Use the capabilities getmap / gettile url as the "base" for templates,

fall back to using the URL of the capabilities document itself.

Update MapMLBaseProxyTest.java to check the cascaded request against the
request URL from the capabilities document OR if that is null, use the
URL OF the capabilities document as the base.

Update assertCascading in MapMLWMTSProxyTest.java to compare against
resource request URL from capabilities document OR if that is null,
use the URL OF the capabilities document as the base.

src/extension/mapml/src/main/java/org/geoserver/mapml/MapMLURLBuilder.java

@@ -140,21 +140,6 @@ private boolean canCascade(LayerInfo layerInfo) {
             // Not supporting cross-requests yet:
             // GetTiles against remote WMS
             // GetMap against remote WMTS
-            String service = params.get(SERVICE);
-            String request = params.get(REQUEST);
-            if (storeInfo instanceof WMTSStoreInfo) {
-                if (GETMAP.equalsIgnoreCase(request)
-                        || (GETFEATUREINFO.equalsIgnoreCase(request)
-                                && WMS.equalsIgnoreCase(service))) {
-                    return false;
-                }
-            } else if (storeInfo instanceof WMSStoreInfo) {
-                if (GETTILE.equalsIgnoreCase(request)
-                        || (GETFEATUREINFO.equalsIgnoreCase(request)
-                                && WMTS.equalsIgnoreCase(service))) {
-                    return false;
-                }
-            }
             return TiledCRSConstants.getSupportedOutputCRS(proj) != null;
         }
         return false;
@@ -184,6 +169,7 @@ private String generateURL(String path, HashMap<String, String> params, LayerInf
             boolean isSupportedOutputCRS = outputCRS != null;
             if (resourceInfo != null) {
                 String capabilitiesURL = null;
+                URL getResourceURL = null;
                 String tileMatrixSet = null;
                 StoreInfo storeInfo = resourceInfo.getStore();
                 String requestedCRS = isSupportedOutputCRS ? outputCRS : proj;
@@ -195,6 +181,7 @@ private String generateURL(String path, HashMap<String, String> params, LayerInf
                     try {
                         WMSCapabilities capabilities =
                                 wmsStoreInfo.getWebMapServer(null).getCapabilities();
+                        getResourceURL = capabilities.getRequest().getGetMap().getGet();
                         version = capabilities.getVersion();
                         List<Layer> layerList = capabilities.getLayerList();
                         // Check on GetFeatureInfo
@@ -241,6 +228,7 @@ private String generateURL(String path, HashMap<String, String> params, LayerInf
                     try {
                         WMTSCapabilities capabilities =
                                 wmtsStoreInfo.getWebMapTileServer(null).getCapabilities();
+                        getResourceURL = capabilities.getRequest().getGetTile().getGet();
                         version = capabilities.getVersion();
                         List<WMTSLayer> layerList = capabilities.getLayerList();
                         // Check on GetFeatureInfo
@@ -284,9 +272,24 @@ private String generateURL(String path, HashMap<String, String> params, LayerInf
                 if (cascadeToRemote) {
                     // if we reach this point, we can finally cascade.
                     // Let's update all the params for the cascading
-                    String[] baseUrlAndPath = getBaseUrlAndPath(capabilitiesURL);
-                    baseUrl = baseUrlAndPath[0];
-                    path = baseUrlAndPath[1];
+                    // getResourceURL may be null if the capabilities doc is misconfigured;
+                    if (getResourceURL != null) {
+                        baseUrl =
+                                getResourceURL.getProtocol()
+                                        + "://"
+                                        + getResourceURL.getHost()
+                                        + (getResourceURL.getPort() == -1
+                                                ? ""
+                                                : ":" + getResourceURL.getPort())
+                                        + "/";
+
+                        path = getResourceURL.getPath();
+                    } else {
+                        // if misconfigured capabilites, use cap document URL as base
+                        String[] baseUrlAndPath = getBaseUrlAndPath(capabilitiesURL);
+                        baseUrl = baseUrlAndPath[0];
+                        path = baseUrlAndPath[1];
+                    }
                     urlType = URLMangler.URLType.EXTERNAL;
                     updateRequestParams(
                             params, layerName, version, requestedCRS, tileMatrixSet, infoFormats);

src/extension/mapml/src/test/java/org/geoserver/mapml/MapMLBaseProxyTest.java

@@ -13,9 +13,13 @@
 import com.github.tomakehurst.wiremock.client.WireMock;
 import com.github.tomakehurst.wiremock.core.WireMockConfiguration;
 import java.io.ByteArrayInputStream;
+import java.net.URL;
 import java.util.Map;
+import java.util.regex.Pattern;
 import org.custommonkey.xmlunit.XMLUnit;
 import org.custommonkey.xmlunit.XpathEngine;
+import org.geotools.ows.wms.WMSCapabilities;
+import org.geotools.ows.wms.WebMapServer;
 import org.junit.AfterClass;
 import org.junit.Before;
 import org.springframework.http.MediaType;
@@ -105,11 +109,29 @@ protected void checkCascading(
         }
     }
 
