]> git.scottworley.com Git - git-cache/blame - git_cache.py
Release 1.4.1
[git-cache] / git_cache.py
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1# It would be nice if we could share the nix git cache, but as of the
2# time of writing it is transitioning from gitv2 (deprecated) to gitv3
3# (not ready yet), and trying to straddle them both is too far into nix
4# implementation details for my comfort. So we re-implement here half of
5# nix's builtins.fetchGit. :(
6
d1ab0853 7import argparse
35000f72 8import functools
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9import hashlib
10import logging
11import os
12import subprocess
347be7cf 13import sys
35000f72 14import time
bef7ce53 15
35000f72 16from typing import Iterator, NamedTuple, Optional, TypeVar, Tuple, Union
bef7ce53 17
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18import backoff
19
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20Path = str # eg: "/home/user/.cache/git-cache/v1"
21Repo = str # eg: "https://github.com/NixOS/nixpkgs.git"
22Ref = str # eg: "master" or "v1.0.0"
23Rev = str # eg: "53a27350551844e1ed1a9257690294767389ef0d"
a5d42d8d 24RefOrRev = Union[Ref, Rev]
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25
26
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27class _LogEntry(NamedTuple):
28 ref: Ref
29 rev: Rev
30
31
32T = TypeVar('T')
33
34
35def _repo_hashname(repo: Repo) -> str:
36 return hashlib.sha256(repo.encode()).hexdigest()
37
38
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39def git_cachedir(repo: Repo) -> Path:
40 # Use xdg module when it's less painful to have as a dependency
41 XDG_CACHE_HOME = Path(
42 os.environ.get('XDG_CACHE_HOME', os.path.expanduser('~/.cache')))
43
44 return Path(os.path.join(
45 XDG_CACHE_HOME,
46 'git-cache/v1',
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47 _repo_hashname(repo)))
48
49
50def _log_filename(repo: Repo) -> Path:
51 # Use xdg module when it's less painful to have as a dependency
52 XDG_DATA_HOME = Path(
53 os.environ.get('XDG_DATA_HOME', os.path.expanduser('~/.local/share')))
54
55 return Path(os.path.join(
56 XDG_DATA_HOME,
57 'git-cache/v1',
58 _repo_hashname(repo)))
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59
60
a5d42d8d 61def is_ancestor(repo: Repo, descendant: RefOrRev, ancestor: RefOrRev) -> bool:
bef7ce53 62 cachedir = git_cachedir(repo)
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63 logging.debug('Checking if %s is an ancestor of %s', ancestor, descendant)
64 process = subprocess.run(['git',
65 '-C',
66 cachedir,
67 'merge-base',
68 '--is-ancestor',
69 ancestor,
70 descendant],
71 check=False)
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72 return process.returncode == 0
73
74
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75def verify_ancestry(
76 repo: Repo,
77 descendant: RefOrRev,
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78 ancestor: RefOrRev,
79 force: bool = False) -> None:
80 if not force and not is_ancestor(repo, descendant, ancestor):
a5d42d8d 81 raise Exception('%s is not an ancestor of %s' % (ancestor, descendant))
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82
83
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84def _read_fetch_log(repo: Repo) -> Iterator[_LogEntry]:
85 filename = _log_filename(repo)
86 if not os.path.exists(filename):
87 return
88 with open(filename, 'r') as f:
89 for line in f:
90 _, _, rev, ref = line.strip().split(maxsplit=3)
91 yield _LogEntry(ref, rev)
92
93
94def _last(it: Iterator[T]) -> Optional[T]:
95 return functools.reduce(lambda a, b: b, it, None)
96
97
98def _previous_fetched_rev(repo: Repo, ref: Ref) -> Optional[Rev]:
99 return _last(entry.rev for entry in _read_fetch_log(
100 repo) if entry.ref == ref)
101
102
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103def _log_fetch(repo: Repo, ref: Ref, rev: Rev, force: bool = False) -> None:
104 if not force:
105 prev_rev = _previous_fetched_rev(repo, ref)
106 if prev_rev is not None:
107 verify_ancestry(repo, rev, prev_rev)
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108 filename = _log_filename(repo)
109 os.makedirs(os.path.dirname(filename), exist_ok=True)
110 with open(filename, 'a') as f:
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111 f.write('%s %s %s %s\n' %
112 (time.strftime('%Y-%m%d-%H:%M:%S%z'),
113 ('FORCEDFETCH' if force else 'fetch'), rev, ref))
114
115
116def _show_force_warning() -> None:
117 print('''
118**************************************************************************
119* WARNING: git-cache INVOKED WITH --force! *
120* *
121* This mode allows previously-fetched refs to be overwritten to point to *
122* non-descendants -- commits that don't have the previous version of the *
123* the ref in their history! *
124* *
125* This should only be invoked by a human operator who knows what they're *
126* doing to correct a specific, known, problem. Care should be taken to *
127* prevent recurrence. *
128* *
