tools/bisect-builds.py

   1 #!/usr/bin/env python
   2 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
   3 # Use of this source code is governed by a BSD-style license that can be
   4 # found in the LICENSE file.
   5
   6 """Snapshot Build Bisect Tool
   7
   8 This script bisects a snapshot archive using binary search. It starts at
   9 a bad revision (it will try to guess HEAD) and asks for a last known-good
  10 revision. It will then binary search across this revision range by downloading,
  11 unzipping, and opening Chromium for you. After testing the specific revision,
  12 it will ask you whether it is good or bad before continuing the search.
  13 """
  14
  15 # The root URL for storage.
  16 BASE_URL = 'http://commondatastorage.googleapis.com/chromium-browser-snapshots'
  17
  18 # The root URL for official builds.
  19 OFFICIAL_BASE_URL = 'http://master.chrome.corp.google.com/official_builds'
  20
  21 # Changelogs URL.
  22 CHANGELOG_URL = 'http://build.chromium.org/f/chromium/' \
  23                 'perf/dashboard/ui/changelog.html?' \
  24                 'url=/trunk/src&range=%d%%3A%d'
  25
  26 # Official Changelogs URL.
  27 OFFICIAL_CHANGELOG_URL = 'http://omahaproxy.appspot.com/'\
  28                          'changelog?old_version=%s&new_version=%s'
  29
  30 # DEPS file URL.
  31 DEPS_FILE= 'http://src.chromium.org/viewvc/chrome/trunk/src/DEPS?revision=%d'
  32 # Blink Changelogs URL.
  33 BLINK_CHANGELOG_URL = 'http://build.chromium.org/f/chromium/' \
  34                       'perf/dashboard/ui/changelog_blink.html?' \
  35                       'url=/trunk&range=%d%%3A%d'
  36
  37 DONE_MESSAGE_GOOD_MIN = 'You are probably looking for a change made after %s ' \
  38                         '(known good), but no later than %s (first known bad).'
  39 DONE_MESSAGE_GOOD_MAX = 'You are probably looking for a change made after %s ' \
  40                         '(known bad), but no later than %s (first known good).'
  41
  42 ###############################################################################
  43
  44 import math
  45 import optparse
  46 import os
  47 import pipes
  48 import re
  49 import shutil
  50 import subprocess
  51 import sys
  52 import tempfile
  53 import threading
  54 import urllib
  55 from distutils.version import LooseVersion
  56 from xml.etree import ElementTree
  57 import zipfile
  58
  59
  60 class PathContext(object):
  61   """A PathContext is used to carry the information used to construct URLs and
  62   paths when dealing with the storage server and archives."""
  63   def __init__(self, platform, good_revision, bad_revision, is_official,
  64                is_aura):
  65     super(PathContext, self).__init__()
  66     # Store off the input parameters.
  67     self.platform = platform  # What's passed in to the '-a/--archive' option.
  68     self.good_revision = good_revision
  69     self.bad_revision = bad_revision
  70     self.is_official = is_official
  71     self.is_aura = is_aura
  72
  73     # The name of the ZIP file in a revision directory on the server.
  74     self.archive_name = None
  75
  76     # Set some internal members:
  77     #   _listing_platform_dir = Directory that holds revisions. Ends with a '/'.
  78     #   _archive_extract_dir = Uncompressed directory in the archive_name file.
  79     #   _binary_name = The name of the executable to run.
