net/http: pool transport gzip readers

goos: linux
goarch: amd64
pkg: net/http
             │   HEAD~1    │              HEAD              │
             │   sec/op    │    sec/op     vs base          │
ClientGzip-8   621.0µ ± 2%   616.3µ ± 10%  ~ (p=0.971 n=10)

             │    HEAD~1     │                 HEAD                 │
             │     B/op      │     B/op      vs base                │
ClientGzip-8   49.765Ki ± 0%   9.514Ki ± 2%  -80.88% (p=0.000 n=10)

             │   HEAD~1   │               HEAD                │
             │ allocs/op  │ allocs/op   vs base               │
ClientGzip-8   57.00 ± 0%   52.00 ± 0%  -8.77% (p=0.000 n=10)

Allocation saving comes from absent compress/flate.(*dictDecoder).init

This change also improves concurrent body read detection by returning an explicit error.

Updates #61353

Change-Id: I380acfca912dc009b3b9c8283e27b3526cedd546
GitHub-Last-Rev: df12f6a48af4854ba686fe431a9aeb6d9ba3c303
GitHub-Pull-Request: golang/go#61390
Reviewed-on: https://go-review.googlesource.com/c/go/+/510255
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/net/http/serve_test.go

@@ -12,6 +12,7 @@ import (
 	"compress/gzip"
 	"compress/zlib"
 	"context"
+	crand "crypto/rand"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/json"
@@ -5281,8 +5282,8 @@ func benchmarkClientServerParallel(b *testing.B, parallelism int, mode testMode)
 func BenchmarkServer(b *testing.B) {
 	b.ReportAllocs()
 	// Child process mode;
-	if url := os.Getenv("TEST_BENCH_SERVER_URL"); url != "" {
+	if url := os.Getenv("GO_TEST_BENCH_SERVER_URL"); url != "" {
-		n, err := strconv.Atoi(os.Getenv("TEST_BENCH_CLIENT_N"))
+		n, err := strconv.Atoi(os.Getenv("GO_TEST_BENCH_CLIENT_N"))
 		if err != nil {
 			panic(err)
 		}
@@ -5316,8 +5317,8 @@ func BenchmarkServer(b *testing.B) {
 
 	cmd := testenv.Command(b, os.Args[0], "-test.run=^$", "-test.bench=^BenchmarkServer$")
 	cmd.Env = append([]string{
-		fmt.Sprintf("TEST_BENCH_CLIENT_N=%d", b.N),
+		fmt.Sprintf("GO_TEST_BENCH_CLIENT_N=%d", b.N),
-		fmt.Sprintf("TEST_BENCH_SERVER_URL=%s", ts.URL),
+		fmt.Sprintf("GO_TEST_BENCH_SERVER_URL=%s", ts.URL),
 	}, os.Environ()...)
 	out, err := cmd.CombinedOutput()
 	if err != nil {
@@ -5338,68 +5339,12 @@ func getNoBody(urlStr string) (*Response, error) {
 // A benchmark for profiling the client without the HTTP server code.
 // The server code runs in a subprocess.
 func BenchmarkClient(b *testing.B) {
-	b.ReportAllocs()
-	b.StopTimer()
-	defer afterTest(b)
-
 	var data = []byte("Hello world.\n")
-	if server := os.Getenv("TEST_BENCH_SERVER"); server != "" {
-		// Server process mode.
-		port := os.Getenv("TEST_BENCH_SERVER_PORT") // can be set by user
-		if port == "" {
-			port = "0"
-		}
-		ln, err := net.Listen("tcp", "localhost:"+port)
-		if err != nil {
-			fmt.Fprintln(os.Stderr, err.Error())
-			os.Exit(1)
-		}
-		fmt.Println(ln.Addr().String())
-		HandleFunc("/", func(w ResponseWriter, r *Request) {
-			r.ParseForm()
-			if r.Form.Get("stop") != "" {
-				os.Exit(0)
-			}
-			w.Header().Set("Content-Type", "text/html; charset=utf-8")
-			w.Write(data)
-		})
-		var srv Server
-		log.Fatal(srv.Serve(ln))
-	}
 
