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buffers.py
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buffers.py
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import hashlib
import sys
from contextlib import contextmanager
from functools import partial
from io import StringIO
@contextmanager
def rewind(buffer=None, *, default=StringIO):
"""
>>> with rewind() as buffer:
... buffer.write('ayy')
3
>>> buffer.read()
'ayy'
>>> with rewind(buffer):
... buffer.write('lmao')
4
>>> buffer.read()
'lmao'
>>> buffer.seek(0)
0
>>> buffer.read()
'ayylmao'
"""
if buffer is None:
buffer = default()
start = buffer.tell()
try:
yield buffer
finally:
buffer.seek(start)
def chunks(readinto, buffer):
"""Read chunks of bytes into the provided buffer.
Yields memoryview slices of the buffer to avoid unnecessary copies.
>>> from io import BytesIO
>>> input = BytesIO(b'ayy lmao')
>>> buffer = bytearray(3)
>>> for chunk in chunks(input.readinto, buffer):
... print(buffer, chunk.tobytes())
bytearray(b'ayy') b'ayy'
bytearray(b' lm') b' lm'
bytearray(b'aom') b'ao'
"""
assert len(buffer) > 0
view = memoryview(buffer)
while True:
bytes_read = readinto(buffer)
if not bytes_read:
break
# Slice the memoryview to avoid copying data from the buffer.
yield view[:bytes_read]
def relay(readinto, consume, *, buffer=None):
"""Relay chunks of bytes from a producer to a consumer.
>>> from io import BytesIO
>>> out = BytesIO()
>>> relay(BytesIO(b'ayy lmao').readinto, out.write)
>>> out.getvalue()
b'ayy lmao'
>>> relay(
... readinto=BytesIO(b'ayy lmao').readinto,
... consume=lambda x: print(x.tobytes()),
... buffer=bytearray(2),
... )
b'ay'
b'y '
b'lm'
b'ao'
"""
if buffer is None:
buffer = bytearray(2048)
for chunk in chunks(readinto, buffer):
consume(chunk)
class writeflush:
def __init__(self, buffer):
self.buffer = buffer
def __call__(self, chunk):
written = self.buffer.write(chunk)
self.buffer.flush()
return written
cat = partial(
relay,
readinto=sys.stdin.buffer.readinto1,
consume=writeflush(sys.stdout.buffer),
)
class fanout(list):
def __call__(self, *args, **kwargs):
for func in self:
func(*args, **kwargs)
def multihash(names, stream, **kwargs):
"""Compute multiple hashes in a single pass.
>>> from io import BytesIO
>>> hashes = multihash(['md5', 'sha1', 'sha256'], BytesIO(b'ayy lmao'))
>>> for name, digest in hashes.items():
... print(f"{name}: {digest}")
md5: 2b14f6a69199243f570031bf94865bb6
sha1: 1ac4eb815f2b72da8fe50cc44f236a41368c121c
sha256: 363bd719f9697e46e6514bf1f0efce0e5ace75683697fb820065a05c8fb3135e
"""
hashers = [hashlib.new(name) for name in names]
consume = fanout([hasher.update for hasher in hashers])
relay(readinto=stream.readinto, consume=consume, **kwargs)
return {name: hasher.hexdigest() for name, hasher in zip(names, hashers)}
if __name__ == '__main__':
# Echo stdin to stderr, and print several hashes to stdout.
names = ['md5', 'sha1', 'sha256']
hashers = [hashlib.new(name) for name in names]
relay(
readinto=sys.stdin.buffer.readinto1,
consume=fanout([
# sys.stderr.buffer.write,
# sys.stderr.buffer.write,
# writeflush(sys.stdout.buffer),
writeflush(sys.stderr.buffer),
*[hasher.update for hasher in hashers],
]),
)
for name, hasher in zip(names, hashers):
print(f"{name}: {hasher.hexdigest()}")