[MM-61458] Fix errcheck issues in server/channels/app/plugin_requests.go (#29121)

server/.golangci.yml

@@ -133,7 +133,6 @@ issues:
         channels/app/plugin_api_tests/manual.test_serve_metrics_plugin/main.go|\
         channels/app/plugin_api_tests/test_update_user_auth_plugin/main.go|\
         channels/app/plugin_install.go|\
-        channels/app/plugin_requests.go|\
         channels/app/plugin_signature.go|\
         channels/app/plugin_signature_test.go|\
         channels/app/plugin_test.go|\

server/channels/app/plugin_requests.go

@@ -25,11 +25,13 @@ func (ch *Channels) ServePluginRequest(w http.ResponseWriter, r *http.Request) {
 
 	pluginsEnvironment := ch.GetPluginsEnvironment()
 	if pluginsEnvironment == nil {
-		err := model.NewAppError("ServePluginRequest", "app.plugin.disabled.app_error", nil, "Enable plugins to serve plugin requests", http.StatusNotImplemented)
+		appErr := model.NewAppError("ServePluginRequest", "app.plugin.disabled.app_error", nil, "Enable plugins to serve plugin requests", http.StatusNotImplemented)
-		mlog.Error(err.Error())
+		mlog.Error(appErr.Error())
-		w.WriteHeader(err.StatusCode)
+		w.WriteHeader(appErr.StatusCode)
 		w.Header().Set("Content-Type", "application/json")
-		w.Write([]byte(err.ToJSON()))
+		if _, err := w.Write([]byte(appErr.ToJSON())); err != nil {
+			mlog.Warn("Error while writing response", mlog.Err(err))
+		}
 		return
 	}
 
@@ -49,11 +51,13 @@ func (ch *Channels) ServePluginRequest(w http.ResponseWriter, r *http.Request) {
 func (a *App) ServeInterPluginRequest(w http.ResponseWriter, r *http.Request, sourcePluginId, destinationPluginId string) {
 	pluginsEnvironment := a.ch.GetPluginsEnvironment()
 	if pluginsEnvironment == nil {
-		err := model.NewAppError("ServeInterPluginRequest", "app.plugin.disabled.app_error", nil, "Plugin environment not found.", http.StatusNotImplemented)
+		appErr := model.NewAppError("ServeInterPluginRequest", "app.plugin.disabled.app_error", nil, "Plugin environment not found.", http.StatusNotImplemented)
-		a.Log().Error(err.Error())
+		a.Log().Error(appErr.Error())
-		w.WriteHeader(err.StatusCode)
+		w.WriteHeader(appErr.StatusCode)
 		w.Header().Set("Content-Type", "application/json")
-		w.Write([]byte(err.ToJSON()))
+		if _, err := w.Write([]byte(appErr.ToJSON())); err != nil {
+			mlog.Warn("Error while writing response", mlog.Err(err))
+		}
 		return
 	}
 
@@ -147,17 +151,19 @@ func (ch *Channels) servePluginRequest(w http.ResponseWriter, r *http.Request, h
 
 	r.Header.Del("Mattermost-User-Id")
 	if token != "" {
-		session, err := New(ServerConnector(ch)).GetSession(token)
+		session, appErr := New(ServerConnector(ch)).GetSession(token)
 
 		csrfCheckPassed := false
 
-		if session != nil && err == nil && cookieAuth && r.Method != "GET" {
+		if session != nil && appErr == nil && cookieAuth && r.Method != "GET" {
 			sentToken := ""
 
 			if r.Header.Get(model.HeaderCsrfToken) == "" {
 				bodyBytes, _ := io.ReadAll(r.Body)
 				r.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
-				r.ParseForm()
+				if err := r.ParseForm(); err != nil {
+					mlog.Warn("Failed to parse form data for plugin request", mlog.Err(err))
+				}
 				sentToken = r.FormValue("csrf")
 				r.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
 			} else {
@@ -199,7 +205,7 @@ func (ch *Channels) servePluginRequest(w http.ResponseWriter, r *http.Request, h
 			csrfCheckPassed = true
 		}
 
-		if (session != nil && session.Id != "") && err == nil && csrfCheckPassed {
+		if (session != nil && session.Id != "") && appErr == nil && csrfCheckPassed {
 			r.Header.Set("Mattermost-User-Id", session.UserId)
 			context.SessionId = session.Id