From f36d5c6f216b5b8cc92e04b2a6f3148e95e50585 Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Fri, 17 Jul 2020 17:29:18 -0700
Subject: [PATCH] Retry fetch with backoff

---
 Changelog         |  2 ++
 default.nix       | 29 ++++++++++++++++++++++++++---
 git_cache.py      | 18 ++++++++++++++----
 test.sh           |  2 +-
 test_git_cache.py |  2 ++
 5 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/Changelog b/Changelog
index 44b04c1..b5ae99c 100644
--- a/Changelog
+++ b/Changelog
@@ -1,4 +1,6 @@
 ## [Unreleased]
+### Added
+- Retry fetch with backoff
 
 
 ## [1.1.0] - 2020-07-16
diff --git a/default.nix b/default.nix
index 6c57b0d..6ac06fa 100644
--- a/default.nix
+++ b/default.nix
@@ -1,11 +1,34 @@
 { pkgs ? import <nixpkgs> { }, lint ? false }:
-pkgs.python3Packages.callPackage
-({ lib, buildPythonPackage, nix, git, autopep8, mypy, pylint, }:
+
+let
+  # Remove this package definition after https://github.com/NixOS/nixpkgs/pull/93377 reaches stable
+  backoff-fallback = { lib, buildPythonPackage, fetchPypi }:
+    buildPythonPackage rec {
+      pname = "backoff";
+      version = "1.10.0";
+      src = fetchPypi {
+        inherit pname version;
+        sha256 = "190rdpfhpjvb6bjh99fhdkgfsfkjwky7nz7b0nn5ah67z8hs1yxq";
+      };
+      meta = with lib; {
+        description = "Function decoration for backoff and retry";
+        homepage = "https://github.com/litl/backoff";
+        license = licenses.mit;
+        maintainers = with maintainers; [ chkno ];
+      };
+    };
+
+in pkgs.python3Packages.callPackage
+({ lib, buildPythonPackage, nix, git, backoff, autopep8, mypy, pylint, }:
   buildPythonPackage rec {
     pname = "git-cache";
     version = "1.2.0-pre";
     src = lib.cleanSource ./.;
+    propagatedBuildInputs = [ backoff ];
     checkInputs = [ nix git mypy ] ++ lib.optionals lint [ autopep8 pylint ];
     doCheck = true;
     checkPhase = "./test.sh";
-  }) { }
+  }) {
+    backoff = pkgs.python3Packages.backoff or (pkgs.python3Packages.callPackage
+      backoff-fallback { });
+  }
diff --git a/git_cache.py b/git_cache.py
index 594fb8a..c848161 100644
--- 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())
diff --git a/test.sh b/test.sh
index a0e3f5b..dbdf643 100755
--- a/test.sh
+++ b/test.sh
@@ -5,7 +5,7 @@ set -e
 PARALLELISM=4
 
 find . -name build -prune -o -name dist -prune -o -name '*.py' -print0 |
-  xargs -0 mypy --strict --ignore-missing-imports --no-warn-unused-ignores
+  xargs -0 mypy --strict --ignore-missing-imports --no-warn-unused-ignores --allow-untyped-decorators
 
 python3 -m unittest
 
diff --git a/test_git_cache.py b/test_git_cache.py
index 7408cad..ecb11e8 100644
--- a/test_git_cache.py
+++ b/test_git_cache.py
@@ -37,6 +37,8 @@ class TestGitCache(unittest.TestCase):
         os.environ['GIT_AUTHOR_EMAIL'] = 'test_git_cache@example.com'
         os.environ['GIT_COMMITTER_EMAIL'] = 'test_git_cache@example.com'
 
+        os.environ['BACKOFF_MAX_TIME'] = '0'
+
         self.tempdir = tempfile.TemporaryDirectory(prefix='git_cache_test-')
         self.upstream = os.path.join(self.tempdir.name, 'upstream')
         subprocess.run(['git', 'init', self.upstream], check=True)
-- 
2.44.1