git_cache.py

#!/usr/bin/env python
# Copyright 2014 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""A git command for managing a local cache of git repositories."""

from __future__ import print_function

import contextlib
import errno
import logging
import optparse
import os
import re
import subprocess
import sys
import tempfile
import threading
import time

try:
  import urlparse
except ImportError:  # For Py3 compatibility
  import urllib.parse as urlparse

from download_from_google_storage import Gsutil
import gclient_utils
import lockfile
import subcommand

# Analogous to gc.autopacklimit git config.
GC_AUTOPACKLIMIT = 50

GIT_CACHE_CORRUPT_MESSAGE = 'WARNING: The Git cache is corrupt.'

try:
  # pylint: disable=undefined-variable
  WinErr = WindowsError
except NameError:
  class WinErr(Exception):
    pass

class ClobberNeeded(Exception):
  pass


def exponential_backoff_retry(fn, excs=(Exception,), name=None, count=10,
                              sleep_time=0.25, printerr=None):
  """Executes |fn| up to |count| times, backing off exponentially.

  Args:
    fn (callable): The function to execute. If this raises a handled
        exception, the function will retry with exponential backoff.
    excs (tuple): A tuple of Exception types to handle. If one of these is
        raised by |fn|, a retry will be attempted. If |fn| raises an Exception
        that is not in this list, it will immediately pass through. If |excs|
        is empty, the Exception base class will be used.
    name (str): Optional operation name to print in the retry string.
    count (int): The number of times to try before allowing the exception to
        pass through.
    sleep_time (float): The initial number of seconds to sleep in between
        retries. This will be doubled each retry.
    printerr (callable): Function that will be called with the error string upon
        failures. If None, |logging.warning| will be used.

  Returns: The return value of the successful fn.
  """
  printerr = printerr or logging.warning
  for i in range(count):
    try:
      return fn()
    except excs as e:
      if (i+1) >= count:
        raise

      printerr('Retrying %s in %.2f second(s) (%d / %d attempts): %s' % (
          (name or 'operation'), sleep_time, (i+1), count, e))
      time.sleep(sleep_time)
      sleep_time *= 2


class Mirror(object):

  git_exe = 'git.bat' if sys.platform.startswith('win') else 'git'
  gsutil_exe = os.path.join(
    os.path.dirname(os.path.abspath(__file__)), 'gsutil.py')
  cachepath_lock = threading.Lock()

  UNSET_CACHEPATH = object()

  # Used for tests
  _GIT_CONFIG_LOCATION = []

  @staticmethod
  def parse_fetch_spec(spec):
    """Parses and canonicalizes a fetch spec.

    Returns (fetchspec, value_regex), where value_regex can be used
    with 'git config --replace-all'.
    """
    parts = spec.split(':', 1)
    src = parts[0].lstrip('+').rstrip('/')
    if not src.startswith('refs/'):
      src = 'refs/heads/%s' % src
    dest = parts[1].rstrip('/') if len(parts) > 1 else src
    regex = r'\+%s:.*' % src.replace('*', r'\*')
    return ('+%s:%s' % (src, dest), regex)

  def __init__(self, url, refs=None, print_func=None):
    self.url = url
    self.fetch_specs = set([self.parse_fetch_spec(ref) for ref in (refs or [])])
    self.basedir = self.UrlToCacheDir(url)
    self.mirror_path = os.path.join(self.GetCachePath(), self.basedir)
    if print_func:
      self.print = self.print_without_file
      self.print_func = print_func
    else:
      self.print = print

  def print_without_file(self, message, **_kwargs):
    self.print_func(message)

  @contextlib.contextmanager
  def print_duration_of(self, what):
    start = time.time()
    try:
      yield
    finally:
      self.print('%s took %.1f minutes' % (what, (time.time() - start) / 60.0))

  @property
  def bootstrap_bucket(self):
    b = os.getenv('OVERRIDE_BOOTSTRAP_BUCKET')
    if b:
      return b
    u = urlparse.urlparse(self.url)
    if u.netloc == 'chromium.googlesource.com':
      return 'chromium-git-cache'
    # Not recognized.
    return None

  @property
  def _gs_path(self):
    return 'gs://%s/v2/%s' % (self.bootstrap_bucket, self.basedir)

