Meta: Add file download and archive extraction tools to gn build

Use them to download and extract the TZDB files

Meta/gn/build/download_file.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+r"""Downloads a file as a build artifact.
+
+The file is downloaded to the specified directory.
+
+It's intended to be used for files that are cached between runs.
+
+"""
+
+import argparse
+import os
+import pathlib
+import shutil
+import sys
+import tempfile
+import urllib.request
+
+
+def main():
+    parser = argparse.ArgumentParser(
+                 epilog=__doc__,
+                 formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument('url', help='input url')
+    parser.add_argument('-o', '--output', required=True,
+                        help='output file')
+    parser.add_argument('-v', '--version', required=True,
+                        help='version of file to detect mismatches and redownload')
+    parser.add_argument('-f', '--version-file', required=True,
+                        help='filesystem location to cache version')
+    parser.add_argument('-c', "--cache-path", required=False,
+                        help='path for cached files to clear on version mismatch')
+    args = parser.parse_args()
+
+    version_from_file = ''
+    version_file = pathlib.Path(args.version_file)
+    if version_file.exists():
+        with version_file.open('r') as f:
+            version_from_file = f.readline().strip()
+
+    if version_from_file == args.version:
+        return 0
+
+    # Fresh build or version mismatch, delete old cache
+    if (args.cache_path):
+        cache_path = pathlib.Path(args.cache_path)
+        shutil.rmtree(cache_path, ignore_errors=True)
+        cache_path.mkdir(parents=True)
+
+    print(f"Downloading version {args.version} of {args.output}...", end='')
+
+    with urllib.request.urlopen(args.url) as f:
+        try:
+            with tempfile.NamedTemporaryFile(delete=False,
+                                             dir=pathlib.Path(args.output).parent) as out:
+                out.write(f.read())
+                os.rename(out.name, args.output)
+        except IOError:
+            os.unlink(out.name)
+
+    print("done")
+
+    with open(version_file, 'w') as f:
+        f.write(args.version)
+
+
+if __name__ == '__main__':
+    sys.exit(main())