org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java - jgit - Git at Google

 /*
  * Copyright (C) 2008, 2020 Google Inc. 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
  * https://www.eclipse.org/org/documents/edl-v10.php.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */

 package org.eclipse.jgit.transport;

 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SYMREF;
 import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_PEELED;
 import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_SYMREF_TARGET;

 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.CharBuffer;
 import java.nio.charset.CharacterCodingException;
 import java.nio.charset.CharsetEncoder;
 import java.nio.charset.CoderResult;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;

 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.RefComparator;
 import org.eclipse.jgit.lib.Repository;

 /**
  * Support for the start of {@link org.eclipse.jgit.transport.UploadPack} and
  * {@link org.eclipse.jgit.transport.ReceivePack}.
  */
 public abstract class RefAdvertiser {
 	/** Advertiser which frames lines in a {@link PacketLineOut} format. */
 	public static class PacketLineOutRefAdvertiser extends RefAdvertiser {
 		private final CharsetEncoder utf8 = UTF_8.newEncoder();
 		private final PacketLineOut pckOut;

 		private byte[] binArr = new byte[256];
 		private ByteBuffer binBuf = ByteBuffer.wrap(binArr);

 		private char[] chArr = new char[256];
 		private CharBuffer chBuf = CharBuffer.wrap(chArr);

 		/**
 		 * Create a new advertiser for the supplied stream.
 		 *
 		 * @param out
 		 *            the output stream.
 		 */
 		public PacketLineOutRefAdvertiser(PacketLineOut out) {
 			pckOut = out;
 		}

 		@Override
 		public void advertiseId(AnyObjectId id, String refName)
 				throws IOException {
 			id.copyTo(binArr, 0);
 			binArr[OBJECT_ID_STRING_LENGTH] = ' ';
 			binBuf.position(OBJECT_ID_STRING_LENGTH + 1);
 			append(refName);
 			if (first) {
 				first = false;
 				if (!capablities.isEmpty()) {
 					append('\0');
 					for (String cap : capablities) {
 						append(' ');
 						append(cap);
 					}
 				}
 			}
 			append('\n');
 			pckOut.writePacket(binArr, 0, binBuf.position());
 		}

 		private void append(String str) throws CharacterCodingException {
 			int n = str.length();
 			if (n > chArr.length) {
 				chArr = new char[n + 256];
 				chBuf = CharBuffer.wrap(chArr);
 			}
 			str.getChars(0, n, chArr, 0);
 			chBuf.position(0).limit(n);
 			utf8.reset();
 			for (;;) {
 				CoderResult cr = utf8.encode(chBuf, binBuf, true);
 				if (cr.isOverflow()) {
 					grow();
 				} else if (cr.isUnderflow()) {
 					break;
 				} else {
 					cr.throwException();
 				}
 			}
 		}

 		private void append(int b) {
 			if (!binBuf.hasRemaining()) {
 				grow();
 			}
 			binBuf.put((byte) b);
 		}

 		private void grow() {
 			int cnt = binBuf.position();
 			byte[] tmp = new byte[binArr.length << 1];
 			System.arraycopy(binArr, 0, tmp, 0, cnt);
 			binArr = tmp;
 			binBuf = ByteBuffer.wrap(binArr);
 			binBuf.position(cnt);
 		}

 		@Override
 		protected void writeOne(CharSequence line) throws IOException {
 			pckOut.writeString(line.toString());
 		}

 		@Override
 		protected void end() throws IOException {
 			pckOut.end();
 		}
 	}

 	private final StringBuilder tmpLine = new StringBuilder(100);

 	private final char[] tmpId = new char[Constants.OBJECT_ID_STRING_LENGTH];

 	final Set<String> capablities = new LinkedHashSet<>();

 	private final Set<ObjectId> sent = new HashSet<>();

 	private Repository repository;

 	private boolean derefTags;

 	boolean first = true;

 	private boolean useProtocolV2;

 	/* only used in protocol v2 */
 	private final Map<String, String> symrefs = new HashMap<>();

