net/http: TestTransportMaxConnsPerHost still flaky

[cuonglm]

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

$ go version
go version devel +83f205fa88 Sun May 12 02:55:19 2019 +0000 linux/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
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/cuonglm/.cache/go-build"
GOENV="/home/cuonglm/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/cuonglm/go"
GOPROXY="direct"
GOROOT="/home/cuonglm/sources/go"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/home/cuonglm/sources/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
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-build766721718=/tmp/go-build -gno-record-gcc-switches"

What did you do?

From git root repo
$ cd src/net/http
$ go test -run TestTransportMaxConnsPerHost -count=100 -race

What did you expect to see?

Test passed

What did you see instead?

--- FAIL: TestTransportMaxConnsPerHost (0.07s)
    transport_test.go:661: Too many get connections (http2): 2
    transport_test.go:676: Too many get connections (http2): 3
--- FAIL: TestTransportMaxConnsPerHost (0.03s)
    transport_test.go:661: Too many get connections (http2): 2
    transport_test.go:676: Too many get connections (http2): 3
--- FAIL: TestTransportMaxConnsPerHost (0.08s)
    transport_test.go:661: Too many get connections (http2): 2
    transport_test.go:676: Too many get connections (http2): 3
--- FAIL: TestTransportMaxConnsPerHost (0.06s)
    transport_test.go:661: Too many get connections (http2): 2
    transport_test.go:676: Too many get connections (http2): 3
--- FAIL: TestTransportMaxConnsPerHost (0.03s)
    transport_test.go:661: Too many get connections (http2): 2
    transport_test.go:676: Too many get connections (http2): 3
FAIL
exit status 1
FAIL	net/http	4.433s

[fraenkel]

This is a bit interesting because we get the right number of dials and TLS handshakes but the connection returned is supposed not marked reused.

[fraenkel]

The problem is that the GotConn for http2 (h2_bundle:6878) is called before we know whether we are creating a new stream (h2_bundle: 7449) which is what determines reuse.

This is not a flaky test but a real bug.

[fraenkel]

Using the nextStreamID is flawed anyhow. If you allow HTTP, we start at 3 which means its immediately reused.

[fraenkel]

If we move the GotConn call into getClientConn(h2_bundle:749), we can distinguish between a new connection and a used connection.

[anakin]

➜ http go test -run TestTransportMaxConnsPerHost -count=100 -race
PASS
ok net/http 1.641s

[anakin]

by the way,
➜ http go version
go version go1.12.5 darwin/amd64

[gopherbot]

Change https://golang.org/cl/176720 mentions this issue: http2: track reused connections

[fraenkel]

I submitted a fix which does highlight the issue with http2. I did some other testing and found some of the other ClientTrace calls like TLSHandshakreXXX are missing.

[bcmills]

The darwin-amd64-race builder caught this too:
https://build.golang.org/log/06b60fdfdf4a88e04ae4181d80ddd39db9aaafa0

[bcmills]

I just got another TryBot flake on this:
https://storage.googleapis.com/go-build-log/06afa4b7/freebsd-amd64-12_0_63953b9e.log