borg/attic/repository.py

from configparser import RawConfigParser
from binascii import hexlify
import errno
import os
import re
import shutil
import struct
import sys
from zlib import crc32

from .hashindex import NSIndex
from .helpers import Error, IntegrityError, read_msgpack, write_msgpack, unhexlify, UpgradableLock
from .lrucache import LRUCache

MAX_OBJECT_SIZE = 20 * 1024 * 1024
MAGIC = b'ATTICSEG'
TAG_PUT = 0
TAG_DELETE = 1
TAG_COMMIT = 2


class Repository(object):
    """Filesystem based transactional key value store

    On disk layout:
    dir/README
    dir/config
    dir/data/<X / SEGMENTS_PER_DIR>/<X>
    dir/index.X
    dir/hints.X
    """
    DEFAULT_MAX_SEGMENT_SIZE = 5 * 1024 * 1024
    DEFAULT_SEGMENTS_PER_DIR = 10000

    class DoesNotExist(Error):
        """Repository {} does not exist"""

    class AlreadyExists(Error):
        """Repository {} already exists"""

    class InvalidRepository(Error):
        """{} is not a valid repository"""


    def __init__(self, path, create=False):
        self.path = path
        self.io = None
        self.lock = None
        if create:
            self.create(path)
        self.open(path)

    def __del__(self):
        self.close()

    def create(self, path):
        """Create a new empty repository at `path`
        """
        if os.path.exists(path) and (not os.path.isdir(path) or os.listdir(path)):
            raise self.AlreadyExists(path)
        if not os.path.exists(path):
            os.mkdir(path)
        with open(os.path.join(path, 'README'), 'w') as fd:
            fd.write('This is an Attic repository\n')
        os.mkdir(os.path.join(path, 'data'))
        config = RawConfigParser()
        config.add_section('repository')
        config.set('repository', 'version', '1')
        config.set('repository', 'segments_per_dir', self.DEFAULT_SEGMENTS_PER_DIR)
        config.set('repository', 'max_segment_size', self.DEFAULT_MAX_SEGMENT_SIZE)
        config.set('repository', 'id', hexlify(os.urandom(32)).decode('ascii'))
        with open(os.path.join(path, 'config'), 'w') as fd:
            config.write(fd)

    def open(self, path):
        self.head = None
        self.path = path
        if not os.path.isdir(path):
            raise self.DoesNotExist(path)
        self.config = RawConfigParser()
        self.config.read(os.path.join(self.path, 'config'))
        if not 'repository' in self.config.sections() or self.config.getint('repository', 'version') != 1:
            raise self.InvalidRepository(path)
        self.lock = UpgradableLock(os.path.join(path, 'config'))
        self.max_segment_size = self.config.getint('repository', 'max_segment_size')
        self.segments_per_dir = self.config.getint('repository', 'segments_per_dir')
        self.id = unhexlify(self.config.get('repository', 'id').strip())
        self.rollback()

    def close(self):
        if self.lock:
            self.rollback()
            self.lock.release()
            self.lock = None

    def commit(self, rollback=True):
        """Commit transaction
        """
        self.io.write_commit()
        self.compact_segments()
        self.write_index()
        self.rollback()

    def _available_indices(self, reverse=False):
        names = [int(name[6:]) for name in os.listdir(self.path) if re.match('index\.\d+', name)]
        names.sort(reverse=reverse)
        return names

    def open_index(self, head, read_only=False):
        if head is None:
            self.index = NSIndex.create(os.path.join(self.path, 'index.tmp').encode('utf-8'))
            self.segments = {}
            self.compact = set()
        else:
            if read_only:
                self.index = NSIndex((os.path.join(self.path, 'index.%d') % head).encode('utf-8'), readonly=True)
            else:
                shutil.copy(os.path.join(self.path, 'index.%d' % head),
                            os.path.join(self.path, 'index.tmp'))
                self.index = NSIndex(os.path.join(self.path, 'index.tmp').encode('utf-8'))
            hints = read_msgpack(os.path.join(self.path, 'hints.%d' % head))
            if hints[b'version'] != 1:
                raise ValueError('Unknown hints file version: %d' % hints['version'])
            self.segments = hints[b'segments']
            self.compact = set(hints[b'compact'])

