Source code for swh.objstorage.backends.pathslicing

# Copyright (C) 2015-2019  The Software Heritage developers
# See the AUTHORS file at the top-level directory of this distribution
# License: GNU General Public License version 3, or any later version
# See top-level LICENSE file for more information

from collections.abc import Iterator
from contextlib import contextmanager
from itertools import islice
import os
import random
import tempfile
from typing import List

from swh.model import hashutil
from swh.objstorage.exc import Error, ObjNotFoundError
from swh.objstorage.objstorage import (
    DEFAULT_CHUNK_SIZE,
    DEFAULT_LIMIT,
    ID_HASH_ALGO,
    ID_HASH_LENGTH,
    ObjStorage,
    compressors,
    compute_hash,
    decompressors,
)

BUFSIZ = 1048576

DIR_MODE = 0o755
FILE_MODE = 0o644


[docs]class PathSlicer: """Helper class to compute a path based on a hash. Used to compute a directory path based on the object hash according to a given slicing. Each slicing correspond to a directory that is named according to the hash of its content. For instance a file with SHA1 34973274ccef6ab4dfaaf86599792fa9c3fe4689 will have the following computed path: - 0:2/2:4/4:6 : 34/97/32/34973274ccef6ab4dfaaf86599792fa9c3fe4689 - 0:1/0:5/ : 3/34973/34973274ccef6ab4dfaaf86599792fa9c3fe4689 Args: root (str): path to the root directory of the storage on the disk. slicing (str): the slicing configuration. """ def __init__(self, root: str, slicing: str): self.root = root # Make a list of tuples where each tuple contains the beginning # and the end of each slicing. try: self.bounds = [ slice(*(int(x) if x else None for x in sbounds.split(":"))) for sbounds in slicing.split("/") if sbounds ] except TypeError: raise ValueError( "Invalid slicing declaration; " "it should be a of the form '<int>:<int>[/<int>:<int>]..." )
[docs] def check_config(self): """Check the slicing configuration is valid. Raises: ValueError: if the slicing configuration is invalid. """ if len(self): max_char = max( max(bound.start or 0, bound.stop or 0) for bound in self.bounds ) if ID_HASH_LENGTH < max_char: raise ValueError( "Algorithm %s has too short hash for slicing to char %d" % (ID_HASH_ALGO, max_char) )
[docs] def get_directory(self, hex_obj_id: str) -> str: """ Compute the storage directory of an object. See also: PathSlicer::get_path Args: hex_obj_id: object id as hexlified string. Returns: Absolute path (including root) to the directory that contains the given object id. """ return os.path.join(self.root, *self.get_slices(hex_obj_id))
[docs] def get_path(self, hex_obj_id: str) -> str: """ Compute the full path to an object into the current storage. See also: PathSlicer::get_directory Args: hex_obj_id(str): object id as hexlified string. Returns: Absolute path (including root) to the object corresponding to the given object id. """ return os.path.join(self.get_directory(hex_obj_id), hex_obj_id)
[docs] def get_slices(self, hex_obj_id: str) -> List[str]: """Compute the path elements for the given hash. Args: hex_obj_id(str): object id as hexlified string. Returns: Relative path to the actual object corresponding to the given id as a list. """ assert len(hex_obj_id) == ID_HASH_LENGTH return [hex_obj_id[bound] for bound in self.bounds]
def __len__(self) -> int: """Number of slices of the slicer""" return len(self.bounds)