 	/**
 	 * Initialize this advertiser with a repository for peeling tags.
 	 *
 	 * @param src
 	 *            the repository to read from.
 	 */
 	public void init(Repository src) {
 		repository = src;
 	}

 	/**
 	 * Set whether this advertiser should use protocol v2
 	 *
 	 * @param b
 	 *            true if this advertiser should advertise using the protocol v2
 	 *            format, false otherwise
 	 * @since 5.0
 	 */
 	public void setUseProtocolV2(boolean b) {
 		useProtocolV2 = b;
 	}

 	/**
 	 * Toggle tag peeling.
 	 * <p>
 	 *
 	 * This method must be invoked prior to any of the following:
 	 * <ul>
 	 * <li>{@link #send(Map)}</li>
 	 * <li>{@link #send(Collection)}</li>
 	 * </ul>
 	 *
 	 * @param deref
 	 *            true to show the dereferenced value of a tag as the special
 	 *            ref <code>$tag^{}</code> ; false to omit it from the output.
 	 */
 	public void setDerefTags(boolean deref) {
 		derefTags = deref;
 	}

 	/**
 	 * Add one protocol capability to the initial advertisement.
 	 * <p>
 	 * This method must be invoked prior to any of the following:
 	 * <ul>
 	 * <li>{@link #send(Map)}</li>
 	 * <li>{@link #send(Collection)}</li>
 	 * <li>{@link #advertiseHave(AnyObjectId)}</li>
 	 * </ul>
 	 *
 	 * @param name
 	 *            the name of a single protocol capability supported by the
 	 *            caller. The set of capabilities are sent to the client in the
 	 *            advertisement, allowing the client to later selectively enable
 	 *            features it recognizes.
 	 */
 	public void advertiseCapability(String name) {
 		capablities.add(name);
 	}

 	/**
 	 * Add one protocol capability with a value ({@code "name=value"}).
 	 *
 	 * @param name
 	 *            name of the capability.
 	 * @param value
 	 *            value. If null the capability will not be added.
 	 * @since 4.0
 	 */
 	public void advertiseCapability(String name, String value) {
 		if (value != null) {
 			capablities.add(name + '=' + value);
 		}
 	}

 	/**
 	 * Add a symbolic ref to capabilities.
 	 * <p>
 	 * This method must be invoked prior to any of the following:
 	 * <ul>
 	 * <li>{@link #send(Map)}</li>
 	 * <li>{@link #send(Collection)}</li>
 	 * <li>{@link #advertiseHave(AnyObjectId)}</li>
 	 * </ul>
 	 *
 	 * @param from
 	 *            The symbolic ref, e.g. "HEAD"
 	 * @param to
 	 *            The real ref it points to, e.g. "refs/heads/master"
 	 * @since 3.6
 	 */
 	public void addSymref(String from, String to) {
 		if (useProtocolV2) {
 			symrefs.put(from, to);
 		} else {
 			advertiseCapability(OPTION_SYMREF, from + ':' + to);
 		}
 	}

 	/**
 	 * Format an advertisement for the supplied refs.
 	 *
 	 * @param refs
 	 *            zero or more refs to format for the client. The collection is
 	 *            sorted before display if necessary, and therefore may appear
 	 *            in any order.
 	 * @return set of ObjectIds that were advertised to the client.
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 * @deprecated use {@link #send(Collection)} instead.
 	 */
 	@Deprecated
 	public Set<ObjectId> send(Map<String, Ref> refs) throws IOException {
 		return send(refs.values());
 	}

