backends/flint/flint_databasereplicator.cc

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/* Copyright 2008 Lemur Consulting Ltd
 * Copyright 2009,2010 Olly Betts
 * Copyright 2010 Richard Boulton
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
 * USA
 */

#include <config.h>

#include "flint_databasereplicator.h"

#include "xapian/error.h"

#include "../flint_lock.h"
#include "flint_record.h"
#include "flint_replicate_internal.h"
#include "flint_types.h"
#include "flint_utils.h"
#include "flint_version.h"
#include "debuglog.h"
#include "io_utils.h"
#include "remoteconnection.h"
#include "replicate_utils.h"
#include "replicationprotocol.h"
#include "safeerrno.h"
#include "str.h"
#include "stringutils.h"
#include "utils.h"

#ifdef __WIN32__
# include "msvc_posix_wrapper.h"
#endif

#include <cstdio> // For rename().

using namespace std;
using namespace Xapian;

FlintDatabaseReplicator::FlintDatabaseReplicator(const string & db_dir_)
        : db_dir(db_dir_),
          max_changesets(0)
{
    const char *p = getenv("XAPIAN_MAX_CHANGESETS");
    if (p)
        max_changesets = atoi(p);
}

bool
FlintDatabaseReplicator::check_revision_at_least(const string & rev,
                                                 const string & target) const
{
    LOGCALL(DB, bool, "FlintDatabaseReplicator::check_revision_at_least", rev | target);

    flint_revision_number_t rev_val;
    flint_revision_number_t target_val;

    const char * ptr = rev.data();
    const char * end = ptr + rev.size();
    if (!F_unpack_uint(&ptr, end, &rev_val)) {
        throw NetworkError("Invalid revision string supplied to check_revision_at_least");
    }

    ptr = target.data();
    end = ptr + target.size();
    if (!F_unpack_uint(&ptr, end, &target_val)) {
        throw NetworkError("Invalid revision string supplied to check_revision_at_least");
    }

    RETURN(rev_val >= target_val);
}

void
FlintDatabaseReplicator::process_changeset_chunk_base(const string & tablename,
                                                      string & buf,
                                                      RemoteConnection & conn,
                                                      double end_time,
                                                      int changes_fd) const
{
    const char *ptr = buf.data();
    const char *end = ptr + buf.size();

    // Get the letter
    char letter = ptr[0];
    if (letter != 'A' && letter != 'B')
        throw NetworkError("Invalid base file letter in changeset");
    ++ptr;


    // Get the base size
    if (ptr == end)
        throw NetworkError("Unexpected end of changeset (5)");
    string::size_type base_size;
    if (!F_unpack_uint(&ptr, end, &base_size))
        throw NetworkError("Invalid base file size in changeset");

    // Get the new base file into buf.
    write_and_clear_changes(changes_fd, buf, ptr - buf.data());
    conn.get_message_chunk(buf, base_size, end_time);

    if (buf.size() < base_size)
        throw NetworkError("Unexpected end of changeset (6)");

    // Write base_size bytes from start of buf to base file for tablename
    string tmp_path = db_dir + "/" + tablename + "tmp";
    string base_path = db_dir + "/" + tablename + ".base" + letter;
#ifdef __WIN32__
    int fd = msvc_posix_open(tmp_path.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_BINARY);
#else
    int fd = ::open(tmp_path.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0666);
#endif
    if (fd == -1) {
        string msg = "Failed to open ";
        msg += tmp_path;
        throw DatabaseError(msg, errno);
    }
    {
        fdcloser closer(fd);

        io_write(fd, buf.data(), base_size);
        io_sync(fd);
    }

    // Finish writing the changeset before moving the base file into place.
    write_and_clear_changes(changes_fd, buf, base_size);

