[JEP-234] Customizable header

core/src/main/java/jenkins/views/FullHeader.java

@@ -0,0 +1,16 @@
+package jenkins.views;
+
+/**
+ * {@link Header} that provides its own resources as full replacement. It does not
+ * depends on any core resource (images, CSS, JS, etc.)
+ * 
+ * Given this kind of header is totally independent, it will be compatible by default.
+ * 
+ * @see Header
+ */
+public abstract class FullHeader extends Header {
+
+    public boolean isCompatible() {
+        return true;
+    }
+}

core/src/main/java/jenkins/views/Header.java

@@ -0,0 +1,60 @@
+package jenkins.views;
+
+import java.util.Optional;
+
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import hudson.ExtensionList;
+import hudson.ExtensionPoint;
+
+/**
+ * Extension point that provides capabilities to render a specific header.
+ *  
+ * Extend {@link PartialHeader} or {@link FullHeader} depending on the use case.
+ * 
+ * The default Jenkins header is provided as an implementation of a {@link FullHeader} 
+ * named {@link JenkinsHeader}.
+ * 
+ * All headers will provide a prioritization technique, via the usual ordinal field of 
+ * the {@link Extension} annotation.
+ * 
+ * The header content will be injected inside the pageHeader.jelly, based on the header
+ * retrieved by the {@link Header#get()} method. That header content will be provided
+ * inside a resource called headerContent.jelly. It performs a full replacement
+ * of the header.
+ * 
+ * @see PartialHeader
+ * @see FullHeader
+ * @see JenkinsHeader
+ * @since TODO
+ */
+public abstract class Header implements ExtensionPoint {
+
+    /**
+     * Checks if header is available
+     * @return if header is available
+     */
+    public boolean isAvailable() {
+        return isCompatible() && isEnabled();
+    }
+
+    /**
+     * Checks API compatibility of the header
+     * @return if header is compatible
+     */
+    public abstract boolean isCompatible();
+
+    /**
+     * Checks if header is enabled.
+     * @return if header is enabled
+     */
+    public abstract boolean isEnabled();
+
+    @Restricted(NoExternalUse.class)
+    public static Header get() {
+        Optional<Header> header = ExtensionList.lookup(Header.class).stream().filter(Header::isAvailable).findFirst();
+        return header.orElseGet(() -> new JenkinsHeader());
+    }
+
+}

core/src/main/java/jenkins/views/JenkinsHeader.java

@@ -0,0 +1,18 @@
+package jenkins.views;
+
+import hudson.Extension;
+
+/**
+ * Default {@link Header} provided by Jenkins
+ * 
+ * @see Header
+ */
+@Extension(ordinal = Integer.MIN_VALUE)
+public class JenkinsHeader extends FullHeader {
+
+    @Override
+    public boolean isEnabled() {
+        return true;
+    }
+
+}

core/src/main/java/jenkins/views/PartialHeader.java

@@ -0,0 +1,49 @@
+package jenkins.views;
+
+import java.util.logging.Logger;
+
+import hudson.ExtensionList;
+import hudson.init.InitMilestone;
+import hudson.init.Initializer;
+import hudson.util.AdministrativeError;
+import jenkins.model.Jenkins;
+
+/**
+ * {@link Header} that relies on core resources (images, CSS, JS, etc.) to perform
+ * partial replacements.
+ * 
+ * Given this kind of header is not independent, compatibility should be managed by the
+ * specific {@link Header} compatibility header version value
+ * 
+ * @see Header
+ */
+public abstract class PartialHeader extends Header {
+
+    private static Logger LOGGER = Logger.getLogger(PartialHeader.class.getName());
+
+    /**
+     * The current compatibility version of the Header API.
+     * 
+     * Increment this number when an incompatible change is made to the header (like the search form API).
+     */
+    private static final int compatibilityHeaderVersion = 1;
+
+    @Override
+    public final boolean isCompatible() {
+        return compatibilityHeaderVersion == getSupportedHeaderVersion();
+    }
+
+    /**
+     * @return the supported header version
+     */
+    public abstract int getSupportedHeaderVersion();
+
+    @Initializer(after = InitMilestone.JOB_LOADED, before = InitMilestone.JOB_CONFIG_ADAPTED)
+    @SuppressWarnings("unused")
+    public static void incompatibleHeaders() {
+        ExtensionList.lookup(PartialHeader.class).stream().filter(h -> !h.isCompatible()).forEach(header -> {
+            LOGGER.warning(String.format("%s:%s not compatible with %s", header.getClass().getName(), header.getSupportedHeaderVersion(), compatibilityHeaderVersion));
+            new AdministrativeError(header.getClass().getName(), "Incompatible Header", String.format("The plugin %s is attempting to replace the Jenkins header but is not compatible with this version of Jenkins. The plugin should be updated or removed.", Jenkins.get().getPluginManager().whichPlugin(header.getClass())), null);
+        });
+    }
+}