  @classmethod
  def FromPath(cls, path):
    return cls(cls.CacheDirToUrl(path))

  @staticmethod
  def UrlToCacheDir(url):
    """Convert a git url to a normalized form for the cache dir path."""
    if os.path.isdir(url):
      # Ignore the drive letter in Windows
      url = os.path.splitdrive(url)[1]
      return url.replace('-', '--').replace(os.sep, '-')

    parsed = urlparse.urlparse(url)
    norm_url = parsed.netloc + parsed.path
    if norm_url.endswith('.git'):
      norm_url = norm_url[:-len('.git')]

    # Use the same dir for authenticated URLs and unauthenticated URLs.
    norm_url = norm_url.replace('googlesource.com/a/', 'googlesource.com/')

    return norm_url.replace('-', '--').replace('/', '-').lower()

  @staticmethod
  def CacheDirToUrl(path):
    """Convert a cache dir path to its corresponding url."""
    netpath = re.sub(r'\b-\b', '/', os.path.basename(path)).replace('--', '-')
    return 'https://%s' % netpath

  @classmethod
  def SetCachePath(cls, cachepath):
    with cls.cachepath_lock:
      setattr(cls, 'cachepath', cachepath)

  @classmethod
  def GetCachePath(cls):
    with cls.cachepath_lock:
      if not hasattr(cls, 'cachepath'):
        try:
          cachepath = subprocess.check_output(
              [cls.git_exe, 'config'] +
              cls._GIT_CONFIG_LOCATION +
              ['cache.cachepath']).decode('utf-8', 'ignore').strip()
        except subprocess.CalledProcessError:
          cachepath = os.environ.get('GIT_CACHE_PATH', cls.UNSET_CACHEPATH)
        setattr(cls, 'cachepath', cachepath)

      ret = getattr(cls, 'cachepath')
      if ret is cls.UNSET_CACHEPATH:
        raise RuntimeError('No cache.cachepath git configuration or '
                           '$GIT_CACHE_PATH is set.')
      return ret

  @staticmethod
  def _GetMostRecentCacheDirectory(ls_out_set):
    ready_file_pattern = re.compile(r'.*/(\d+).ready$')
    ready_dirs = []

    for name in ls_out_set:
      m = ready_file_pattern.match(name)
      # Given <path>/<number>.ready,
      # we are interested in <path>/<number> directory
      if m and (name[:-len('.ready')] + '/') in ls_out_set:
        ready_dirs.append((int(m.group(1)), name[:-len('.ready')]))

    if not ready_dirs:
      return None

    return max(ready_dirs)[1]

  def Rename(self, src, dst):
    # This is somehow racy on Windows.
    # Catching OSError because WindowsError isn't portable and
    # pylint complains.
    exponential_backoff_retry(
        lambda: os.rename(src, dst),
        excs=(OSError,),
        name='rename [%s] => [%s]' % (src, dst),
        printerr=self.print)

  def RunGit(self, cmd, **kwargs):
    """Run git in a subprocess."""
    cwd = kwargs.setdefault('cwd', self.mirror_path)
    kwargs.setdefault('print_stdout', False)
    kwargs.setdefault('filter_fn', self.print)
    env = kwargs.get('env') or kwargs.setdefault('env', os.environ.copy())
    env.setdefault('GIT_ASKPASS', 'true')
    env.setdefault('SSH_ASKPASS', 'true')
    self.print('running "git %s" in "%s"' % (' '.join(cmd), cwd))
    gclient_utils.CheckCallAndFilter([self.git_exe] + cmd, **kwargs)

  def config(self, cwd=None, reset_fetch_config=False):
    if cwd is None:
      cwd = self.mirror_path

    if reset_fetch_config:
      try:
        self.RunGit(['config', '--unset-all', 'remote.origin.fetch'], cwd=cwd)
      except subprocess.CalledProcessError as e:
        # If exit code was 5, it means we attempted to unset a config that
        # didn't exist. Ignore it.
        if e.returncode != 5:
          raise

    # Don't run git-gc in a daemon.  Bad things can happen if it gets killed.
    try:
      self.RunGit(['config', 'gc.autodetach', '0'], cwd=cwd)
    except subprocess.CalledProcessError:
      # Hard error, need to clobber.
      raise ClobberNeeded()

