proxy: Added support for HTTP trailers

caddyhttp/proxy/proxy.go

@@ -247,12 +247,28 @@ func createUpstreamRequest(r *http.Request) *http.Request {
 		outreq.URL.Opaque = outreq.URL.RawPath
 	}
 
+	// We are modifying the same underlying map from req (shallow
+	// copied above) so we only copy it if necessary.
+	copiedHeaders := false
+
+	// Remove hop-by-hop headers listed in the "Connection" header.
+	// See RFC 2616, section 14.10.
+	if c := outreq.Header.Get("Connection"); c != "" {
+		for _, f := range strings.Split(c, ",") {
+			if f = strings.TrimSpace(f); f != "" {
+				if !copiedHeaders {
+					outreq.Header = make(http.Header)
+					copyHeader(outreq.Header, r.Header)
+					copiedHeaders = true
+				}
+				outreq.Header.Del(f)
+			}
+		}
+	}
+
 	// Remove hop-by-hop headers to the backend. Especially
 	// important is "Connection" because we want a persistent
-	// connection, regardless of what the client sent to us. This
-	// is modifying the same underlying map from r (shallow
-	// copied above) so we only copy it if necessary.
-	var copiedHeaders bool
+	// connection, regardless of what the client sent to us.
 	for _, h := range hopHeaders {
 		if outreq.Header.Get(h) != "" {
 			if !copiedHeaders {