noto-fonts-monochrome-emoji: Automatically collect file hashes

pkgs/data/fonts/noto-fonts/default.nix

@@ -229,6 +229,7 @@ rec {
     # Metadata fetched from
     #  https://www.googleapis.com/webfonts/v1/webfonts?key=${GOOGLE_FONTS_TOKEN}&family=Noto+Emoji
     let metadata = with builtins; head (fromJSON (readFile ./noto-emoji.json)).items;
+        urlHashes = with builtins; fromJSON (readFile ./noto-emoji.hashes.json);
 
     in
     stdenvNoCC.mkDerivation {
@@ -245,17 +246,10 @@ rec {
           "600"   = "SemiBold";
           "700"   = "Bold";
         };
-        fileHashes = {
-          "NotoEmoji-Bold.ttf"     = "ce426e27c6254eb515fb6f301c8aa7cb7c90be3bd9a843c6e165d899a2dc63c0";
-          "NotoEmoji-Light.ttf"    = "f67750a89273b02911e8a71844d556df05d6331707fb44331604107421bcbd2a";
-          "NotoEmoji-Medium.ttf"   = "c3317d90a34c7904d86764144f9a4881aba1976a8ca59da730b35378026eaad4";
-          "NotoEmoji-Regular.ttf"  = "01718b75679b75dc8985328c5bf0ffead5bc38371a5eb50cf7a9b684df706258";
-          "NotoEmoji-SemiBold.ttf" = "3487a513c5fe94ab47eb24f77853d957bcd8511dd8e469cda1b01b7fb01c911d";
-        };
       in lib.mapAttrsToList
-        (variant: url: fetchurl rec { name = "NotoEmoji-${weightNames.${variant}}.ttf";
-                                      sha256 = fileHashes.${name};
-                                      inherit url; } )
+        (variant: url: fetchurl { name = "NotoEmoji-${weightNames.${variant}}.ttf";
+                                  hash = urlHashes.${url};
+                                  inherit url; } )
         metadata.files;
 
       installPhase = ''

pkgs/data/fonts/noto-fonts/noto-emoji.hashes.json

@@ -0,0 +1,7 @@
+{
+  "http://fonts.gstatic.com/s/notoemoji/v46/bMrnmSyK7YY-MEu6aWjPDs-ar6uWaGWuob_10jwvS-FGJCMY.ttf": "sha256-9ndQqJJzsCkR6KcYRNVW3wXWMxcH+0QzFgQQdCG8vSo=",
+  "http://fonts.gstatic.com/s/notoemoji/v46/bMrnmSyK7YY-MEu6aWjPDs-ar6uWaGWuob-r0jwvS-FGJCMY.ttf": "sha256-AXGLdWebddyJhTKMW/D/6tW8ODcaXrUM96m2hN9wYlg=",
+  "http://fonts.gstatic.com/s/notoemoji/v46/bMrnmSyK7YY-MEu6aWjPDs-ar6uWaGWuob-Z0jwvS-FGJCMY.ttf": "sha256-wzF9kKNMeQTYZ2QUT5pIgauhl2qMpZ2nMLNTeAJuqtQ=",
+  "http://fonts.gstatic.com/s/notoemoji/v46/bMrnmSyK7YY-MEu6aWjPDs-ar6uWaGWuob911TwvS-FGJCMY.ttf": "sha256-NIelE8X+lKtH6yT3eFPZV7zYUR3Y5GnNobAbf7AckR0=",
+  "http://fonts.gstatic.com/s/notoemoji/v46/bMrnmSyK7YY-MEu6aWjPDs-ar6uWaGWuob9M1TwvS-FGJCMY.ttf": "sha256-zkJuJ8YlTrUV+28wHIqny3yQvjvZqEPG4WXYmaLcY8A="
+}

pkgs/data/fonts/noto-fonts/noto-emoji.py

@@ -0,0 +1,102 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i "python3 -I" -p python3
+
+from contextlib import contextmanager
+from pathlib import Path
+from typing import Iterable
+from urllib import request
+
+import json
+
+
+def getUrls(metadata) -> Iterable[str]:
+    '''Fetch all files' URLs from Google Fonts' metadata.
+
+    The metadata must obey the API v1 schema, and can be obtained from:
+      https://www.googleapis.com/webfonts/v1/webfonts?key=${GOOGLE_FONTS_TOKEN}&family=${FAMILY}
+    '''
+    return ( url for i in metadata['items'] for _, url in i['files'].items() )
+
+
+def hashUrl(url: str, *, hash: str = 'sha256'):
+    '''Compute the hash of the data from HTTP GETing a given `url`.
+
+    The `hash` must be an algorithm name `hashlib.new` accepts.
+    '''
+    import hashlib
+    with request.urlopen(url) as req:
+        return hashlib.new(hash, req.read())
+
+def sriEncode(h) -> str:
+    '''Encode a hash in the SRI format.
+
+    Takes a `hashlib` object, and produces a string that
+    nixpkgs' `fetchurl` accepts as `hash` parameter.
+    '''
+    from base64 import b64encode
+    return f"{h.name}-{b64encode(h.digest()).decode()}"
+
+def hashUrls(
+    urls: Iterable[str],
+    knownHashes: dict[str, str] = {},
+) -> dict[str, str]:
+    '''Generate a `dict` mapping URLs to SRI-encoded hashes.
+
+    The `knownHashes` optional parameter can be used to avoid
+    re-downloading files whose URL have not changed.
+    '''
+    return {
+        url: knownHashes.get(url) or sriEncode(hashUrl(url))
+        for url in urls
+    }
+
+
+@contextmanager
+def atomicFileUpdate(target: Path):
+    '''Atomically replace the contents of a file.
+
+    Yields an open file to write into; upon exiting the context,
+    the file is closed and (atomically) replaces the `target`.
+
+    Guarantees that the `target` was either successfully overwritten
+    with new content and no exception was raised, or the temporary
+    file was cleaned up.
+    '''
+    from tempfile import mkstemp
+    fd, _p = mkstemp(
+        dir = target.parent,
+        prefix = target.name,
+    )
+    tmpPath = Path(_p)
+
+    try:
+        with open(fd, 'w') as f:
+            yield f
+
+        tmpPath.replace(target)
+
+    except Exception:
+        tmpPath.unlink(missing_ok = True)
+        raise
+
+
+if __name__ == "__main__":
+    currentDir = Path(__file__).parent
+
+    with (currentDir / 'noto-emoji.json').open() as f:
+        metadata = json.load(f)
+
+    hashPath = currentDir / 'noto-emoji.hashes.json'
+    try:
+        with hashPath.open() as hashFile:
+            hashes = json.load(hashFile)
+    except FileNotFoundError:
+        hashes = {}
+
+    with atomicFileUpdate(hashPath) as hashFile:
+        json.dump(
+            hashUrls(getUrls(metadata), knownHashes = hashes),
+            hashFile,
+            indent = 2,
+        )
+        hashFile.write("\n")  # Pacify nixpkgs' dumb editor config check