Add interface to configure details of JGit's pack implementation

docs/git.md

@@ -39,6 +39,26 @@ sshd.setCommandFactory(new GitPackCommandFactory().withGitLocationResolver(resol
 
 ```
 
+To further control what happens in response to `git-receive-pack` and `git-upload-pack`, you can implement a `GitPackConfiguration` which will be used
+to configure JGit's `ReceivePack` and `UploadPack`, respectively:
+
+```java
+sshd.setCommandFactory(new GitPackCommandFactory()
+    .withGitPackConfiguration(new GitPackConfiguration() {
+        @Override
+        public void configureReceivePack(ServerSession session, ReceivePack pack) {
+            pack.setPreReceiveHook(...);
+            // ...
+        }
+
+        @Override
+        public void configureUploadPack(ServerSession session, UploadPack pack) {
+            pack.setRefFilter(...);
+            // ...
+        }
+    }));
+```
+
 These command factories also accept a delegate to which non-_git_ commands are routed:
 
 ```java

sshd-git/src/main/java/org/apache/sshd/git/pack/GitPackCommand.java

@@ -45,6 +45,9 @@
  * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
  */
 public class GitPackCommand extends AbstractGitCommand {
+
+    private GitPackConfiguration packConfiguration = GitPackConfiguration.NOTHING;
+
     /**
      * @param rootDirResolver Resolver for GIT root directory
      * @param command         Command to execute
@@ -61,7 +64,7 @@ public void run() {
         String command = getCommand();
         try {
             List<String> strs = parseDelimitedString(command, " ", true);
-            String[] args = strs.toArray(new String[strs.size()]);
+            String[] args = strs.toArray(new String[0]);
             for (int i = 0; i < args.length; i++) {
                 String argVal = args[i];
                 if (argVal.startsWith("'") && argVal.endsWith("'")) {
@@ -83,6 +86,7 @@ public void run() {
             String subCommand = args[0];
             if (RemoteConfig.DEFAULT_UPLOAD_PACK.equals(subCommand)) {
                 UploadPack uploadPack = new UploadPack(db);
+                packConfiguration.configureUploadPack(getSession(), uploadPack);
                 Environment environment = getEnvironment();
                 Map<String, String> envVars = environment.getEnv();
                 String protocol = MapEntryUtils.isEmpty(envVars)
@@ -92,7 +96,9 @@ public void run() {
                 }
                 uploadPack.upload(getInputStream(), getOutputStream(), getErrorStream());
             } else if (RemoteConfig.DEFAULT_RECEIVE_PACK.equals(subCommand)) {
-                new ReceivePack(db).receive(getInputStream(), getOutputStream(), getErrorStream());
+                ReceivePack receivePack = new ReceivePack(db);
+                packConfiguration.configureReceivePack(getSession(), receivePack);
+                receivePack.receive(getInputStream(), getOutputStream(), getErrorStream());
             } else {
                 throw new IllegalArgumentException("Unknown git command: " + command);
             }
@@ -118,4 +124,9 @@ protected Path resolveRootDirectory(String command, String[] args) throws IOExce
         ValidateUtils.checkNotNullAndNotEmpty(pathArg, "No %s command sub-path specified", args[0]);
         return rootDir.resolve(pathArg);
     }
+
+    public void setPackConfiguration(GitPackConfiguration packConfiguration) {
+        this.packConfiguration = ValidateUtils.checkNotNull(packConfiguration,
+                "Pack configuration must not be null");
+    }
 }

sshd-git/src/main/java/org/apache/sshd/git/pack/GitPackCommandFactory.java

@@ -34,6 +34,8 @@ public class GitPackCommandFactory extends AbstractGitCommandFactory {
     public static final String GIT_FACTORY_NAME = "git-pack";
     public static final String GIT_COMMAND_PREFIX = "git-";
 
+    private GitPackConfiguration packConfiguration;
+
     public GitPackCommandFactory() {
         this(null);
     }
@@ -61,6 +63,25 @@ public GitPackCommandFactory withExecutorServiceProvider(
 