  80     if self.platform in ('linux', 'linux64', 'linux-arm'):
  81       self._binary_name = 'chrome'
  82     elif self.platform == 'mac':
  83       self.archive_name = 'chrome-mac.zip'
  84       self._archive_extract_dir = 'chrome-mac'
  85     elif self.platform == 'win':
  86       self.archive_name = 'chrome-win32.zip'
  87       self._archive_extract_dir = 'chrome-win32'
  88       self._binary_name = 'chrome.exe'
  89     else:
  90       raise Exception('Invalid platform: %s' % self.platform)
  91
  92     if is_official:
  93       if self.platform == 'linux':
  94         self._listing_platform_dir = 'precise32bit/'
  95         self.archive_name = 'chrome-precise32bit.zip'
  96         self._archive_extract_dir = 'chrome-precise32bit'
  97       elif self.platform == 'linux64':
  98         self._listing_platform_dir = 'precise64bit/'
  99         self.archive_name = 'chrome-precise64bit.zip'
 100         self._archive_extract_dir = 'chrome-precise64bit'
 101       elif self.platform == 'mac':
 102         self._listing_platform_dir = 'mac/'
 103         self._binary_name = 'Google Chrome.app/Contents/MacOS/Google Chrome'
 104       elif self.platform == 'win':
 105         if self.is_aura:
 106           self._listing_platform_dir = 'win-aura/'
 107         else:
 108           self._listing_platform_dir = 'win/'
 109     else:
 110       if self.platform in ('linux', 'linux64', 'linux-arm'):
 111         self.archive_name = 'chrome-linux.zip'
 112         self._archive_extract_dir = 'chrome-linux'
 113         if self.platform == 'linux':
 114           self._listing_platform_dir = 'Linux/'
 115         elif self.platform == 'linux64':
 116           self._listing_platform_dir = 'Linux_x64/'
 117         elif self.platform == 'linux-arm':
 118           self._listing_platform_dir = 'Linux_ARM_Cross-Compile/'
 119       elif self.platform == 'mac':
 120         self._listing_platform_dir = 'Mac/'
 121         self._binary_name = 'Chromium.app/Contents/MacOS/Chromium'
 122       elif self.platform == 'win':
 123         self._listing_platform_dir = 'Win/'
 124
 125   def GetListingURL(self, marker=None):
 126     """Returns the URL for a directory listing, with an optional marker."""
 127     marker_param = ''
 128     if marker:
 129       marker_param = '&marker=' + str(marker)
 130     return BASE_URL + '/?delimiter=/&prefix=' + self._listing_platform_dir + \
 131         marker_param
 132
 133   def GetDownloadURL(self, revision):
 134     """Gets the download URL for a build archive of a specific revision."""
 135     if self.is_official:
 136       return "%s/%s/%s%s" % (
 137           OFFICIAL_BASE_URL, revision, self._listing_platform_dir,
 138           self.archive_name)
 139     else:
 140       return "%s/%s%s/%s" % (
 141           BASE_URL, self._listing_platform_dir, revision, self.archive_name)
 142
 143   def GetLastChangeURL(self):
 144     """Returns a URL to the LAST_CHANGE file."""
 145     return BASE_URL + '/' + self._listing_platform_dir + 'LAST_CHANGE'
 146
 147   def GetLaunchPath(self):
 148     """Returns a relative path (presumably from the archive extraction location)
 149     that is used to run the executable."""
 150     return os.path.join(self._archive_extract_dir, self._binary_name)
 151
 152   def IsAuraBuild(self, build):
 153     """Check the given build is Aura."""
 154     return build.split('.')[3] == '1'
 155
 156   def IsASANBuild(self, build):
 157     """Check the given build is ASAN build."""
 158     return build.split('.')[3] == '2'
 159
 160   def ParseDirectoryIndex(self):
 161     """Parses the Google Storage directory listing into a list of revision
 162     numbers."""
 163
 164     def _FetchAndParse(url):
 165       """Fetches a URL and returns a 2-Tuple of ([revisions], next-marker). If
 166       next-marker is not None, then the listing is a partial listing and another
 167       fetch should be performed with next-marker being the marker= GET
 168       parameter."""
 169       handle = urllib.urlopen(url)
 170       document = ElementTree.parse(handle)
 171
 172       # All nodes in the tree are namespaced. Get the root's tag name to extract
 173       # the namespace. Etree does namespaces as |{namespace}tag|.
 174       root_tag = document.getroot().tag
 175       end_ns_pos = root_tag.find('}')
 176       if end_ns_pos == -1:
 177         raise Exception("Could not locate end namespace for directory index")
 178       namespace = root_tag[:end_ns_pos + 1]
 179
 180       # Find the prefix (_listing_platform_dir) and whether or not the list is
 181       # truncated.
 182       prefix_len = len(document.find(namespace + 'Prefix').text)
 183       next_marker = None
 184       is_truncated = document.find(namespace + 'IsTruncated')
 185       if is_truncated is not None and is_truncated.text.lower() == 'true':
 186         next_marker = document.find(namespace + 'NextMarker').text
 187
 188       # Get a list of all the revisions.