-	// Start server process.
+	url := startClientBenchmarkServer(b, HandlerFunc(func(w ResponseWriter, _ *Request) {
-	ctx, cancel := context.WithCancel(context.Background())
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
-	cmd := testenv.CommandContext(b, ctx, os.Args[0], "-test.run=^$", "-test.bench=^BenchmarkClient$")
+		w.Write(data)
-	cmd.Env = append(cmd.Environ(), "TEST_BENCH_SERVER=yes")
+	}))
-	cmd.Stderr = os.Stderr
-	stdout, err := cmd.StdoutPipe()
-	if err != nil {
-		b.Fatal(err)
-	}
-	if err := cmd.Start(); err != nil {
-		b.Fatalf("subprocess failed to start: %v", err)
-	}
-
-	done := make(chan error, 1)
-	go func() {
-		done <- cmd.Wait()
-		close(done)
-	}()
-	defer func() {
-		cancel()
-		<-done
-	}()
-
-	// Wait for the server in the child process to respond and tell us
-	// its listening address, once it's started listening:
-	bs := bufio.NewScanner(stdout)
-	if !bs.Scan() {
-		b.Fatalf("failed to read listening URL from child: %v", bs.Err())
-	}
-	url := "http://" + strings.TrimSpace(bs.Text()) + "/"
-	if _, err := getNoBody(url); err != nil {
-		b.Fatalf("initial probe of child process failed: %v", err)
-	}
 
 	// Do b.N requests to the server.
 	b.StartTimer()
@@ -5418,12 +5363,115 @@ func BenchmarkClient(b *testing.B) {
 		}
 	}
 	b.StopTimer()
+}
+
+func startClientBenchmarkServer(b *testing.B, handler Handler) string {
+	b.ReportAllocs()
+	b.StopTimer()
+
+	if server := os.Getenv("GO_TEST_BENCH_SERVER"); server != "" {
+		// Server process mode.
+		port := os.Getenv("GO_TEST_BENCH_SERVER_PORT") // can be set by user
+		if port == "" {
+			port = "0"
+		}
+		ln, err := net.Listen("tcp", "localhost:"+port)
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println(ln.Addr().String())
+
+		HandleFunc("/", func(w ResponseWriter, r *Request) {
+			r.ParseForm()
+			if r.Form.Get("stop") != "" {
+				os.Exit(0)
+			}
+			handler.ServeHTTP(w, r)
+		})
+		var srv Server
+		log.Fatal(srv.Serve(ln))
+	}
+
+	// Start server process.
+	ctx, cancel := context.WithCancel(context.Background())
+	cmd := testenv.CommandContext(b, ctx, os.Args[0], "-test.run=^$", "-test.bench=^"+b.Name()+"$")
+	cmd.Env = append(cmd.Environ(), "GO_TEST_BENCH_SERVER=yes")
+	cmd.Stderr = os.Stderr
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		b.Fatal(err)
+	}
+	if err := cmd.Start(); err != nil {
+		b.Fatalf("subprocess failed to start: %v", err)
+	}
+
+	done := make(chan error, 1)
+	go func() {
+		done <- cmd.Wait()
+		close(done)
+	}()
+
+	// Wait for the server in the child process to respond and tell us
+	// its listening address, once it's started listening:
+	bs := bufio.NewScanner(stdout)
+	if !bs.Scan() {
+		b.Fatalf("failed to read listening URL from child: %v", bs.Err())
+	}
+	url := "http://" + strings.TrimSpace(bs.Text()) + "/"
+	if _, err := getNoBody(url); err != nil {
+		b.Fatalf("initial probe of child process failed: %v", err)
+	}
 
 	// Instruct server process to stop.
-	getNoBody(url + "?stop=yes")
+	b.Cleanup(func() {
-	if err := <-done; err != nil {
+		getNoBody(url + "?stop=yes")
-		b.Fatalf("subprocess failed: %v", err)
+		if err := <-done; err != nil {
+			b.Fatalf("subprocess failed: %v", err)
+		}
+
+		cancel()
+		<-done
+
+		afterTest(b)
+	})
+
+	return url
+}
+
+func BenchmarkClientGzip(b *testing.B) {
+	const responseSize = 1024 * 1024
+
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+	if _, err := io.CopyN(gz, crand.Reader, responseSize); err != nil {
+		b.Fatal(err)
 	}
+	gz.Close()
+
+	data := buf.Bytes()
+
+	url := startClientBenchmarkServer(b, HandlerFunc(func(w ResponseWriter, _ *Request) {
+		w.Header().Set("Content-Encoding", "gzip")
+		w.Write(data)
+	}))
+
+	// Do b.N requests to the server.
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		res, err := Get(url)
+		if err != nil {
+			b.Fatalf("Get: %v", err)
+		}
+		n, err := io.Copy(io.Discard, res.Body)
+		res.Body.Close()
+		if err != nil {
+			b.Fatalf("ReadAll: %v", err)
+		}
+		if n != responseSize {
+			b.Fatalf("ReadAll: expected %d bytes, got %d", responseSize, n)
+		}
+	}
+	b.StopTimer()
 }
 
 func BenchmarkServerFakeConnNoKeepAlive(b *testing.B) {

src/net/http/transport.go

@@ -11,6 +11,7 @@ package http
 
 import (
 	"bufio"
+	"compress/flate"
 	"compress/gzip"
 	"container/list"
 	"context"
@@ -2988,6 +2989,7 @@ type bodyEOFSignal struct {
 }
 
 var errReadOnClosedResBody = errors.New("http: read on closed response body")
+var errConcurrentReadOnResBody = errors.New("http: concurrent read on response body")
 
 func (es *bodyEOFSignal) Read(p []byte) (n int, err error) {
 	es.mu.Lock()
@@ -3037,37 +3039,98 @@ func (es *bodyEOFSignal) condfn(err error) error {
 }
 
