UserAgent.java

/*
 * Copyright (C) 2015, 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 org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;

import java.util.Set;

import org.eclipse.jgit.util.StringUtils;

/**
 * User agent to be reported by this JGit client and server on the network.
 * <p>
 * On HTTP transports this user agent string is always supplied by the JGit
 * client in the {@code User-Agent} HTTP header.
 * <p>
 * On native transports this user agent string is always sent when JGit is a
 * server. When JGit is a client the user agent string will be supplied to the
 * remote server only if the remote server advertises its own agent identity.
 *
 * @since 4.0
 */
public class UserAgent {
    private static volatile String userAgent = computeUserAgent();

    private static String computeUserAgent() {
        return clean("JGit/" + computeVersion()); //$NON-NLS-1$
    }

    private static String computeVersion() {
        Package pkg = UserAgent.class.getPackage();
        if (pkg != null) {
            String ver = pkg.getImplementationVersion();
            if (!StringUtils.isEmptyOrNull(ver)) {
                return ver;
            }
        }
        return "unknown"; //$NON-NLS-1$
    }

    static String clean(String s) {
        s = s.trim();
        StringBuilder b = new StringBuilder(s.length());
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c <= 32 || c >= 127) {
                if (b.length() > 0 && b.charAt(b.length() - 1) == '.')
                    continue;
                c = '.';
            }
            b.append(c);
        }
        return b.length() > 0 ? b.toString() : null;
    }

    /**
     * Get the user agent string advertised by JGit.
     *
     * @return a string similar to {@code "JGit/4.0"}; null if the agent has
     *         been cleared and should not be shared with a peer.
     */
    public static String get() {
        return userAgent;
    }

    /**
     * Change the user agent string advertised by JGit.
     * <p>
     * The new string should start with {@code "JGit/"} (for example
     * {@code "JGit/4.0"}) to advertise the implementation as JGit based.
     * <p>
     * Spaces and other whitespace should be avoided as these will be
     * automatically converted to {@code "."}.
     * <p>
     * User agent strings are restricted to printable ASCII.
     *
     * @param agent
     *            new user agent string for this running JGit library. Setting
     *            to null or empty string will avoid sending any identification
     *            to the peer.
     */
    public static void set(String agent) {
        userAgent = StringUtils.isEmptyOrNull(agent) ? null : clean(agent);
    }

    /**
     *
     * @param options
     * @param transportAgent
     * @return The transport agent.
     * @deprecated Capabilities with <key>=<value> shape are now parsed
     *             alongside other capabilities in the ReceivePack flow.
     */
    @Deprecated
    static String getAgent(Set<String> options, String transportAgent) {
        if (options == null || options.isEmpty()) {
            return transportAgent;
        }
        for (String o : options) {
            if (o.startsWith(OPTION_AGENT)
                    && o.length() > OPTION_AGENT.length()
                    && o.charAt(OPTION_AGENT.length()) == '=') {
                return o.substring(OPTION_AGENT.length() + 1);
            }
        }
        return transportAgent;
    }

    /**
     *
     * @param options
     * @return True if the transport agent is set. False otherwise.
     * @deprecated Capabilities with <key>=<value> shape are now parsed
     *             alongside other capabilities in the ReceivePack flow.
     */
    @Deprecated
    static boolean hasAgent(Set<String> options) {
        return getAgent(options, null) != null;
    }

    private UserAgent() {
    }
}