    def write_index(self):
        hints = {b'version': 1,
                 b'segments': self.segments,
                 b'compact': list(self.compact)}
        write_msgpack(os.path.join(self.path, 'hints.%d' % self.io.head), hints)
        self.index.flush()
        os.rename(os.path.join(self.path, 'index.tmp'),
                  os.path.join(self.path, 'index.%d' % self.io.head))
        # Remove old indices
        current = '.%d' % self.io.head
        for name in os.listdir(self.path):
            if not name.startswith('index.') and not name.startswith('hints.'):
                continue
            if name.endswith(current):
                continue
            os.unlink(os.path.join(self.path, name))

    def compact_segments(self):
        """Compact sparse segments by copying data into new segments
        """
        if not self.compact:
            return

        def lookup(tag, key):
            return tag == TAG_PUT and self.index.get(key, (-1, -1))[0] == segment
        segments = self.segments
        for segment in sorted(self.compact):
            if segments[segment] > 0:
                for tag, key, data in self.io.iter_objects(segment, lookup, include_data=True):
                    new_segment, offset = self.io.write_put(key, data)
                    self.index[key] = new_segment, offset
                    segments.setdefault(new_segment, 0)
                    segments[new_segment] += 1
                    segments[segment] -= 1
                assert segments[segment] == 0
        self.io.write_commit()
        for segment in self.compact:
            assert self.segments.pop(segment) == 0
            self.io.delete_segment(segment)
        self.compact = set()

    def recover(self, path):
        """Recover missing index by replaying logs"""
        start = None
        available = self._available_indices()
        if available:
            start = available[-1]
        self.open_index(start)
        for segment, filename in self.io._segment_names():
            if start is not None and segment <= start:
                continue
            self.segments[segment] = 0
            for tag, key, offset in self.io.iter_objects(segment):
                if tag == TAG_PUT:
                    try:
                        s, _ = self.index[key]
                        self.compact.add(s)
                        self.segments[s] -= 1
                    except KeyError:
                        pass
                    self.index[key] = segment, offset
                    self.segments[segment] += 1
                elif tag == TAG_DELETE:
                    try:
                        s, _ = self.index.pop(key)
                        self.segments[s] -= 1
                        self.compact.add(s)
                        self.compact.add(segment)
                    except KeyError:
                        pass
            if self.segments[segment] == 0:
                self.compact.add(segment)
        if self.io.head is not None:
            self.write_index()

    def check(self, progress=False):
        """Check repository consistency

        This method verifies all segment checksums and makes sure
        the index is consistent with the data stored in the segments.
        """
        error_found = False
        def report_error(msg):
            nonlocal error_found
            error_found = True
            print(msg, file=sys.stderr)
        seen = set()
        for segment, filename in self.io._segment_names():
            if progress:
                print('Checking segment {}/{}'.format(segment, self.io.head))
            try:
                objects = list(self.io.iter_objects(segment))
            except (IntegrityError, struct.error):
                report_error('Error reading segment {}'.format(segment))
                objects = []
            for tag, key, offset in objects:
                if tag == TAG_PUT:
                    if key in seen:
                        report_error('Key found in more than one segment. Segment={}, key={}'.format(segment, hexlify(key)))
                    seen.add(key)
                    if self.index.get(key, (0, 0)) != (segment, offset):
                        report_error('Index vs segment header mismatch. Segment={}, key={}'.format(segment, hexlify(key)))
                elif tag == TAG_COMMIT:
                    continue
                else:
                    raise self.RepositoryCheckFailed(self.path, 'Unexpected tag {} in segment {}'.format(tag, segment))
        if len(self.index) != len(seen):
            report_error('Index object count mismatch. {} != {}'.format(len(self.index), len(seen)))
        return not error_found

