net/http: Transport.RoundTrip regression when retrying requests on Request.Body read error

[bradfitz]

Bug report from Docker:

https://twitter.com/cpuguy83/status/806263794368397312 from moby/moby#29030

Repro from the change where I'm working on a fix:

func TestTransportBodyReadError(t *testing.T) {  
        defer afterTest(t)  
        ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {  
                if r.URL.Path == "/ping" {  
                        return  
                }  
                buf := make([]byte, 1)  
                n, err := r.Body.Read(buf)  
                w.Header().Set("X-Body-Read", fmt.Sprintf("%v, %v", n, err))  
        }))  
        defer ts.Close()  
        tr := &Transport{}  
        defer tr.CloseIdleConnections()  
        c := &Client{Transport: tr}  
  
        res, err := c.Get(ts.URL + "/ping")  
        if err != nil {  
                t.Fatal(err)  
        }  
        res.Body.Close()  
  
        r, w := io.Pipe()  
        errClose := errors.New("some error")  
        w.CloseWithError(errClose)  
        if _, err := c.Post(ts.URL+"/test", "", r); err != nil {  
                t.Logf("Got error: %v", err)  
        }  
}  

Go 1.7 always says "some error" as the error. In Go 1.8, we read from the request body, get an error, and then try to send the request again since we never wrote anything. But the first write ends up closing the request body (the pipe), and it can't be read the second time.

We need to do the same thing @tombergan and I did for http2 in golang/net@8dab929 and not retry a request once its Body has been messed with, unless it has a GetBody func that can be used to reset itself.

/cc @cpuguy83

[cpuguy83]

Thanks for opening, was going to do this once the kids went to bed!

[gopherbot]

CL https://golang.org/cl/34134 mentions this issue.

[cpuguy83]

Confirmed the changes in the CL fix our issue.

[cpuguy83]

🎉