Allow Bases with rdf:nil or null next pages (#102)

CHANGELOG.md

@@ -24,6 +24,7 @@
 ### Fixed
 
 - Make sure every Lyo dependency uses the same version of Guava (30.0)
+- Fix a few issues around rdf:nil handling in the TRS Client
 
 ## [4.0.0] - 2020-12-16
 

trs/client/trs-client/src/main/java/org/eclipse/lyo/trs/client/config/TrsProviderConfiguration.java

@@ -0,0 +1,39 @@
+package org.eclipse.lyo.trs.client.config;
+
+import java.net.URI;
+
+public final class TrsProviderConfiguration {
+    private final URI trsUri;
+    private final String basicAuthUsername;
+    private final String basicAuthPassword;
+
+    public final URI getTrsUri() {
+        return this.trsUri;
+    }
+
+    public final String getBasicAuthUsername() {
+        return this.basicAuthUsername;
+    }
+
+    public final String getBasicAuthPassword() {
+        return this.basicAuthPassword;
+    }
+
+    public TrsProviderConfiguration(URI trsUri, String basicAuthUsername, String basicAuthPassword) {
+        super();
+        this.trsUri = trsUri;
+        this.basicAuthUsername = basicAuthUsername;
+        this.basicAuthPassword = basicAuthPassword;
+    }
+
+    public static final TrsProviderConfiguration forHttp(String trsEndpointUri) {
+        URI trsUri = URI.create(trsEndpointUri);
+        return new TrsProviderConfiguration(trsUri, null, null);
+    }
+
+    public static final TrsProviderConfiguration forHttpWithBasicAuth(String trsEndpointUri, String trsEndpointUsername, String trsEndpointPassword) {
+        URI trsUri = URI.create(trsEndpointUri);
+        return new TrsProviderConfiguration(trsUri, trsEndpointUsername, trsEndpointPassword);
+    }
+
+}

trs/client/trs-client/src/main/java/org/eclipse/lyo/trs/client/handlers/ConcurrentTrsProviderHandler.java

@@ -22,6 +22,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
+
 import org.apache.jena.rdf.model.Model;
 import org.apache.jena.vocabulary.RDF;
 import org.eclipse.lyo.core.trs.Base;
@@ -98,6 +99,16 @@ public boolean fetchRemoteChangeLogs(ChangeLog currentChangeLog, List<ChangeLog>
                     break;
                 }
                 previousChangeLog = currentChangeLog.getPrevious();
+                if(previousChangeLog == null || URI.create(RDF.nil.getURI()).equals(previousChangeLog)) {
+                    if(URI.create(RDF.nil.getURI()).equals(lastProcessedChangeEventUri)) {
+                        log.debug("First ChangeLog page reached");
+                        foundChangeEvent = true;
+                    }
+                    else {
+                        log.error("Changelog read to the end without finding the cutoff event URI");
+                    }
+                    break;
+                }
                 currentChangeLog = trsClient.fetchRemoteChangeLog(previousChangeLog);
             } else {
                 break;

trs/client/trs-client/src/main/java/org/eclipse/lyo/trs/client/util/ClientUtil.java

@@ -97,19 +97,20 @@ static Base extractBaseFromRdfModel(Model rdFModel) throws LyoModelException {
         }
 
         if (baseObj == null) {
-            // FIXME Andrew@2019-07-15: nulls
+            log.error("Base page object is null");
+            //FIXME nulls
+//            throw new IllegalStateException();
             return null;
         }
 
         if (ProviderUtil.isNotEmptySingletonArray(nextPageArray) && nextPageArray[0] instanceof Page) {
             nextPage = (Page) nextPageArray[0];
             baseObj.setNextPage(nextPage);
-            log.debug("finished extracting base from rdf model");
-            return baseObj;
+        } else {
+            log.debug("Base page {} is the last one", baseObj.getAbout());
         }
         log.debug("finished extracting base from rdf model");
-        // FIXME Andrew@2019-07-15: nulls
-        return null;
+        return baseObj;
     }
 
     /**