Add support for built-in clean filters

JGit supports clean filters defined in repository configuration. The
filters are implemented as external programs filtering content by
accepting the original content (as seen in the working tree) on stdin
and which emit the filtered content on stdout. To run such a filter JGit
has to start an external process and pump data into/from this process.

This commit adds support for clean filters which are implemented
in Java and which are executed by jgit's main thread. When a filter is
defined in the configuration as
"jgit://builtin/<filterDriverName>/clean" then JGit will lookup in a
static map whether a filter is registered under this name. If found
such a filter is called to do the filtering.

The functionality in this commit requires that a program using JGit
explicitly calls the JGit API to register built-in implementations for
specific clean filters. In follow-up commits configuration parameters
will be added which trigger such registrations. Other commits will add
implementations for lfs filters.

Change-Id: I0344d3c54801c9a46e5a606c5df17e5f2e17b2be

6 files changed, 476 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FilterCommandsTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FilterCommandsTest.java
new file mode 100644
index 0000000000..5fb894e911
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FilterCommandsTest.java
@@ -0,0 +1,157 @@
+/*
+ * Copyright (C) 2016, Christian Halstrick <christian.halstrick@sap.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.util;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.attributes.FilterCommand;
+import org.eclipse.jgit.attributes.FilterCommandFactory;
+import org.eclipse.jgit.attributes.FilterCommandRegistry;
+import org.eclipse.jgit.junit.RepositoryTestCase;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.RefUpdate;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.lib.StoredConfig;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.junit.Before;
+import org.junit.Test;
+
+public class FilterCommandsTest extends RepositoryTestCase {
+	private Git git;
+
+	RevCommit initialCommit;
+
+	RevCommit secondCommit;
+
+	class TestCommandFactory implements FilterCommandFactory {
+		private int prefix;
+
+		public TestCommandFactory(int prefix) {
+			this.prefix = prefix;
+		}
+
+		@Override
+		public FilterCommand create(Repository repo, InputStream in,
+				final OutputStream out) {
+			FilterCommand cmd = new FilterCommand(in, out) {
+
+				@Override
+				public int run() throws IOException {
+					int b = in.read();
+					if (b == -1) {
+						return b;
+					}
+					out.write(prefix);
+					out.write(b);
+					return 1;
+				}
+			};
+			return cmd;
+		}
+	}
+
+	@Override
+	@Before
+	public void setUp() throws Exception {
+		super.setUp();
+		git = new Git(db);
+		// commit something
+		writeTrashFile("Test.txt", "Hello world");
+		git.add().addFilepattern("Test.txt").call();
+		initialCommit = git.commit().setMessage("Initial commit").call();
+
+		// create a master branch and switch to it
+		git.branchCreate().setName("test").call();
+		RefUpdate rup = db.updateRef(Constants.HEAD);
+		rup.link("refs/heads/test");
+
+		// commit something on the test branch
+		writeTrashFile("Test.txt", "Some change");
+		git.add().addFilepattern("Test.txt").call();
+		secondCommit = git.commit().setMessage("Second commit").call();
+	}
+
+	@Test
+	public void testBuiltinCleanFilter()
+			throws IOException, GitAPIException {
+		String builtinCommandName = "jgit://builtin/test/clean";
+		FilterCommandRegistry.register(builtinCommandName,
+				new TestCommandFactory('c'));
+		StoredConfig config = git.getRepository().getConfig();
+		config.setString("filter", "test", "clean", builtinCommandName);
+		config.save();
+
+		writeTrashFile(".gitattributes", "*.txt filter=test");
+		git.add().addFilepattern(".gitattributes").call();
+		git.commit().setMessage("add filter").call();
+
+		writeTrashFile("Test.txt", "Hello again");
+		git.add().addFilepattern("Test.txt").call();
+		assertEquals(
+				"[.gitattributes, mode:100644, content:*.txt filter=test][Test.txt, mode:100644, content:cHceclclcoc cacgcacicn]",
+				indexState(CONTENT));
+
+		writeTrashFile("Test.bin", "Hello again");
+		git.add().addFilepattern("Test.bin").call();
+		assertEquals(
+				"[.gitattributes, mode:100644, content:*.txt filter=test][Test.bin, mode:100644, content:Hello again][Test.txt, mode:100644, content:cHceclclcoc cacgcacicn]",
+				indexState(CONTENT));
+
+		config.setString("filter", "test", "clean", null);
+		config.save();
+
+		git.add().addFilepattern("Test.txt").call();
+		assertEquals(
+				"[.gitattributes, mode:100644, content:*.txt filter=test][Test.bin, mode:100644, content:Hello again][Test.txt, mode:100644, content:Hello again]",
+				indexState(CONTENT));
+
+		config.setString("filter", "test", "clean", null);
+		config.save();
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommand.java
new file mode 100644
index 0000000000..10be58880c
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommand.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2016, Christian Halstrick <christian.halstrick@sap.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.attributes;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * An abstraction for JGit's builtin implementations for hooks and filters.
+ * Instead of spawning an external processes to start a filter/hook and to pump
+ * data from/to stdin/stdout these builtin commmands may be used. They are
+ * constructed by {@link FilterCommandFactory}.
+ *
+ * @since 4.6
+ */
+public abstract class FilterCommand {
+	/**
+	 * The {@link InputStream} this command should read from
+	 */
+	protected InputStream in;
+
+	/**
+	 * The {@link OutputStream} this command should write to
+	 */
+	protected OutputStream out;
+
+	/**
+	 * @param in
+	 *            The {@link InputStream} this command should read from