core/src/main/resources/jenkins/views/JenkinsHeader/headerContent.jelly

@@ -0,0 +1,80 @@
+<?jelly escape-by-default='true'?>
+<j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:i="jelly:fmt" xmlns:x="jelly:xml">
+    <header id="header" class="page-header">
+        <div class="page-header__brand">
+            <div class="logo">
+                <a id="jenkins-home-link" href="${rootURL}/">
+                    <img id="jenkins-head-icon" src="${imagesURL}/svgs/logo.svg" alt="[${logoAlt}]" />
+                    <img id="jenkins-name-icon" src="${imagesURL}/title.svg" alt="${title}" width="139" height="34" />
+                </a>
+            </div>
+
+            <a class="page-header__brand-link" href="${rootURL}/">
+                <img src="${imagesURL}/svgs/logo.svg"
+                     alt="[${logoAlt}]"
+                     class="page-header__brand-image" />
+                <span class="page-header__brand-name">Jenkins</span>
+            </a>
+        </div>
+
+        <div class="searchbox hidden-xs">
+            <!-- search box -->
+            <j:set var="searchURL" value="${h.searchURL}"/>
+            <form action="${searchURL}" method="get" style="position:relative;" class="no-json" name="search" role="search">
+                <!-- this div is used to calculate the width of the text box -->
+                <div id="search-box-sizer"/>
+                <div id="searchform">
+                    <input name="q" placeholder="${searchPlaceholder}" id="search-box" class="main-search__input" value="${request.getParameter('q')}" role="searchbox" />
+
+                    <span class="main-search__icon-leading">
+                        <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_search_24px" />
+                    </span>
+                    <a href="${searchHelpUrl}" class="main-search__icon-trailing">
+                        <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_help_outline_24px" />
+                    </a>
+
+                    <div id="search-box-completion" />
+                    <script>createSearchBox("${searchURL}");</script>
+                </div>
+            </form>
+        </div>
+
+        <div class="login page-header__hyperlinks">
+            <div id="visible-am-insertion" class="page-header__am-wrapper" />
+            <div id="visible-sec-am-insertion" class="page-header__am-wrapper" />
+
+            <!-- login field -->
+            <j:if test="${app.useSecurity}">
+                <j:choose>
+                    <j:when test="${!h.isAnonymous()}">
+                        <j:invokeStatic var="user" className="hudson.model.User" method="current" />
+                        <j:choose>
+                            <j:when test="${user.fullName == null || user.fullName.trim().isEmpty()}">
+                                <j:set var="userName" value="${user.id}"/>
+                            </j:when>
+                            <j:otherwise>
+                                <j:set var="userName" value="${user.fullName}"/>
+                            </j:otherwise>
+                        </j:choose>
+                        <a href="${rootURL}/${user.url}" class="model-link inside inverse">
+                            <l:svgIcon
+                                       class="am-monitor-icon" >
+                                <use href="${resURL}/images/material-icons/svg-sprite-social-symbol.svg#ic_person_24px"></use>
+                            </l:svgIcon>
+                            <span class="hidden-xs hidden-sm">${userName}</span>
+                        </a>
+                        <j:if test="${app.securityRealm.canLogOut()}">
+                            <a href="${rootURL}/logout">
+                                <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_input_24px" />
+                                <span class="hidden-xs hidden-sm">${logout}</span>
+                            </a>
+                        </j:if>
+                    </j:when>
+                    <j:otherwise>
+                        <st:include it="${app.securityRealm}" page="loginLink.jelly" />
+                    </j:otherwise>
+                </j:choose>
+            </j:if>
+        </div>
+    </header>
+</j:jelly>

