[JENKINS-69032] Plugin manager update site URL can be saved empty

core/src/main/java/hudson/PluginManager.java

@@ -1887,6 +1887,20 @@ public HttpResponse doUploadPlugin(StaplerRequest req) throws IOException, Servl
         return FormValidation.ok();
     }
 
+    @Restricted(NoExternalUse.class)
+    @RequirePOST public FormValidation doCheckUpdateSiteUrl(StaplerRequest request, @QueryParameter String value) throws IOException {
+        if (StringUtils.isNotBlank(value)) {
+            try {
+                new URL(value);
+                return FormValidation.ok();
+            } catch (MalformedURLException e) {
+                return FormValidation.error(e.getMessage());
+            }
+        } else {
+            return FormValidation.error(Messages.PluginManager_emptyUpdateSiteUrl());
+        }
+    }
+
     @Restricted(NoExternalUse.class)
     @RequirePOST public HttpResponse doCheckUpdatesServer() throws IOException {
         Jenkins.get().checkPermission(Jenkins.SYSTEM_READ);

core/src/main/resources/hudson/Messages.properties

@@ -102,6 +102,8 @@ PluginManager.insecureUrl=\
 PluginManager.invalidUrl=\
   You are using an invalid URL to download the plugin, only https and http (not recommended) are supported.
 
+PluginManager.emptyUpdateSiteUrl=\
+  The update site cannot be empty. Please enter a valid url.
 
 AboutJenkins.DisplayName=About Jenkins
 AboutJenkins.Description=See the version and license information.

core/src/main/resources/hudson/Messages_zh_TW.properties

@@ -102,3 +102,4 @@ PluginWrapper.NoSuchPlugin=找不到名為「{0}」的外掛
 PluginWrapper.Error.Disabling=停用外掛「{0}」時發生錯誤，錯誤\: 「{1}」
 TcpSlaveAgentListener.PingAgentProtocol.displayName=Ping 協定
 
+PluginManager.emptyUpdateSiteUrl=更新站台網址不得為空，請輸入網址

core/src/main/resources/hudson/PluginManager/_updateSite.js

@@ -0,0 +1,6 @@
+document.getElementById("reset-to-default").onclick = function (event) {
+  event.preventDefault();
+  const siteUrlInput = document.getElementById("update-site-url");
+  siteUrlInput.value = "https://updates.jenkins.io/current/update-center.json";
+  siteUrlInput.dispatchEvent(new Event('change'));
+}

core/src/main/resources/hudson/PluginManager/advanced.jelly

@@ -78,9 +78,13 @@ THE SOFTWARE.
                 <h2 class="jenkins-section__title">${%Update Site}</h2>
                 <f:form method="post" action="siteConfigure" name="siteConfigure">
                     <f:entry title="${%URL}">
-                        <f:textbox name="site"
-                                   value="${app.updateCenter.getSite(app.updateCenter.ID_DEFAULT).url}"/>
+                      <a id="reset-to-default" href="#">${%Reset to default}</a>
+                      <f:textbox name="site"
+                                 id="update-site-url"
+                                 value="${app.updateCenter.getSite(app.updateCenter.ID_DEFAULT).url}"
+                                 checkUrl="'checkUpdateSiteUrl?value='+this.value"/>
                     </f:entry>
+                    <st:adjunct includes="hudson.PluginManager._updateSite"/>
                     <l:isAdmin>
                         <f:block>
                             <f:submit/>

core/src/main/resources/hudson/PluginManager/advanced_zh_TW.properties

@@ -34,3 +34,4 @@ Deploy\ Plugin=部署外掛
 Deploy=部署
 Advanced\ Settings=進階設定
 Or=或
+Reset\ to\ default=重設回預設值