borg/attic/cache.py

from configparser import RawConfigParser
from attic.remote import cache_if_remote
import msgpack
import os
from binascii import hexlify
import shutil

from .helpers import Error, get_cache_dir, decode_dict, st_mtime_ns, unhexlify, UpgradableLock
from .hashindex import ChunkIndex


class Cache(object):
    """Client Side cache
    """
    # Do not cache file metadata for files smaller than this
    FILE_MIN_SIZE = 4096

    class RepositoryReplay(Error):
        """Cache is newer than repository, refusing to continue"""

    def __init__(self, repository, key, manifest, path=None, sync=True):
        self.timestamp = None
        self.txn_active = False
        self.repository = repository
        self.key = key
        self.manifest = manifest
        self.path = path or os.path.join(get_cache_dir(), hexlify(repository.id).decode('ascii'))
        if not os.path.exists(self.path):
            self.create()
        self.open()
        if sync and self.manifest.id != self.manifest_id:
            # If repository is older than the cache something fishy is going on
            if self.timestamp and self.timestamp > manifest.timestamp:
                raise self.RepositoryReplay()
            self.sync()
            self.commit()

    def __del__(self):
        self.close()

    def create(self):
        """Create a new empty cache at `path`
        """
        os.makedirs(self.path)
        with open(os.path.join(self.path, 'README'), 'w') as fd:
            fd.write('This is an Attic cache')
        config = RawConfigParser()
        config.add_section('cache')
        config.set('cache', 'version', '1')
        config.set('cache', 'repository', hexlify(self.repository.id).decode('ascii'))
        config.set('cache', 'manifest', '')
        with open(os.path.join(self.path, 'config'), 'w') as fd:
            config.write(fd)
        ChunkIndex.create(os.path.join(self.path, 'chunks').encode('utf-8'))
        with open(os.path.join(self.path, 'files'), 'w') as fd:
            pass  # empty file

    def open(self):
        if not os.path.isdir(self.path):
            raise Exception('%s Does not look like an Attic cache' % self.path)
        self.lock = UpgradableLock(os.path.join(self.path, 'config'), exclusive=True)
        self.rollback()
        self.config = RawConfigParser()
        self.config.read(os.path.join(self.path, 'config'))
        if self.config.getint('cache', 'version') != 1:
            raise Exception('%s Does not look like an Attic cache')
        self.id = self.config.get('cache', 'repository')
        self.manifest_id = unhexlify(self.config.get('cache', 'manifest'))
        self.timestamp = self.config.get('cache', 'timestamp', fallback=None)
        self.chunks = ChunkIndex(os.path.join(self.path, 'chunks').encode('utf-8'))
        self.files = None

    def close(self):
        self.lock.release()

    def _read_files(self):
        self.files = {}
        self._newest_mtime = 0
        with open(os.path.join(self.path, 'files'), 'rb') as fd:
            u = msgpack.Unpacker(use_list=True)
            while True:
                data = fd.read(64 * 1024)
                if not data:
                    break
                u.feed(data)
                for path_hash, item in u:
                    if item[2] > self.FILE_MIN_SIZE:
                        item[0] += 1
                        self.files[path_hash] = item

    def begin_txn(self):
        # Initialize transaction snapshot
        txn_dir = os.path.join(self.path, 'txn.tmp')
        os.mkdir(txn_dir)
        shutil.copy(os.path.join(self.path, 'config'), txn_dir)
        shutil.copy(os.path.join(self.path, 'chunks'), txn_dir)
        shutil.copy(os.path.join(self.path, 'files'), txn_dir)
        os.rename(os.path.join(self.path, 'txn.tmp'),
                  os.path.join(self.path, 'txn.active'))
        self.txn_active = True

    def commit(self):
        """Commit transaction
        """
        if not self.txn_active:
            return
        if self.files is not None:
            with open(os.path.join(self.path, 'files'), 'wb') as fd:
                for item in self.files.items():
                    # Discard cached files with the newest mtime to avoid
                    # issues with filesystem snapshots and mtime precision
                    if item[1][0] < 10 and item[1][3] < self._newest_mtime:
                        msgpack.pack(item, fd)
        self.config.set('cache', 'manifest', hexlify(self.manifest.id).decode('ascii'))
        self.config.set('cache', 'timestamp', self.manifest.timestamp)
        with open(os.path.join(self.path, 'config'), 'w') as fd:
            self.config.write(fd)
        self.chunks.flush()
        os.rename(os.path.join(self.path, 'txn.active'),
                  os.path.join(self.path, 'txn.tmp'))
        shutil.rmtree(os.path.join(self.path, 'txn.tmp'))
        self.txn_active = False

