Azure: Improve resource request error handling (#99017)

* Improve resource request error handling

- Correctly parse JSON responses
- Log erroneous failures in JSON marshalling/unmarshalling
- Correctly set response status code
- Do not attempt to use the response writer as it will be nil

* Minor change

* Improve type assertion handling

pkg/tsdb/azuremonitor/azuremonitor-resource-handler.go

@@ -33,30 +33,36 @@ func (s *httpServiceProxy) writeErrorResponse(rw http.ResponseWriter, statusCode
 	rw.Header().Set("Content-Type", "application/json")
 	rw.WriteHeader(statusCode)
 
+	// Set error response to initial error message
+	errorBody := map[string]string{"error": message}
+
 	// Attempt to locate JSON portion in error message
 	re := regexp.MustCompile(`\{.*?\}`)
 	jsonPart := re.FindString(message)
-
-	var jsonData map[string]interface{}
-	if unmarshalErr := json.Unmarshal([]byte(jsonPart), &jsonData); unmarshalErr != nil {
-		errorMsg, _ := json.Marshal(map[string]string{"error": "Invalid JSON format in error message"})
-		_, err := rw.Write(errorMsg)
-		if err != nil {
-			return fmt.Errorf("unable to write HTTP response: %v", err)
+	if jsonPart != "" {
+		var jsonData map[string]interface{}
+		if unmarshalErr := json.Unmarshal([]byte(jsonPart), &jsonData); unmarshalErr != nil {
+			errorBody["error"] = fmt.Sprintf("Invalid JSON format in error message. Raw error: %s", message)
+			s.logger.Error("failed to unmarshal JSON error message", "error", unmarshalErr)
+		} else {
+			// Extract relevant fields for a formatted error message
+			errorType, _ := jsonData["error"].(string)
+			errorDescription, ok := jsonData["error_description"].(string)
+			if !ok {
+				s.logger.Error("unable to convert error_description to string", "rawError", jsonData["error_description"])
+				// Attempt to just format the error as a string
+				errorDescription = fmt.Sprintf("%v", jsonData["error_description"])
+			}
+			if errorType == "" {
+				errorType = "UnknownError"
+			}
+
+			errorBody["error"] = fmt.Sprintf("%s: %s", errorType, errorDescription)
 		}
-		return unmarshalErr
-	}
-
-	// Extract relevant fields for a formatted error message
-	errorType, _ := jsonData["error"].(string)
-	errorDescription, _ := jsonData["error_description"].(string)
-	if errorType == "" {
-		errorType = "UnknownError"
 	}
-	formattedError := fmt.Sprintf("%s: %s", errorType, errorDescription)
 
-	errorMsg, _ := json.Marshal(map[string]string{"error": formattedError})
-	_, err := rw.Write(errorMsg)
+	jsonRes, _ := json.Marshal(errorBody)
+	_, err := rw.Write(jsonRes)
 	if err != nil {
 		return fmt.Errorf("unable to write HTTP response: %v", err)
 	}
@@ -117,7 +123,7 @@ func (s *Service) getDataSourceFromHTTPReq(req *http.Request) (types.DatasourceI
 }
 
 func writeErrorResponse(rw http.ResponseWriter, code int, msg string) {
-	rw.WriteHeader(http.StatusBadRequest)
+	rw.WriteHeader(code)
 	errorBody := map[string]string{
 		"error": msg,
 	}
@@ -154,9 +160,11 @@ func (s *Service) handleResourceReq(subDataSource string) func(rw http.ResponseW
 		req.URL.Host = serviceURL.Host
 		req.URL.Scheme = serviceURL.Scheme
 
-		rw, err = s.executors[subDataSource].ResourceRequest(rw, req, service.HTTPClient)
+		_, err = s.executors[subDataSource].ResourceRequest(rw, req, service.HTTPClient)
 		if err != nil {
-			writeErrorResponse(rw, http.StatusInternalServerError, fmt.Sprintf("unexpected error %v", err))
+			// The ResourceRequest function should handle writing the error response
+			// We log the error here to ensure it's captured
+			s.logger.Error("error in resource request", "error", err)
 			return
 		}
 	}