FastCGI: separate standard and error output responses.

middleware/fastcgi/fastcgi.go

@@ -115,7 +115,12 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error)
 				return http.StatusBadGateway, err
 			}
 
-			return 0, nil
+			// FastCGI stderr outputs
+			if fcgi.stderr.Len() != 0 {
+				err = LogError(fcgi.stderr.String())
+			}
+
+			return 0, err
 		}
 	}
 
@@ -281,3 +286,11 @@ var (
 	// ErrIndexMissingSplit describes an index configuration error.
 	ErrIndexMissingSplit = errors.New("configured index file(s) must include split value")
 )
+
+// LogError is a non fatal error that allows requests to go through.
+type LogError string
+
+// Error satisfies error interface.
+func (l LogError) Error() string {
+	return string(l)
+}

middleware/fastcgi/fcgiclient.go

@@ -164,6 +164,7 @@ type FCGIClient struct {
 	rwc       io.ReadWriteCloser
 	h         header
 	buf       bytes.Buffer
+	stderr    bytes.Buffer
 	keepAlive bool
 	reqID     uint16
 }
@@ -346,11 +347,23 @@ func (w *streamReader) Read(p []byte) (n int, err error) {
 
 	if len(p) > 0 {
 		if len(w.buf) == 0 {
+
+			// filter outputs for error log
+			for {
 				rec := &record{}
-			w.buf, err = rec.read(w.c.rwc)
+				var buf []byte
+				buf, err = rec.read(w.c.rwc)
 				if err != nil {
 					return
 				}
+				// standard error output
+				if rec.h.Type == Stderr {
+					w.c.stderr.Write(buf)
+					continue
+				}
+				w.buf = buf
+				break
+			}
 		}
 
 		n = len(p)