net/http/httputil: log err encountered during reverseproxy body copying

Fixes #16659

Change-Id: I13dd797e93e0b572eaf8726f1be594870d40183b
Reviewed-on: https://go-review.googlesource.com/30692
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 29 insertions, 1 deletions

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index 76f23bcf9a..f18dd886cc 100644
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -260,12 +260,40 @@ func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
 	if p.BufferPool != nil {
 		buf = p.BufferPool.Get()
 	}
-	io.CopyBuffer(dst, src, buf)
+	p.copyBuffer(dst, src, buf)
 	if p.BufferPool != nil {
 		p.BufferPool.Put(buf)
 	}
 }
 
+func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
+	if len(buf) == 0 {
+		buf = make([]byte, 32*1024)
+	}
+	var written int64
+	for {
+		nr, rerr := src.Read(buf)
+		if rerr != nil && rerr != io.EOF {
+			p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
+		}
+		if nr > 0 {
+			nw, werr := dst.Write(buf[:nr])
+			if nw > 0 {
+				written += int64(nw)
+			}
+			if werr != nil {
+				return written, werr
+			}
+			if nr != nw {
+				return written, io.ErrShortWrite
+			}
+		}
+		if rerr != nil {
+			return written, rerr
+		}
+	}
+}
+
 func (p *ReverseProxy) logf(format string, args ...interface{}) {
 	if p.ErrorLog != nil {
 		p.ErrorLog.Printf(format, args...)