 189       all_prefixes = document.findall(namespace + 'CommonPrefixes/' +
 190                                       namespace + 'Prefix')
 191       # The <Prefix> nodes have content of the form of
 192       # |_listing_platform_dir/revision/|. Strip off the platform dir and the
 193       # trailing slash to just have a number.
 194       revisions = []
 195       for prefix in all_prefixes:
 196         revnum = prefix.text[prefix_len:-1]
 197         try:
 198           revnum = int(revnum)
 199           revisions.append(revnum)
 200         except ValueError:
 201           pass
 202       return (revisions, next_marker)
 203
 204     # Fetch the first list of revisions.
 205     (revisions, next_marker) = _FetchAndParse(self.GetListingURL())
 206
 207     # If the result list was truncated, refetch with the next marker. Do this
 208     # until an entire directory listing is done.
 209     while next_marker:
 210       next_url = self.GetListingURL(next_marker)
 211       (new_revisions, next_marker) = _FetchAndParse(next_url)
 212       revisions.extend(new_revisions)
 213     return revisions
 214
 215   def GetRevList(self):
 216     """Gets the list of revision numbers between self.good_revision and
 217     self.bad_revision."""
 218     # Download the revlist and filter for just the range between good and bad.
 219     minrev = min(self.good_revision, self.bad_revision)
 220     maxrev = max(self.good_revision, self.bad_revision)
 221     revlist = map(int, self.ParseDirectoryIndex())
 222     revlist = [x for x in revlist if x >= int(minrev) and x <= int(maxrev)]
 223     revlist.sort()
 224     return revlist
 225
 226   def GetOfficialBuildsList(self):
 227     """Gets the list of official build numbers between self.good_revision and
 228     self.bad_revision."""
 229     # Download the revlist and filter for just the range between good and bad.
 230     minrev = min(self.good_revision, self.bad_revision)
 231     maxrev = max(self.good_revision, self.bad_revision)
 232     handle = urllib.urlopen(OFFICIAL_BASE_URL)
 233     dirindex = handle.read()
 234     handle.close()
 235     build_numbers = re.findall(r'<a href="([0-9][0-9].*)/">', dirindex)
 236     final_list = []
 237     i = 0
 238     parsed_build_numbers = [LooseVersion(x) for x in build_numbers]
 239     for build_number in sorted(parsed_build_numbers):
 240       path = OFFICIAL_BASE_URL + '/' + str(build_number) + '/' + \
 241              self._listing_platform_dir + self.archive_name
 242       i = i + 1
 243       try:
 244         connection = urllib.urlopen(path)
 245         connection.close()
 246         if build_number > maxrev:
 247           break
 248         if build_number >= minrev:
 249           # If we are bisecting Aura, we want to include only builds which
 250           # ends with ".1".
 251           if self.is_aura:
 252             if self.IsAuraBuild(str(build_number)):
 253               final_list.append(str(build_number))
 254           # If we are bisecting only official builds (without --aura),
 255           # we can not include builds which ends with '.1' or '.2' since
 256           # they have different folder hierarchy inside.
 257           elif (not self.IsAuraBuild(str(build_number)) and
 258                 not self.IsASANBuild(str(build_number))):
 259             final_list.append(str(build_number))
 260       except urllib.HTTPError, e:
 261         pass
 262     return final_list
 263
 264 def UnzipFilenameToDir(filename, dir):
 265   """Unzip |filename| to directory |dir|."""
 266   cwd = os.getcwd()
 267   if not os.path.isabs(filename):
 268     filename = os.path.join(cwd, filename)
 269   zf = zipfile.ZipFile(filename)
 270   # Make base.
 271   if not os.path.isdir(dir):
 272     os.mkdir(dir)
 273   os.chdir(dir)
 274   # Extract files.
 275   for info in zf.infolist():
 276     name = info.filename
 277     if name.endswith('/'):  # dir
 278       if not os.path.isdir(name):
 279         os.makedirs(name)
 280     else:  # file
 281       dir = os.path.dirname(name)
 282       if not os.path.isdir(dir):
 283         os.makedirs(dir)
 284       out = open(name, 'wb')
 285       out.write(zf.read(name))
 286       out.close()
 287     # Set permissions. Permission info in external_attr is shifted 16 bits.
