pythonbuild: retry failed downloads

The network in GitHub Actions is horribly unreliable. Why, I'm not
sure. Let's add automatic retry logic to downloads to hopefully
reduce the base rate of errors.

Author: indygreg

pythonbuild/utils.py

@@ -4,6 +4,7 @@
 
 import gzip
 import hashlib
+import http.client
 import io
 import multiprocessing
 import os
@@ -243,13 +244,19 @@ def download_to_path(url: str, path: pathlib.Path, size: int, sha256: str):
 
     tmp = path.with_name("%s.tmp" % path.name)
 
-    try:
-        with tmp.open("wb") as fh:
-            for chunk in secure_download_stream(url, size, sha256):
-                fh.write(chunk)
-    except IntegrityError:
-        tmp.unlink()
-        raise
+    for _ in range(5):
+        try:
+            try:
+                with tmp.open("wb") as fh:
+                    for chunk in secure_download_stream(url, size, sha256):
+                        fh.write(chunk)
+
+                break
+            except IntegrityError:
+                tmp.unlink()
+                raise
+        except http.client.HTTPException as e:
+            print("HTTP exception; retrying: %s" % e)
 
     tmp.rename(path)
     print("successfully downloaded %s" % url)