103 lines
2.8 KiB
Python
103 lines
2.8 KiB
Python
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#!/usr/bin/env nix-shell
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#! nix-shell -i "python3 -I" -p python3
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from contextlib import contextmanager
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from pathlib import Path
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from typing import Iterable
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from urllib import request
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import json
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def getUrls(metadata) -> Iterable[str]:
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'''Fetch all files' URLs from Google Fonts' metadata.
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The metadata must obey the API v1 schema, and can be obtained from:
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https://www.googleapis.com/webfonts/v1/webfonts?key=${GOOGLE_FONTS_TOKEN}&family=${FAMILY}
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'''
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return ( url for i in metadata['items'] for _, url in i['files'].items() )
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def hashUrl(url: str, *, hash: str = 'sha256'):
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'''Compute the hash of the data from HTTP GETing a given `url`.
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The `hash` must be an algorithm name `hashlib.new` accepts.
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'''
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import hashlib
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with request.urlopen(url) as req:
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return hashlib.new(hash, req.read())
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def sriEncode(h) -> str:
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'''Encode a hash in the SRI format.
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Takes a `hashlib` object, and produces a string that
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nixpkgs' `fetchurl` accepts as `hash` parameter.
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'''
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from base64 import b64encode
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return f"{h.name}-{b64encode(h.digest()).decode()}"
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def hashUrls(
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urls: Iterable[str],
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knownHashes: dict[str, str] = {},
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) -> dict[str, str]:
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'''Generate a `dict` mapping URLs to SRI-encoded hashes.
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The `knownHashes` optional parameter can be used to avoid
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re-downloading files whose URL have not changed.
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'''
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return {
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url: knownHashes.get(url) or sriEncode(hashUrl(url))
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for url in urls
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}
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@contextmanager
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def atomicFileUpdate(target: Path):
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'''Atomically replace the contents of a file.
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Yields an open file to write into; upon exiting the context,
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the file is closed and (atomically) replaces the `target`.
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Guarantees that the `target` was either successfully overwritten
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with new content and no exception was raised, or the temporary
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file was cleaned up.
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'''
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from tempfile import mkstemp
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fd, _p = mkstemp(
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dir = target.parent,
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prefix = target.name,
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)
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tmpPath = Path(_p)
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try:
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with open(fd, 'w') as f:
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yield f
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tmpPath.replace(target)
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except Exception:
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tmpPath.unlink(missing_ok = True)
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raise
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if __name__ == "__main__":
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currentDir = Path(__file__).parent
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with (currentDir / 'noto-emoji.json').open() as f:
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metadata = json.load(f)
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hashPath = currentDir / 'noto-emoji.hashes.json'
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try:
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with hashPath.open() as hashFile:
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hashes = json.load(hashFile)
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except FileNotFoundError:
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hashes = {}
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with atomicFileUpdate(hashPath) as hashFile:
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json.dump(
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hashUrls(getUrls(metadata), knownHashes = hashes),
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hashFile,
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indent = 2,
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)
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hashFile.write("\n") # Pacify nixpkgs' dumb editor config check
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