Update

vendor/tailscale.com/tsweb/compserve/zstd.go

@@ -0,0 +1,81 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package compserve
+
+import (
+	"io"
+	"io/fs"
+
+	"github.com/klauspost/compress/zstd"
+	"tailscale.com/util/zstdframe"
+)
+
+// Zstd serves zstd-precompressed variants ("*.zst", as generated by
+// util/precompress). [Encoding.Decompress] lets ServeFile transcode the
+// variant for clients that do not accept zstd.
+var Zstd = Encoding{
+	Token:      "zstd",
+	Ext:        ".zst",
+	Decompress: decompressZstd,
+	Compress:   compressZstdLive,
+}
+
+// compressZstdLive wraps w in a streaming zstd compressor using the fastest
+// compression level and a small window suitable for low-latency live
+// compression. Close on the returned writer finishes the zstd frame and
+// returns the encoder to the shared pool.
+func compressZstdLive(w io.Writer) (io.WriteCloser, error) {
+	enc, put := zstdframe.GetStreamingEncoder(
+		zstdframe.FastestCompression,
+		zstdframe.MaxWindowSize(64<<10),
+	)
+	// Encoder.Reset (streaming) cannot fail; only Decoder.Reset can.
+	enc.Reset(w)
+	return &pooledZstdWriter{Encoder: enc, put: put}, nil
+}
+
+// pooledZstdWriter is a zstd.Encoder writing to the underlying writer;
+// Close finishes the frame and returns the encoder to the shared pool.
+type pooledZstdWriter struct {
+	put    func()
+	closed bool
+	*zstd.Encoder
+}
+
+func (p *pooledZstdWriter) Close() error {
+	if p.closed {
+		return nil
+	}
+	p.closed = true
+	err := p.Encoder.Close()
+	p.put()
+	return err
+}
+
+// decompressZstd wraps f in a streaming zstd decompressor backed by the
+// shared decoder pool in util/zstdframe (concurrency=1, so streaming decode
+// neither spawns goroutines nor retains unbounded memory). It takes
+// ownership of f.
+func decompressZstd(f fs.File) (io.ReadCloser, error) {
+	dec, put := zstdframe.GetDecoder()
+	if err := dec.Reset(f); err != nil {
+		put()
+		f.Close()
+		return nil, err
+	}
+	return &pooledZstdReader{f: f, put: put, Decoder: dec}, nil
+}
+
+// pooledZstdReader is a zstd.Decoder reading from f; Close returns the
+// decoder to the shared pool and closes f.
+type pooledZstdReader struct {
+	f   fs.File
+	put func()
+	*zstd.Decoder
+}
+
+func (p *pooledZstdReader) Close() error {
+	p.put()
+	return p.f.Close()
+}