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#!/usr/bin/env nix-shell
#! nix-shell -i "python3 -I" -p python3
from contextlib import contextmanager
from pathlib import Path
import re
nix32alphabet = "0123456789abcdfghijklmnpqrsvwxyz"
nix32inverted = { c: i for i, c in enumerate(nix32alphabet) }
def nix32decode(s: str) -> bytes:
# only support sha256 hashes for now
assert len(s) == 52
out = [ 0 for _ in range(32) ]
# TODO: Do better than a list of byte-sized ints
for n, c in enumerate(reversed(s)):
digit = nix32inverted[c]
i, j = divmod(5 * n, 8)
out[i] = out[i] | (digit << j) & 0xff
rem = digit >> (8 - j)
if rem == 0:
continue
elif i < 31:
out[i+1] = rem
else:
raise ValueError(f"Invalid nix32 hash: '{s}'")
return bytes(out)
def toSRI(digest: bytes) -> str:
from base64 import b64encode
assert len(digest) == 32
return f"sha256-{b64encode(digest).decode()}"
RE = {
'nix32': f"[{nix32alphabet}]" "{52}",
'hex': "[0-9A-Fa-f]{64}",
'base64': "[A-Za-z0-9+/]{43}=",
}
RE['sha256'] = '|'.join(
f"{'(sha256-)?' if name == 'base64' else ''}"
f"(?P<{name}>{r})"
for name, r in RE.items()
)
def sha256toSRI(m: re.Match) -> str:
"""Produce the equivalent SRI string for any match of RE['sha256']"""
if m['nix32'] is not None:
return toSRI(nix32decode(m['nix32']))
if m['hex'] is not None:
from binascii import unhexlify
return toSRI(unhexlify(m['hex']))
if m['base64'] is not None:
from base64 import b64decode
return toSRI(b64decode(m['base64']))
begin, end = m.span()
raise ValueError("Got a match where none of the groups captured:\n"
f"'{m.string[begin:end]}'")
# Ohno I used evil, irregular backrefs instead of making 2 variants ^^'
_def_re = re.compile(
"sha256 = (?P<quote>[\"'])"
f"({RE['sha256']})"
"(?P=quote);"
)
def defToSRI(s: str) -> str:
return _def_re.sub(
lambda m: f'hash = "{sha256toSRI(m)}";',
s,
)
@contextmanager
def atomicFileUpdate(target: Path):
'''Atomically replace the contents of a file.
Guarantees that no temporary files are left behind, and `target` is either
left untouched, or overwritten with new content if no exception was raised.
Yields a pair `(original, new)` of open files.
`original` is the pre-existing file at `target`, open for reading;
`new` is an empty, temporary file in the same filder, open for writing.
Upon exiting the context, the files are closed; if no exception was
raised, `new` (atomically) replaces the `target`, otherwise it is deleted.
'''
# That's mostly copied from noto-emoji.py, should DRY it out
from tempfile import mkstemp
fd, _p = mkstemp(
dir = target.parent,
prefix = target.name,
)
tmpPath = Path(_p)
try:
with target.open() as original:
with tmpPath.open('w') as new:
yield (original, new)
tmpPath.replace(target)
except Exception:
tmpPath.unlink(missing_ok = True)
raise
def fileToSRI(p: Path):
with atomicFileUpdate(p) as (og, new):
for line in og:
new.write(defToSRI(line))
if __name__ == "__main__":
from sys import argv, stderr
for arg in argv[1:]:
p = Path(arg)
if not p.is_file():
print(f"Argument '{arg}' is not a regular file's path", file=stderr)
else:
print(f"Processing '{arg}'")
fileToSRI(p)
|