 288     os.chmod(name, info.external_attr >> 16L)
 289   os.chdir(cwd)
 290
 291
 292 def FetchRevision(context, rev, filename, quit_event=None, progress_event=None):
 293   """Downloads and unzips revision |rev|.
 294   @param context A PathContext instance.
 295   @param rev The Chromium revision number/tag to download.
 296   @param filename The destination for the downloaded file.
 297   @param quit_event A threading.Event which will be set by the master thread to
 298                     indicate that the download should be aborted.
 299   @param progress_event A threading.Event which will be set by the master thread
 300                     to indicate that the progress of the download should be
 301                     displayed.
 302   """
 303   def ReportHook(blocknum, blocksize, totalsize):
 304     if quit_event and quit_event.isSet():
 305       raise RuntimeError("Aborting download of revision %s" % str(rev))
 306     if progress_event and progress_event.isSet():
 307       size = blocknum * blocksize
 308       if totalsize == -1:  # Total size not known.
 309         progress = "Received %d bytes" % size
 310       else:
 311         size = min(totalsize, size)
 312         progress = "Received %d of %d bytes, %.2f%%" % (
 313             size, totalsize, 100.0 * size / totalsize)
 314       # Send a \r to let all progress messages use just one line of output.
 315       sys.stdout.write("\r" + progress)
 316       sys.stdout.flush()
 317
 318   download_url = context.GetDownloadURL(rev)
 319   try:
 320     urllib.urlretrieve(download_url, filename, ReportHook)
 321     if progress_event and progress_event.isSet():
 322       print
 323   except RuntimeError, e:
 324     pass
 325
 326
 327 def RunRevision(context, revision, zipfile, profile, num_runs, command, args):
 328   """Given a zipped revision, unzip it and run the test."""
 329   print "Trying revision %s..." % str(revision)
 330
 331   # Create a temp directory and unzip the revision into it.
 332   cwd = os.getcwd()
 333   tempdir = tempfile.mkdtemp(prefix='bisect_tmp')
 334   UnzipFilenameToDir(zipfile, tempdir)
 335   os.chdir(tempdir)
 336
 337   # Run the build as many times as specified.
 338   testargs = ['--user-data-dir=%s' % profile] + args
 339   # The sandbox must be run as root on Official Chrome, so bypass it.
 340   if context.is_official and context.platform.startswith('linux'):
 341     testargs.append('--no-sandbox')
 342
 343   runcommand = []
 344   for token in command.split():
 345     if token == "%a":
 346       runcommand.extend(testargs)
 347     else:
 348       runcommand.append( \
 349           token.replace('%p', context.GetLaunchPath()) \
 350                .replace('%s', ' '.join(testargs)))
 351
 352   for i in range(0, num_runs):
 353     subproc = subprocess.Popen(runcommand,
 354                                bufsize=-1,
 355                                stdout=subprocess.PIPE,
 356                                stderr=subprocess.PIPE)
 357     (stdout, stderr) = subproc.communicate()
 358
 359   os.chdir(cwd)
 360   try:
 361     shutil.rmtree(tempdir, True)
 362   except Exception, e:
 363     pass
 364
 365   return (subproc.returncode, stdout, stderr)
 366
 367
 368 def AskIsGoodBuild(rev, official_builds, status, stdout, stderr):
 369   """Ask the user whether build |rev| is good or bad."""
 370   # Loop until we get a response that we can parse.
 371   while True:
 372     response = raw_input('Revision %s is ' \
 373                          '[(g)ood/(b)ad/(r)etry/(u)nknown/(q)uit]: ' %
 374                          str(rev))
 375     if response and response in ('g', 'b', 'r', 'u'):
 376       return response
 377     if response and response == 'q':
 378       raise SystemExit()
 379
 380
 381 class DownloadJob(object):
 382   """DownloadJob represents a task to download a given Chromium revision."""
 383   def __init__(self, context, name, rev, zipfile):
 384     super(DownloadJob, self).__init__()
 385     # Store off the input parameters.
 386     self.context = context
 387     self.name = name
 388     self.rev = rev
 389     self.zipfile = zipfile
 390     self.quit_event = threading.Event()
 391     self.progress_event = threading.Event()
 392
 393   def Start(self):
 394     """Starts the download."""