    # Don't combine pack files into one big pack file.  It's really slow for
    # repositories, and there's no way to track progress and make sure it's
    # not stuck.
    if self.supported_project():
      self.RunGit(['config', 'gc.autopacklimit', '0'], cwd=cwd)

    # Allocate more RAM for cache-ing delta chains, for better performance
    # of "Resolving deltas".
    self.RunGit(['config', 'core.deltaBaseCacheLimit',
                 gclient_utils.DefaultDeltaBaseCacheLimit()], cwd=cwd)

    self.RunGit(['config', 'remote.origin.url', self.url], cwd=cwd)
    self.RunGit(['config', '--replace-all', 'remote.origin.fetch',
                 '+refs/heads/*:refs/heads/*', r'\+refs/heads/\*:.*'], cwd=cwd)
    for spec, value_regex in self.fetch_specs:
      self.RunGit(
          ['config', '--replace-all', 'remote.origin.fetch', spec, value_regex],
          cwd=cwd)

  def bootstrap_repo(self, directory):
    """Bootstrap the repo from Google Storage if possible.

    More apt-ly named bootstrap_repo_from_cloud_if_possible_else_do_nothing().
    """
    if not self.bootstrap_bucket:
      return False

    gsutil = Gsutil(self.gsutil_exe, boto_path=None)

    # Get the most recent version of the directory.
    # This is determined from the most recent version of a .ready file.
    # The .ready file is only uploaded when an entire directory has been
    # uploaded to GS.
    _, ls_out, ls_err = gsutil.check_call('ls', self._gs_path)
    ls_out_set = set(ls_out.strip().splitlines())
    latest_dir = self._GetMostRecentCacheDirectory(ls_out_set)

    if not latest_dir:
      self.print('No bootstrap file for %s found in %s, stderr:\n  %s' %
                 (self.mirror_path, self.bootstrap_bucket,
                '  '.join((ls_err or '').splitlines(True))))
      return False

    try:
      # create new temporary directory locally
      tempdir = tempfile.mkdtemp(prefix='_cache_tmp', dir=self.GetCachePath())
      self.RunGit(['init', '--bare'], cwd=tempdir)
      self.print('Downloading files in %s/* into %s.' %
                 (latest_dir, tempdir))
      with self.print_duration_of('download'):
        code = gsutil.call('-m', 'cp', '-r', latest_dir + "/*",
                           tempdir)
      if code:
        return False
    except Exception as e:
      self.print('Encountered error: %s' % str(e), file=sys.stderr)
      gclient_utils.rmtree(tempdir)
      return False
    # delete the old directory
    if os.path.exists(directory):
      gclient_utils.rmtree(directory)
    self.Rename(tempdir, directory)
    return True

  def contains_revision(self, revision):
    if not self.exists():
      return False

    if sys.platform.startswith('win'):
      # Windows .bat scripts use ^ as escape sequence, which means we have to
      # escape it with itself for every .bat invocation.
      needle = '%s^^^^{commit}' % revision
    else:
      needle = '%s^{commit}' % revision
    try:
      # cat-file exits with 0 on success, that is git object of given hash was
      # found.
      self.RunGit(['cat-file', '-e', needle])
      return True
    except subprocess.CalledProcessError:
      return False

  def exists(self):
    return os.path.isfile(os.path.join(self.mirror_path, 'config'))

  def supported_project(self):
    """Returns true if this repo is known to have a bootstrap zip file."""
    u = urlparse.urlparse(self.url)
    return u.netloc in [
        'chromium.googlesource.com',
        'chrome-internal.googlesource.com']

  def _preserve_fetchspec(self):
    """Read and preserve remote.origin.fetch from an existing mirror.

