Allow batch handler to set http status

src/main/java/graphql/servlet/AbstractGraphQLHttpServlet.java

@@ -365,12 +365,7 @@ private void query(GraphQLQueryInvoker queryInvoker, GraphQLObjectMapper graphQL
     }
 
     private void queryBatched(GraphQLQueryInvoker queryInvoker, GraphQLObjectMapper graphQLObjectMapper, GraphQLBatchedInvocationInput invocationInput, HttpServletResponse resp) throws Exception {
-        resp.setContentType(APPLICATION_JSON_UTF8);
-        resp.setStatus(STATUS_OK);
-
-        Writer respWriter = resp.getWriter();
-
-        queryInvoker.query(invocationInput, respWriter, graphQLObjectMapper);
+        queryInvoker.query(invocationInput, resp, graphQLObjectMapper);
     }
 
     private <R> List<R> runListeners(Function<? super GraphQLServletListener, R> action) {

src/main/java/graphql/servlet/BatchExecutionHandler.java

@@ -3,6 +3,7 @@
 import graphql.ExecutionInput;
 import graphql.ExecutionResult;
 
+import javax.servlet.http.HttpServletResponse;
 import java.io.Writer;
 import java.util.function.BiFunction;
 
@@ -16,9 +17,9 @@ public interface BatchExecutionHandler {
      * @param batchedInvocationInput the batch query input
      * @param queryFunction Function to produce query results.
      * @param graphQLObjectMapper object mapper used to serialize results
-     * @param writer request writer to ouput results.
+     * @param response http response object
      */
-    void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, Writer writer, GraphQLObjectMapper graphQLObjectMapper,
+    void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, HttpServletResponse response, GraphQLObjectMapper graphQLObjectMapper,
                      BiFunction<GraphQLInvocationInput, ExecutionInput, ExecutionResult> queryFunction);
 }
 

src/main/java/graphql/servlet/DefaultBatchExecutionHandler.java

@@ -3,6 +3,7 @@
 import graphql.ExecutionInput;
 import graphql.ExecutionResult;
 
+import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.io.Writer;
 import java.util.Iterator;
@@ -11,10 +12,14 @@
 public class DefaultBatchExecutionHandler implements BatchExecutionHandler {
 
     @Override
-    public void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, Writer writer, GraphQLObjectMapper graphQLObjectMapper,
+    public void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, HttpServletResponse response, GraphQLObjectMapper graphQLObjectMapper,
                             BiFunction<GraphQLInvocationInput, ExecutionInput, ExecutionResult> queryFunction) {
-        Iterator<ExecutionInput> executionInputIterator = batchedInvocationInput.getExecutionInputs().iterator();
+        response.setContentType(AbstractGraphQLHttpServlet.APPLICATION_JSON_UTF8);
+        response.setStatus(AbstractGraphQLHttpServlet.STATUS_OK);
         try {
+            Writer writer = response.getWriter();
+            Iterator<ExecutionInput> executionInputIterator = batchedInvocationInput.getExecutionInputs().iterator();
+
             writer.write("[");
             while (executionInputIterator.hasNext()) {
                 ExecutionResult result = queryFunction.apply(batchedInvocationInput, executionInputIterator.next());

src/main/java/graphql/servlet/GraphQLQueryInvoker.java

@@ -13,6 +13,7 @@
 import graphql.schema.GraphQLSchema;
 
 import javax.security.auth.Subject;
+import javax.servlet.http.HttpServletResponse;
 import java.io.Writer;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
@@ -43,8 +44,8 @@ public ExecutionResult query(GraphQLSingleInvocationInput singleInvocationInput)
         return query(singleInvocationInput, singleInvocationInput.getExecutionInput());
     }
 
