GH-4084: Fix ByteBufferPool sizing in Fuseki's Jetty Server

jena-fuseki2/jena-fuseki-main/src/main/java/org/apache/jena/fuseki/main/JettyServer.java

@@ -50,12 +50,15 @@
 import org.eclipse.jetty.ee11.servlet.ServletContextHandler;
 import org.eclipse.jetty.ee11.servlet.ServletHolder;
 import org.eclipse.jetty.http.MimeTypes;
+import org.eclipse.jetty.io.ArrayByteBufferPool;
+import org.eclipse.jetty.io.ByteBufferPool;
 import org.eclipse.jetty.security.SecurityHandler;
 import org.eclipse.jetty.server.*;
 import org.eclipse.jetty.server.handler.ErrorHandler;
 import org.eclipse.jetty.util.Callback;
 import org.eclipse.jetty.util.resource.Resource;
 import org.eclipse.jetty.util.thread.QueuedThreadPool;
+import org.eclipse.jetty.util.thread.Scheduler;
 import org.eclipse.jetty.util.thread.ThreadPool;
 import org.eclipse.jetty.xml.XmlConfiguration;
 import org.slf4j.Logger;
@@ -473,10 +476,18 @@ public static Server jettyServer(int minThreads, int maxThreads) {
         maxThreads = Math.max(minThreads, maxThreads);
         // Args reversed: Jetty uses (max,min)
         threadPool = new QueuedThreadPool(maxThreads, minThreads);
-        Server server = new Server(threadPool);
+        // Server(ThreadPool) alone installs a default 64KB ArrayByteBufferPool; pass ours explicitly.
+        Server server = new Server(threadPool, (Scheduler)null, newByteBufferPool());
         return server;
     }
 
+    /** ByteBufferPool sized so its maximum pooled buffer capacity is at least
+     * {@link FusekiSystemConstants#jettyOutputBufferSize}. */
+    private static ByteBufferPool newByteBufferPool() {
+        int maxCapacity = FusekiSystemConstants.jettyOutputBufferSize;
+        return new ArrayByteBufferPool(0, -1, maxCapacity, -1, -1, -1);
+    }
+
     private static void serverAddConnectors(Server server, int port,  boolean loopback) {
         HttpConfiguration httpConnectionFactory = JettyLib.httpConfiguration();
         HttpConnectionFactory f1 = new HttpConnectionFactory(httpConnectionFactory);

jena-fuseki2/jena-fuseki-main/src/main/java/org/apache/jena/fuseki/main/sys/FusekiSystemConstants.java

@@ -55,7 +55,7 @@ private static int getValueInt(String propertyKey, int defaultValue) {
      * Setting for HttpConfiguration.setOutputBufferSize (set in
      * {@link JettyLib#httpConfiguration}).
      */
-    public static final int jettyOutputBufferSize = 5 * 1024 * 1024;
+    public static final int jettyOutputBufferSize = 2 * 1024 * 1024;
 
     /**
      * JettyrRequest header size.

jena-fuseki2/jena-fuseki-main/src/test/java/org/apache/jena/fuseki/main/TestFusekiServerBuild.java

@@ -54,8 +54,11 @@
 import org.apache.jena.sparql.exec.http.GSP;
 import org.apache.jena.sparql.exec.http.QueryExecHTTP;
 import org.apache.jena.sparql.sse.SSE;
+import org.apache.jena.fuseki.main.sys.FusekiSystemConstants;
 import org.apache.jena.system.Txn;
 import org.apache.jena.update.UpdateExecution;
+import org.eclipse.jetty.io.ArrayByteBufferPool;
+import org.eclipse.jetty.server.Server;
 import org.junit.jupiter.api.Test;
 import org.slf4j.Logger;
 
@@ -85,6 +88,14 @@ public class TestFusekiServerBuild {
         } finally { server.stop(); }
     }
 
+    @Test public void fuseki_build_byte_buffer_pool() {
+        FusekiServer server = FusekiServer.create().port(0).build();
+        Server jettyServer = server.getJettyServer();
+        ArrayByteBufferPool pool = jettyServer.getBean(ArrayByteBufferPool.class);
+        assertNotNull(pool);
+        assertTrue(pool.getMaxCapacity() >= FusekiSystemConstants.jettyOutputBufferSize);
+    }
+
     // The port in "testing/jetty.xml" is 1077
 
     @Test public void fuseki_ext_jetty_xml_1() {