Added support for dashboard links to external services.

bundles/org.openhab.ui.dashboard/OSGI-INF/dashboardservice.xml

@@ -9,7 +9,7 @@
     http://www.eclipse.org/legal/epl-v10.html
 
 -->
-<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" immediate="true" name="org.openhab.ui.dashboard">
+<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" immediate="true" name="org.openhab.dashboard">
    <implementation class="org.openhab.ui.dashboard.internal.DashboardService"/>
    <reference bind="setHttpService" cardinality="1..1" interface="org.osgi.service.http.HttpService" name="HttpService" policy="static" unbind="unsetHttpService"/>
    <reference bind="addDashboardTile" cardinality="0..n" interface="org.openhab.ui.dashboard.DashboardTile" name="DashboardTile" policy="dynamic" unbind="removeDashboardTile"/>

bundles/org.openhab.ui.dashboard/README.md

@@ -0,0 +1,34 @@
+# Dashboard
+
+openHAB dashboard is landing page for the user where all openHAB UIs can be found. Dashboard support also links to external services. Links can be added to the dashboard by editing the ```conf/services/dashboard.cfg``` configuration file.
+
+## Link Configuration
+
+| Parameter name  | Type    | Description                                                                             |
+|-----------------|---------|-----------------------------------------------------------------------------------------|
+| X.link-name     | String  | Name which is shown in the openHAB dashboard.                                           |
+| X.link-url      | String  | URL to external service.                                                                |
+| X.link-overlay  | String  | Image overlay icon. Supported values are empty (no icon), "html5", "android" or "apple" |
+| X.link-imageurl | String  | URL to image which is shown in the dashboard.                                           |
+
+Where X is link unique identifier (see examples).
+
+## Image URL
+
+Browser fetch image from image URL. URL can be direct http link or data URIs according to [RFC2397](https://tools.ietf.org/html/rfc2397). If data URIs are used, browser should support them as well. All five major browsers (Chrome, Firefox, IE, Opera and Safari) support data URIs . See e.g. [https://www.base64-image.de](https://www.base64-image.de) to convert images to base64 coded data. 
+
+## Example configuration file
+```
+frontail.link-name=openHAB Log Viewer
+frontail.link-url=http://<server-adddress>:9001
+frontail.link-overlay=
+frontail.link-imageurl=../static/image.png
+
+nodered.link-name=Node-RED
+nodered.link-url=http://<server-adddress>:1880
+nodered.link-overlay=
+nodered.link-imageurl=data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAXwAAACfCAIAAA...QmCC
+
+```
+
+Note: **nodered** image data URL is not valid (it's shorten for the sake of clarity).

bundles/org.openhab.ui.dashboard/src/main/java/org/openhab/ui/dashboard/internal/DashboardService.java

@@ -11,6 +11,7 @@
 import java.io.IOException;
 import java.net.URL;
 import java.util.Hashtable;
+import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 
@@ -50,7 +51,13 @@ public class DashboardService {
 
     private BundleContext bundleContext;
 
-    protected void activate(ComponentContext componentContext) {
+    private final static String LINK_NAME = "link-name";
+    private final static String LINK_URL = "link-url";
+    private final static String LINK_OVERLAY = "link-overlay";
+    private final static String LINK_IMAGEURL = "link-imageurl";
+
+    protected void activate(ComponentContext componentContext, Map<String, Object> properties) {
+
         try {
             bundleContext = componentContext.getBundleContext();
             Hashtable<String, String> props = new Hashtable<>();
@@ -69,6 +76,8 @@ protected void activate(ComponentContext componentContext) {
         } catch (NamespaceException | ServletException e) {
             logger.error("Error during dashboard startup: {}", e.getMessage());
         }
+
+        addTilesForExternalServices(properties);
     }
 
     protected void deactivate(ComponentContext componentContext) {
@@ -153,4 +162,25 @@ protected HttpServlet createServlet() {
         return new DashboardServlet(configurationAdmin, indexTemplate, entryTemplate, warnTemplate, setupTemplate,
                 tiles);
     }
+
+    private void addTilesForExternalServices(Map<String, Object> properties) {
+        for (String key : properties.keySet()) {
+            if (key.endsWith(LINK_NAME)) {
+                if (key.length() > LINK_NAME.length()) {
+                    // get prefix from link name
+                    String linkname = key.substring(0, key.length() - LINK_NAME.length());
+
+                    String name = (String) properties.get(linkname + LINK_NAME);
+                    String url = (String) properties.get(linkname + LINK_URL);
+                    String overlay = (String) properties.get(linkname + LINK_OVERLAY);
+                    String imageUrl = (String) properties.get(linkname + LINK_IMAGEURL);
+
+                    logger.debug("Add link: {}", name);
+
+                    addDashboardTile(new ExternalServiceTile.DashboardTileBuilder().withName(name).withUrl(url)
+                            .withOverlay(overlay).withImageUrl(imageUrl).build());
+                }
+            }
+        }
+    }
 }

bundles/org.openhab.ui.dashboard/src/main/java/org/openhab/ui/dashboard/internal/ExternalServiceTile.java

@@ -0,0 +1,82 @@
+/**
+ * Copyright (c) 2010-2017 by the respective copyright holders.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.openhab.ui.dashboard.internal;
+
+import org.openhab.ui.dashboard.DashboardTile;
+
+/**
+ * The dashboard tile for external services.
+ *
+ * @author Pauli Anttila - Initial contribution
+ */
+public class ExternalServiceTile implements DashboardTile {
+    private String name;
+    private String url;
+    private String overlay;
+    private String imageUrl;
+
+    private ExternalServiceTile(DashboardTileBuilder builder) {
+        this.name = builder.name;
+        this.url = builder.url;
+        this.overlay = builder.overlay;
+        this.imageUrl = builder.imageUrl;
+    }
+
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public String getUrl() {
+        return url;
+    }
+
+    @Override
+    public String getOverlay() {
+        return overlay;
+    }
+
+    @Override
+    public String getImageUrl() {
+        return imageUrl;
+    }
+
+    public static class DashboardTileBuilder {
+
+        private String name;
+        private String url;
+        private String overlay;
+        private String imageUrl;
+
+        public DashboardTileBuilder withName(String name) {
+            this.name = name;
+            return this;
+        }
+
+        public DashboardTileBuilder withUrl(String url) {
+            this.url = url;
+            return this;
+        }
+
+        public DashboardTileBuilder withOverlay(String overlay) {
+            this.overlay = overlay;
+            return this;
+        }
+
+        public DashboardTileBuilder withImageUrl(String imageUrl) {
+            this.imageUrl = imageUrl;
+            return this;
+        }
+
+        public ExternalServiceTile build() {
+            return new ExternalServiceTile(this);
+        }
+    }
+}