Map all HTTP errors to 502

main.go

@@ -113,7 +113,8 @@ func main() {
 		log.Fatal(err)
 	}
 
-	var authTransport http.RoundTripper
+	// Create Proxy Transport
+	authTransport := http.DefaultTransport
 	if *authSocket != "" {
 		dialer := &net.Dialer{
 			// The values below are taken from http.DefaultTransport
@@ -126,6 +127,7 @@ func main() {
 			},
 		}
 	}
+	proxyTransport := &proxyRoundTripper{transport: authTransport}
 
 	// The profiler will only be activated by HTTP requests. HTTP
 	// requests can only reach the profiler if we start a listener. So by
@@ -137,7 +139,7 @@ func main() {
 		}()
 	}
 
-	upstream := newUpstream(*authBackend, authTransport)
+	upstream := newUpstream(*authBackend, proxyTransport)
 	upstream.SetRelativeUrlRoot(*relativeUrlRoot)
 	upstream.SetProxyTimeout(*proxyTimeout)
 

proxy.go

 package main
 
 import (
+	"bytes"
+	"io/ioutil"
 	"net/http"
 )
 
+type proxyRoundTripper struct {
+	transport http.RoundTripper
+}
+
+func (p *proxyRoundTripper) RoundTrip(r *http.Request) (res *http.Response, err error) {
+	res, err = p.transport.RoundTrip(r)
+
+	// Map error to 502 response
+	if err != nil {
+		res = &http.Response{
+			StatusCode: 502,
+			Status:     err.Error(),
+
+			Request:    r,
+			ProtoMajor: r.ProtoMajor,
+			ProtoMinor: r.ProtoMinor,
+			Proto:      r.Proto,
+			Header:     make(http.Header),
+			Trailer:    make(http.Header),
+			Body:       ioutil.NopCloser(&bytes.Buffer{}),
+		}
+		err = nil
+	}
+	return
+}
+
 func headerClone(h http.Header) http.Header {
 	h2 := make(http.Header, len(h))
 	for k, vv := range h {