 	/**
 	 * Format an advertisement for the supplied refs.
 	 *
 	 * @param refs
 	 *            zero or more refs to format for the client. The collection is
 	 *            sorted before display if necessary, and therefore may appear
 	 *            in any order.
 	 * @return set of ObjectIds that were advertised to the client.
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 * @since 5.0
 	 */
 	public Set<ObjectId> send(Collection<Ref> refs) throws IOException {
 		for (Ref ref : RefComparator.sort(refs)) {
 			// TODO(jrn) revive the SortedMap optimization e.g. by introducing
 			// SortedList
 			ObjectId objectId = ref.getObjectId();
 			if (objectId == null) {
 				continue;
 			}

 			if (useProtocolV2) {
 				String symrefPart = symrefs.containsKey(ref.getName())
 						? (' ' + REF_ATTR_SYMREF_TARGET
 								+ symrefs.get(ref.getName()))
 						: ""; //$NON-NLS-1$
 				String peelPart = ""; //$NON-NLS-1$
 				if (derefTags) {
 					if (!ref.isPeeled() && repository != null) {
 						ref = repository.getRefDatabase().peel(ref);
 					}
 					ObjectId peeledObjectId = ref.getPeeledObjectId();
 					if (peeledObjectId != null) {
 						peelPart = ' ' + REF_ATTR_PEELED
 								+ peeledObjectId.getName();
 					}
 				}
 				writeOne(objectId.getName() + " " + ref.getName() + symrefPart //$NON-NLS-1$
 						+ peelPart + "\n"); //$NON-NLS-1$
 				continue;
 			}

 			advertiseAny(objectId, ref.getName());

 			if (!derefTags)
 				continue;

 			if (!ref.isPeeled()) {
 				if (repository == null)
 					continue;
 				ref = repository.getRefDatabase().peel(ref);
 			}

 			if (ref.getPeeledObjectId() != null)
 				advertiseAny(ref.getPeeledObjectId(), ref.getName() + "^{}"); //$NON-NLS-1$
 		}
 		return sent;
 	}

 	/**
 	 * Advertise one object is available using the magic {@code .have}.
 	 * <p>
 	 * The magic {@code .have} advertisement is not available for fetching by a
 	 * client, but can be used by a client when considering a delta base
 	 * candidate before transferring data in a push. Within the record created
 	 * by this method the ref name is simply the invalid string {@code .have}.
 	 *
 	 * @param id
 	 *            identity of the object that is assumed to exist.
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 */
 	public void advertiseHave(AnyObjectId id) throws IOException {
 		advertiseAnyOnce(id, ".have"); //$NON-NLS-1$
 	}

 	/**
 	 * Whether no advertisements have been sent yet.
 	 *
 	 * @return true if no advertisements have been sent yet.
 	 */
 	public boolean isEmpty() {
 		return first;
 	}

 	private void advertiseAnyOnce(AnyObjectId obj, String refName)
 			throws IOException {
 		if (!sent.contains(obj))
 			advertiseAny(obj, refName);
 	}

 	private void advertiseAny(AnyObjectId obj, String refName)
 			throws IOException {
 		sent.add(obj.toObjectId());
 		advertiseId(obj, refName);
 	}

 	/**
 	 * Advertise one object under a specific name.
 	 * <p>
 	 * If the advertised object is a tag, this method does not advertise the
 	 * peeled version of it.
 	 *
 	 * @param id
 	 *            the object to advertise.
 	 * @param refName
 	 *            name of the reference to advertise the object as, can be any
 	 *            string not including the NUL byte.
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 */
 	public void advertiseId(AnyObjectId id, String refName)
 			throws IOException {
 		tmpLine.setLength(0);
 		id.copyTo(tmpId, tmpLine);
 		tmpLine.append(' ');
 		tmpLine.append(refName);
 		if (first) {
 			first = false;
 			if (!capablities.isEmpty()) {
 				tmpLine.append('\0');
 				for (String capName : capablities) {
 					tmpLine.append(' ');
 					tmpLine.append(capName);
 				}
 				tmpLine.append(' ');
 			}
 		}
 		tmpLine.append('\n');
 		writeOne(tmpLine);
 	}

 	/**
 	 * Write a single advertisement line.
 	 *
 	 * @param line
 	 *            the advertisement line to be written. The line always ends
 	 *            with LF. Never null or the empty string.
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 */
 	protected abstract void writeOne(CharSequence line) throws IOException;