-    protected void assertCascading(boolean shouldCascade, String url) {
+    protected void assertCascading(boolean shouldCascade, String url) throws Exception {
+
         if (shouldCascade) {
-            assertTrue(
-                    url.startsWith(
-                            "http://localhost:" + mockService.port() + MOCK_SERVER + CONTEXT));
+            URL getResourceURL = null;
+            Pattern serviceTypeRE = Pattern.compile(".*SERVICE=WMS.*", Pattern.CASE_INSENSITIVE);
+            boolean cascadingWMS = serviceTypeRE.matcher(getCapabilitiesURL()).find();
+            assertTrue(cascadingWMS);
+            WebMapServer wms = new WebMapServer(new URL(getCapabilitiesURL()));
+            WMSCapabilities capabilities = wms.getCapabilities();
+            getResourceURL = capabilities.getRequest().getGetMap().getGet();
+            URL baseResourceURL =
+                    getResourceURL != null ? getResourceURL : new URL(getCapabilitiesURL());
+            URL base =
+                    new URL(
+                            baseResourceURL.getProtocol()
+                                    + "://"
+                                    + baseResourceURL.getHost()
+                                    + (baseResourceURL.getPort() == -1
+                                            ? ""
+                                            : ":" + baseResourceURL.getPort())
+                                    + "/");
+            String path = baseResourceURL.getPath();
+            assertTrue(url.startsWith((new URL(base, path)).toString()));
             assertTrue(url.contains("layers=topp:states"));
         } else {
             assertTrue(url.startsWith("http://localhost:8080/geoserver" + CONTEXT));

src/extension/mapml/src/test/java/org/geoserver/mapml/MapMLWMTSProxyTest.java

@@ -4,11 +4,14 @@
  */
 package org.geoserver.mapml;
 
+import static org.geoserver.mapml.MapMLBaseProxyTest.getCapabilitiesURL;
 import static org.geowebcache.grid.GridSubsetFactory.createGridSubSet;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
+import java.net.URL;
+import java.util.regex.Pattern;
 import org.geoserver.catalog.Catalog;
 import org.geoserver.catalog.LayerInfo;
 import org.geoserver.catalog.ResourceInfo;
@@ -19,6 +22,8 @@
 import org.geoserver.gwc.config.GWCConfig;
 import org.geoserver.gwc.layer.GeoServerTileLayer;
 import org.geoserver.mapml.gwc.gridset.MapMLGridsets;
+import org.geotools.ows.wmts.WebMapTileServer;
+import org.geotools.ows.wmts.model.WMTSCapabilities;
 import org.geowebcache.grid.GridSubset;
 import org.geowebcache.mime.TextMime;
 import org.junit.BeforeClass;
@@ -118,15 +123,31 @@ public void testRemoteVsNotRemote() throws Exception {
     }
 
     @Override
-    protected void assertCascading(boolean shouldCascade, String url) {
-        assertTrue(url.contains("service=WMTS"));
+    protected void assertCascading(boolean shouldCascade, String url) throws Exception {
+        URL getResourceURL = null;
+        Pattern serviceTypeRE = Pattern.compile(".*SERVICE=WMTS.*", Pattern.CASE_INSENSITIVE);
+        boolean isWMTSService = serviceTypeRE.matcher(getCapabilitiesURL()).find();
+        assertTrue(isWMTSService);
         if (shouldCascade) {
+            WebMapTileServer wmts = new WebMapTileServer(new URL(getCapabilitiesURL()));
+            WMTSCapabilities capabilities = wmts.getCapabilities();
+            getResourceURL = capabilities.getRequest().getGetTile().getGet();
+            URL baseResourceURL =
+                    getResourceURL != null ? getResourceURL : new URL(getCapabilitiesURL());
+            URL base =
+                    new URL(
+                            baseResourceURL.getProtocol()
+                                    + "://"
+                                    + baseResourceURL.getHost()
+                                    + (baseResourceURL.getPort() == -1
+                                            ? ""
+                                            : ":" + baseResourceURL.getPort())
+                                    + "/");
+            String path = baseResourceURL.getPath();
+            assertTrue(url.startsWith((new URL(base, path)).toString()));
             // The remote capabilities defines a custom GridSet that matches
             // the OSMTILE with a different name: MATCHING_OSMTILE
             // Identifiers are also not simple numbers but contain a common prefix.
-            assertTrue(
-                    url.startsWith(
-                            "http://localhost:" + mockService.port() + MOCK_SERVER + CONTEXT));
             assertTrue(url.contains("layer=topp:states"));
             assertTrue(url.contains("tilematrixset=MATCHING_OSMTILE"));
             // Common prefix has been pre-pended to the tilematrix z input