net/http/httputil: ReverseProxy does not log errors during CopyBuffer

[fraenkel]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go 1.6.3
2. What operating system and processor architecture are you using (go env)?
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="darwin"
   GOOS="darwin"
3. 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.

We have a router using the ReverseProxy. The application was sending back content with a Content-Length but stopping before all the body data was transmitted.

1. What did you expect to see?

I would have expected an error to be logged when we get the UnexpectedEOF during io.CopyBuffer

1. What did you see instead?
   Nothing.

[gopherbot]

CL https://golang.org/cl/30692 mentions this issue.