Fangliding：报告 Go 1.27 新 http2 缺 single-flight 致每请求拨号

FanglidingXray-core 代码贡献者

GitHub·2026.09.22 13:15:28（UTC+8）

Fangliding：报告 Go 1.27 新 http2 缺 single-flight 致每请求拨号

Fangliding 在 golang/go 报告：Go 1.27 新包装 http2 缺旧版 single flight，100 并发会拨号 100 次，而 http2legacy 只拨 1 次。他认为这影响连接复用。原文见下方引用。

作者原文@Fangliding

Go version

go 1.27 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/codespace/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/codespace/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2735046389=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/workspaces/Xray-core/go.mod'
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/codespace/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

run this code to count dial calls in http2

package main

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"net"
	"net/http"
	"sync"
	"sync/atomic"

	"golang.org/x/net/http2"
)

func main() {
	totalRequests := 100
	targetURL := "https://cp.cloudflare.com/cdn-cgi/trace"

	var dialCount atomic.Int64

	client := &http.Client{
		Transport: &http2.Transport{
			DialTLSContext: func(ctx context.Context, network, addr string, cfg *tls.Config) (c net.Conn, err error) {
				dialCount.Add(1)
				dialer := &tls.Dialer{Config: cfg}
				return dialer.DialContext(ctx, network, addr)
			},
		},
	}

	var wg sync.WaitGroup
	start := make(chan struct{})

	for range totalRequests {
		wg.Add(1)
		go func() {
			defer wg.Done()
			<-start
			resp, err := client.Get(targetURL)
			if err == nil {
				io.Copy(io.Discard, resp.Body)
				resp.Body.Close()
			}
		}()
	}

	close(start)
	wg.Wait()

	fmt.Printf("Total Dial Calls: %d\n", dialCount.Load())
}

What did you see happen?

It made 100 tcp dial calls for every http request

Total Dial Calls: 100

What did you expect to see?

In old http2 implementation, instantly sending multiple requests will only make one TCP dial, this is the expected behavior of http2
run code above with this

go run -tags http2legacy .

And it will return

Total Dial Calls: 1

I understand that HTTP package needs to dial multiple connections because the server HTTP version is unknown, but we have prior knowledge in net/x/http2, and perhaps we can add a config to enable the single flight mechanism in http package (or automatically use when alpn only contains h2?)