    This modifies self.fetch_specs.
    """
    if not self.exists():
      return
    try:
      config_fetchspecs = subprocess.check_output(
          [self.git_exe, 'config', '--get-all', 'remote.origin.fetch'],
          cwd=self.mirror_path).decode('utf-8', 'ignore')
      for fetchspec in config_fetchspecs.splitlines():
        self.fetch_specs.add(self.parse_fetch_spec(fetchspec))
    except subprocess.CalledProcessError:
      logging.warning(
          'Tried and failed to preserve remote.origin.fetch from the '
          'existing cache directory.  You may need to manually edit '
          '%s and "git cache fetch" again.' %
          os.path.join(self.mirror_path, 'config'))

  def _ensure_bootstrapped(
      self, depth, bootstrap, reset_fetch_config, force=False):
    pack_dir = os.path.join(self.mirror_path, 'objects', 'pack')
    pack_files = []
    if os.path.isdir(pack_dir):
      pack_files = [f for f in os.listdir(pack_dir) if f.endswith('.pack')]
      self.print('%s has %d .pack files, re-bootstrapping if >%d or ==0' %
                (self.mirror_path, len(pack_files), GC_AUTOPACKLIMIT))

    should_bootstrap = (force or
                        not self.exists() or
                        len(pack_files) > GC_AUTOPACKLIMIT or
                        len(pack_files) == 0)

    if not should_bootstrap:
      if depth and os.path.exists(os.path.join(self.mirror_path, 'shallow')):
        logging.warning(
            'Shallow fetch requested, but repo cache already exists.')
      return

    if not self.exists():
      if os.path.exists(self.mirror_path):
        # If the mirror path exists but self.exists() returns false, we're
        # in an unexpected state. Nuke the previous mirror directory and
        # start fresh.
        gclient_utils.rmtree(self.mirror_path)
      os.mkdir(self.mirror_path)
    elif not reset_fetch_config:
      # Re-bootstrapping an existing mirror; preserve existing fetch spec.
      self._preserve_fetchspec()

    bootstrapped = (not depth and bootstrap and
                    self.bootstrap_repo(self.mirror_path))

    if not bootstrapped:
      if not self.exists() or not self.supported_project():
        # Bootstrap failed due to:
        # 1. No previous cache.
        # 2. Project doesn't have a bootstrap folder.
        # Start with a bare git dir.
        self.RunGit(['init', '--bare'], cwd=self.mirror_path)
      else:
        # Bootstrap failed, previous cache exists; warn and continue.
        logging.warning(
            'Git cache has a lot of pack files (%d). Tried to re-bootstrap '
            'but failed. Continuing with non-optimized repository.' %
            len(pack_files))

  def _fetch(self,
             rundir,
             verbose,
             depth,
             no_fetch_tags,
             reset_fetch_config,
             prune=True):
    self.config(rundir, reset_fetch_config)

    fetch_cmd = ['fetch']
    if verbose:
      fetch_cmd.extend(['-v', '--progress'])
    if depth:
      fetch_cmd.extend(['--depth', str(depth)])
    if no_fetch_tags:
      fetch_cmd.append('--no-tags')
    if prune:
      fetch_cmd.append('--prune')
    fetch_cmd.append('origin')

    fetch_specs = subprocess.check_output(
        [self.git_exe, 'config', '--get-all', 'remote.origin.fetch'],
        cwd=rundir).decode('utf-8', 'ignore').strip().splitlines()
    for spec in fetch_specs:
      try:
        self.print('Fetching %s' % spec)
        with self.print_duration_of('fetch %s' % spec):
          self.RunGit(fetch_cmd + [spec], cwd=rundir, retry=True)
      except subprocess.CalledProcessError:
        if spec == '+refs/heads/*:refs/heads/*':
          raise ClobberNeeded()  # Corrupted cache.
        logging.warning('Fetch of %s failed' % spec)

  def populate(self,
               depth=None,
               no_fetch_tags=False,
               shallow=False,
               bootstrap=False,
               verbose=False,
               lock_timeout=0,
               reset_fetch_config=False):
    assert self.GetCachePath()
    if shallow and not depth:
      depth = 10000
    gclient_utils.safe_makedirs(self.GetCachePath())

    with lockfile.lock(self.mirror_path, lock_timeout):
      try:
        self._ensure_bootstrapped(depth, bootstrap, reset_fetch_config)
        self._fetch(self.mirror_path, verbose, depth, no_fetch_tags,
                    reset_fetch_config)
      except ClobberNeeded:
        # This is a major failure, we need to clean and force a bootstrap.
        gclient_utils.rmtree(self.mirror_path)
        self.print(GIT_CACHE_CORRUPT_MESSAGE)
        self._ensure_bootstrapped(depth,
                                  bootstrap,
                                  reset_fetch_config,
                                  force=True)
        self._fetch(self.mirror_path, verbose, depth, no_fetch_tags,
                    reset_fetch_config)

