Switch jgit library to the EDL (3-clause BSD)

[egit/zawir.git] / org.spearce.jgit / src / org / spearce / jgit / transport / WalkRemoteObjectDatabase.java

/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 *
 * 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 Git Development Community 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.spearce.jgit.transport;

import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collection;

import org.spearce.jgit.lib.Constants;
import org.spearce.jgit.util.NB;

/**
 * Transfers object data through a dumb transport.
 * <p>
 * Implementations are responsible for resolving path names relative to the
 * <code>objects/</code> subdirectory of a single remote Git repository or
 * nake object database and make the content available as a Java input stream
 * for reading during fetch. The actual object traversal logic to determine the
 * names of files to retrieve is handled through the generic, protocol
 * independent {@link WalkFetchConnection}.
 */
abstract class WalkRemoteObjectDatabase {
        static final String CHARENC = Constants.CHARACTER_ENCODING;

        static final String INFO_PACKS = "info/packs";

        static final String INFO_ALTERNATES = "info/alternates";

        static final String INFO_HTTP_ALTERNATES = "info/http-alternates";

        /**
         * Obtain the list of available packs (if any).
         * <p>
         * Pack names should be the file name in the packs directory, that is
         * <code>pack-035760ab452d6eebd123add421f253ce7682355a.pack</code>. Index
         * names should not be included in the returned collection.
         * 
         * @return list of pack names; null or empty list if none are available.
         * @throws IOException
         *             The connection is unable to read the remote repository's list
         *             of available pack files.
         */
        abstract Collection<String> getPackNames() throws IOException;

        /**
         * Obtain alternate connections to alternate object databases (if any).
         * <p>
         * Alternates are typically read from the file {@link #INFO_ALTERNATES} or
         * {@link #INFO_HTTP_ALTERNATES}. The content of each line must be resolved
         * by the implementation and a new database reference should be returned to
         * represent the additional location.
         * <p>
         * Alternates may reuse the same network connection handle, however the
         * fetch connection will {@link #close()} each created alternate.
         * 
         * @return list of additional object databases the caller could fetch from;
         *         null or empty list if none are configured.
         * @throws IOException
         *             The connection is unable to read the remote repository's list
         *             of configured alternates.
         */
        abstract Collection<WalkRemoteObjectDatabase> getAlternates()
                        throws IOException;

        /**
         * Open a single file for reading.
         * <p>
         * Implementors should make every attempt possible to ensure
         * {@link FileNotFoundException} is used when the remote object does not
         * exist. However when fetching over HTTP some misconfigured servers may
         * generate a 200 OK status message (rather than a 404 Not Found) with an
         * HTML formatted message explaining the requested resource does not exist.
         * Callers such as {@link WalkFetchConnection} are prepared to handle this
         * by validating the content received, and assuming content that fails to
         * match its hash is an incorrectly phrased FileNotFoundException.
         * 
         * @param path
         *            location of the file to read, relative to this objects
         *            directory (e.g.
         *            <code>cb/95df6ab7ae9e57571511ef451cf33767c26dd2</code> or
         *            <code>pack/pack-035760ab452d6eebd123add421f253ce7682355a.pack</code>).
         * @return a stream to read from the file. Never null.
         * @throws FileNotFoundException
         *             the requested file does not exist at the given location.
         * @throws IOException
         *             The connection is unable to read the remote's file, and the
         *             failure occurred prior to being able to determine if the file
         *             exists, or after it was determined to exist but before the
         *             stream could be created.
         */
        abstract FileStream open(String path) throws FileNotFoundException,
                        IOException;

        /**
         * Create a new connection for a discovered alternate object database
         * <p>
         * This method is typically called by {@link #readAlternates(String)} when
         * subclasses us the generic alternate parsing logic for their
         * implementation of {@link #getAlternates()}.
         * 
         * @param location
         *            the location of the new alternate, relative to the current
         *            object database.
         * @return a new database connection that can read from the specified
         *         alternate.
         * @throws IOException
         *             The database connection cannot be established with the
         *             alternate, such as if the alternate location does not
         *             actually exist and the connection's constructor attempts to
         *             verify that.
         */
        abstract WalkRemoteObjectDatabase openAlternate(String location)
                        throws IOException;