 // gzipReader wraps a response body so it can lazily
-// call gzip.NewReader on the first call to Read
+// get gzip.Reader from the pool on the first call to Read.
+// After Close is called it puts gzip.Reader to the pool immediately
+// if there is no Read in progress or later when Read completes.
 type gzipReader struct {
 	_    incomparable
 	body *bodyEOFSignal // underlying HTTP/1 response body framing
-	zr   *gzip.Reader   // lazily-initialized gzip reader
+	mu   sync.Mutex     // guards zr and zerr
-	zerr error          // any error from gzip.NewReader; sticky
+	zr   *gzip.Reader
+	zerr error
+}
+
+type eofReader struct{}
+
+func (eofReader) Read([]byte) (int, error) { return 0, io.EOF }
+func (eofReader) ReadByte() (byte, error)  { return 0, io.EOF }
+
+var gzipPool = sync.Pool{New: func() any { return new(gzip.Reader) }}
+
+// gzipPoolGet gets a gzip.Reader from the pool and resets it to read from r.
+func gzipPoolGet(r io.Reader) (*gzip.Reader, error) {
+	zr := gzipPool.Get().(*gzip.Reader)
+	if err := zr.Reset(r); err != nil {
+		gzipPoolPut(zr)
+		return nil, err
+	}
+	return zr, nil
+}
+
+// gzipPoolPut puts a gzip.Reader back into the pool.
+func gzipPoolPut(zr *gzip.Reader) {
+	// Reset will allocate bufio.Reader if we pass it anything
+	// other than a flate.Reader, so ensure that it's getting one.
+	var r flate.Reader = eofReader{}
+	zr.Reset(r)
+	gzipPool.Put(zr)
+}
+
+// acquire returns a gzip.Reader for reading response body.
+// The reader must be released after use.
+func (gz *gzipReader) acquire() (*gzip.Reader, error) {
+	gz.mu.Lock()
+	defer gz.mu.Unlock()
+	if gz.zerr != nil {
+		return nil, gz.zerr
+	}
+	if gz.zr == nil {
+		gz.zr, gz.zerr = gzipPoolGet(gz.body)
+		if gz.zerr != nil {
+			return nil, gz.zerr
+		}
+	}
+	ret := gz.zr
+	gz.zr, gz.zerr = nil, errConcurrentReadOnResBody
+	return ret, nil
+}
+
+// release returns the gzip.Reader to the pool if Close was called during Read.
+func (gz *gzipReader) release(zr *gzip.Reader) {
+	gz.mu.Lock()
+	defer gz.mu.Unlock()
+	if gz.zerr == errConcurrentReadOnResBody {
+		gz.zr, gz.zerr = zr, nil
+	} else { // errReadOnClosedResBody
+		gzipPoolPut(zr)
+	}
+}
+
+// close returns the gzip.Reader to the pool immediately or
+// signals release to do so after Read completes.
+func (gz *gzipReader) close() {
+	gz.mu.Lock()
+	defer gz.mu.Unlock()
+	if gz.zerr == nil && gz.zr != nil {
+		gzipPoolPut(gz.zr)
+		gz.zr = nil
+	}
+	gz.zerr = errReadOnClosedResBody
 }
 
 func (gz *gzipReader) Read(p []byte) (n int, err error) {
-	if gz.zr == nil {
+	zr, err := gz.acquire()
-		if gz.zerr == nil {
-			gz.zr, gz.zerr = gzip.NewReader(gz.body)
-		}
-		if gz.zerr != nil {
-			return 0, gz.zerr
-		}
-	}
-
-	gz.body.mu.Lock()
-	if gz.body.closed {
-		err = errReadOnClosedResBody
-	}
-	gz.body.mu.Unlock()
-
 	if err != nil {
 		return 0, err
 	}
-	return gz.zr.Read(p)
+	defer gz.release(zr)
+
+	return zr.Read(p)
 }
 
 func (gz *gzipReader) Close() error {
+	gz.close()
+
 	return gz.body.Close()
 }