Add maxrequestbody directive (#1163)

caddyhttp/proxy/proxy.go

@@ -174,6 +174,10 @@ func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 			return 0, nil
 		}
 
+		if _, ok := backendErr.(httpserver.MaxBytesExceeded); ok {
+			return http.StatusRequestEntityTooLarge, backendErr
+		}
+
 		// failover; remember this failure for some time if
 		// request failure counting is enabled
 		timeout := host.FailTimeout