+	 * @param out
+	 *            The {@link OutputStream} this command should write to
+	 */
+	public FilterCommand(InputStream in, OutputStream out) {
+		this.in = in;
+		this.out = out;
+	}
+
+	/**
+	 * Execute the command. The command is supposed to read data from
+	 * {@link #in} and to write the result to {@link #out}. It returns the
+	 * number of bytes it read from {@link #in}. It should be called in a loop
+	 * until it returns -1 signaling that the {@link InputStream} is completely
+	 * processed.
+	 *
+	 * @return the number of bytes read from the {@link InputStream} or -1. -1
+	 *         means that the {@link InputStream} is completely processed.
+	 * @throws IOException
+	 *             when {@link IOException} occured while reading from
+	 *             {@link #in} or writing to {@link #out}
+	 *
+	 */
+	public abstract int run() throws IOException;
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandFactory.java b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandFactory.java
new file mode 100644
index 0000000000..6b973da35f
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandFactory.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2016, Christian Halstrick <christian.halstrick@sap.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.attributes;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import org.eclipse.jgit.lib.Repository;
+
+/**
+ * The factory responsible for creating instances of {@link FilterCommand}.
+ *
+ * @since 4.6
+ */
+public interface FilterCommandFactory {
+	/**
+	 * Create a new {@link FilterCommand}.
+	 *
+	 * @param db
+	 *            the repository this command should work on
+	 * @param in
+	 *            the {@link InputStream} this command should read from
+	 * @param out
+	 *            the {@link OutputStream} this command should write to
+	 * @return the created {@link FilterCommand}
+	 * @throws IOException
+	 *             thrown when the command constructor throws an IOException
+	 */
+	public FilterCommand create(Repository db, InputStream in,
+			OutputStream out) throws IOException;
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java
new file mode 100644
index 0000000000..4729f347d9
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/attributes/FilterCommandRegistry.java
@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2016, Matthias Sohn <matthias.sohn@sap.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.attributes;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.eclipse.jgit.lib.Repository;
+
+/**
+ * Registry for built-in filters
+ *
+ * @since 4.6
+ */
+public class FilterCommandRegistry {
+	private static ConcurrentHashMap<String, FilterCommandFactory> filterCommandRegistry = new ConcurrentHashMap<>();
+
+	/**
+	 * Registers a {@link FilterCommandFactory} responsible for creating
+	 * {@link FilterCommand}s for a certain command name. If the factory f1 is
+	 * registered for the name "jgit://builtin/x" then a call to
+	 * <code>getCommand("jgit://builtin/x", ...)</code> will call
+	 * <code>f1(...)</code> to create a new instance of {@link FilterCommand}
+	 *
+	 * @param filterCommandName
+	 *            the command name for which this factory is registered
+	 * @param factory
+	 *            the factory responsible for creating {@link FilterCommand}s
+	 *            for the specified name
+	 * @return the previous factory associated with <tt>commandName</tt>, or
+	 *         <tt>null</tt> if there was no mapping for <tt>commandName</tt>
+	 */
+	public static FilterCommandFactory register(String filterCommandName,
+			FilterCommandFactory factory) {
+		return filterCommandRegistry.put(filterCommandName, factory);
+	}
+
+	/**
+	 * Unregisters the {@link FilterCommandFactory} registered for the given
+	 * command name
+	 *
+	 * @param filterCommandName
+	 *            the FilterCommandFactory's filter command name
+	 * @return the previous factory associated with <tt>filterCommandName</tt>,
+	 *         or <tt>null</tt> if there was no mapping for <tt>commandName</tt>
+	 */
+	public static FilterCommandFactory unregister(String filterCommandName) {
+		return filterCommandRegistry.remove(filterCommandName);
+	}
+
+	/**
+	 * Checks whether any {@link FilterCommandFactory} is registered for a given
+	 * command name
+	 *
+	 * @param filterCommandName
+	 *            the name for which the registry should be checked
+	 * @return <code>true</code> if any factory was registered for the name
+	 */
+	public static boolean isRegistered(String filterCommandName) {
+		return filterCommandRegistry.containsKey(filterCommandName);
+	}
+
+	/**
+	 * Creates a new {@link FilterCommand} for the given name. A factory must be
+	 * registered for the name in advance.
+	 *
+	 * @param filterCommandName
+	 *            The name for which a new {@link FilterCommand} should be
+	 *            created
+	 * @param db
+	 *            the repository this command should work on
+	 * @param in
+	 *            the {@link InputStream} this {@link FilterCommand} should read
+	 *            from
+	 * @param out
+	 *            the {@link OutputStream} this {@link FilterCommand} should
+	 *            write to
+	 * @return the command if a command could be created or <code>null</code> if
+	 *         there was no factory registered for that name
+	 * @throws IOException
+	 */
+	public static FilterCommand createFilterCommand(String filterCommandName,
+			Repository db, InputStream in, OutputStream out)
+			throws IOException {
+		FilterCommandFactory cf = filterCommandRegistry.get(filterCommandName);
+		return (cf == null) ? null : cf.create(db, in, out);
+	}
+
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
index d30edaf41b..ff80672f80 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
@@ -391,6 +391,13 @@ public final class Constants {
 	 */
 	public static final String ATTR_FILTER_TYPE_SMUDGE = "smudge";
 