core/src/main/resources/lib/layout/pageHeader.jelly

@@ -25,82 +25,6 @@
             Text for the logout link
         </st:attribute>
     </st:documentation>
-
-    <header id="header" class="page-header">
-        <div class="page-header__brand">
-            <div class="logo">
-                <a id="jenkins-home-link" href="${rootURL}/">
-                    <img id="jenkins-head-icon" src="${imagesURL}/svgs/logo.svg" alt="[${logoAlt}]" />
-                    <img id="jenkins-name-icon" src="${imagesURL}/title.svg" alt="${title}" width="139" height="34" />
-                </a>
-            </div>
-
-            <a class="page-header__brand-link" href="${rootURL}/">
-                <img src="${imagesURL}/svgs/logo.svg"
-                     alt="[${logoAlt}]"
-                     class="page-header__brand-image" />
-                <span class="page-header__brand-name">Jenkins</span>
-            </a>
-        </div>
-
-        <div class="searchbox hidden-xs">
-            <!-- search box -->
-            <j:set var="searchURL" value="${h.searchURL}"/>
-            <form action="${searchURL}" method="get" style="position:relative;" class="no-json" name="search" role="search">
-                <!-- this div is used to calculate the width of the text box -->
-                <div id="search-box-sizer"/>
-                <div id="searchform">
-                    <input name="q" placeholder="${searchPlaceholder}" id="search-box" class="main-search__input" value="${request.getParameter('q')}" role="searchbox" />
-
-                    <span class="main-search__icon-leading">
-                        <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_search_24px" />
-                    </span>
-                    <a href="${searchHelpUrl}" class="main-search__icon-trailing">
-                        <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_help_outline_24px" />
-                    </a>
-
-                    <div id="search-box-completion" />
-                    <script>createSearchBox("${searchURL}");</script>
-                </div>
-            </form>
-        </div>
-
-        <div class="login page-header__hyperlinks">
-            <div id="visible-am-insertion" class="page-header__am-wrapper" />
-            <div id="visible-sec-am-insertion" class="page-header__am-wrapper" />
-
-            <!-- login field -->
-            <j:if test="${app.useSecurity}">
-                <j:choose>
-                    <j:when test="${!h.isAnonymous()}">
-                        <j:invokeStatic var="user" className="hudson.model.User" method="current" />
-                        <j:choose>
-                            <j:when test="${user.fullName == null || user.fullName.trim().isEmpty()}">
-                                <j:set var="userName" value="${user.id}"/>
-                            </j:when>
-                            <j:otherwise>
-                                <j:set var="userName" value="${user.fullName}"/>
-                            </j:otherwise>
-                        </j:choose>
-                        <a href="${rootURL}/${user.url}" class="model-link inside inverse">
-                            <l:svgIcon
-                                       class="am-monitor-icon" >
-                                <use href="${resURL}/images/material-icons/svg-sprite-social-symbol.svg#ic_person_24px"></use>
-                            </l:svgIcon>
-                            <span class="hidden-xs hidden-sm">${userName}</span>
-                        </a>
-                        <j:if test="${app.securityRealm.canLogOut()}">
-                            <a href="${rootURL}/logout">
-                                <l:svgIcon href="${resURL}/images/material-icons/svg-sprite-action-symbol.svg#ic_input_24px" />
-                                <span class="hidden-xs hidden-sm">${logout}</span>
-                            </a>
-                        </j:if>
-                    </j:when>
-                    <j:otherwise>
-                        <st:include it="${app.securityRealm}" page="loginLink.jelly" />
-                    </j:otherwise>
-                </j:choose>
-            </j:if>
-        </div>
-    </header>
+    <j:invokeStatic var="header" className="jenkins.views.Header" method="get"/>
+    <st:include it="${header}" page="headerContent.jelly"/>
 </j:jelly>