#if defined __WIN32__
    if (msvc_posix_rename(tmp_path.c_str(), base_path.c_str()) < 0) {
#else
    if (rename(tmp_path.c_str(), base_path.c_str()) < 0) {
#endif
        // With NFS, rename() failing may just mean that the server crashed
        // after successfully renaming, but before reporting this, and then
        // the retried operation fails.  So we need to check if the source
        // file still exists, which we do by calling unlink(), since we want
        // to remove the temporary file anyway.
        int saved_errno = errno;
        if (unlink(tmp_path) == 0 || errno != ENOENT) {
            string msg("Couldn't update base file ");
            msg += tablename;
            msg += ".base";
            msg += letter;
            throw DatabaseError(msg, saved_errno);
        }
    }
}

void
FlintDatabaseReplicator::process_changeset_chunk_blocks(const string & tablename,
                                                        string & buf,
                                                        RemoteConnection & conn,
                                                        double end_time,
                                                        int changes_fd) const
{
    const char *ptr = buf.data();
    const char *end = ptr + buf.size();

    unsigned int changeset_blocksize;
    if (!F_unpack_uint(&ptr, end, &changeset_blocksize))
        throw NetworkError("Invalid blocksize in changeset");
    write_and_clear_changes(changes_fd, buf, ptr - buf.data());

    string db_path = db_dir + "/" + tablename + ".DB";
#ifdef __WIN32__
    int fd = msvc_posix_open(db_path.c_str(), O_WRONLY | O_BINARY);
#else
    int fd = ::open(db_path.c_str(), O_WRONLY | O_BINARY, 0666);
#endif
    if (fd == -1) {
        if (file_exists(db_path)) {
            string msg = "Failed to open ";
            msg += db_path;
            throw DatabaseError(msg, errno);
        }
#ifdef __WIN32__
        fd = msvc_posix_open(db_path.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_BINARY);
#else
        fd = ::open(db_path.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0666);
#endif
        if (fd == -1) {
            string msg = "Failed to create and open ";
            msg += db_path;
            throw DatabaseError(msg, errno);
        }
    }
    {
        fdcloser closer(fd);

        while (true) {
            conn.get_message_chunk(buf, REASONABLE_CHANGESET_SIZE, end_time);
            ptr = buf.data();
            end = ptr + buf.size();

            uint4 block_number;
            if (!F_unpack_uint(&ptr, end, &block_number))
                throw NetworkError("Invalid block number in changeset");
            write_and_clear_changes(changes_fd, buf, ptr - buf.data());
            if (block_number == 0)
                break;
            --block_number;

            conn.get_message_chunk(buf, changeset_blocksize, end_time);
            if (buf.size() < changeset_blocksize)
                throw NetworkError("Incomplete block in changeset");

            // Write the block.
            // FIXME - should use pwrite if that's available.
            if (lseek(fd, off_t(changeset_blocksize) * block_number, SEEK_SET) == -1) {
                string msg = "Failed to seek to block ";
                msg += str(block_number);
                throw DatabaseError(msg, errno);
            }
            io_write(fd, buf.data(), changeset_blocksize);

            write_and_clear_changes(changes_fd, buf, changeset_blocksize);
        }
        io_sync(fd);
    }
}

string
FlintDatabaseReplicator::apply_changeset_from_conn(RemoteConnection & conn,
                                                   double end_time,
                                                   bool valid) const
{
    LOGCALL(DB, string, "FlintDatabaseReplicator::apply_changeset_from_conn", conn | end_time | valid);

    // Lock the database to perform modifications.
    FlintLock lock(db_dir);
    string explanation;
    FlintLock::reason why = lock.lock(true, explanation);
    if (why != FlintLock::SUCCESS) {
        lock.throw_databaselockerror(why, db_dir, explanation);
    }

    char type = conn.get_message_chunked(end_time);
    (void) type; // Don't give warning about unused variable.
    AssertEq(type, REPL_REPLY_CHANGESET);

    string buf;
    // Read enough to be certain that we've got the header part of the
    // changeset.

