client/web: add support for zst precomppressed assets

This will enable us to reduce the size of these embedded assets.

Updates tailscale/corp#20099

Signed-off-by: James Tucker <james@tailscale.com>

client/web/assets.go

@@ -16,7 +16,9 @@ import (
 	"strings"
 	"time"
 
+	"github.com/klauspost/compress/zstd"
 	prebuilt "github.com/tailscale/web-client-prebuilt"
+	"tailscale.com/tsweb"
 )
 
 var start = time.Now()
@@ -63,7 +65,33 @@ func assetsHandler(devMode bool) (_ http.Handler, cleanup func()) {
 	}), nil
 }
 
-func openPrecompressedFile(w http.ResponseWriter, r *http.Request, path string, fs fs.FS) (fs.File, error) {
+type zstFile struct {
+	f fs.File
+	*zstd.Decoder
+}
+
+func newZSTFile(f fs.File) (*zstFile, error) {
+	zr, err := zstd.NewReader(f)
+	if err != nil {
+		return nil, err
+	}
+	return &zstFile{f: f, Decoder: zr}, nil
+}
+
+func (z *zstFile) Close() error {
+	z.Close()
+	return z.f.Close()
+}
+
+func openPrecompressedFile(w http.ResponseWriter, r *http.Request, path string, fs fs.FS) (io.ReadCloser, error) {
+	if f, err := fs.Open(path + ".zst"); err == nil {
+		if tsweb.AcceptsEncoding(r, "zstd") {
+			w.Header().Set("Content-Encoding", "zstd")
+			return f, nil
+		}
+		return newZSTFile(f)
+	}
+	// TODO(raggi): remove this code path when no longer used
 	if f, err := fs.Open(path + ".gz"); err == nil {
 		w.Header().Set("Content-Encoding", "gzip")
 		return f, nil

cmd/build-webclient/build-webclient.go

@@ -73,10 +73,14 @@ func build(toolDir, appDir string) error {
 		if err := os.Remove(f); err != nil {
 			log.Printf("Failed to cleanup %q: %v", f, err)
 		}
-		// Removing intermediate ".br" version, we use ".gz" asset.
+		// Removing ".br" version, we use the ".zst" asset.
 		if err := os.Remove(f + ".br"); err != nil {
 			log.Printf("Failed to cleanup %q: %v", f+".gz", err)
 		}
+		// Removing ".gz" version, we use the ".zst" asset.
+		if err := os.Remove(f + ".gz"); err != nil {
+			log.Printf("Failed to cleanup %q: %v", f+".gz", err)
+		}
 	}
 
 	return nil

util/precompress/precompress.go

@@ -17,6 +17,7 @@ import (
 	"path/filepath"
 
 	"github.com/andybalholm/brotli"
+	"github.com/klauspost/compress/zstd"
 	"golang.org/x/sync/errgroup"
 	"tailscale.com/tsweb"
 )
@@ -63,6 +64,12 @@ type Options struct {
 // OpenPrecompressedFile opens a file from fs, preferring compressed versions
 // generated by PrecompressDir if possible.
 func OpenPrecompressedFile(w http.ResponseWriter, r *http.Request, path string, fs fs.FS) (fs.File, error) {
+	if tsweb.AcceptsEncoding(r, "zstd") {
+		if f, err := fs.Open(path + ".zst"); err == nil {
+			w.Header().Set("Content-Encoding", "zstd")
+			return f, nil
+		}
+	}
 	if tsweb.AcceptsEncoding(r, "br") {
 		if f, err := fs.Open(path + ".br"); err == nil {
 			w.Header().Set("Content-Encoding", "br")
@@ -104,6 +111,13 @@ func Precompress(path string, options Options) error {
 	if err != nil {
 		return err
 	}
+	zstdLevel := zstd.WithEncoderLevel(zstd.SpeedBestCompression)
+	if options.FastCompression {
+		zstdLevel = zstd.WithEncoderLevel(zstd.SpeedFastest)
+	}
+	err = writeCompressed(contents, func(w io.Writer) (io.WriteCloser, error) {
+		return zstd.NewWriter(w, zstdLevel)
+	}, path+".zst", fi.Mode())
 	brotliLevel := brotli.BestCompression
 	if options.FastCompression {
 		brotliLevel = brotli.BestSpeed