net/http: `readLoopPeekFailLocked: <nil>` from client when server sends response immediately

[logrusorgru]

What version of Go are you using (go version)?

$ go version
go version go1.12.1 linux/amd64

Does this issue reproduce with the latest release?

Yep. 1.12.1

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/user/go"
GOPROXY=""
GORACE=""
GOROOT="/opt/go"
GOTMPDIR=""
GOTOOLDIR="/opt/go/pkg/tool/linux_amd64"
GCCGO="/usr/bin/gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build705707104=/tmp/go-build -gno-record-gcc-switches"

What did you do?

100% reproducible on Linux X64, and play.golang.org. The behavior is unpredictable and the code (see below) to reproduce should be executed few times to got the error and the log.

The error is:

Get http://127.0.0.1:9101/path: readLoopPeekFailLocked: <nil>

The log is:

transport.go:1829: Unsolicited response received on idle HTTP channel starting with "HTTP/1.1 502 Bad Gateway\r\n\r\n"; err=<nil>

What happens?

HTTP server sends response without reading request and without a delay. This approach is good for proxy servers where a client determined by his IP (i.e. using white-list). Thus, we haven't to read request, if the user is not white-listed.

Reproducing

(try few times to got error)

play.golang.org

package main

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"net/url"
	"sync"
	"time"
)

func mustParseURL(uri string) *url.URL {
	x, err := url.Parse(uri)
	if err != nil {
		panic(err)
	}
	return x
}

func main() {

	l, err := net.Listen("tcp", "127.0.0.1:9100")
	if err != nil {
		log.Fatal(err)
	}
	go func(l net.Listener) {
		for {
			c, err := l.Accept()
			if err != nil {
				log.Fatal(err)
			}
			go func(c net.Conn) {
				defer c.Close()
				fmt.Fprint(c, "HTTP/1.1 502 Bad Gateway\r\n\r\n")
			}(c)
		}
	}(l)
	time.Sleep(100 * time.Millisecond)

	var cl http.Client
	cl.Transport = &http.Transport{
		Proxy:           http.ProxyURL(mustParseURL("http://127.0.0.1:9100/")),
		MaxConnsPerHost: 100,
	}

	const N = 100

	var wg sync.WaitGroup
	wg.Add(N)
	for i := 0; i < N; i++ {
		go func() {
			defer wg.Done()
			resp, err := cl.Get("http://127.0.0.1:9101/path")
			if err != nil {
				log.Print("error:", err)
				return
			}
			if resp.StatusCode != 502 {
				log.Println("status:", resp.StatusCode)
			}
			resp.Body.Close()
		}()
	}

	wg.Wait()

}

Also, playing with the N constant I've got this error for N=10, N=100 and N=1000. For N=1000 this error occurs every time. For N=10 rarely. Seems, it depends on goroutines scheduling.

What did you expect to see?

Got this error every time or never.

What did you see instead?

It's unpredictable. That makes testing a bit harder.

Also

Probably related issues #15253, #15446

[bcmills]

CC @bradfitz

[lamg]

Go version

go version go1.13 linux/amd64

Behavior

Running the following code with go test -race fails most of the times, but not always. I've never seen it fail with go test.

package race

import (
	"bytes"
	"context"
	"net"
	h "net/http"
	ht "net/http/httptest"
	"testing"
	"time"
)

func TestDataRace(t *testing.T) {
	d := &dialer{content: "HTTP/1.1 502 Bad Gateway\r\n\r\n"}
	tr := &h.Transport{
		DialContext: d.dial,
	}
	req := ht.NewRequest(h.MethodGet, "http://example.com", nil)
	resp, e := tr.RoundTrip(req)
	if e != nil {
		t.Error(e)
	} else if resp.StatusCode != h.StatusBadGateway {
		t.Error("status:", resp.Status)
	}
}

type dialer struct {
	content string
}

func (d *dialer) dial(ctx context.Context, network,
	addr string) (n net.Conn, e error) {
	n = newMockConn(d.content)
	return
}

type mockConn struct {
	read  *bytes.Buffer
	write *bytes.Buffer
}

func newMockConn(content string) (m *mockConn) {
	m = &mockConn{
		read:  bytes.NewBufferString(content),
		write: new(bytes.Buffer),
	}
	return
}

func (m *mockConn) Read(p []byte) (n int, e error) {
	n, e = m.read.Read(p)
	return
}

func (m *mockConn) Write(p []byte) (n int, e error) {
	n, e = m.write.Write(p)
	return
}

func (m *mockConn) Close() (e error) { return }

func (m *mockConn) LocalAddr() (a net.Addr) { return }

func (m *mockConn) RemoteAddr() (a net.Addr) { return }

func (m *mockConn) SetDeadline(t time.Time) (e error) { return }

func (m *mockConn) SetReadDeadline(t time.Time) (e error) {
	return
}

func (m *mockConn) SetWriteDeadline(t time.Time) (e error) {
	return
}

Output when failing

2019/10/11 17:19:50 Unsolicited response received on idle HTTP channel starting with "HTTP/1.1 502 Bad Gateway\r\n\r\n"; err=<nil>
--- FAIL: TestDataRace (0.00s)
    race_test.go:21: readLoopPeekFailLocked: <nil>
FAIL
exit status 1

[lamg]

Defining in the previous code mockConn, newMockConn, mockConn.Read and mockConn.Write the following way, the error never appeared so far, with go test or go test -race:

type mockConn struct {
	read    *bytes.Buffer
	write   *bytes.Buffer
	writeOk chan bool
}

func newMockConn(content string) (m *mockConn) {
	m = &mockConn{
		read:    bytes.NewBufferString(content),
		write:   new(bytes.Buffer),
		writeOk: make(chan bool, 0),
	}
	return
}

func (m *mockConn) Read(p []byte) (n int, e error) {
	<-m.writeOk
	n, e = m.read.Read(p)
	return
}

func (m *mockConn) Write(p []byte) (n int, e error) {
	n, e = m.write.Write(p)
	m.writeOk <- true
	return
}

[cuonglm]

Maybe related #34066