129* Press ^C to abort. *
130* *
131''', end='', file=sys.stderr)
132 warn_time_override = os.environ.get('FORCE_WARNING_TIME', None)
133 warn_time: int
134 if warn_time_override is None:
135 warn_time = 15
136 else:
137 warn_time = int(warn_time_override)
138 print(
139 '''* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *
140* !! WARNING DISPLAY TIME OVERRIDDEN !! *
141* !! !! *
142* !! This message is intended to be displayed long enough for a !! *
143* !! human operator to read it and have a chance to abort. An !! *
144* !! override for the delay time is provided FOR THE UNIT TESTS !! *
145* !! to avoid delaying software builds unnecessarily. This is !! *
146* !! INTENDED FOR USE IN UNIT TESTS ONLY; THIS MESSAGE SHOULD !! *
147* !! NEVER BE SEEN OUTSIDE BUILD LOGS! !! *
148* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *
149* *
150''', end='', file=sys.stderr)
151
152 for i in range(warn_time, 0, -1):
153 msg = '* %-70s *' % ("Continuing in %d seconds..." % i)
154 print(msg, file=sys.stderr)
155 time.sleep(1)
156 print('*' * 74, file=sys.stderr)
157
35000f72 158
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159@backoff.on_exception(
160 backoff.expo,
161 subprocess.CalledProcessError,
162 max_time=lambda: int(os.environ.get('BACKOFF_MAX_TIME', '30')))
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163def _git_fetch(
164 cachedir: Path,
165 repo: Repo,
166 ref: Ref,
167 force: bool = False) -> None:
168 subprocess.run(['git', '-C', cachedir, 'fetch'] +
169 (['--force'] if force else []) +
170 [repo, '%s:%s' % (ref, ref)], check=True)
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171
172
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173def fetch(repo: Repo, ref: Ref, force: bool = False) -> Tuple[Path, Rev]:
174 if force:
175 _show_force_warning()
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176 cachedir = git_cachedir(repo)
177 if not os.path.exists(cachedir):
178 logging.debug("Initializing git repo")
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179 subprocess.run(['git',
180 '-c',
181 'init.defaultBranch=git-cache--no-default-branch',
182 'init',
183 '--bare',
184 cachedir],
185 check=True,
186 stdout=sys.stderr)
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187
188 logging.debug('Fetching ref "%s" from %s', ref, repo)
083b90e7 189 _git_fetch(cachedir, repo, ref, force=force)
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190
191 with open(os.path.join(cachedir, 'refs', 'heads', ref)) as rev_file:
192 rev = Rev(rev_file.read(999).strip())
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193 verify_ancestry(repo, ref, rev, force=force)
194 _log_fetch(repo, ref, rev, force=force)
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195
196 return cachedir, rev
197
198
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199def ensure_rev_available(
200 repo: Repo,
201 ref: Ref,
202 rev: Rev,
203 force: bool = False) -> Path:
bef7ce53 204 cachedir = git_cachedir(repo)
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205 if os.path.exists(cachedir) and is_ancestor(repo, ref, rev):
206 return cachedir
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207
208 logging.debug(
209 'We do not have rev %s. We will fetch ref "%s" and hope it appears.',
210 rev, ref)
083b90e7 211 fetch(repo, ref, force=force)
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212 logging.debug('Verifying that fetch retrieved rev %s', rev)
213 subprocess.run(['git', '-C', cachedir, 'cat-file', '-e', rev], check=True)
083b90e7 214 verify_ancestry(repo, ref, rev, force=force)
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215
216 return cachedir
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217
218
219def _main() -> None:
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220 parser = argparse.ArgumentParser(
221 description='Cache remote git repositories locally.',
222 epilog='example usage: git-cache https://github.com/NixOS/nixpkgs.git master')
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223 parser.add_argument(
224 '--force',
225 action='store_true',
226 help='Recover from a force-push in the remote repo')
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227 parser.add_argument(
228 'repo',
229 metavar='Repo',
230 type=Repo,
231 help='Git repository URL')
232 parser.add_argument(
233 'ref',
234 metavar='Ref',
235 type=Ref,
236 help='Ref (branch or tag) in the git repo')
237 parser.add_argument(
238 'rev',
239 metavar='Rev',
240 type=Rev,
241 nargs='?',
242 help='Ensure that this revision is present. ' +
243 'If this revision is already present locally, no network operations are performed.')
244 args = parser.parse_args()
245
246 if args.rev is None:
083b90e7 247 print('{1} {0}'.format(*fetch(args.repo, args.ref, force=args.force)))
347be7cf 248 else:
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249 print(
250 ensure_rev_available(
251 args.repo,
252 args.ref,
253 args.rev,
254 force=args.force))