-    public void query(GraphQLBatchedInvocationInput batchedInvocationInput, Writer writer, GraphQLObjectMapper graphQLObjectMapper) {
-        batchExecutionHandler.handleBatch(batchedInvocationInput, writer, graphQLObjectMapper, this::query);
+    public void query(GraphQLBatchedInvocationInput batchedInvocationInput, HttpServletResponse response, GraphQLObjectMapper graphQLObjectMapper) {
+        batchExecutionHandler.handleBatch(batchedInvocationInput, response, graphQLObjectMapper, this::query);
     }
 
     private GraphQL newGraphQL(GraphQLSchema schema, Object context) {

src/test/groovy/graphql/servlet/AbstractGraphQLHttpServletSpec.groovy

@@ -285,7 +285,7 @@ class AbstractGraphQLHttpServletSpec extends Specification {
         getBatchedResponseContent()[1].data.echo == "test"
     }
 
-    def "Execution Result Handler allows limiting number of queries"() {
+    def "Batch Execution Handler allows limiting batches and sending error messages."() {
         setup:
         servlet = TestUtils.createBatchCustomizedServlet({ env -> env.arguments.arg }, { env -> env.arguments.arg }, { env ->
             AtomicReference<SingleSubscriberPublisher<String>> publisherRef = new AtomicReference<>()
@@ -304,9 +304,8 @@ class AbstractGraphQLHttpServletSpec extends Specification {
         servlet.doGet(request, response)
 
         then:
-        response.getStatus() == STATUS_OK
-        response.getContentType() == CONTENT_TYPE_JSON_UTF8
-        getBatchedResponseContent().size() == 2
+        response.getStatus() == STATUS_BAD_REQUEST
+        response.getErrorMessage() == TestBatchExecutionHandler.BATCH_ERROR_MESSAGE
     }
 
     def "Default Execution Result Handler does not limit number of queries"() {

src/test/groovy/graphql/servlet/TestBatchExecutionHandler.java

@@ -3,6 +3,7 @@
 import graphql.ExecutionInput;
 import graphql.ExecutionResult;
 
+import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.io.Writer;
 import java.util.Iterator;
@@ -12,18 +13,34 @@
 
 public class TestBatchExecutionHandler implements BatchExecutionHandler {
 
+    public static String BATCH_ERROR_MESSAGE = "Batch limit exceeded";
+
     @Override
-    public void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, Writer writer, GraphQLObjectMapper graphQLObjectMapper,
+    public void handleBatch(GraphQLBatchedInvocationInput batchedInvocationInput, HttpServletResponse response, GraphQLObjectMapper graphQLObjectMapper,
                             BiFunction<GraphQLInvocationInput, ExecutionInput, ExecutionResult> queryFunction) {
-        List<ExecutionResult> results = batchedInvocationInput.getExecutionInputs().parallelStream()
-            .limit(2)
+        List<ExecutionInput> inputs = batchedInvocationInput.getExecutionInputs();
+        if (inputs.size() > 2) {
+            handleBadInput(response);
+        }
+        List<ExecutionResult> results = inputs.parallelStream()
             .map(input -> queryFunction.apply(batchedInvocationInput, input))
             .collect(Collectors.toList());
-        writeResults(results, writer, graphQLObjectMapper);
+        writeResults(results, response, graphQLObjectMapper);
+    }
+
+    private void handleBadInput(HttpServletResponse response) {
+        try {
+            response.sendError(HttpServletResponse.SC_BAD_REQUEST, BATCH_ERROR_MESSAGE);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
     }
 
-    private void writeResults(List<ExecutionResult> results, Writer writer, GraphQLObjectMapper mapper) {
+    private void writeResults(List<ExecutionResult> results, HttpServletResponse response, GraphQLObjectMapper mapper) {
+        response.setContentType(AbstractGraphQLHttpServlet.APPLICATION_JSON_UTF8);
+        response.setStatus(AbstractGraphQLHttpServlet.STATUS_OK);
         try {
+            Writer writer = response.getWriter();
             writer.write("[");
             Iterator<ExecutionResult> iter = results.iterator();
             while (iter.hasNext()) {