 395     fetchargs = (self.context,
 396                  self.rev,
 397                  self.zipfile,
 398                  self.quit_event,
 399                  self.progress_event)
 400     self.thread = threading.Thread(target=FetchRevision,
 401                                    name=self.name,
 402                                    args=fetchargs)
 403     self.thread.start()
 404
 405   def Stop(self):
 406     """Stops the download which must have been started previously."""
 407     self.quit_event.set()
 408     self.thread.join()
 409     os.unlink(self.zipfile)
 410
 411   def WaitFor(self):
 412     """Prints a message and waits for the download to complete. The download
 413     must have been started previously."""
 414     print "Downloading revision %s..." % str(self.rev)
 415     self.progress_event.set()  # Display progress of download.
 416     self.thread.join()
 417
 418
 419 def Bisect(platform,
 420            official_builds,
 421            is_aura,
 422            good_rev=0,
 423            bad_rev=0,
 424            num_runs=1,
 425            command="%p %a",
 426            try_args=(),
 427            profile=None,
 428            evaluate=AskIsGoodBuild):
 429   """Given known good and known bad revisions, run a binary search on all
 430   archived revisions to determine the last known good revision.
 431
 432   @param platform Which build to download/run ('mac', 'win', 'linux64', etc.).
 433   @param official_builds Specify build type (Chromium or Official build).
 434   @param good_rev Number/tag of the known good revision.
 435   @param bad_rev Number/tag of the known bad revision.
 436   @param num_runs Number of times to run each build for asking good/bad.
 437   @param try_args A tuple of arguments to pass to the test application.
 438   @param profile The name of the user profile to run with.
 439   @param evaluate A function which returns 'g' if the argument build is good,
 440                   'b' if it's bad or 'u' if unknown.
 441
 442   Threading is used to fetch Chromium revisions in the background, speeding up
 443   the user's experience. For example, suppose the bounds of the search are
 444   good_rev=0, bad_rev=100. The first revision to be checked is 50. Depending on
 445   whether revision 50 is good or bad, the next revision to check will be either
 446   25 or 75. So, while revision 50 is being checked, the script will download
 447   revisions 25 and 75 in the background. Once the good/bad verdict on rev 50 is
 448   known:
 449
 450     - If rev 50 is good, the download of rev 25 is cancelled, and the next test
 451       is run on rev 75.
 452
 453     - If rev 50 is bad, the download of rev 75 is cancelled, and the next test
 454       is run on rev 25.
 455   """
 456
 457   if not profile:
 458     profile = 'profile'
 459
 460   context = PathContext(platform, good_rev, bad_rev, official_builds, is_aura)
 461   cwd = os.getcwd()
 462
 463
 464
 465   print "Downloading list of known revisions..."
 466   _GetDownloadPath = lambda rev: os.path.join(cwd,
 467       '%s-%s' % (str(rev), context.archive_name))
 468   if official_builds:
 469     revlist = context.GetOfficialBuildsList()
 470   else:
 471     revlist = context.GetRevList()
 472
 473   # Get a list of revisions to bisect across.
 474   if len(revlist) < 2:  # Don't have enough builds to bisect.
 475     msg = 'We don\'t have enough builds to bisect. revlist: %s' % revlist
 476     raise RuntimeError(msg)
 477
 478   # Figure out our bookends and first pivot point; fetch the pivot revision.
 479   minrev = 0
 480   maxrev = len(revlist) - 1
 481   pivot = maxrev / 2
 482   rev = revlist[pivot]
 483   zipfile = _GetDownloadPath(rev)
 484   fetch = DownloadJob(context, 'initial_fetch', rev, zipfile)
 485   fetch.Start()
 486   fetch.WaitFor()
 487
 488   # Binary search time!
 489   while fetch and fetch.zipfile and maxrev - minrev > 1:
 490     if bad_rev < good_rev:
 491       min_str, max_str = "bad", "good"
 492     else:
 493       min_str, max_str = "good", "bad"
 494     print 'Bisecting range [%s (%s), %s (%s)].' % (revlist[minrev], min_str, \
 495                                                    revlist[maxrev], max_str)
 496
 497     # Pre-fetch next two possible pivots
 498     #   - down_pivot is the next revision to check if the current revision turns
 499     #     out to be bad.
 500     #   - up_pivot is the next revision to check if the current revision turns
 501     #     out to be good.