  def update_bootstrap(self, prune=False, gc_aggressive=False, branch='master'):
    # The folder is <git number>
    gen_number = subprocess.check_output(
        [self.git_exe, 'number', branch],
        cwd=self.mirror_path).decode('utf-8', 'ignore').strip()
    gsutil = Gsutil(path=self.gsutil_exe, boto_path=None)

    src_name = self.mirror_path
    dest_prefix = '%s/%s' % (self._gs_path, gen_number)

    # ls_out lists contents in the format: gs://blah/blah/123...
    _, ls_out, _ = gsutil.check_call('ls', self._gs_path)

    # Check to see if folder already exists in gs
    ls_out_set = set(ls_out.strip().splitlines())
    if (dest_prefix + '/' in ls_out_set and
        dest_prefix + '.ready' in ls_out_set):
      print('Cache %s already exists.' % dest_prefix)
      return

    # Reduce the number of individual files to download & write on disk.
    self.RunGit(['pack-refs', '--all'])

    # Run Garbage Collect to compress packfile.
    gc_args = ['gc', '--prune=all']
    if gc_aggressive:
      # The default "gc --aggressive" is often too aggressive for some machines,
      # since it attempts to create as many threads as there are CPU cores,
      # while not limiting per-thread memory usage, which puts too much pressure
      # on RAM on high-core machines, causing them to thrash. Using lower-level
      # commands gives more control over those settings.

      # This might not be strictly necessary, but it's fast and is normally run
      # by 'gc --aggressive', so it shouldn't hurt.
      self.RunGit(['reflog', 'expire', '--all'])

      # These are the default repack settings for 'gc --aggressive'.
      gc_args = ['repack', '-d', '-l', '-f', '--depth=50', '--window=250', '-A',
                 '--unpack-unreachable=all']
      # A 1G memory limit seems to provide comparable pack results as the
      # default, even for our largest repos, while preventing runaway memory (at
      # least on current Chromium builders which have about 4G RAM per core).
      gc_args.append('--window-memory=1g')
      # NOTE: It might also be possible to avoid thrashing with a larger window
      # (e.g. "--window-memory=2g") by limiting the number of threads created
      # (e.g. "--threads=[cores/2]"). Some limited testing didn't show much
      # difference in outcomes on our current repos, but it might be worth
      # trying if the repos grow much larger and the packs don't seem to be
      # getting compressed enough.
    self.RunGit(gc_args)

    gsutil.call('-m', 'cp', '-r', src_name, dest_prefix)

    # Create .ready file and upload
    _, ready_file_name =  tempfile.mkstemp(suffix='.ready')
    try:
      gsutil.call('cp', ready_file_name, '%s.ready' % (dest_prefix))
    finally:
      os.remove(ready_file_name)

    # remove all other directory/.ready files in the same gs_path
    # except for the directory/.ready file previously created
    # which can be used for bootstrapping while the current one is
    # being uploaded
    if not prune:
      return
    prev_dest_prefix = self._GetMostRecentCacheDirectory(ls_out_set)
    if not prev_dest_prefix:
      return
    for path in ls_out_set:
      if (path == prev_dest_prefix + '/' or
          path == prev_dest_prefix + '.ready'):
        continue
      if path.endswith('.ready'):
        gsutil.call('rm', path)
        continue
      gsutil.call('-m', 'rm', '-r', path)


  @staticmethod
  def DeleteTmpPackFiles(path):
    pack_dir = os.path.join(path, 'objects', 'pack')
    if not os.path.isdir(pack_dir):
      return
    pack_files = [f for f in os.listdir(pack_dir) if
                  f.startswith('.tmp-') or f.startswith('tmp_pack_')]
    for f in pack_files:
      f = os.path.join(pack_dir, f)
      try:
        os.remove(f)
        logging.warning('Deleted stale temporary pack file %s' % f)
      except OSError:
        logging.warning('Unable to delete temporary pack file %s' % f)


