From 34b451532b71249e666428a6bd779eaf289958a7 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Thu, 29 May 2025 01:47:26 +0200
Subject: [3.14] gh-134262: Add retries to downloads in PCbuild\get_external.py
 (GH-134865)

(cherry picked from commit e9d845b41dca9ad84b76ef777d05e647a4b4d8cd)

Includes fix for off-by-one error from GH-134867
(cherry-picked from commit e64395e8eb8d3a9e35e3e534e87d427ff27ab0a5)

Co-authored-by: Emma Smith <emma@emmatyping.dev>
---
 PCbuild/get_external.py | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/PCbuild/get_external.py b/PCbuild/get_external.py
index 4ecc892..8c1155c 100755
--- a/PCbuild/get_external.py
+++ b/PCbuild/get_external.py
@@ -9,6 +9,25 @@ import zipfile
 from urllib.request import urlretrieve
 
 
+def retrieve_with_retries(download_location, output_path, reporthook,
+                          max_retries=7):
+    """Download a file with exponential backoff retry and save to disk."""
+    for attempt in range(max_retries + 1):
+        try:
+            resp = urlretrieve(
+                download_location,
+                output_path,
+                reporthook=reporthook,
+            )
+        except ConnectionError as ex:
+            if attempt == max_retries:
+                msg = f"Download from {download_location} failed."
+                raise OSError(msg) from ex
+            time.sleep(2.25**attempt)
+        else:
+            return resp
+
+
 def fetch_zip(commit_hash, zip_dir, *, org='python', binary=False, verbose):
     repo = f'cpython-{"bin" if binary else "source"}-deps'
     url = f'https://github.com/{org}/{repo}/archive/{commit_hash}.zip'
@@ -16,10 +35,10 @@ def fetch_zip(commit_hash, zip_dir, *, org='python', binary=False, verbose):
     if verbose:
         reporthook = print
     zip_dir.mkdir(parents=True, exist_ok=True)
-    filename, headers = urlretrieve(
+    filename, _headers = retrieve_with_retries(
         url,
         zip_dir / f'{commit_hash}.zip',
-        reporthook=reporthook,
+        reporthook
     )
     return filename
 
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