 502     down_pivot = int((pivot - minrev) / 2) + minrev
 503     down_fetch = None
 504     if down_pivot != pivot and down_pivot != minrev:
 505       down_rev = revlist[down_pivot]
 506       down_fetch = DownloadJob(context, 'down_fetch', down_rev,
 507                                _GetDownloadPath(down_rev))
 508       down_fetch.Start()
 509
 510     up_pivot = int((maxrev - pivot) / 2) + pivot
 511     up_fetch = None
 512     if up_pivot != pivot and up_pivot != maxrev:
 513       up_rev = revlist[up_pivot]
 514       up_fetch = DownloadJob(context, 'up_fetch', up_rev,
 515                              _GetDownloadPath(up_rev))
 516       up_fetch.Start()
 517
 518     # Run test on the pivot revision.
 519     status = None
 520     stdout = None
 521     stderr = None
 522     try:
 523       (status, stdout, stderr) = RunRevision(context,
 524                                              rev,
 525                                              fetch.zipfile,
 526                                              profile,
 527                                              num_runs,
 528                                              command,
 529                                              try_args)
 530     except Exception, e:
 531       print >>sys.stderr, e
 532
 533     # Call the evaluate function to see if the current revision is good or bad.
 534     # On that basis, kill one of the background downloads and complete the
 535     # other, as described in the comments above.
 536     try:
 537       answer = evaluate(rev, official_builds, status, stdout, stderr)
 538       if answer == 'g' and good_rev < bad_rev or \
 539           answer == 'b' and bad_rev < good_rev:
 540         fetch.Stop()
 541         minrev = pivot
 542         if down_fetch:
 543           down_fetch.Stop()  # Kill the download of the older revision.
 544           fetch = None
 545         if up_fetch:
 546           up_fetch.WaitFor()
 547           pivot = up_pivot
 548           fetch = up_fetch
 549       elif answer == 'b' and good_rev < bad_rev or \
 550           answer == 'g' and bad_rev < good_rev:
 551         fetch.Stop()
 552         maxrev = pivot
 553         if up_fetch:
 554           up_fetch.Stop()  # Kill the download of the newer revision.
 555           fetch = None
 556         if down_fetch:
 557           down_fetch.WaitFor()
 558           pivot = down_pivot
 559           fetch = down_fetch
 560       elif answer == 'r':
 561         pass  # Retry requires no changes.
 562       elif answer == 'u':
 563         # Nuke the revision from the revlist and choose a new pivot.
 564         fetch.Stop()
 565         revlist.pop(pivot)
 566         maxrev -= 1  # Assumes maxrev >= pivot.
 567
 568         if maxrev - minrev > 1:
 569           # Alternate between using down_pivot or up_pivot for the new pivot
 570           # point, without affecting the range. Do this instead of setting the
 571           # pivot to the midpoint of the new range because adjacent revisions
 572           # are likely affected by the same issue that caused the (u)nknown
 573           # response.
 574           if up_fetch and down_fetch:
 575             fetch = [up_fetch, down_fetch][len(revlist) % 2]
 576           elif up_fetch:
 577             fetch = up_fetch
 578           else:
 579             fetch = down_fetch
 580           fetch.WaitFor()
 581           if fetch == up_fetch:
 582             pivot = up_pivot - 1  # Subtracts 1 because revlist was resized.
 583           else:
 584             pivot = down_pivot
 585           zipfile = fetch.zipfile
 586
 587         if down_fetch and fetch != down_fetch:
 588           down_fetch.Stop()
 589         if up_fetch and fetch != up_fetch:
 590           up_fetch.Stop()
 591       else:
 592         assert False, "Unexpected return value from evaluate(): " + answer
 593     except SystemExit:
 594       print "Cleaning up..."
 595       for f in [_GetDownloadPath(revlist[down_pivot]),
 596                 _GetDownloadPath(revlist[up_pivot])]:
 597         try:
 598           os.unlink(f)
 599         except OSError:
 600           pass
 601       sys.exit(0)
 602
 603     rev = revlist[pivot]
 604
 605   return (revlist[minrev], revlist[maxrev])
 606
 607
 608 def GetBlinkRevisionForChromiumRevision(rev):
 609   """Returns the blink revision that was in chromium's DEPS file at
 610   chromium revision |rev|."""