[docs]class PathSlicingObjStorage(ObjStorage): """Implementation of the ObjStorage API based on the hash of the content. On disk, an object storage is a directory tree containing files named after their object IDs. An object ID is a checksum of its content, depending on the value of the ID_HASH_ALGO constant (see swh.model.hashutil for its meaning). To avoid directories that contain too many files, the object storage has a given slicing. Each slicing correspond to a directory that is named according to the hash of its content. So for instance a file with SHA1 34973274ccef6ab4dfaaf86599792fa9c3fe4689 will be stored in the given object storages : - 0:2/2:4/4:6 : 34/97/32/34973274ccef6ab4dfaaf86599792fa9c3fe4689 - 0:1/0:5/ : 3/34973/34973274ccef6ab4dfaaf86599792fa9c3fe4689 The files in the storage are stored in gzipped compressed format. Args: root (str): path to the root directory of the storage on the disk. slicing (str): string that indicates the slicing to perform on the hash of the content to know the path where it should be stored (see the documentation of the PathSlicer class). """ def __init__(self, root, slicing, compression="gzip", **kwargs): super().__init__(**kwargs) self.root = root self.slicer = PathSlicer(root, slicing) self.use_fdatasync = hasattr(os, "fdatasync") self.compression = compression self.check_config(check_write=False)
[docs] def check_config(self, *, check_write): """Check whether this object storage is properly configured""" self.slicer.check_config() if not os.path.isdir(self.root): raise ValueError( 'PathSlicingObjStorage root "%s" is not a directory' % self.root ) if check_write: if not os.access(self.root, os.W_OK): raise PermissionError( 'PathSlicingObjStorage root "%s" is not writable' % self.root ) if self.compression not in compressors: raise ValueError( 'Unknown compression algorithm "%s" for ' "PathSlicingObjStorage" % self.compression ) return True
def __contains__(self, obj_id): hex_obj_id = hashutil.hash_to_hex(obj_id) return os.path.isfile(self.slicer.get_path(hex_obj_id)) def __iter__(self): """Iterate over the object identifiers currently available in the storage. Warning: with the current implementation of the object storage, this method will walk the filesystem to list objects, meaning that listing all objects will be very slow for large storages. You almost certainly don't want to use this method in production. Return: Iterator over object IDs """ def obj_iterator(): # XXX hackish: it does not verify that the depth of found files # matches the slicing depth of the storage for root, _dirs, files in os.walk(self.root): _dirs.sort() for f in sorted(files): yield bytes.fromhex(f) return obj_iterator() def __len__(self): """Compute the number of objects available in the storage. Warning: this currently uses `__iter__`, its warning about bad performances applies Return: number of objects contained in the storage """ return sum(1 for i in self)
[docs] def add(self, content, obj_id=None, check_presence=True): if obj_id is None: obj_id = compute_hash(content) if check_presence and obj_id in self: # If the object is already present, return immediately. return obj_id hex_obj_id = hashutil.hash_to_hex(obj_id) if not isinstance(content, Iterator): content = [content] compressor = compressors[self.compression]() with self._write_obj_file(hex_obj_id) as f: for chunk in content: f.write(compressor.compress(chunk)) f.write(compressor.flush()) return obj_id
[docs] def get(self, obj_id): if obj_id not in self: raise ObjNotFoundError(obj_id) # Open the file and return its content as bytes hex_obj_id = hashutil.hash_to_hex(obj_id) d = decompressors[self.compression]() with open(self.slicer.get_path(hex_obj_id), "rb") as f: out = d.decompress(f.read()) if d.unused_data: raise Error("Corrupt object %s: trailing data found" % hex_obj_id,) return out
[docs] def check(self, obj_id): try: data = self.get(obj_id) except OSError: hex_obj_id = hashutil.hash_to_hex(obj_id) raise Error("Corrupt object %s: not a proper compressed file" % hex_obj_id,) checksums = hashutil.MultiHash.from_data( data, hash_names=[ID_HASH_ALGO] ).digest() actual_obj_id = checksums[ID_HASH_ALGO] hex_obj_id = hashutil.hash_to_hex(obj_id) if hex_obj_id != hashutil.hash_to_hex(actual_obj_id): raise Error( "Corrupt object %s should have id %s" % (hashutil.hash_to_hex(obj_id), hashutil.hash_to_hex(actual_obj_id)) )
