transport: Let users specify an error handler for unpacking a pack file

Currently, there's no way for a user to customize the error handler for
the exception happened during unpacking an incoming pack file. Create an
error handler class and let them specify one.

Change-Id: Id07638ee58c88e1365181c3ddd17ee0266f3934d
Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/ReceivePack.java

@@ -299,6 +299,8 @@ public class ReceivePack {
 		// Use the default implementation.
 	};
 
+	private UnpackErrorHandler unpackErrorHandler = new DefaultUnpackErrorHandler();
+
 	/** Hook to report on the commands after execution. */
 	private PostReceiveHook postReceive;
 
@@ -2144,6 +2146,15 @@ public class ReceivePack {
 		postReceive = h != null ? h : PostReceiveHook.NULL;
 	}
 
+	/**
+	 * @param unpackErrorHandler
+	 *            the unpackErrorHandler to set
+	 * @since 5.7
+	 */
+	public void setUnpackErrorHandler(UnpackErrorHandler unpackErrorHandler) {
+		this.unpackErrorHandler = unpackErrorHandler;
+	}
+
 	/**
 	 * Set whether this class will report command failures as warning messages
 	 * before sending the command results.
@@ -2220,7 +2231,7 @@ public class ReceivePack {
 					} catch (IOException | RuntimeException
 							| SubmoduleValidationException | Error err) {
 						unlockPack();
-						sendStatusReport(err);
+						unpackErrorHandler.handleUnpackException(err);
 						throw new UnpackException(err);
 					}
 				}
@@ -2289,4 +2300,11 @@ public class ReceivePack {
 					filterCommands(Result.OK));
 		}
 	}
+
+	private class DefaultUnpackErrorHandler implements UnpackErrorHandler {
+		@Override
+		public void handleUnpackException(Throwable t) throws IOException {
+			sendStatusReport(t);
+		}
+	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/transport/UnpackErrorHandler.java

@@ -0,0 +1,29 @@
+/*
+ * 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.transport;
+
+import java.io.IOException;
+
+/**
+ * Exception handler for processing an incoming pack file.
+ *
+ * @since 5.7
+ */
+public interface UnpackErrorHandler {
+	/**
+	 * Handle an exception thrown while unpacking the pack file.
+	 *
+	 * @param t
+	 *            exception thrown
+	 * @throws IOException
+	 *             thrown when failed to write an error back to the client.
+	 */
+	void handleUnpackException(Throwable t) throws IOException;
+}