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

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

@@ -72,6 +72,7 @@
 import java.io.InputStream;
 import java.io.UncheckedIOException;
 import java.lang.reflect.Method;
+import java.net.HttpURLConnection;
 import java.net.JarURLConnection;
 import java.net.MalformedURLException;
 import java.net.URISyntaxException;
@@ -1923,6 +1924,35 @@ public HttpResponse doUploadPlugin(StaplerRequest req) throws IOException, Servl
         return FormValidation.ok();
     }
 
+    @Restricted(NoExternalUse.class)
+    @RequirePOST public FormValidation doCheckUpdateSiteUrl(StaplerRequest request, @QueryParameter String value) {
+        Jenkins.get().checkPermission(Jenkins.ADMINISTER);
+        if (StringUtils.isNotBlank(value)) {
+            try {
+                value += ((value.contains("?")) ? "&" : "?") + "version=" + Jenkins.VERSION + "&uctest";
+
+                URL url = new URL(value);
+
+                // Connect to the URL
+                HttpURLConnection conn = (HttpURLConnection) ProxyConfiguration.open(url);
+                conn.setRequestMethod("HEAD");
+                conn.setConnectTimeout(5000);
+                if (100 <= conn.getResponseCode() && conn.getResponseCode() <= 399) {
+                    return FormValidation.ok();
+                } else {
+                    LOGGER.log(Level.FINE, "Obtained a non OK ({0}) response from the update center",
+                            new Object[]{conn.getResponseCode(), url});
+                    return FormValidation.error(Messages.PluginManager_connectionFailed());
+                }
+            } catch (IOException e) {
+                LOGGER.log(Level.FINE, "Failed to check update site", e);
+                return FormValidation.error(Messages.PluginManager_connectionFailed());
+            }
+        } 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 +102,11 @@ 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.
+
+PluginManager.connectionFailed=\
+  Unable to connect to the URL.
 
 AboutJenkins.DisplayName=About Jenkins
 AboutJenkins.Description=See the version and license information.

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

@@ -102,3 +102,5 @@ 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
+PluginManager.connectionFailed=無法連線至這個URL

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

@@ -0,0 +1,23 @@
+(function () {
+  showResetToDefaultButtonOrNot();
+})();
+
+function showResetToDefaultButtonOrNot() {
+  const resetButton = document.getElementById("reset-to-default");
+  const siteUrlInput = document.getElementById("update-site-url");
+  if (siteUrlInput.value === "https://updates.jenkins.io/update-center.json") {
+    resetButton.style.display = "none";
+  } else {
+    resetButton.style.display = "";
+  }
+}
+
+document.getElementById("update-site-url").onchange =
+  showResetToDefaultButtonOrNot;
+
+document.getElementById("reset-to-default").onclick = function (event) {
+  event.preventDefault();
+  const siteUrlInput = document.getElementById("update-site-url");
+  siteUrlInput.value = "https://updates.jenkins.io/update-center.json";
+  siteUrlInput.dispatchEvent(new Event("change"));
+};

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

@@ -78,9 +78,15 @@ THE SOFTWARE.
                 <h2 class="jenkins-section__title">${%Update Site}</h2>
                 <f:form method="post" action="siteConfigure" name="siteConfigure">
                     <f:entry title="${%URL}">
+                        <j:if test="${app.updateCenter.ID_DEFAULT.equals(app.updateCenter.PREDEFINED_UPDATE_SITE_ID)}">
+                          <a id="reset-to-default" href="#">${%Reset to default}</a>
+                        </j:if>
                         <f:textbox name="site"
-                                   value="${app.updateCenter.getSite(app.updateCenter.ID_DEFAULT).url}"/>
+                                   id="update-site-url"
+                                   value="${app.updateCenter.getSite(app.updateCenter.ID_DEFAULT).url}"
+                                   checkUrl="checkUpdateSiteUrl" checkDependsOn=""/>
                     </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