 	/**
 	 * Mark the end of the advertisements.
 	 *
 	 * @throws java.io.IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 */
 	protected abstract void end() throws IOException;
 }
	/*
	* Copyright (C) 2008, 2020 Google Inc. 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
	* https://www.eclipse.org/org/documents/edl-v10.php.
	*
	* SPDX-License-Identifier: BSD-3-Clause
	*/

	package org.eclipse.jgit.transport;

	import static java.nio.charset.StandardCharsets.UTF_8;
	import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
	import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SYMREF;
	import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_PEELED;
	import static org.eclipse.jgit.transport.GitProtocolConstants.REF_ATTR_SYMREF_TARGET;

	import java.io.IOException;
	import java.nio.ByteBuffer;
	import java.nio.CharBuffer;
	import java.nio.charset.CharacterCodingException;
	import java.nio.charset.CharsetEncoder;
	import java.nio.charset.CoderResult;
	import java.util.Collection;
	import java.util.HashMap;
	import java.util.HashSet;
	import java.util.LinkedHashSet;
	import java.util.Map;
	import java.util.Set;

	import org.eclipse.jgit.lib.AnyObjectId;
	import org.eclipse.jgit.lib.Constants;
	import org.eclipse.jgit.lib.ObjectId;
	import org.eclipse.jgit.lib.Ref;
	import org.eclipse.jgit.lib.RefComparator;
	import org.eclipse.jgit.lib.Repository;

	/**
	* Support for the start of {@link org.eclipse.jgit.transport.UploadPack} and
	* {@link org.eclipse.jgit.transport.ReceivePack}.
	*/
	public abstract class RefAdvertiser {
	/** Advertiser which frames lines in a {@link PacketLineOut} format. */
	public static class PacketLineOutRefAdvertiser extends RefAdvertiser {
	private final CharsetEncoder utf8 = UTF_8.newEncoder();
	private final PacketLineOut pckOut;

	private byte[] binArr = new byte[256];
	private ByteBuffer binBuf = ByteBuffer.wrap(binArr);

	private char[] chArr = new char[256];
	private CharBuffer chBuf = CharBuffer.wrap(chArr);

	/**
	* Create a new advertiser for the supplied stream.
	*
	* @param out
	* the output stream.
	*/
	public PacketLineOutRefAdvertiser(PacketLineOut out) {
	pckOut = out;
	}

	@Override
	public void advertiseId(AnyObjectId id, String refName)
	throws IOException {
	id.copyTo(binArr, 0);
	binArr[OBJECT_ID_STRING_LENGTH] = ' ';
	binBuf.position(OBJECT_ID_STRING_LENGTH + 1);
	append(refName);
	if (first) {
	first = false;
	if (!capablities.isEmpty()) {
	append('\0');
	for (String cap : capablities) {
	append(' ');
	append(cap);
	}
	}
	}
	append('\n');
	pckOut.writePacket(binArr, 0, binBuf.position());
	}

	private void append(String str) throws CharacterCodingException {
	int n = str.length();
	if (n > chArr.length) {
	chArr = new char[n + 256];
	chBuf = CharBuffer.wrap(chArr);
	}
	str.getChars(0, n, chArr, 0);
	chBuf.position(0).limit(n);
	utf8.reset();
	for (;;) {
	CoderResult cr = utf8.encode(chBuf, binBuf, true);
	if (cr.isOverflow()) {
	grow();
	} else if (cr.isUnderflow()) {
	break;
	} else {
	cr.throwException();
	}
	}
	}

	private void append(int b) {
	if (!binBuf.hasRemaining()) {
	grow();
	}
	binBuf.put((byte) b);
	}

	private void grow() {
	int cnt = binBuf.position();
	byte[] tmp = new byte[binArr.length << 1];
	System.arraycopy(binArr, 0, tmp, 0, cnt);
	binArr = tmp;
	binBuf = ByteBuffer.wrap(binArr);
	binBuf.position(cnt);
	}

