x/net/http2: cannot create 'MaxConcurrentStreams' streams with a single ClientConn #35860
Description
What version of Go are you using (go version)?
$ go version go version go1.13.3 darwin/amd64
Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GO111MODULE="" GOARCH="amd64" GOBIN="" GOCACHE="/Users/wit/Library/Caches/go-build" GOENV="/Users/wit/Library/Application Support/go/env" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/wit/gocode" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/Cellar/go/1.13.3/libexec" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/Cellar/go/1.13.3/libexec/pkg/tool/darwin_amd64" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" 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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/mq/qzdh1j2n5fg3kylx9v7n79p40000gn/T/go-build653171154=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
Attempt to create max concurrent streams with one client connection.
package main
import (
"crypto/tls"
"fmt"
"net"
"net/http"
"net/http/httptest"
"strings"
"sync"
"time"
"golang.org/x/net/http2"
"golang.org/x/net/http2/h2c"
)
const maxConcurrentStreams = 10
func handlerFunc(delayChan chan struct{}) http.HandlerFunc {
return func(rw http.ResponseWriter, req *http.Request) {
defer req.Body.Close()
if delayChan != nil {
<-delayChan
}
rw.WriteHeader(204)
rw.Write([]byte("ok"))
}
}
func main() {
delayChan := make(chan struct{})
h2cServer := httptest.NewServer(
h2c.NewHandler(http.HandlerFunc(handlerFunc(delayChan)),
&http2.Server{
MaxConcurrentStreams: maxConcurrentStreams,
},
),
)
defer h2cServer.Close()
req, err := http.NewRequest("GET", "http://"+h2cServer.Listener.Addr().String(), strings.NewReader(""))
if err != nil {
panic(err)
}
h2Transport := &http2.Transport{
AllowHTTP: true,
DialTLS: func(netw, addr string, cfg *tls.Config) (net.Conn, error) {
return net.Dial(netw, addr)
},
}
conn, err := net.Dial("tcp", h2cServer.Listener.Addr().String())
if err != nil {
panic(err)
}
cc, err := h2Transport.NewClientConn(conn)
if err != nil {
panic(err)
}
var wg sync.WaitGroup
wg.Add(1)
go func() {
defer wg.Done()
wg.Add(maxConcurrentStreams-1)
for i := 0; i < maxConcurrentStreams-1; i++ {
go func(i int) {
defer wg.Done()
resp, err := cc.RoundTrip(req)
fmt.Println("request:", i, resp, err)
}(i)
}
}()
time.Sleep(50 * time.Millisecond)
wg.Add(1)
go func() {
defer wg.Done()
resp, err := cc.RoundTrip(req)
fmt.Println("max streams request:", resp, err)
}()
close(delayChan)
wg.Wait()
}What did you expect to see?
Expected to see the last RoundTrip request succeed.
What did you see instead?
$ go run go_http2_max_streams.go
max streams request: <nil> http2: client conn not usable
request: 6 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 8 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 1 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 5 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 7 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 4 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 2 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 0 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
request: 3 &{204 No Content 204 HTTP/2.0 2 0 map[Date:[Wed, 27 Nov 2019 00:08:17 GMT]] {0xc00008ef30} 0 [] false false map[] 0xc0000da000 <nil>} <nil>
The issue appears to be at https://github.com/golang/net/blob/master/http2/transport.go#L735:
maxConcurrentOkay = int64(len(cc.streams)+1) < int64(cc.maxConcurrentStreams)where the test is to see whether an additional stream can be handled, but the condition should be <= instead of <.