XWIKI-22547: Make websocket work with Root servlet context (#3539)

(cherry picked from commit f696d5e2)

xwiki-platform-core/xwiki-platform-websocket/src/main/java/org/xwiki/websocket/script/WebSocketScriptService.java

@@ -84,9 +84,14 @@ public String url(String pathOrRoleHint)
             XWikiContext xcontext = this.xcontextProvider.get();
 
             StringBuilder path = new StringBuilder("/");
-            path.append(xcontext.getWiki().getWebAppPath(xcontext));
-            path.append("websocket").append(path(pathOrRoleHint));
 
+            // Test if installed with ROOT servlet context and avoid double slash.
+            String webAppPath = xcontext.getWiki().getWebAppPath(xcontext);
+            if (!"/".equals(webAppPath)) {
+                path.append(webAppPath);
+            }
+
+            path.append("websocket").append(path(pathOrRoleHint));
             URL serverURL = xcontext.getURLFactory().getServerURL(xcontext);
             String scheme = "https".equals(serverURL.getProtocol()) ? "wss" : "ws";
             // We have to add the path afterwards because the URI constructor double encodes it.

xwiki-platform-core/xwiki-platform-websocket/src/test/java/org/xwiki/websocket/script/WebSocketScriptServiceTest.java

@@ -109,4 +109,11 @@ void urlWithException() throws Exception
             "Failed to create WebSocket URL for [test]. Root cause is [MalformedURLException: Invalid server URL!].",
             this.logCapture.getMessage(0));
     }
+
+    @Test
+    void urlWithRootServletContext() {
+        when(this.xcontext.getWiki().getWebAppPath(xcontext)).thenReturn("/");
+        assertEquals("ws://www.xwiki.org:80/websocket/one/two", this.service.url("/one/two"));
+    }
+
 }