From 038e10f436c17bcecae5861d02b822a861af3ac5 Mon Sep 17 00:00:00 2001
From: Will Norris <will@willnorris.com>
Date: Sat, 17 Jun 2017 08:49:21 -0400
Subject: [PATCH] reverseproxy: refactor error printing

allow errors to specify HTTP status code that should be returned.
---
 third_party/httputil/reverseproxy.go | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/third_party/httputil/reverseproxy.go b/third_party/httputil/reverseproxy.go
index d66dfa2..71f7093 100644
--- a/third_party/httputil/reverseproxy.go
+++ b/third_party/httputil/reverseproxy.go
@@ -130,8 +130,7 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	}
 
 	if err := p.Director(outreq); err != nil {
-		p.logf("http: proxy error: %v", err)
-		rw.WriteHeader(http.StatusBadGateway)
+		p.writeError(rw, err)
 		return
 	}
 
@@ -182,8 +181,7 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 	res, err := transport.RoundTrip(outreq)
 	if err != nil {
-		p.logf("http: proxy error: %v", err)
-		rw.WriteHeader(http.StatusBadGateway)
+		p.writeError(rw, err)
 		return
 	}
 
@@ -203,8 +201,7 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 	if p.ModifyResponse != nil {
 		if err := p.ModifyResponse(res); err != nil {
-			p.logf("http: proxy error: %v", err)
-			rw.WriteHeader(http.StatusBadGateway)
+			p.writeError(rw, err)
 			return
 		}
 	}
@@ -247,6 +244,20 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	}
 }
 
+// writerError writes err to the http response.
+func (p *ReverseProxy) writeError(w http.ResponseWriter, err error) {
+	type statusCoder interface {
+		StatusCode() int
+	}
+
+	p.logf("http: proxy error: %v", err)
+	code := http.StatusBadGateway
+	if err, ok := err.(statusCoder); ok {
+		code = err.StatusCode()
+	}
+	http.Error(w, err.Error(), code)
+}
+
 func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
 	if p.FlushInterval != 0 {
 		if wf, ok := dst.(writeFlusher); ok {