server: Add a custom error handler

Same as UploadPack, add a custom error handler.

Change-Id: I9c708aa5a22e01214c1d997fa6f72f4b8bf814f0
Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/GitFilter.java

@@ -96,6 +96,8 @@ public class GitFilter extends MetaFilter {
 
 	private ReceivePackFactory<HttpServletRequest> receivePackFactory = new DefaultReceivePackFactory();
 
+	private ReceivePackErrorHandler receivePackErrorHandler;
+
 	private final List<Filter> uploadPackFilters = new LinkedList<>();
 
 	private final List<Filter> receivePackFilters = new LinkedList<>();
@@ -189,6 +191,17 @@ public class GitFilter extends MetaFilter {
 		this.receivePackFactory = f != null ? f : (ReceivePackFactory<HttpServletRequest>)ReceivePackFactory.DISABLED;
 	}
 
+	/**
+	 * Set a custom error handler for git-receive-pack.
+	 *
+	 * @param h
+	 *            A custom error handler for git-receive-pack.
+	 */
+	public void setReceivePackErrorHandler(ReceivePackErrorHandler h) {
+		assertNotInitialized();
+		this.receivePackErrorHandler = h;
+	}
+
 	/**
 	 * Add receive-pack filter
 	 *
@@ -233,7 +246,7 @@ public class GitFilter extends MetaFilter {
 			b = b.through(new ReceivePackServlet.Factory(receivePackFactory));
 			for (Filter f : receivePackFilters)
 				b = b.through(f);
-			b.with(new ReceivePackServlet());
+			b.with(new ReceivePackServlet(receivePackErrorHandler));
 		}
 
 		ServletBinder refs = serve("*/" + Constants.INFO_REFS);

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ReceivePackErrorHandler.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2019, Google LLC  and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.http.server;
+
+import java.io.IOException;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.eclipse.jgit.transport.ReceivePack;
+import org.eclipse.jgit.transport.ServiceMayNotContinueException;
+
+/**
+ * Handle git-receive-pack errors.
+ *
+ * <p>
+ * This is an entry point for customizing an error handler for git-receive-pack.
+ * Right before calling {@link ReceivePack#receiveWithExceptionPropagation},
+ * JGit will call this handler if specified through {@link GitFilter}. The
+ * implementation of this handler is responsible for calling
+ * {@link ReceivePackRunnable} and handling exceptions for clients.
+ *
+ * <p>
+ * If a custom handler is not specified, JGit will use the default error
+ * handler.
+ *
+ * @since 5.6
+ */
+public interface ReceivePackErrorHandler {
+	/**
+	 * @param req
+	 *            The HTTP request
+	 * @param rsp
+	 *            The HTTP response
+	 * @param r
+	 *            A continuation that handles a git-receive-pack request.
+	 * @throws IOException
+	 */
+	void receive(HttpServletRequest req, HttpServletResponse rsp,
+			ReceivePackRunnable r) throws IOException;
+
+	/** Process a git-receive-pack request. */
+	public interface ReceivePackRunnable {
+		/**
+		 * See {@link ReceivePack#receiveWithExceptionPropagation}.
+		 *
+		 * @throws ServiceMayNotContinueException
+		 * @throws IOException
+		 */
+		void receive() throws ServiceMayNotContinueException, IOException;
+	}
+
+}

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/ReceivePackServlet.java

@@ -71,6 +71,7 @@ import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.PackProtocolException;
 import org.eclipse.jgit.errors.UnpackException;
@@ -161,6 +162,13 @@ class ReceivePackServlet extends HttpServlet {
 		}
 	}
 
+	@Nullable
+	private final ReceivePackErrorHandler handler;
+
+	ReceivePackServlet(@Nullable ReceivePackErrorHandler handler) {
+		this.handler = handler;
+	}
+
 	/** {@inheritDoc} */
 	@Override
 	public void doPost(final HttpServletRequest req,
@@ -178,10 +186,17 @@ class ReceivePackServlet extends HttpServlet {
 		};
 
 		ReceivePack rp = (ReceivePack) req.getAttribute(ATTRIBUTE_HANDLER);
-		try {
 		rp.setBiDirectionalPipe(false);
 		rsp.setContentType(RECEIVE_PACK_RESULT_TYPE);
 
+		if (handler != null) {
+			handler.receive(req, rsp, () -> {
+				rp.receiveWithExceptionPropagation(getInputStream(req), out,
+						null);
+				out.close();
+			});
+		} else {
+			try {
 				rp.receive(getInputStream(req), out, null);
 				out.close();
 			} catch (CorruptObjectException e ) {
@@ -208,6 +223,7 @@ class ReceivePackServlet extends HttpServlet {
 				return;
 			}
 		}
+	}
 
 	private void log(Repository git, Throwable e) {
 		getServletContext().log(MessageFormat.format(