chert_version.cc

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/* Copyright (C) 2006,2007,2008,2009,2013 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 <xapian/error.h>

#include "chert_version.h"
#include "io_utils.h"
#include "stringutils.h" // For STRINGIZE() and CONST_STRLEN().
#include "str.h"

#include <cerrno>
#include <cstring> // For memcmp() and memcpy().
#include <string>

#include "backends/uuids.h"

using namespace std;

// YYYYMMDDX where X allows multiple format revisions in a day
#define CHERT_VERSION 200912150
// 200804180       Chert debuts.
// 200903070 1.1.0 doclen bounds and wdf upper bound.
// 200912150 1.1.4 shorter position, postlist, record and termlist keys.

#define MAGIC_STRING "IAmChert"

#define MAGIC_LEN CONST_STRLEN(MAGIC_STRING)
// 4 for the version number; 16 for the UUID.
#define VERSIONFILE_SIZE (MAGIC_LEN + 4 + 16)

// Literal version of VERSIONFILE_SIZE, used for error message.  This needs
// to be updated by hand should VERSIONFILE_SIZE change, but that rarely
// happens so this isn't an onerous requirement.
#define VERSIONFILE_SIZE_LITERAL 28

void
ChertVersion::create()
{
    char buf[VERSIONFILE_SIZE] = MAGIC_STRING;
    unsigned char *v = reinterpret_cast<unsigned char *>(buf) + MAGIC_LEN;
    v[0] = static_cast<unsigned char>(CHERT_VERSION & 0xff);
    v[1] = static_cast<unsigned char>((CHERT_VERSION >> 8) & 0xff);
    v[2] = static_cast<unsigned char>((CHERT_VERSION >> 16) & 0xff);
    v[3] = static_cast<unsigned char>((CHERT_VERSION >> 24) & 0xff);

    uuid.generate();
    memcpy(buf + MAGIC_LEN + 4, uuid.data(), 16);

    int fd = ::open(filename.c_str(), O_WRONLY|O_CREAT|O_TRUNC|O_BINARY|O_CLOEXEC, 0666);

    if (fd < 0) {
        string msg("Failed to create chert version file: ");
        msg += filename;
        throw Xapian::DatabaseOpeningError(msg, errno);
    }

    try {
        io_write(fd, buf, VERSIONFILE_SIZE);
    } catch (...) {
        (void)close(fd);
        throw;
    }

    io_sync(fd);
    if (close(fd) != 0) {
        string msg("Failed to create chert version file: ");
        msg += filename;
        throw Xapian::DatabaseOpeningError(msg, errno);
    }
}

void
ChertVersion::read_and_check()
{
    int fd = ::open(filename.c_str(), O_RDONLY|O_BINARY|O_CLOEXEC);

    if (fd < 0) {
        string msg = filename;
        msg += ": Failed to open chert version file for reading";
        if (errno == ENOENT || errno == ENOTDIR) {
            throw Xapian::DatabaseNotFoundError(msg, errno);
        }
        throw Xapian::DatabaseOpeningError(msg, errno);
    }

    // Try to read an extra byte so we know if the file is too long.
    char buf[VERSIONFILE_SIZE + 1];
    size_t size;
    try {
        size = io_read(fd, buf, VERSIONFILE_SIZE + 1);
    } catch (...) {
        (void)close(fd);
        throw;
    }
    (void)close(fd);

    if (size != VERSIONFILE_SIZE) {
        static_assert(VERSIONFILE_SIZE == VERSIONFILE_SIZE_LITERAL,
                      "VERSIONFILE_SIZE_LITERAL needs updating");
        string msg = filename;
        msg += ": Chert version file should be "
               STRINGIZE(VERSIONFILE_SIZE_LITERAL)" bytes, actually ";
        msg += str(size);
        throw Xapian::DatabaseCorruptError(msg);
    }

    if (memcmp(buf, MAGIC_STRING, MAGIC_LEN) != 0) {
        string msg = filename;
        msg += ": Chert version file doesn't contain the right magic string";
        throw Xapian::DatabaseCorruptError(msg);
    }

    const unsigned char *v;
    v = reinterpret_cast<const unsigned char *>(buf) + MAGIC_LEN;
    unsigned int version = v[0] | (v[1] << 8) | (v[2] << 16) | (v[3] << 24);
    if (version != CHERT_VERSION) {
        string msg = filename;
        msg += ": Chert version file is version ";
        msg += str(version);
        msg += " but I only understand " STRINGIZE(CHERT_VERSION);
        throw Xapian::DatabaseVersionError(msg);
    }

    uuid.assign(buf + MAGIC_LEN + 4);
}