@subcommand.usage('[url of repo to check for caching]')
def CMDexists(parser, args):
  """Check to see if there already is a cache of the given repo."""
  _, args = parser.parse_args(args)
  if not len(args) == 1:
    parser.error('git cache exists only takes exactly one repo url.')
  url = args[0]
  mirror = Mirror(url)
  if mirror.exists():
    print(mirror.mirror_path)
    return 0
  return 1


@subcommand.usage('[url of repo to create a bootstrap zip file]')
def CMDupdate_bootstrap(parser, args):
  """Create and uploads a bootstrap tarball."""
  # Lets just assert we can't do this on Windows.
  if sys.platform.startswith('win'):
    print('Sorry, update bootstrap will not work on Windows.', file=sys.stderr)
    return 1

  parser.add_option('--skip-populate', action='store_true',
                    help='Skips "populate" step if mirror already exists.')
  parser.add_option('--gc-aggressive', action='store_true',
                    help='Run aggressive repacking of the repo.')
  parser.add_option('--prune', action='store_true',
                    help='Prune all other cached bundles of the same repo.')
  parser.add_option('--branch', default='master',
                    help='Branch to use for bootstrap. (Default \'master\')')

  populate_args = args[:]
  options, args = parser.parse_args(args)
  url = args[0]
  mirror = Mirror(url)
  if not options.skip_populate or not mirror.exists():
    CMDpopulate(parser, populate_args)
  else:
    print('Skipped populate step.')

  # Get the repo directory.
  _, args2 = parser.parse_args(args)
  url = args2[0]
  mirror = Mirror(url)
  mirror.update_bootstrap(options.prune, options.gc_aggressive, options.branch)
  return 0


@subcommand.usage('[url of repo to add to or update in cache]')
def CMDpopulate(parser, args):
  """Ensure that the cache has all up-to-date objects for the given repo."""
  parser.add_option('--depth', type='int',
                    help='Only cache DEPTH commits of history')
  parser.add_option(
      '--no-fetch-tags',
      action='store_true',
      help=('Don\'t fetch tags from the server. This can speed up '
            'fetch considerably when there are many tags.'))
  parser.add_option('--shallow', '-s', action='store_true',
                    help='Only cache 10000 commits of history')
  parser.add_option('--ref', action='append',
                    help='Specify additional refs to be fetched')
  parser.add_option('--no_bootstrap', '--no-bootstrap',
                    action='store_true',
                    help='Don\'t bootstrap from Google Storage')
  parser.add_option('--ignore_locks',
                    '--ignore-locks',
                    action='store_true',
                    help='NOOP. This flag will be removed in the future.')
  parser.add_option('--break-locks',
                    action='store_true',
                    help='Break any existing lock instead of just ignoring it')
  parser.add_option('--reset-fetch-config', action='store_true', default=False,
                    help='Reset the fetch config before populating the cache.')

  options, args = parser.parse_args(args)
  if not len(args) == 1:
    parser.error('git cache populate only takes exactly one repo url.')
  if options.ignore_locks:
    print('ignore_locks is no longer used. Please remove its usage.')
  if options.break_locks:
    print('break_locks is no longer used. Please remove its usage.')
  url = args[0]

  mirror = Mirror(url, refs=options.ref)
  kwargs = {
      'no_fetch_tags': options.no_fetch_tags,
      'verbose': options.verbose,
      'shallow': options.shallow,
      'bootstrap': not options.no_bootstrap,
      'lock_timeout': options.timeout,
      'reset_fetch_config': options.reset_fetch_config,
  }
  if options.depth:
    kwargs['depth'] = options.depth
  mirror.populate(**kwargs)


@subcommand.usage('Fetch new commits into cache and current checkout')
def CMDfetch(parser, args):
  """Update mirror, and fetch in cwd."""
  parser.add_option('--all', action='store_true', help='Fetch all remotes')
  parser.add_option('--no_bootstrap', '--no-bootstrap',
                    action='store_true',
                    help='Don\'t (re)bootstrap from Google Storage')
  parser.add_option(
      '--no-fetch-tags',
      action='store_true',
      help=('Don\'t fetch tags from the server. This can speed up '
            'fetch considerably when there are many tags.'))
  options, args = parser.parse_args(args)

