Allowed external http and https targets for LinkNodes

src/main/java/it/inaf/oats/vospace/UriService.java

@@ -346,7 +346,7 @@ public class UriService {
 
     public enum ProtocolType {
         // Please keep the URIs in this enum UNIQUE!
-        // will add a unit test to check this
+        // added a unit test to check this
         HTTPGET("ivo://ivoa.net/vospace/core#httpget", "http"),
         HTTPSGET("ivo://ivoa.net/vospace/core#httpsget", "https"),
         HTTPPUT("ivo://ivoa.net/vospace/core#httpput", "http"),

src/test/java/it/inaf/oats/vospace/UriServiceTest.java

@@ -7,6 +7,7 @@ package it.inaf.oats.vospace;
 
 import it.inaf.ia2.aa.ServletRapClient;
 import it.inaf.ia2.aa.data.User;
+import it.inaf.oats.vospace.UriService.ProtocolType;
 import it.inaf.oats.vospace.datamodel.NodeProperties;
 import it.inaf.oats.vospace.datamodel.NodeUtils;
 import it.inaf.oats.vospace.datamodel.Views;
@@ -20,7 +21,9 @@ import it.inaf.oats.vospace.persistence.LocationDAO;
 import it.inaf.oats.vospace.persistence.NodeDAO;
 import it.inaf.oats.vospace.persistence.model.Location;
 import it.inaf.oats.vospace.persistence.model.LocationType;
+import java.util.List;
 import java.util.Optional;
+import java.util.stream.Collectors;
 import javax.servlet.http.HttpServletRequest;
 import net.ivoa.xml.uws.v1.JobSummary;
 import net.ivoa.xml.vospace.v2.ContainerNode;
@@ -671,4 +674,14 @@ public class UriServiceTest {
 
         return job;
     }
+    
+    @Test
+    public void testProtocolType() {
+        List<ProtocolType> pts = List.of(ProtocolType.values());
+        
+        int distinctUris = 
+                pts.stream().map(pt -> pt.getUri()).distinct().collect(Collectors.toList()).size();
+        
+        assertEquals(pts.size(), distinctUris);
+    }
 }