[#328] Log error on failed response writing

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/middleware/response.go

@@ -118,7 +118,8 @@ var s3ErrorResponseMap = map[string]string{
 }
 
 // WriteErrorResponse writes error headers.
-func WriteErrorResponse(w http.ResponseWriter, reqInfo *ReqInfo, err error) int {
+// returns http error code and error in case of failure of response writing.
+func WriteErrorResponse(w http.ResponseWriter, reqInfo *ReqInfo, err error) (int, error) {
 	code := http.StatusInternalServerError
 
 	if e, ok := err.(errors.Error); ok {
@@ -134,9 +135,14 @@ func WriteErrorResponse(w http.ResponseWriter, reqInfo *ReqInfo, err error) int
 
 	// Generates error response.
 	errorResponse := getAPIErrorResponse(reqInfo, err)
-	encodedErrorResponse := EncodeResponse(errorResponse)
-	WriteResponse(w, code, encodedErrorResponse, MimeXML)
-	return code
+	encodedErrorResponse, err := EncodeResponse(errorResponse)
+	if err != nil {
+		return 0, fmt.Errorf("encode response: %w", err)
+	}
+	if err = WriteResponse(w, code, encodedErrorResponse, MimeXML); err != nil {
+		return 0, fmt.Errorf("write response: %w", err)
+	}
+	return code, nil
 }
 
 // Write http common headers.
@@ -157,7 +163,7 @@ func removeSensitiveHeaders(h http.Header) {
 }
 
 // WriteResponse writes given statusCode and response into w (with mType header if set).
-func WriteResponse(w http.ResponseWriter, statusCode int, response []byte, mType mimeType) {
+func WriteResponse(w http.ResponseWriter, statusCode int, response []byte, mType mimeType) error {
 	setCommonHeaders(w)
 	if mType != MimeNone {
 		w.Header().Set(hdrContentType, string(mType))
@@ -165,37 +171,46 @@ func WriteResponse(w http.ResponseWriter, statusCode int, response []byte, mType
 	w.Header().Set(hdrContentLength, strconv.Itoa(len(response)))
 	w.WriteHeader(statusCode)
 	if response == nil {
-		return
+		return nil
 	}
 
-	WriteResponseBody(w, response)
+	return WriteResponseBody(w, response)
 }
 
 // WriteResponseBody writes response into w.
-func WriteResponseBody(w http.ResponseWriter, response []byte) {
-	_, _ = w.Write(response)
+func WriteResponseBody(w http.ResponseWriter, response []byte) error {
+	if _, err := w.Write(response); err != nil {
+		return err
+	}
+
 	if flusher, ok := w.(http.Flusher); ok {
 		flusher.Flush()
 	}
+
+	return nil
 }
 
 // EncodeResponse encodes the response headers into XML format.
-func EncodeResponse(response interface{}) []byte {
+func EncodeResponse(response interface{}) ([]byte, error) {
 	var bytesBuffer bytes.Buffer
 	bytesBuffer.WriteString(xml.Header)
-	_ = xml.
-		NewEncoder(&bytesBuffer).
-		Encode(response)
-	return bytesBuffer.Bytes()
+	if err := xml.NewEncoder(&bytesBuffer).Encode(response); err != nil {
+		return nil, err
+	}
+
+	return bytesBuffer.Bytes(), nil
 }
 
 // EncodeResponseNoHeader encodes response without setting xml.Header.
 // Should be used with periodicXMLWriter which sends xml.Header to the client
 // with whitespaces to keep connection alive.
-func EncodeResponseNoHeader(response interface{}) []byte {
+func EncodeResponseNoHeader(response interface{}) ([]byte, error) {
 	var bytesBuffer bytes.Buffer
-	_ = xml.NewEncoder(&bytesBuffer).Encode(response)
-	return bytesBuffer.Bytes()
+	if err := xml.NewEncoder(&bytesBuffer).Encode(response); err != nil {
+		return nil, err
+	}
+
+	return bytesBuffer.Bytes(), nil
 }
 
 // EncodeToResponse encodes the response into ResponseWriter.
@@ -227,8 +242,8 @@ func EncodeToResponseNoHeader(w http.ResponseWriter, response interface{}) error
 
 // WriteSuccessResponseHeadersOnly writes HTTP (200) OK response with no data
 // to the client.
-func WriteSuccessResponseHeadersOnly(w http.ResponseWriter) {
-	WriteResponse(w, http.StatusOK, nil, MimeNone)
+func WriteSuccessResponseHeadersOnly(w http.ResponseWriter) error {
+	return WriteResponse(w, http.StatusOK, nil, MimeNone)
 }
 
 // Error -- Returns S3 error string.