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 * Copyright (C) 2018, Google LLC.
 * 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.
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 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
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 * - Redistributions of source code must retain the above copyright
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package org.eclipse.jgit.internal.transport.parser;

import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import org.eclipse.jgit.annotations.Nullable;
import org.eclipse.jgit.errors.PackProtocolException;
import org.eclipse.jgit.internal.JGitText;

In the pack negotiation phase (protocol v0/v1), the client sends a list of
wants. The first "want" line is special, as it (can) have a list of
capabilities appended.
E.g. "want oid cap1 cap2 cap3"
Do not confuse this line with the first one in the reference advertisement,
which is sent by the server, looks like
"b8f7c471373b8583ced0025cfad8c9916c484b76 HEAD\0 cap1 cap2 cap3" and is
parsed by the BasePackConnection.readAdvertisedRefs method.
This class parses the input want line and holds the results: the actual want
line and the capabilities.
/**
 * In the pack negotiation phase (protocol v0/v1), the client sends a list of
 * wants. The first "want" line is special, as it (can) have a list of
 * capabilities appended.
 *
 * E.g. "want oid cap1 cap2 cap3"
 *
 * Do not confuse this line with the first one in the reference advertisement,
 * which is sent by the server, looks like
 * "b8f7c471373b8583ced0025cfad8c9916c484b76 HEAD\0 cap1 cap2 cap3" and is
 * parsed by the BasePackConnection.readAdvertisedRefs method.
 *
 * This class parses the input want line and holds the results: the actual want
 * line and the capabilities.
 *
 */
public class FirstWant {
	private final String line;

	private final Set<String> capabilities;

	@Nullable
	private final String agent;

	private static final String AGENT_PREFIX = OPTION_AGENT + '=';

	
Parse the first want line in the protocol v0/v1 pack negotiation.
Params:
line – 
           line from the client.
Throws:
PackProtocolException – 
            if the line doesn't follow the protocol format.
Returns:
an instance of FirstWant/**
	 * Parse the first want line in the protocol v0/v1 pack negotiation.
	 *
	 * @param line
	 *            line from the client.
	 * @return an instance of FirstWant
	 * @throws PackProtocolException
	 *             if the line doesn't follow the protocol format.
	 */
	public static FirstWant fromLine(String line) throws PackProtocolException {
		String wantLine;
		Set<String> capabilities;
		String agent = null;

		if (line.length() > 45) {
			String opt = line.substring(45);
			if (!opt.startsWith(" ")) { //$NON-NLS-1$
				throw new PackProtocolException(JGitText.get().wantNoSpaceWithCapabilities);
			}
			opt = opt.substring(1);

			HashSet<String> opts = new HashSet<>();
			for (String clientCapability : opt.split(" ")) { //$NON-NLS-1$
				if (clientCapability.startsWith(AGENT_PREFIX)) {
					agent = clientCapability.substring(AGENT_PREFIX.length());
				} else {
					opts.add(clientCapability);
				}
			}
			wantLine = line.substring(0, 45);
			capabilities = Collections.unmodifiableSet(opts);
		} else {
			wantLine = line;
			capabilities = Collections.emptySet();
		}

		return new FirstWant(wantLine, capabilities, agent);
	}

	private FirstWant(String line, Set<String> capabilities,
			@Nullable String agent) {
		this.line = line;
		this.capabilities = capabilities;
		this.agent = agent;
	}

	
Returns:
non-capabilities part of the line./** @return non-capabilities part of the line. */
	public String getLine() {
		return line;
	}

	
Returns:
capabilities parsed from the line as an immutable set (excluding
        agent)./**
	 * @return capabilities parsed from the line as an immutable set (excluding
	 *         agent).
	 */
	public Set<String> getCapabilities() {
		return capabilities;
	}

	
Returns:
client user agent parsed from the line./** @return client user agent parsed from the line. */
	@Nullable
	public String getAgent() {
		return agent;
	}
}