        /**
         * Close any resources used by this connection.
         * <p>
         * If the remote repository is contacted by a network socket this method
         * must close that network socket, disconnecting the two peers. If the
         * remote repository is actually local (same system) this method must close
         * any open file handles used to read the "remote" repository.
         */
        abstract void close();

        /**
         * Open a buffered reader around a file.
         * <p>
         * This is shorthand for calling {@link #open(String)} and then wrapping it
         * in a reader suitable for line oriented files like the alternates list.
         * 
         * @return a stream to read from the file. Never null.
         * @param path
         *            location of the file to read, relative to this objects
         *            directory (e.g. <code>info/packs</code>).
         * @throws FileNotFoundException
         *             the requested file does not exist at the given location.
         * @throws IOException
         *             The connection is unable to read the remote's file, and the
         *             failure occurred prior to being able to determine if the file
         *             exists, or after it was determined to exist but before the
         *             stream could be created.
         */
        BufferedReader openReader(final String path) throws IOException {
                return new BufferedReader(new InputStreamReader(open(path).in, CHARENC));
        }

        /**
         * Read a standard Git alternates file to discover other object databases.
         * <p>
         * This method is suitable for reading the standard formats of the
         * alternates file, such as found in <code>objects/info/alternates</code>
         * or <code>objects/info/http-alternates</code> within a Git repository.
         * <p>
         * Alternates appear one per line, with paths expressed relative to this
         * object database.
         * 
         * @param listPath
         *            location of the alternate file to read, relative to this
         *            object database (e.g. <code>info/alternates</code>).
         * @return the list of discovered alternates. Empty list if the file exists,
         *         but no entries were discovered.
         * @throws FileNotFoundException
         *             the requested file does not exist at the given location.
         * @throws IOException
         *             The connection is unable to read the remote's file, and the
         *             failure occurred prior to being able to determine if the file
         *             exists, or after it was determined to exist but before the
         *             stream could be created.
         */
        Collection<WalkRemoteObjectDatabase> readAlternates(final String listPath)
                        throws IOException {
                final BufferedReader br = openReader(listPath);
                try {
                        final Collection<WalkRemoteObjectDatabase> alts = new ArrayList<WalkRemoteObjectDatabase>();
                        for (;;) {
                                String line = br.readLine();
                                if (line == null)
                                        break;
                                if (!line.endsWith("/"))
                                        line += "/";
                                alts.add(openAlternate(line));
                        }
                        return alts;
                } finally {
                        br.close();
                }
        }

        static final class FileStream {
                final InputStream in;

                final long length;

                /**
                 * Create a new stream of unknown length.
                 * 
                 * @param i
                 *            stream containing the file data. This stream will be
                 *            closed by the caller when reading is complete.
                 */
                FileStream(final InputStream i) {
                        in = i;
                        length = -1;
                }

                /**
                 * Create a new stream of known length.
                 * 
                 * @param i
                 *            stream containing the file data. This stream will be
                 *            closed by the caller when reading is complete.
                 * @param n
                 *            total number of bytes available for reading through
                 *            <code>i</code>.
                 */
                FileStream(final InputStream i, final long n) {
                        in = i;
                        length = n;
                }

                byte[] toArray() throws IOException {
                        try {
                                if (length >= 0) {
                                        final byte[] r = new byte[(int) length];
                                        NB.readFully(in, r, 0, r.length);
                                        return r;
                                }

                                final ByteArrayOutputStream r = new ByteArrayOutputStream();
                                final byte[] buf = new byte[2048];
                                int n;
                                while ((n = in.read(buf)) >= 0)
                                        r.write(buf, 0, n);
                                return r.toByteArray();
                        } finally {
                                in.close();
                        }
                }
        }
}