    conn.get_message_chunk(buf, REASONABLE_CHANGESET_SIZE, end_time);
    // Check the magic string.
    if (!startswith(buf, CHANGES_MAGIC_STRING)) {
        throw NetworkError("Invalid ChangeSet magic string");
    }
    const char *ptr = buf.data();
    const char *end = ptr + buf.size();
    ptr += CONST_STRLEN(CHANGES_MAGIC_STRING);

    unsigned int changes_version;
    if (!F_unpack_uint(&ptr, end, &changes_version))
        throw NetworkError("Couldn't read a valid version number from changeset");
    if (changes_version != CHANGES_VERSION)
        throw NetworkError("Unsupported changeset version");

    flint_revision_number_t startrev;
    flint_revision_number_t endrev;

    if (!F_unpack_uint(&ptr, end, &startrev))
        throw NetworkError("Couldn't read a valid start revision from changeset");
    if (!F_unpack_uint(&ptr, end, &endrev))
        throw NetworkError("Couldn't read a valid end revision from changeset");

    if (endrev <= startrev)
        throw NetworkError("End revision in changeset is not later than start revision");

    if (ptr == end)
        throw NetworkError("Unexpected end of changeset (1)");

    int changes_fd = -1;
    string changes_name;
    if (max_changesets > 0) {
        changes_fd = create_changeset_file(db_dir, "changes" + str(startrev),
                                           changes_name);
    }
    fdcloser closer(changes_fd);

    if (valid) {
        // Check the revision number.
        // If the database was not known to be valid, we cannot
        // reliably determine its revision number, so must skip this
        // check.
        FlintRecordTable record_table(db_dir, true);
        record_table.open();
        if (startrev != record_table.get_open_revision_number())
            throw NetworkError("Changeset supplied is for wrong revision number");
    }

    unsigned char changes_type = ptr[0];
    if (changes_type != 0) {
        throw NetworkError("Unsupported changeset type: " + str(changes_type));
        // FIXME - support changes of type 1, produced when DANGEROUS mode is
        // on.
    }

    // Write and clear the bits of the buffer which have been read.
    write_and_clear_changes(changes_fd, buf, ptr + 1 - buf.data());

    // Read the items from the changeset.
    while (true) {
        conn.get_message_chunk(buf, REASONABLE_CHANGESET_SIZE, end_time);
        ptr = buf.data();
        end = ptr + buf.size();

        // Read the type of the next chunk of data
        if (ptr == end)
            throw NetworkError("Unexpected end of changeset (2)");
        unsigned char chunk_type = ptr[0];
        ++ptr;
        if (chunk_type == 0)
            break;

        // Get the tablename.
        string tablename;
        if (!F_unpack_string(&ptr, end, tablename))
            throw NetworkError("Unexpected end of changeset (3)");
        if (tablename.empty())
            throw NetworkError("Missing tablename in changeset");
        if (tablename.find_first_not_of("abcdefghijklmnopqrstuvwxyz") !=
            tablename.npos)
            throw NetworkError("Invalid character in tablename in changeset");

        // Process the chunk
        if (ptr == end)
            throw NetworkError("Unexpected end of changeset (4)");
        write_and_clear_changes(changes_fd, buf, ptr - buf.data());

        switch (chunk_type) {
            case 1:
                process_changeset_chunk_base(tablename, buf, conn, end_time,
                                             changes_fd);
                break;
            case 2:
                process_changeset_chunk_blocks(tablename, buf, conn, end_time,
                                               changes_fd);
                break;
            default:
                throw NetworkError("Unrecognised item type in changeset");
        }
    }
    flint_revision_number_t reqrev;
    if (!F_unpack_uint(&ptr, end, &reqrev))
        throw NetworkError("Couldn't read a valid required revision from changeset");
    if (reqrev < endrev)
        throw NetworkError("Required revision in changeset is earlier than end revision");
    if (ptr != end)
        throw NetworkError("Junk found at end of changeset");

    write_and_clear_changes(changes_fd, buf, buf.size());
    buf = F_pack_uint(reqrev);
    RETURN(buf);
}

string
FlintDatabaseReplicator::get_uuid() const
{
    LOGCALL(DB, string, "FlintDatabaseReplicator::get_uuid", NO_ARGS);
    FlintVersion version_file(db_dir);
    try {
        version_file.read_and_check(true);
    } catch (const DatabaseError &) {
        RETURN(string());
    }
    RETURN(version_file.get_uuid_string());
}

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