X-Git-Url: http://git.scottworley.com/git-cache/blobdiff_plain/f36d5c6f216b5b8cc92e04b2a6f3148e95e50585..a3835f508d4a441c64156d4669378e080064d4bf:/git_cache.py diff --git a/git_cache.py b/git_cache.py index c848161..8171b48 100644 --- a/git_cache.py +++ b/git_cache.py @@ -1,23 +1,51 @@ +# git-cache: Cache git content locally +# +# This program is free software: you can redistribute it and/or modify it +# under the terms of the GNU General Public License as published by the +# Free Software Foundation, version 3. + + # It would be nice if we could share the nix git cache, but as of the # time of writing it is transitioning from gitv2 (deprecated) to gitv3 # (not ready yet), and trying to straddle them both is too far into nix # implementation details for my comfort. So we re-implement here half of # nix's builtins.fetchGit. :( +import argparse +import functools import hashlib import logging import os import subprocess import sys +import time -from typing import Tuple +from typing import Iterator, NamedTuple, Optional, TypeVar, Tuple, Union 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" -Rev = str # eg: "53a27350551844e1ed1a9257690294767389ef0d" + +class GitCacheError(Exception): + pass + + +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" +Rev = str # eg: "53a27350551844e1ed1a9257690294767389ef0d" +RefOrRev = Union[Ref, Rev] + + +class _LogEntry(NamedTuple): + ref: Ref + rev: Rev + + +T = TypeVar('T') + + +def _repo_hashname(repo: Repo) -> str: + return hashlib.sha256(repo.encode()).hexdigest() def git_cachedir(repo: Repo) -> Path: @@ -28,76 +56,213 @@ def git_cachedir(repo: Repo) -> Path: return Path(os.path.join( XDG_CACHE_HOME, 'git-cache/v1', - hashlib.sha256(repo.encode()).hexdigest())) + _repo_hashname(repo))) + + +def _log_filename(repo: Repo) -> Path: + # Use xdg module when it's less painful to have as a dependency + XDG_DATA_HOME = Path( + os.environ.get('XDG_DATA_HOME', os.path.expanduser('~/.local/share'))) + + return Path(os.path.join( + XDG_DATA_HOME, + 'git-cache/v1', + _repo_hashname(repo))) -def verify_ancestry(repo: Repo, ref: Ref, rev: Rev) -> None: +def is_ancestor(repo: Repo, descendant: RefOrRev, ancestor: RefOrRev) -> bool: cachedir = git_cachedir(repo) - logging.debug('Verifying rev %s is an ancestor of ref "%s"', rev, ref) - subprocess.run(['git', '-C', cachedir, 'merge-base', '--is-ancestor', - rev, ref], check=True) + logging.debug('Checking if %s is an ancestor of %s', ancestor, descendant) + process = subprocess.run(['git', + '-C', + cachedir, + 'merge-base', + '--is-ancestor', + ancestor, + descendant], + check=False) + return process.returncode == 0 + + +def verify_ancestry( + repo: Repo, + descendant: RefOrRev, + ancestor: RefOrRev, + force: bool = False) -> None: + if not force and not is_ancestor(repo, descendant, ancestor): + raise GitCacheError(f'{ancestor} is not an ancestor of {descendant}') + + +def _read_fetch_log(repo: Repo) -> Iterator[_LogEntry]: + filename = _log_filename(repo) + if not os.path.exists(filename): + return + with open(filename, 'r', encoding='utf-8') as f: + for line in f: + _, _, rev, ref = line.strip().split(maxsplit=3) + yield _LogEntry(ref, rev) + + +def _last(it: Iterator[T]) -> Optional[T]: + return functools.reduce(lambda a, b: b, it, None) + + +def _previous_fetched_rev(repo: Repo, ref: Ref) -> Optional[Rev]: + return _last(entry.rev for entry in _read_fetch_log( + repo) if entry.ref == ref) + + +def _log_fetch(repo: Repo, ref: Ref, rev: Rev, force: bool = False) -> None: + if not force: + prev_rev = _previous_fetched_rev(repo, ref) + if prev_rev is not None: + verify_ancestry(repo, rev, prev_rev) + filename = _log_filename(repo) + os.makedirs(os.path.dirname(filename), exist_ok=True) + with open(filename, 'a', encoding='utf-8') as f: + f.write( + f'{time.strftime("%Y-%m%d-%H:%M:%S%z")} ' + f'{"FORCEDFETCH" if force else "fetch"} {rev} {ref}\n' + ) + + +def _show_force_warning() -> None: + print(''' +************************************************************************** +* WARNING: git-cache INVOKED WITH --force! * +* * +* This mode allows previously-fetched refs to be overwritten to point to * +* non-descendants -- commits that don't have the previous version of the * +* the ref in their history! * +* * +* This should only be invoked by a human operator who knows what they're * +* doing to correct a specific, known, problem. Care should be taken to * +* prevent recurrence. * +* * +* Press ^C to abort. * +* * +''', end='', file=sys.stderr) + warn_time_override = os.environ.get('FORCE_WARNING_TIME', None) + warn_time: int + if warn_time_override is None: + warn_time = 15 + else: + warn_time = int(warn_time_override) + print( + '''* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! * +* !! WARNING DISPLAY TIME OVERRIDDEN !! * +* !! !! * +* !! This message is intended to be displayed long enough for a !! * +* !! human operator to read it and have a chance to abort. An !! * +* !! override for the delay time is provided FOR THE UNIT TESTS !! * +* !! to avoid delaying software builds unnecessarily. This is !! * +* !! INTENDED FOR USE IN UNIT TESTS ONLY; THIS MESSAGE SHOULD !! * +* !! NEVER BE SEEN OUTSIDE BUILD LOGS! !! * +* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! * +* * +''', end='', file=sys.stderr) + + for i in range(warn_time, 0, -1): + msg = f'* {f"Continuing in {i} seconds...":-70s} *' + print(msg, file=sys.stderr) + time.sleep(1) + print('*' * 74, file=sys.stderr) @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 _git_fetch( + cachedir: Path, + repo: Repo, + ref: Ref, + force: bool = False) -> None: + subprocess.run(['git', '-C', cachedir, 'fetch'] + + (['--force'] if force else []) + + [repo, f'{ref}:{ref}'], check=True) -def fetch(repo: Repo, ref: Ref) -> Tuple[Path, Rev]: +def fetch(repo: Repo, ref: Ref, force: bool = False) -> Tuple[Path, Rev]: + if force: + _show_force_warning() cachedir = git_cachedir(repo) if not os.path.exists(cachedir): logging.debug("Initializing git repo") - subprocess.run(['git', 'init', '--bare', cachedir], check=True) + subprocess.run(['git', + '-c', + 'init.defaultBranch=git-cache--no-default-branch', + 'init', + '--bare', + cachedir], + check=True, + stdout=sys.stderr) logging.debug('Fetching ref "%s" from %s', ref, repo) - _git_fetch(cachedir, repo, ref) + _git_fetch(cachedir, repo, ref, force=force) - with open(os.path.join(cachedir, 'refs', 'heads', ref)) as rev_file: + with open(os.path.join(cachedir, 'refs', 'heads', ref), encoding='utf-8') as rev_file: rev = Rev(rev_file.read(999).strip()) - verify_ancestry(repo, ref, rev) + verify_ancestry(repo, ref, rev, force=force) + _log_fetch(repo, ref, rev, force=force) return cachedir, rev -def ensure_rev_available(repo: Repo, ref: Ref, rev: Rev) -> Path: +def ensure_rev_available( + repo: Repo, + ref: Ref, + rev: Rev, + force: bool = False) -> Path: cachedir = git_cachedir(repo) - if os.path.exists(cachedir): - logging.debug('Checking if we already have rev %s', rev) - process = subprocess.run( - ['git', '-C', cachedir, 'cat-file', '-e', rev], check=False) - if process.returncode == 0: - logging.debug('We already have rev %s', rev) - verify_ancestry(repo, ref, rev) - return cachedir - if process.returncode != 1: - raise Exception( - 'Could not test for presence of rev %s. Is cache dir "%s" messed up?' % - (rev, cachedir)) + if os.path.exists(cachedir) and is_ancestor(repo, ref, rev): + return cachedir logging.debug( 'We do not have rev %s. We will fetch ref "%s" and hope it appears.', rev, ref) - fetch(repo, ref) + fetch(repo, ref, force=force) logging.debug('Verifying that fetch retrieved rev %s', rev) subprocess.run(['git', '-C', cachedir, 'cat-file', '-e', rev], check=True) + verify_ancestry(repo, ref, rev, force=force) return cachedir def _main() -> None: - if len(sys.argv) == 3: - print('{1} {0}'.format(*fetch(Repo(sys.argv[1]), Ref(sys.argv[2])))) - elif len(sys.argv) == 4: - print(ensure_rev_available( - Repo(sys.argv[1]), Ref(sys.argv[2]), Rev(sys.argv[3]))) + parser = argparse.ArgumentParser( + description='Cache remote git repositories locally.', + epilog='example usage: git-cache https://github.com/NixOS/nixpkgs.git master') + parser.add_argument( + '--force', + action='store_true', + help='Recover from a force-push in the remote repo') + parser.add_argument( + 'repo', + metavar='Repo', + type=Repo, + help='Git repository URL') + parser.add_argument( + 'ref', + metavar='Ref', + type=Ref, + help='Ref (branch or tag) in the git repo') + parser.add_argument( + 'rev', + metavar='Rev', + type=Rev, + nargs='?', + help='Ensure that this revision is present. ' + + 'If this revision is already present locally, no network operations are performed.') + args = parser.parse_args() + + if args.rev is None: + cachedir, rev = fetch(args.repo, args.ref, force=args.force) + print(f'{rev} {cachedir}') else: - usage = '''usage: git-cache repo ref [rev] -example: git-cache https://github.com/NixOS/nixpkgs.git master''' - print(usage, file=sys.stderr) - sys.exit(1) + print( + ensure_rev_available( + args.repo, + args.ref, + args.rev, + force=args.force))