshotArtifact(_ context.Context, w http.ResponseWriter, r *http.Request, reader io.ReadCloser, headers http.Header) error {
for key, values := range headers {
for _, value := range values {
w.Header().Add(key, value)
}
}
if _, err := io.Copy(w, reader); err != nil {
if _, err := serveReaderFast(w, r, reader); err != nil {
return errors.Wrap(err, "streaming artifact")
}
return nil
}

// serveReaderFast serves the content from reader using the most efficient method
// available. When reader is an *os.File, it uses http.ServeContent which enables
// sendfile(2) zero-copy I/O and automatic Content-Length/Range support. For other
// reader types it falls back to io.Copy. Returns bytes served for metrics.
func serveReaderFast(w http.ResponseWriter, r *http.Request, reader io.Reader) (int64, error) {
if f, ok := reader.(*os.File); ok {
info, err := f.Stat()
if err != nil {
return 0, errors.Wrap(err, "stat file for serving")
}
// http.ServeContent handles Content-Length, Range requests, and uses
// sendfile(2) for zero-copy transfer from file to socket.
http.ServeContent(w, r, "", time.Time{}, f)
return info.Size(), nil
}
n, err := io.Copy(w, reader)
return n, errors.Wrap(err, "copy to response")
}

func (s *Strategy) handleBundleRequest(w http.ResponseWriter, r *http.Request, host, pathValue string) {
ctx := r.Context()
logger := logging.FromContext(ctx)
Expand Down Expand Up @@ -351,7 +370,7 @@ func (s *Strategy) handleBundleRequest(w http.ResponseWriter, r *http.Request, h
}
}

func (s *Strategy) serveSnapshotWithBundle(ctx context.Context, w http.ResponseWriter, reader io.ReadCloser, headers http.Header, repo *gitclone.Repository, upstreamURL, repoName string) error {
func (s *Strategy) serveSnapshotWithBundle(ctx context.Context, w http.ResponseWriter, r *http.Request, reader io.ReadCloser, headers http.Header, repo *gitclone.Repository, upstreamURL, repoName string) error {
snapshotCommit := headers.Get("X-Cachew-Snapshot-Commit")
mirrorHead := s.getMirrorHead(ctx, repo)

Expand Down Expand Up @@ -384,7 +403,7 @@ func (s *Strategy) serveSnapshotWithBundle(ctx context.Context, w http.ResponseW
}

w.Header().Set("Content-Type", "application/zstd")
n, err := io.Copy(w, reader)
n, err := serveReaderFast(w, r, reader)
s.metrics.recordSnapshotServe(ctx, "cache", repoName, n)
return errors.Wrap(err, "stream snapshot")
}
Expand Down Expand Up @@ -782,7 +801,7 @@ func (s *Strategy) handleLFSSnapshotRequest(w http.ResponseWriter, r *http.Reque
if reader != nil {
defer reader.Close()
logger.DebugContext(ctx, "Serving cached LFS snapshot", "upstream", upstreamURL)
if err := s.streamSnapshotArtifact(ctx, w, reader, headers); err != nil {
if err := s.streamSnapshotArtifact(ctx, w, r, reader, headers); err != nil {
logger.ErrorContext(ctx, "Failed to stream LFS snapshot", "upstream", upstreamURL, "error", err)
}
return
Expand Down