[docs] def delete(self, obj_id): super().delete(obj_id) # Check delete permission if obj_id not in self: raise ObjNotFoundError(obj_id) hex_obj_id = hashutil.hash_to_hex(obj_id) try: os.remove(self.slicer.get_path(hex_obj_id)) except FileNotFoundError: raise ObjNotFoundError(obj_id) return True
# Management methods
[docs] def get_random(self, batch_size): def get_random_content(self, batch_size): """ Get a batch of content inside a single directory. Returns: a tuple (batch size, batch). """ dirs = [] for level in range(len(self.slicer)): path = os.path.join(self.root, *dirs) dir_list = next(os.walk(path))[1] if "tmp" in dir_list: dir_list.remove("tmp") dirs.append(random.choice(dir_list)) path = os.path.join(self.root, *dirs) content_list = next(os.walk(path))[2] length = min(batch_size, len(content_list)) return ( length, map(hashutil.hash_to_bytes, random.sample(content_list, length)), ) while batch_size: length, it = get_random_content(self, batch_size) batch_size = batch_size - length yield from it
# Streaming methods
[docs] @contextmanager def chunk_writer(self, obj_id): hex_obj_id = hashutil.hash_to_hex(obj_id) compressor = compressors[self.compression]() with self._write_obj_file(hex_obj_id) as f: yield lambda c: f.write(compressor.compress(c)) f.write(compressor.flush())
[docs] def add_stream(self, content_iter, obj_id, check_presence=True): if check_presence and obj_id in self: return obj_id with self.chunk_writer(obj_id) as writer: for chunk in content_iter: writer(chunk) return obj_id
[docs] def get_stream(self, obj_id, chunk_size=DEFAULT_CHUNK_SIZE): if obj_id not in self: raise ObjNotFoundError(obj_id) hex_obj_id = hashutil.hash_to_hex(obj_id) decompressor = decompressors[self.compression]() with open(self.slicer.get_path(hex_obj_id), "rb") as f: while True: raw = f.read(chunk_size) if not raw: break r = decompressor.decompress(raw) if not r: continue yield r
[docs] def list_content(self, last_obj_id=None, limit=DEFAULT_LIMIT): if last_obj_id: it = self.iter_from(last_obj_id) else: it = iter(self) return islice(it, limit)
[docs] def iter_from(self, obj_id, n_leaf=False): hex_obj_id = hashutil.hash_to_hex(obj_id) slices = self.slicer.get_slices(hex_obj_id) rlen = len(self.root.split("/")) i = 0 for root, dirs, files in os.walk(self.root): if not dirs: i += 1 level = len(root.split("/")) - rlen dirs.sort() if dirs and root == os.path.join(self.root, *slices[:level]): cslice = slices[level] for d in dirs[:]: if d < cslice: dirs.remove(d) for f in sorted(files): if f > hex_obj_id: yield bytes.fromhex(f) if n_leaf: yield i
@contextmanager def _write_obj_file(self, hex_obj_id): """ Context manager for writing object files to the object storage. During writing, data are written to a temporary file, which is atomically renamed to the right file name after closing. Usage sample: with objstorage._write_obj_file(hex_obj_id): f.write(obj_data) Yields: a file-like object open for writing bytes. """ # Get the final paths and create the directory if absent. dir = self.slicer.get_directory(hex_obj_id) if not os.path.isdir(dir): os.makedirs(dir, DIR_MODE, exist_ok=True) path = os.path.join(dir, hex_obj_id) # Create a temporary file. (tmp, tmp_path) = tempfile.mkstemp(suffix=".tmp", prefix="hex_obj_id.", dir=dir) # Open the file and yield it for writing. tmp_f = os.fdopen(tmp, "wb") yield tmp_f # Make sure the contents of the temporary file are written to disk tmp_f.flush() if self.use_fdatasync: os.fdatasync(tmp) else: os.fsync(tmp) # Then close the temporary file and move it to the right path. tmp_f.close() os.chmod(tmp_path, FILE_MODE) os.rename(tmp_path, path)