SshSessionFactory.java

/*
 * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2008, 2020 Shawn O. Pearce <spearce@spearce.org> 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 java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.ServiceLoader;

import org.eclipse.jgit.errors.TransportException;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.util.FS;
import org.eclipse.jgit.util.SystemReader;

/**
 * Creates and destroys SSH connections to a remote system.
 * <p>
 * Different implementations of the session factory may be used to control
 * communicating with the end-user as well as reading their personal SSH
 * configuration settings, such as known hosts and private keys.
 * </p>
 * <p>
 * A {@link RemoteSession} must be returned to the factory that created it.
 * Callers are encouraged to retain the SshSessionFactory for the duration of
 * the period they are using the session.
 * </p>
 */
public abstract class SshSessionFactory {

    private static SshSessionFactory INSTANCE = loadSshSessionFactory();

    private static SshSessionFactory loadSshSessionFactory() {
        ServiceLoader<SshSessionFactory> loader = ServiceLoader.load(SshSessionFactory.class);
        Iterator<SshSessionFactory> iter = loader.iterator();
        if(iter.hasNext()) {
            return iter.next();
        }
        return null;
    }

    /**
     * Gets the currently configured JVM-wide factory.
     * <p>
     * By default the factory will read from the user's {@code $HOME/.ssh} and
     * assume OpenSSH compatibility.
     * </p>
     *
     * @return factory the current factory for this JVM.
     */
    public static SshSessionFactory getInstance() {
        return INSTANCE;
    }

    /**
     * Changes the JVM-wide factory to a different implementation.
     *
     * @param newFactory
     *            factory for future sessions to be created through; if
     *            {@code null} the default factory will be restored.
     */
    public static void setInstance(SshSessionFactory newFactory) {
        if (newFactory != null) {
            INSTANCE = newFactory;
        } else {
            INSTANCE = loadSshSessionFactory();
        }
    }

    /**
     * Retrieves the local user name as defined by the system property
     * "user.name".
     *
     * @return the user name
     * @since 5.2
     */
    public static String getLocalUserName() {
        return AccessController
                .doPrivileged((PrivilegedAction<String>) () -> SystemReader
                        .getInstance().getProperty(Constants.OS_USER_NAME_KEY));
    }

    /**
     * Opens (or reuses) a session to a host. The returned session is connected
     * and authenticated and is ready for further use.
     *
     * @param uri
     *            URI of the remote host to connect to
     * @param credentialsProvider
     *            provider to support authentication, may be {@code null} if no
     *            user input for authentication is needed
     * @param fs
     *            the file system abstraction to use for certain file
     *            operations, such as reading configuration files
     * @param tms
     *            connection timeout for creating the session, in milliseconds
     * @return a connected and authenticated session for communicating with the
     *         remote host given by the {@code uri}
     * @throws org.eclipse.jgit.errors.TransportException
     *             if the session could not be created
     */
    public abstract RemoteSession getSession(URIish uri,
            CredentialsProvider credentialsProvider, FS fs, int tms)
            throws TransportException;

    /**
     * The name of the type of session factory.
     *
     * @return the name of the type of session factory.
     *
     * @since 5.8
     */
    public abstract String getType();

    /**
     * Closes (or recycles) a session to a host.
     *
     * @param session
     *            a session previously obtained from this factory's
     *            {@link #getSession(URIish, CredentialsProvider, FS, int)}
     *            method.
     */
    public void releaseSession(RemoteSession session) {
        session.disconnect();
    }
}