    def rollback(self):
        """Roll back partial and aborted transactions
        """
        # Remove partial transaction
        if os.path.exists(os.path.join(self.path, 'txn.tmp')):
            shutil.rmtree(os.path.join(self.path, 'txn.tmp'))
        # Roll back active transaction
        txn_dir = os.path.join(self.path, 'txn.active')
        if os.path.exists(txn_dir):
            shutil.copy(os.path.join(txn_dir, 'config'), self.path)
            shutil.copy(os.path.join(txn_dir, 'chunks'), self.path)
            shutil.copy(os.path.join(txn_dir, 'files'), self.path)
            os.rename(txn_dir, os.path.join(self.path, 'txn.tmp'))
            if os.path.exists(os.path.join(self.path, 'txn.tmp')):
                shutil.rmtree(os.path.join(self.path, 'txn.tmp'))
        self.txn_active = False

    def sync(self):
        """Initializes cache by fetching and reading all archive indicies
        """
        def add(id, size, csize):
            try:
                count, size, csize = self.chunks[id]
                self.chunks[id] = count + 1, size, csize
            except KeyError:
                self.chunks[id] = 1, size, csize
        self.begin_txn()
        print('Initializing cache...')
        self.chunks.clear()
        unpacker = msgpack.Unpacker()
        repository = cache_if_remote(self.repository)
        for name, info in self.manifest.archives.items():
            archive_id = info[b'id']
            cdata = repository.get(archive_id)
            data = self.key.decrypt(archive_id, cdata)
            add(archive_id, len(data), len(cdata))
            archive = msgpack.unpackb(data)
            if archive[b'version'] != 1:
                raise Exception('Unknown archive metadata version')
            decode_dict(archive, (b'name',))
            print('Analyzing archive:', archive[b'name'])
            for key, chunk in zip(archive[b'items'], repository.get_many(archive[b'items'])):
                data = self.key.decrypt(key, chunk)
                add(key, len(data), len(chunk))
                unpacker.feed(data)
                for item in unpacker:
                    if b'chunks' in item:
                        for chunk_id, size, csize in item[b'chunks']:
                            add(chunk_id, size, csize)

    def add_chunk(self, id, data, stats):
        if not self.txn_active:
            self.begin_txn()
        if self.seen_chunk(id):
            return self.chunk_incref(id, stats)
        size = len(data)
        data = self.key.encrypt(data)
        csize = len(data)
        self.repository.put(id, data, wait=False)
        self.chunks[id] = (1, size, csize)
        stats.update(size, csize, True)
        return id, size, csize

    def seen_chunk(self, id):
        return self.chunks.get(id, (0, 0, 0))[0]

    def chunk_incref(self, id, stats):
        if not self.txn_active:
            self.begin_txn()
        count, size, csize = self.chunks[id]
        self.chunks[id] = (count + 1, size, csize)
        stats.update(size, csize, False)
        return id, size, csize

    def chunk_decref(self, id, stats):
        if not self.txn_active:
            self.begin_txn()
        count, size, csize = self.chunks[id]
        if count == 1:
            del self.chunks[id]
            self.repository.delete(id, wait=False)
            stats.update(-size, -csize, True)
        else:
            self.chunks[id] = (count - 1, size, csize)
            stats.update(-size, -csize, False)

    def file_known_and_unchanged(self, path_hash, st):
        if self.files is None:
            self._read_files()
        entry = self.files.get(path_hash)
        if (entry and entry[3] == st_mtime_ns(st)
            and entry[2] == st.st_size and entry[1] == st.st_ino):
            # reset entry age
            if entry[0] != 0:
                self.files[path_hash][0] = 0
            return entry[4]
        else:
            return None

    def memorize_file(self, path_hash, st, ids):
        if st.st_size > self.FILE_MIN_SIZE:
            # Entry: Age, inode, size, mtime, chunk ids
            mtime_ns = st_mtime_ns(st)
            self.files[path_hash] = 0, st.st_ino, st.st_size, mtime_ns, ids
            self._newest_mtime = max(self._newest_mtime, mtime_ns)