  # Figure out which remotes to fetch.  This mimics the behavior of regular
  # 'git fetch'.  Note that in the case of "stacked" or "pipelined" branches,
  # this will NOT try to traverse up the branching structure to find the
  # ultimate remote to update.
  remotes = []
  if options.all:
    assert not args, 'fatal: fetch --all does not take a repository argument'
    remotes = subprocess.check_output([Mirror.git_exe, 'remote'])
    remotes = remotes.decode('utf-8', 'ignore').splitlines()
  elif args:
    remotes = args
  else:
    current_branch = subprocess.check_output(
        [Mirror.git_exe, 'rev-parse', '--abbrev-ref', 'HEAD'])
    current_branch = current_branch.decode('utf-8', 'ignore').strip()
    if current_branch != 'HEAD':
      upstream = subprocess.check_output(
          [Mirror.git_exe, 'config', 'branch.%s.remote' % current_branch])
      upstream = upstream.decode('utf-8', 'ignore').strip()
      if upstream and upstream != '.':
        remotes = [upstream]
  if not remotes:
    remotes = ['origin']

  cachepath = Mirror.GetCachePath()
  git_dir = os.path.abspath(subprocess.check_output(
      [Mirror.git_exe, 'rev-parse', '--git-dir']).decode('utf-8', 'ignore'))
  git_dir = os.path.abspath(git_dir)
  if git_dir.startswith(cachepath):
    mirror = Mirror.FromPath(git_dir)
    mirror.populate(
        bootstrap=not options.no_bootstrap,
        no_fetch_tags=options.no_fetch_tags,
        lock_timeout=options.timeout)
    return 0
  for remote in remotes:
    remote_url = subprocess.check_output(
        [Mirror.git_exe, 'config', 'remote.%s.url' % remote])
    remote_url = remote_url.decode('utf-8', 'ignore').strip()
    if remote_url.startswith(cachepath):
      mirror = Mirror.FromPath(remote_url)
      mirror.print = lambda *args: None
      print('Updating git cache...')
      mirror.populate(
          bootstrap=not options.no_bootstrap,
          no_fetch_tags=options.no_fetch_tags,
          lock_timeout=options.timeout)
    subprocess.check_call([Mirror.git_exe, 'fetch', remote])
  return 0


@subcommand.usage('do not use - it is a noop.')
def CMDunlock(parser, args):
  """This command does nothing."""
  print('This command does nothing and will be removed in the future.')


class OptionParser(optparse.OptionParser):
  """Wrapper class for OptionParser to handle global options."""

  def __init__(self, *args, **kwargs):
    optparse.OptionParser.__init__(self, *args, prog='git cache', **kwargs)
    self.add_option('-c', '--cache-dir',
                    help=(
                      'Path to the directory containing the caches. Normally '
                      'deduced from git config cache.cachepath or '
                      '$GIT_CACHE_PATH.'))
    self.add_option('-v', '--verbose', action='count', default=1,
                    help='Increase verbosity (can be passed multiple times)')
    self.add_option('-q', '--quiet', action='store_true',
                    help='Suppress all extraneous output')
    self.add_option('--timeout', type='int', default=0,
                    help='Timeout for acquiring cache lock, in seconds')

  def parse_args(self, args=None, values=None):
    options, args = optparse.OptionParser.parse_args(self, args, values)
    if options.quiet:
      options.verbose = 0

    levels = [logging.ERROR, logging.WARNING, logging.INFO, logging.DEBUG]
    logging.basicConfig(level=levels[min(options.verbose, len(levels) - 1)])

    try:
      global_cache_dir = Mirror.GetCachePath()
    except RuntimeError:
      global_cache_dir = None
    if options.cache_dir:
      if global_cache_dir and (
          os.path.abspath(options.cache_dir) !=
          os.path.abspath(global_cache_dir)):
        logging.warning('Overriding globally-configured cache directory.')
      Mirror.SetCachePath(options.cache_dir)

    return options, args


def main(argv):
  dispatcher = subcommand.CommandDispatcher(__name__)
  return dispatcher.execute(OptionParser(), argv)


if __name__ == '__main__':
  try:
    sys.exit(main(sys.argv[1:]))
  except KeyboardInterrupt:
    sys.stderr.write('interrupted\n')
    sys.exit(1)