x/net/http2: Transport hangs forever if using a pipe that has not been written to yet as req.Body

[luna-duclos]

### What version of Go are you using (go version)?
Go 1.7.1

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

set GOARCH=amd64                                                                                                                                                
set GOBIN=                                                                                                                                                      
set GOEXE=.exe                                                                                                                                                  
set GOHOSTARCH=amd64                                                                                                                                            
set GOHOSTOS=windows                                                                                                                                            
set GOOS=windows                                                                                                                                                
set GOPATH=D:\src\psg\server;D:\src\psg\server\vendor                                                                                                           
set GORACE=                                                                                                                                                     
set GOROOT=C:\apps\Go                                                                                                                                           
set GOTOOLDIR=C:\apps\Go\pkg\tool\windows_amd64                                                                                                                 
set CC=gcc                                                                                                                                                      
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\lunad\AppData\Local\Temp\go-build906126950=/tmp/go-build -gno-record-gcc-switches  
set CXX=g++                                                                                                                                                     
set CGO_ENABLED=1                                                                                                                                               

### What did you do?
If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

I ran the following program:

package main

import (
    "crypto/rand"
    "io"
    "log"
    "net/http"
    "runtime/debug"
    "time"

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

func main() {
    // set a 10 second timer for success
    go func() {
        timer := time.NewTimer(10 * time.Second)
        <-timer.C
        debug.SetTraceback("all")
        panic("10 second test period expired")
    }()

    transport := &http2.Transport{}
    c := &http.Client{Transport: transport}

    // Get a set of pipes, we'll use these to send data to the server
    pipeReader, pipeWriter := io.Pipe()

    // Initialize the request
    req, err := http.NewRequest("PUT", "https://http2.golang.org/bidirectional-stream", pipeReader)
    if err != nil {
        pipeWriter.Close()
        log.Fatalf("Error while initializing http request: %v", err)
    }

    // Set the body of the request to the reader end of our pipe, and initiate the request.
    req.Body = pipeReader
    resp, err := c.Do(req)
    if err != nil {
        pipeWriter.Close()
        log.Fatalf("Error during http call: %v", err)
    }

    // Check that we actually got a 200 OK, if not: error out
    if resp.StatusCode != http.StatusOK {
        resp.Body.Close()
        pipeWriter.Close()
        log.Fatalf("http call got non-200 status code %d", resp.StatusCode)
    }

    // Use a 10 byte buffer
    buffer := make([]byte, 10)

    // Read some data
    dataLen, err := resp.Body.Read(buffer)
    if err != nil {
        log.Fatalf("Error while reading data: %v", err)
    }

    log.Printf("Got data: %+v", buffer[:dataLen])

    // Reply
    if _, err := rand.Read(buffer); err != nil {
        log.Fatalf("Error while reading random data: %v", err)
    }

    if _, err := pipeWriter.Write(buffer); err != nil {
        log.Fatalf("Error while writing data: %v", err)
    }
}

### What did you expect to see?
I expected to see a bidirectional http-2 stream, with the server talking first, and the client then replying to the server.

### What did you see instead?
The program hangs within http2/transport.go, in the bodyAndLength function, due to that function doing a Read(), which ofcourse hangs.

[bradfitz]

Workaround: set your Request.ContentLength to -1 after http.NewRequest, before Client.Do.

[luna-duclos]

The workaround works :) Thank you

[bradfitz]

The larger issue is to remind myself why we need to distinguish between explicitly-zero and unset-so-zero in Request.ContentLength. Presumably there was a reason. Or maybe there was only a reason for HTTP/1 and it's less important for HTTP/2.

In any case, investigate.

[gopherbot]

CL https://golang.org/cl/31326 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31361 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31432 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31434 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31437 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31445 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31737 mentions this issue.

[gopherbot]

CL https://golang.org/cl/34668 mentions this issue.