Fix proxy error handling for 502/503/504 HTTP status codes

Move 504 handling from interceptor to parseHttpErrorMessage, add
user-friendly messages for 502/503/504 via httpStatusMessageMap,
and scope isProxyError to only match proxy status codes to avoid
breaking error handling for other HTTP errors.

ui-ngx/src/app/core/interceptors/global-http-interceptor.ts

@@ -125,10 +125,6 @@ export class GlobalHttpInterceptor implements HttpInterceptor {
           this.showError(req.method + ': ' + req.url + '<br/>' +
             errorResponse.status + ': ' + errorResponse.statusText);
         }
-      } else if (errorResponse.status === 504) {
-        if (!ignoreErrors) {
-          this.showError('Request timeout');
-        }
       } else {
         unhandled = true;
       }

ui-ngx/src/app/core/utils.ts

@@ -23,7 +23,7 @@ import { NULL_UUID } from '@shared/models/id/has-uuid';
 import { baseDetailsPageByEntityType, EntityType } from '@shared/models/entity-type.models';
 import { HttpClient, HttpErrorResponse } from '@angular/common/http';
 import { TranslateService } from '@ngx-translate/core';
-import { serverErrorCodesTranslations } from '@shared/models/constants';
+import { httpStatusMessageMap, serverErrorCodesTranslations } from '@shared/models/constants';
 import { SubscriptionEntityInfo } from '@core/api/widget-api.models';
 import {
   CompiledTbFunction,
@@ -825,11 +825,13 @@ export function parseHttpErrorMessage(errorResponse: HttpErrorResponse,
   } else {
     error = errorResponse.error;
   }
-  if (error && !error.message) {
-    errorMessage = prepareMessageFromData(error);
-  } else if (error && error.message) {
+  if (error && error.message) {
     errorMessage = error.message;
     timeout = error.timeout ? error.timeout : 0;
+  } else if (isProxyError(errorResponse)) {
+    errorMessage = httpStatusMessageMap.get(errorResponse.status);
+  } else if (error) {
+    errorMessage = prepareMessageFromData(error);
   } else {
     errorMessage = `Unhandled error code ${error ? error.status : '\'Unknown\''}`;
   }
@@ -866,6 +868,14 @@ function prepareMessageFromData(data): string {
   }
 }
 
+function isProxyError(errorResponse: HttpErrorResponse): boolean {
+  if (!httpStatusMessageMap.has(errorResponse.status)) {
+    return false;
+  }
+  const error = errorResponse.error;
+  return !error || typeof error === 'string' || (typeof error === 'object' && !error.message);
+}
+
 export const genNextLabel = (name: string, datasources: Datasource[]): string => {
   let label = name;
   let i = 1;

ui-ngx/src/app/shared/models/constants.ts

@@ -54,6 +54,12 @@ export const serverErrorCodesTranslations = new Map<number, string>([
   [Constants.serverErrorCode.tooManyUpdates, 'server-error.too-many-updates'],
 ]);
 
+export const httpStatusMessageMap = new Map<number, string>([
+  [502, 'Server is temporarily unavailable (Bad Gateway)'],
+  [503, 'Server is temporarily unavailable'],
+  [504, 'Server did not respond in time (Gateway Timeout)'],
+]);
+
 export const MediaBreakpoints = {
   xs: 'screen and (max-width: 599px)',
   sm: 'screen and (min-width: 600px) and (max-width: 959px)',