Retry fetch with backoff

[git-cache] / git_cache.py

diff --git a/git_cache.py b/git_cache.py
index 594fb8a77cdad825a2783723ffc04bbd6c951b71..c848161076caa44f8bccfa7c28180c2da8ac13d8 100644 (file)
--- a/git_cache.py
+++ b/git_cache.py
@@ -12,6 +12,8 @@ import sys
 
 from typing import Tuple
 
+import backoff
+
 Path = str  # eg: "/home/user/.cache/git-cache/v1"
 Repo = str  # eg: "https://github.com/NixOS/nixpkgs.git"
 Ref = str   # eg: "master" or "v1.0.0"
@@ -36,6 +38,17 @@ def verify_ancestry(repo: Repo, ref: Ref, rev: Rev) -> None:
                     rev, ref], check=True)
 
 
+@backoff.on_exception(
+    backoff.expo,
+    subprocess.CalledProcessError,
+    max_time=lambda: int(os.environ.get('BACKOFF_MAX_TIME', '30')))
+def _git_fetch(cachedir: Path, repo: Repo, ref: Ref) -> None:
+    # We don't use --force here because we want to abort and freak out if forced
+    # updates are happening.
+    subprocess.run(['git', '-C', cachedir, 'fetch', repo,
+                    '%s:%s' % (ref, ref)], check=True)
+
+
 def fetch(repo: Repo, ref: Ref) -> Tuple[Path, Rev]:
     cachedir = git_cachedir(repo)
     if not os.path.exists(cachedir):
@@ -43,10 +56,7 @@ def fetch(repo: Repo, ref: Ref) -> Tuple[Path, Rev]:
         subprocess.run(['git', 'init', '--bare', cachedir], check=True)
 
     logging.debug('Fetching ref "%s" from %s', ref, repo)
-    # We don't use --force here because we want to abort and freak out if forced
-    # updates are happening.
-    subprocess.run(['git', '-C', cachedir, 'fetch', repo,
-                    '%s:%s' % (ref, ref)], check=True)
+    _git_fetch(cachedir, repo, ref)
 
     with open(os.path.join(cachedir, 'refs', 'heads', ref)) as rev_file:
         rev = Rev(rev_file.read(999).strip())