fix(Bridge REST API): no feedback when deleting bridge

This fixes https://emqx.atlassian.net/browse/EMQX-8648. The issue
described in `EMQX-8648` is that when deleting a non-existing bridge the
server gives a success response. See below:

```
curl --head -u admin:public2 -X 'DELETE' 'http://localhost:18083/api/v5/bridges/webhook:i_do_not_exist'
HTTP/1.1 204 No Content
date: Tue, 03 Jan 2023 16:59:01 GMT
server: Cowboy
```

After the fix, deleting a non existing bridge will give the following
response:

```
HTTP/1.1 404 Not Found
content-length: 49
content-type: application/json
date: Thu, 05 Jan 2023 12:40:35 GMT
server: Cowboy
```

Closes: EMQX-8648

apps/emqx_bridge/src/emqx_bridge_api.erl

@@ -328,6 +328,7 @@ schema("/bridges/:id") ->
             responses => #{
                 204 => <<"Bridge deleted">>,
                 400 => error_schema(['INVALID_ID'], "Update bridge failed"),
+                404 => error_schema('NOT_FOUND', "Bridge not found"),
                 403 => error_schema('FORBIDDEN_REQUEST', "Forbidden operation"),
                 503 => error_schema('SERVICE_UNAVAILABLE', "Service unavailable")
             }
@@ -433,6 +434,8 @@ schema("/nodes/:node/bridges/:id/operation/:operation") ->
         end,
     ?TRY_PARSE_ID(
         Id,
+        case emqx_bridge:lookup(BridgeType, BridgeName) of
+            {ok, _} ->
                 case emqx_bridge:check_deps_and_remove(BridgeType, BridgeName, AlsoDeleteActs) of
                     {ok, _} ->
                         204;
@@ -446,6 +449,9 @@ schema("/nodes/:node/bridges/:id/operation/:operation") ->
                         {503, error_msg('SERVICE_UNAVAILABLE', <<"request timeout">>)};
                     {error, Reason} ->
                         {500, error_msg('INTERNAL_ERROR', Reason)}
+                end;
+            {error, not_found} ->
+                {404, error_msg('NOT_FOUND', <<"Bridge not found">>)}
         end
     ).
 

apps/emqx_bridge/test/emqx_bridge_api_SUITE.erl

@@ -303,6 +303,15 @@ t_http_crud_apis(Config) ->
         },
         jsx:decode(ErrMsg2)
     ),
+    %% Deleting a non-existing bridge should result in an error
+    {ok, 404, ErrMsg3} = request(delete, uri(["bridges", BridgeID]), []),
+    ?assertMatch(
+        #{
+            <<"code">> := _,
+            <<"message">> := <<"Bridge not found">>
+        },
+        jsx:decode(ErrMsg3)
+    ),
     ok.
 
 t_check_dependent_actions_on_delete(Config) ->

changes/v5.0.14/fix-8648.en.md

@@ -0,0 +1 @@
+When deleting a non-existing bridge the server gave a success response. This has been fixed so that the server instead gives an error response when the user attempts to delete a non-existing bridge.