    def rollback(self):
        """
        """
        self._active_txn = False
        if self.io:
            self.io.close()
        self.io = LoggedIO(self.path, self.max_segment_size, self.segments_per_dir)
        if self.io.head is not None and not os.path.exists(os.path.join(self.path, 'index.%d' % self.io.head)):
            self.lock.upgrade()
            self.recover(self.path)
        self.open_index(self.io.head, read_only=True)

    def _len(self):
        return len(self.index)

    def get(self, id):
        try:
            segment, offset = self.index[id]
            return self.io.read(segment, offset, id)
        except KeyError:
            raise self.DoesNotExist(self.path)

    def get_many(self, ids, is_preloaded=False):
        for id_ in ids:
            yield self.get(id_)

    def put(self, id, data, wait=True):
        if not self._active_txn:
            self._active_txn = True
            self.lock.upgrade()
            self.open_index(self.io.head)
        try:
            segment, _ = self.index[id]
            self.segments[segment] -= 1
            self.compact.add(segment)
            segment = self.io.write_delete(id)
            self.segments.setdefault(segment, 0)
            self.compact.add(segment)
        except KeyError:
            pass
        segment, offset = self.io.write_put(id, data)
        self.segments.setdefault(segment, 0)
        self.segments[segment] += 1
        self.index[id] = segment, offset

    def delete(self, id, wait=True):
        if not self._active_txn:
            self._active_txn = True
            self.lock.upgrade()
            self.open_index(self.io.head)
        try:
            segment, offset = self.index.pop(id)
            self.segments[segment] -= 1
            self.compact.add(segment)
            segment = self.io.write_delete(id)
            self.compact.add(segment)
            self.segments.setdefault(segment, 0)
        except KeyError:
            raise self.DoesNotExist(self.path)

    def preload(self, ids):
        """Preload objects (only applies to remote repositories
        """


class LoggedIO(object):

    header_fmt = struct.Struct('<IIB')
    assert header_fmt.size == 9
    put_header_fmt = struct.Struct('<IIB32s')
    assert put_header_fmt.size == 41
    header_no_crc_fmt = struct.Struct('<IB')
    assert header_no_crc_fmt.size == 5
    crc_fmt = struct.Struct('<I')
    assert crc_fmt.size == 4

    _commit = header_no_crc_fmt.pack(9, TAG_COMMIT)
    COMMIT = crc_fmt.pack(crc32(_commit)) + _commit

    def __init__(self, path, limit, segments_per_dir, capacity=100):
        self.path = path
        self.fds = LRUCache(capacity)
        self.segment = None
        self.limit = limit
        self.segments_per_dir = segments_per_dir
        self.offset = 0
        self._write_fd = None
        self.head = None
        self.cleanup()

    def close(self):
        for segment in list(self.fds.keys()):
            self.fds.pop(segment).close()
        self.close_segment()
        self.fds = None  # Just to make sure we're disabled

    def _segment_names(self, reverse=False):
        for dirpath, dirs, filenames in os.walk(os.path.join(self.path, 'data')):
            dirs.sort(key=int, reverse=reverse)
            filenames = sorted((filename for filename in filenames if filename.isdigit()), key=int, reverse=reverse)
            for filename in filenames:
                yield int(filename), os.path.join(dirpath, filename)

    def cleanup(self):
        """Delete segment files left by aborted transactions
        """
        self.head = None
        self.segment = 0
        # FIXME: Only delete segments if we're sure there's at least
        # one complete segment somewhere
        for segment, filename in self._segment_names(reverse=True):
            if self.is_complete_segment(filename):
                self.head = segment
                self.segment = self.head + 1
                return
            else:
                os.unlink(filename)

    def is_complete_segment(self, filename):
        with open(filename, 'rb') as fd:
            try:
                fd.seek(-self.header_fmt.size, os.SEEK_END)
            except Exception as e:
                # return False if segment file is empty or too small
                if e.errno == errno.EINVAL:
                    return False
                raise e
            return fd.read(self.header_fmt.size) == self.COMMIT

    def segment_filename(self, segment):
        return os.path.join(self.path, 'data', str(segment // self.segments_per_dir), str(segment))

