Retry cibuildwheel bootstrap download

Author: EthanSteinberg

.github/scripts/run_cibuildwheel.py

@@ -1,14 +1,53 @@
 from __future__ import annotations
 
+import os
+import pathlib
+import shutil
 import subprocess
 import sys
+import time
+import urllib.request
 from collections import deque
 
 
 def escape_workflow_command(value: str) -> str:
     return value.replace("%", "%25").replace("\r", "%0D").replace("\n", "%0A")
 
 
+def prefetch_windows_virtualenv() -> None:
+    if sys.platform != "win32":
+        return
+
+    # Keep these values aligned with the cibuildwheel version pinned in the
+    # workflow. cibuildwheel otherwise downloads this file only once, making a
+    # transient GitHub error fail the entire Windows matrix.
+    version = "20.35.2"
+    cache_path = (
+        pathlib.Path(os.environ["LOCALAPPDATA"]) / "pypa" / "cibuildwheel" / "Cache" / f"virtualenv-{version}.pyz"
+    )
+    if cache_path.exists():
+        return
+
+    url = f"https://github.com/pypa/get-virtualenv/releases/download/{version}/virtualenv.pyz"
+    cache_path.parent.mkdir(parents=True, exist_ok=True)
+    temporary_path = cache_path.with_suffix(".tmp")
+
+    for attempt in range(1, 7):
+        try:
+            print(f"Prefetching {url} (attempt {attempt}/6)", flush=True)
+            with urllib.request.urlopen(url, timeout=60) as response, temporary_path.open("wb") as output:
+                shutil.copyfileobj(response, output)
+            temporary_path.replace(cache_path)
+            return
+        except Exception:
+            temporary_path.unlink(missing_ok=True)
+            if attempt == 6:
+                raise
+            time.sleep(2 ** (attempt - 1))
+
+
+prefetch_windows_virtualenv()
+
 process = subprocess.Popen(
     [sys.executable, "-m", "cibuildwheel", "--output-dir", "wheelhouse"],
     stdout=subprocess.PIPE,