     @Override
     public GitPackCommand createGitCommand(String command) {
-        return new GitPackCommand(getGitLocationResolver(), command, resolveExecutorService(command));
+        GitPackCommand cmd = new GitPackCommand(getGitLocationResolver(), command, resolveExecutorService(command));
+        if (packConfiguration != null) {
+            cmd.setPackConfiguration(packConfiguration);
+        }
+        return cmd;
+    }
+
+    /**
+     * Sets the {@link GitPackConfiguration} that will be set for all {@link GitPackCommand}s created by this factory.
+     * <p>
+     * Every time a {@link GitPackCommand} creates a JGit {@code UploadPack} or {@code ReceivePack}, the corresponding
+     * method of the {@link GitPackConfiguration} set here is called. This allows you to configure JGit further, e.g. to
+     * set pre- and post-receive hooks.
+     *
+     * @param  configuration the configuration to use for git pack commands.
+     * @return               Self instance
+     */
+    public GitPackCommandFactory withGitPackConfiguration(GitPackConfiguration configuration) {
+        this.packConfiguration = configuration;
+        return this;
     }
 }

sshd-git/src/main/java/org/apache/sshd/git/pack/GitPackConfiguration.java

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.sshd.git.pack;
+
+import org.apache.sshd.server.session.ServerSession;
+import org.eclipse.jgit.transport.ReceivePack;
+import org.eclipse.jgit.transport.UploadPack;
+
+/**
+ * Interface specifying methods that can be used to configure JGit's pack objects.
+ */
+public interface GitPackConfiguration {
+
+    GitPackConfiguration NOTHING = new GitPackConfiguration() {
+    };
+
+    default void configureReceivePack(ServerSession session, ReceivePack pack) {
+        // Nothing by default
+    }
+
+    default void configureUploadPack(ServerSession session, UploadPack pack) {
+        // Nothing by default
+    }
+}

sshd-git/src/test/java/org/apache/sshd/git/pack/GitPackCommandTest.java

@@ -32,6 +32,7 @@
 import org.apache.sshd.git.transport.GitSshdSessionFactory;
 import org.apache.sshd.server.SshServer;
 import org.apache.sshd.server.auth.password.AcceptAllPasswordAuthenticator;
+import org.apache.sshd.server.session.ServerSession;
 import org.apache.sshd.sftp.server.SftpSubsystemFactory;
 import org.apache.sshd.util.test.BaseTestSupport;
 import org.apache.sshd.util.test.CommonTestSupportUtils;
@@ -40,7 +41,9 @@
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.transport.CredentialsProvider;
 import org.eclipse.jgit.transport.GitProtocolConstants;
+import org.eclipse.jgit.transport.ReceivePack;
 import org.eclipse.jgit.transport.SshSessionFactory;
+import org.eclipse.jgit.transport.UploadPack;
 import org.eclipse.jgit.transport.UsernamePasswordCredentialsProvider;
 import org.junit.jupiter.api.Assumptions;
 import org.junit.jupiter.api.BeforeAll;
@@ -77,9 +80,11 @@ void gitPack() throws Exception {
 
         Path gitRootDir = getTempTargetRelativeFile(getClass().getSimpleName());
         try (SshServer sshd = setupTestServer()) {
+            GitPackTestConfig packConfig = new GitPackTestConfig();
             Path serverRootDir = gitRootDir.resolve("server");
             sshd.setSubsystemFactories(Collections.singletonList(new SftpSubsystemFactory()));
-            sshd.setCommandFactory(new GitPackCommandFactory(GitLocationResolver.constantPath(serverRootDir)));
+            sshd.setCommandFactory(new GitPackCommandFactory(GitLocationResolver.constantPath(serverRootDir))
+                    .withGitPackConfiguration(packConfig));
             sshd.start();
 
             int port = sshd.getPort();
@@ -124,6 +129,9 @@ void gitPack() throws Exception {
                     git.fetch().call();
                     assertTrue(client.isStarted(),
                             "Client not started after fetch using GIT_PROTOCOL='version=2' env. variable");
+
+                    assertTrue(packConfig.receivePackCalled, "ReceivePack was not configured");
+                    assertTrue(packConfig.uploadPackCalled, "UploadPack was not configured");
                 } finally {
                     client.stop();
                 }
@@ -134,4 +142,19 @@ void gitPack() throws Exception {
             }
         }
     }
+
+    private static class GitPackTestConfig implements GitPackConfiguration {
+        boolean receivePackCalled;
+        boolean uploadPackCalled;
+
+        @Override
+        public void configureReceivePack(ServerSession session, ReceivePack pack) {
+            receivePackCalled = true;
+        }
+
+        @Override
+        public void configureUploadPack(ServerSession session, UploadPack pack) {
+            uploadPackCalled = true;
+        }
+    }
 }