    def get_write_fd(self, no_new=False):
        if not no_new and self.offset and self.offset > self.limit:
            self.close_segment()
        if not self._write_fd:
            if self.segment % self.segments_per_dir == 0:
                dirname = os.path.join(self.path, 'data', str(self.segment // self.segments_per_dir))
                if not os.path.exists(dirname):
                    os.mkdir(dirname)
            self._write_fd = open(self.segment_filename(self.segment), 'ab')
            self._write_fd.write(MAGIC)
            self.offset = 8
        return self._write_fd

    def get_fd(self, segment):
        try:
            return self.fds[segment]
        except KeyError:
            fd = open(self.segment_filename(segment), 'rb')
            self.fds[segment] = fd
            return fd

    def delete_segment(self, segment):
        try:
            os.unlink(self.segment_filename(segment))
        except OSError:
            pass

    def iter_objects(self, segment, lookup=None, include_data=False):
        fd = self.get_fd(segment)
        fd.seek(0)
        if fd.read(8) != MAGIC:
            raise IntegrityError('Invalid segment header')
        offset = 8
        header = fd.read(self.header_fmt.size)
        while header:
            crc, size, tag = self.header_fmt.unpack(header)
            if size > MAX_OBJECT_SIZE:
                raise IntegrityError('Invalid segment object size')
            rest = fd.read(size - self.header_fmt.size)
            if crc32(rest, crc32(memoryview(header)[4:])) & 0xffffffff != crc:
                raise IntegrityError('Segment checksum mismatch')
            if tag not in (TAG_PUT, TAG_DELETE, TAG_COMMIT):
                raise IntegrityError('Invalid segment entry header')
            key = None
            if tag in (TAG_PUT, TAG_DELETE):
                key = rest[:32]
            if not lookup or lookup(tag, key):
                if include_data:
                    yield tag, key, rest[32:]
                else:
                    yield tag, key, offset
            offset += size
            header = fd.read(self.header_fmt.size)

    def read(self, segment, offset, id):
        if segment == self.segment:
            self._write_fd.flush()
        fd = self.get_fd(segment)
        fd.seek(offset)
        header = fd.read(self.put_header_fmt.size)
        crc, size, tag, key = self.put_header_fmt.unpack(header)
        if size > MAX_OBJECT_SIZE:
            raise IntegrityError('Invalid segment object size')
        data = fd.read(size - self.put_header_fmt.size)
        if crc32(data, crc32(memoryview(header)[4:])) & 0xffffffff != crc:
            raise IntegrityError('Segment checksum mismatch')
        if tag != TAG_PUT or id != key:
            raise IntegrityError('Invalid segment entry header')
        return data

    def write_put(self, id, data):
        size = len(data) + self.put_header_fmt.size
        fd = self.get_write_fd()
        offset = self.offset
        header = self.header_no_crc_fmt.pack(size, TAG_PUT)
        crc = self.crc_fmt.pack(crc32(data, crc32(id, crc32(header))) & 0xffffffff)
        fd.write(b''.join((crc, header, id, data)))
        self.offset += size
        return self.segment, offset

    def write_delete(self, id):
        fd = self.get_write_fd()
        header = self.header_no_crc_fmt.pack(self.put_header_fmt.size, TAG_DELETE)
        crc = self.crc_fmt.pack(crc32(id, crc32(header)) & 0xffffffff)
        fd.write(b''.join((crc, header, id)))
        self.offset += self.put_header_fmt.size
        return self.segment

    def write_commit(self):
        fd = self.get_write_fd(no_new=True)
        header = self.header_no_crc_fmt.pack(self.header_fmt.size, TAG_COMMIT)
        crc = self.crc_fmt.pack(crc32(header) & 0xffffffff)
        fd.write(b''.join((crc, header)))
        self.head = self.segment
        self.close_segment()

    def close_segment(self):
        if self._write_fd:
            self.segment += 1
            self.offset = 0
            os.fsync(self._write_fd)
            self._write_fd.close()
            self._write_fd = None