+	/**
+	 * Builtin filter commands start with this prefix
+	 *
+	 * @since 4.6
+	 */
+	public static final String BUILTIN_FILTER_PREFIX = "jgit://builtin/";
+
 	/** Name of the ignore file */
 	public static final String DOT_GIT_IGNORE = ".gitignore";
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
index 9a3fa8060b..be4baef057 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/treewalk/WorkingTreeIterator.java
@@ -65,6 +65,8 @@ import java.util.Comparator;
 import org.eclipse.jgit.api.errors.FilterFailedException;
 import org.eclipse.jgit.attributes.AttributesNode;
 import org.eclipse.jgit.attributes.AttributesRule;
+import org.eclipse.jgit.attributes.FilterCommand;
+import org.eclipse.jgit.attributes.FilterCommandRegistry;
 import org.eclipse.jgit.diff.RawText;
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.dircache.DirCacheEntry;
@@ -93,6 +95,8 @@ import org.eclipse.jgit.util.Holder;
 import org.eclipse.jgit.util.IO;
 import org.eclipse.jgit.util.Paths;
 import org.eclipse.jgit.util.RawParseUtils;
+import org.eclipse.jgit.util.TemporaryBuffer;
+import org.eclipse.jgit.util.TemporaryBuffer.LocalFile;
 import org.eclipse.jgit.util.io.AutoLFInputStream;
 import org.eclipse.jgit.util.io.EolStreamTypeUtil;
 
@@ -461,6 +465,16 @@ public abstract class WorkingTreeIterator extends AbstractTreeIterator {
 		in = handleAutoCRLF(in, opType);
 		String filterCommand = getCleanFilterCommand();
 		if (filterCommand != null) {
+			if (FilterCommandRegistry.isRegistered(filterCommand)) {
+				LocalFile buffer = new TemporaryBuffer.LocalFile(null);
+				FilterCommand command = FilterCommandRegistry
+						.createFilterCommand(filterCommand, repository, in,
+								buffer);
+				while (command.run() != -1) {
+					// loop as long as command.run() tells there is work to do
+				}
+				return buffer.openInputStream();
+			}
 			FS fs = repository.getFS();
 			ProcessBuilder filterProcessBuilder = fs.runInShell(filterCommand,
 					new String[0]);