	@Override
	protected void writeOne(CharSequence line) throws IOException {
	pckOut.writeString(line.toString());
	}

	@Override
	protected void end() throws IOException {
	pckOut.end();
	}
	}

	private final StringBuilder tmpLine = new StringBuilder(100);

	private final char[] tmpId = new char[Constants.OBJECT_ID_STRING_LENGTH];

	final Set<String> capablities = new LinkedHashSet<>();

	private final Set<ObjectId> sent = new HashSet<>();

	private Repository repository;

	private boolean derefTags;

	boolean first = true;

	private boolean useProtocolV2;

	/* only used in protocol v2 */
	private final Map<String, String> symrefs = new HashMap<>();

	/**
	* Initialize this advertiser with a repository for peeling tags.
	*
	* @param src
	* the repository to read from.
	*/
	public void init(Repository src) {
	repository = src;
	}

	/**
	* Set whether this advertiser should use protocol v2
	*
	* @param b
	* true if this advertiser should advertise using the protocol v2
	* format, false otherwise
	* @since 5.0
	*/
	public void setUseProtocolV2(boolean b) {
	useProtocolV2 = b;
	}

	/**
	* Toggle tag peeling.
	* <p>
	*
	* This method must be invoked prior to any of the following:
	* <ul>
	* <li>{@link #send(Map)}</li>
	* <li>{@link #send(Collection)}</li>
	* </ul>
	*
	* @param deref
	* true to show the dereferenced value of a tag as the special
	* ref <code>$tag^{}</code> ; false to omit it from the output.
	*/
	public void setDerefTags(boolean deref) {
	derefTags = deref;
	}

	/**
	* Add one protocol capability to the initial advertisement.
	* <p>
	* This method must be invoked prior to any of the following:
	* <ul>
	* <li>{@link #send(Map)}</li>
	* <li>{@link #send(Collection)}</li>
	* <li>{@link #advertiseHave(AnyObjectId)}</li>
	* </ul>
	*
	* @param name
	* the name of a single protocol capability supported by the
	* caller. The set of capabilities are sent to the client in the
	* advertisement, allowing the client to later selectively enable
	* features it recognizes.
	*/
	public void advertiseCapability(String name) {
	capablities.add(name);
	}

	/**
	* Add one protocol capability with a value ({@code "name=value"}).
	*
	* @param name
	* name of the capability.
	* @param value
	* value. If null the capability will not be added.
	* @since 4.0
	*/
	public void advertiseCapability(String name, String value) {
	if (value != null) {
	capablities.add(name + '=' + value);
	}
	}

	/**
	* Add a symbolic ref to capabilities.
	* <p>
	* This method must be invoked prior to any of the following:
	* <ul>
	* <li>{@link #send(Map)}</li>
	* <li>{@link #send(Collection)}</li>
	* <li>{@link #advertiseHave(AnyObjectId)}</li>
	* </ul>
	*
	* @param from
	* The symbolic ref, e.g. "HEAD"
	* @param to
	* The real ref it points to, e.g. "refs/heads/master"
	* @since 3.6
	*/
	public void addSymref(String from, String to) {
	if (useProtocolV2) {
	symrefs.put(from, to);
	} else {
	advertiseCapability(OPTION_SYMREF, from + ':' + to);
	}
	}

	/**
	* Format an advertisement for the supplied refs.
	*
	* @param refs
	* zero or more refs to format for the client. The collection is
	* sorted before display if necessary, and therefore may appear
	* in any order.
	* @return set of ObjectIds that were advertised to the client.
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	* @deprecated use {@link #send(Collection)} instead.
	*/
	@Deprecated
	public Set<ObjectId> send(Map<String, Ref> refs) throws IOException {
	return send(refs.values());
	}

