OLINGO-855: adding support for odata-isolation header support acknowledgement to ServiceHandler interface

lib/commons-api/src/main/java/org/apache/olingo/commons/api/http/HttpHeader.java

@@ -176,4 +176,6 @@ public interface HttpHeader {
   String ODATA_MAX_VERSION = "OData-MaxVersion";
   /** Custom Header defined in the OData standard. */
   String ODATA_ENTITY_ID = "OData-EntityID";
+  /** Custom Header defined in the OData standard. */
+  String ODATA_ISOLATION= "OData-Isolation";
 }

lib/server-core-ext/src/main/java/org/apache/olingo/server/core/ServiceDispatcher.java

@@ -24,6 +24,8 @@ import java.net.URISyntaxException;
 import java.net.URL;
 
 import org.apache.olingo.commons.api.format.ContentType;
+import org.apache.olingo.commons.api.http.HttpHeader;
+import org.apache.olingo.commons.api.http.HttpStatusCode;
 import org.apache.olingo.server.api.OData;
 import org.apache.olingo.server.api.ODataApplicationException;
 import org.apache.olingo.server.api.ODataRequest;
@@ -81,6 +83,13 @@ public class ServiceDispatcher extends RequestURLHierarchyVisitor {
 
     new UriValidator().validate(uriInfo, odRequest.getMethod());
 
+    // part1, 8.2.6
+    String isolation = odRequest.getHeader(HttpHeader.ODATA_ISOLATION);
+    if (isolation != null && isolation.equals("snapshot") && !this.handler.supportsDataIsolation()) {
+      odResponse.setStatusCode(HttpStatusCode.PRECONDITION_FAILED.getStatusCode());
+      return;
+    }
+    
     visit(uriInfo);
 
     // this should cover for any unsupported calls until they are implemented

lib/server-core-ext/src/main/java/org/apache/olingo/server/core/ServiceHandler.java

@@ -282,4 +282,18 @@ public interface ServiceHandler extends Processor {
    */
   void crossJoin(DataRequest dataRequest, List<String> entitySetNames, ODataResponse response)
       throws ODataLibraryException, ODataApplicationException;
+  
+  /**
+   * Snapshot isolation guarantees that all data returned for a request, including multiple requests within 
+   * a batch or results retrieved across multiple pages, will be consistent as of a single point in time. 
+   * Only data modifications made within the request (for example, by a data modification request 
+   * within the same batch) are visible. The effect is as if the request generates a "snapshot" of 
+   * the committed data as it existed at the start of the request. for more info see OData V4, Part1 8.2.6
+   * 
+   * The contract for this interface is if it returns true, whenever the service deals with $skiptoken based
+   * results, they MUST be from same snapshot of the original request. false, the framework will automatically
+   * returns a 412.
+   * @return
+   */
+  boolean supportsDataIsolation();
 }

lib/server-core-ext/src/main/java/org/apache/olingo/server/core/legacy/ProcessorServiceHandler.java

@@ -437,4 +437,9 @@ public class ProcessorServiceHandler implements ServiceHandler {
     throw new ODataHandlerException("not implemented",
         ODataHandlerException.MessageKeys.FUNCTIONALITY_NOT_IMPLEMENTED);
   }
+
+  @Override
+  public boolean supportsDataIsolation() {
+    return false;
+  }
 }

lib/server-core-ext/src/test/java/org/apache/olingo/server/example/TripPinHandler.java

@@ -556,4 +556,9 @@ public class TripPinHandler implements ServiceHandler {
       updateEntity(request, entity, merge, entityETag, response);
     }
   }
+
+  @Override
+  public boolean supportsDataIsolation() {
+    return false;
+  }
 }

lib/server-core-ext/src/test/java/org/apache/olingo/server/example/TripPinServiceTest.java

@@ -42,6 +42,7 @@ import org.apache.http.entity.ContentType;
 import org.apache.http.entity.StringEntity;
 import org.apache.http.impl.client.DefaultHttpClient;
 import org.apache.http.util.EntityUtils;
+import org.apache.olingo.commons.api.http.HttpHeader;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Ignore;
@@ -732,4 +733,13 @@ public class TripPinServiceTest {
     HttpResponse response = httpGET(editUrl, 200);
     EntityUtils.consumeQuietly(response.getEntity());
   }
+  
+  @Test
+  public void dataIsolation() throws Exception {
+    String url = baseURL + "/People";
+    HttpRequest request = new HttpGet(url);
+    request.setHeader(HttpHeader.ODATA_ISOLATION, "snapshot");
+    HttpResponse response = httpSend(request, 412);
+    EntityUtils.consumeQuietly(response.getEntity());
+  }  
 }