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pathslicing.py
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# 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_HEXDIGEST_LENGTH,
ObjStorage,
compressors,
compute_hash,
decompressors,
)
BUFSIZ = 1048576
DIR_MODE = 0o755
FILE_MODE = 0o644
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>]..."
)
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_HEXDIGEST_LENGTH < max_char:
raise ValueError(
"Algorithm %s has too short hash for slicing to char %d"
% (ID_HASH_ALGO, max_char)
)
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))
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)
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_HEXDIGEST_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)
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)
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)
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
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
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))
)
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
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
@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())
def add_stream(self, content_iter, obj_id, check_presence=True):
"""Add a new object to the object storage using streaming.
This function is identical to add() except it takes a generator that
yields the chunked content instead of the whole content at once.
Args:
content (bytes): chunked generator that yields the object's raw
content to add in storage.
obj_id (bytes): object identifier
check_presence (bool): indicate if the presence of the
content should be verified before adding the file.
Returns:
the id (bytes) of the object into the storage.
"""
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
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
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)
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)

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