	/**
	* Format an advertisement for the supplied refs.
	*
	* @param refs
	* zero or more refs to format for the client. The collection is
	* sorted before display if necessary, and therefore may appear
	* in any order.
	* @return set of ObjectIds that were advertised to the client.
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	* @since 5.0
	*/
	public Set<ObjectId> send(Collection<Ref> refs) throws IOException {
	for (Ref ref : RefComparator.sort(refs)) {
	// TODO(jrn) revive the SortedMap optimization e.g. by introducing
	// SortedList
	ObjectId objectId = ref.getObjectId();
	if (objectId == null) {
	continue;
	}

	if (useProtocolV2) {
	String symrefPart = symrefs.containsKey(ref.getName())
	? (' ' + REF_ATTR_SYMREF_TARGET
	+ symrefs.get(ref.getName()))
	: ""; //$NON-NLS-1$
	String peelPart = ""; //$NON-NLS-1$
	if (derefTags) {
	if (!ref.isPeeled() && repository != null) {
	ref = repository.getRefDatabase().peel(ref);
	}
	ObjectId peeledObjectId = ref.getPeeledObjectId();
	if (peeledObjectId != null) {
	peelPart = ' ' + REF_ATTR_PEELED
	+ peeledObjectId.getName();
	}
	}
	writeOne(objectId.getName() + " " + ref.getName() + symrefPart //$NON-NLS-1$
	+ peelPart + "\n"); //$NON-NLS-1$
	continue;
	}

	advertiseAny(objectId, ref.getName());

	if (!derefTags)
	continue;

	if (!ref.isPeeled()) {
	if (repository == null)
	continue;
	ref = repository.getRefDatabase().peel(ref);
	}

	if (ref.getPeeledObjectId() != null)
	advertiseAny(ref.getPeeledObjectId(), ref.getName() + "^{}"); //$NON-NLS-1$
	}
	return sent;
	}

	/**
	* Advertise one object is available using the magic {@code .have}.
	* <p>
	* The magic {@code .have} advertisement is not available for fetching by a
	* client, but can be used by a client when considering a delta base
	* candidate before transferring data in a push. Within the record created
	* by this method the ref name is simply the invalid string {@code .have}.
	*
	* @param id
	* identity of the object that is assumed to exist.
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	*/
	public void advertiseHave(AnyObjectId id) throws IOException {
	advertiseAnyOnce(id, ".have"); //$NON-NLS-1$
	}

	/**
	* Whether no advertisements have been sent yet.
	*
	* @return true if no advertisements have been sent yet.
	*/
	public boolean isEmpty() {
	return first;
	}

	private void advertiseAnyOnce(AnyObjectId obj, String refName)
	throws IOException {
	if (!sent.contains(obj))
	advertiseAny(obj, refName);
	}

	private void advertiseAny(AnyObjectId obj, String refName)
	throws IOException {
	sent.add(obj.toObjectId());
	advertiseId(obj, refName);
	}

	/**
	* Advertise one object under a specific name.
	* <p>
	* If the advertised object is a tag, this method does not advertise the
	* peeled version of it.
	*
	* @param id
	* the object to advertise.
	* @param refName
	* name of the reference to advertise the object as, can be any
	* string not including the NUL byte.
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	*/
	public void advertiseId(AnyObjectId id, String refName)
	throws IOException {
	tmpLine.setLength(0);
	id.copyTo(tmpId, tmpLine);
	tmpLine.append(' ');
	tmpLine.append(refName);
	if (first) {
	first = false;
	if (!capablities.isEmpty()) {
	tmpLine.append('\0');
	for (String capName : capablities) {
	tmpLine.append(' ');
	tmpLine.append(capName);
	}
	tmpLine.append(' ');
	}
	}
	tmpLine.append('\n');
	writeOne(tmpLine);
	}

	/**
	* Write a single advertisement line.
	*
	* @param line
	* the advertisement line to be written. The line always ends
	* with LF. Never null or the empty string.
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	*/
	protected abstract void writeOne(CharSequence line) throws IOException;

	/**
	* Mark the end of the advertisements.
	*
	* @throws java.io.IOException
	* the underlying output stream failed to write out an
	* advertisement record.
	*/
	protected abstract void end() throws IOException;
	}