 611   # . doesn't match newlines without re.DOTALL, so this is safe.
 612   blink_re = re.compile(r'webkit_revision.:\D*(\d+)')
 613   url = urllib.urlopen(DEPS_FILE % rev)
 614   m = blink_re.search(url.read())
 615   url.close()
 616   if m:
 617     return int(m.group(1))
 618   else:
 619     raise Exception('Could not get blink revision for cr rev %d' % rev)
 620
 621
 622 def GetChromiumRevision(url):
 623   """Returns the chromium revision read from given URL."""
 624   try:
 625     # Location of the latest build revision number
 626     return int(urllib.urlopen(url).read())
 627   except Exception, e:
 628     print('Could not determine latest revision. This could be bad...')
 629     return 999999999
 630
 631
 632 def main():
 633   usage = ('%prog [options] [-- chromium-options]\n'
 634            'Perform binary search on the snapshot builds to find a minimal\n'
 635            'range of revisions where a behavior change happened. The\n'
 636            'behaviors are described as "good" and "bad".\n'
 637            'It is NOT assumed that the behavior of the later revision is\n'
 638            'the bad one.\n'
 639            '\n'
 640            'Revision numbers should use\n'
 641            '  Official versions (e.g. 1.0.1000.0) for official builds. (-o)\n'
 642            '  SVN revisions (e.g. 123456) for chromium builds, from trunk.\n'
 643            '    Use base_trunk_revision from http://omahaproxy.appspot.com/\n'
 644            '    for earlier revs.\n'
 645            '    Chrome\'s about: build number and omahaproxy branch_revision\n'
 646            '    are incorrect, they are from branches.\n'
 647            '\n'
 648            'Tip: add "-- --no-first-run" to bypass the first run prompts.')
 649   parser = optparse.OptionParser(usage=usage)
 650   # Strangely, the default help output doesn't include the choice list.
 651   choices = ['mac', 'win', 'linux', 'linux64', 'linux-arm']
 652             # linux-chromiumos lacks a continuous archive http://crbug.com/78158
 653   parser.add_option('-a', '--archive',
 654                     choices = choices,
 655                     help = 'The buildbot archive to bisect [%s].' %
 656                            '|'.join(choices))
 657   parser.add_option('-o', action="store_true", dest='official_builds',
 658                     help = 'Bisect across official ' +
 659                     'Chrome builds (internal only) instead of ' +
 660                     'Chromium archives.')
 661   parser.add_option('-b', '--bad', type = 'str',
 662                     help = 'A bad revision to start bisection. ' +
 663                     'May be earlier or later than the good revision. ' +
 664                     'Default is HEAD.')
 665   parser.add_option('-g', '--good', type = 'str',
 666                     help = 'A good revision to start bisection. ' +
 667                     'May be earlier or later than the bad revision. ' +
 668                     'Default is 0.')
 669   parser.add_option('-p', '--profile', '--user-data-dir', type = 'str',
 670                     help = 'Profile to use; this will not reset every run. ' +
 671                     'Defaults to a clean profile.', default = 'profile')
 672   parser.add_option('-t', '--times', type = 'int',
 673                     help = 'Number of times to run each build before asking ' +
 674                     'if it\'s good or bad. Temporary profiles are reused.',
 675                     default = 1)
 676   parser.add_option('-c', '--command', type = 'str',
 677                     help = 'Command to execute. %p and %a refer to Chrome ' +
 678                     'executable and specified extra arguments respectively. ' +
 679                     'Use %s to specify all extra arguments as one string. ' +
 680                     'Defaults to "%p %a". Note that any extra paths ' +
 681                     'specified should be absolute.',
 682                     default = '%p %a');
 683   parser.add_option('--aura',
 684                     dest='aura',
 685                     action='store_true',
 686                     default=False,
 687                     help='Allow the script to bisect aura builds')
 688
 689   (opts, args) = parser.parse_args()
 690
 691   if opts.archive is None:
 692     print 'Error: missing required parameter: --archive'
 693     print
 694     parser.print_help()
 695     return 1
 696
 697   if opts.aura:
 698     if opts.archive != 'win' or not opts.official_builds:
 699       print 'Error: Aura is supported only on Windows platform '\
 700             'and official builds.'
 701       return 1
 702
 703   # Create the context. Initialize 0 for the revisions as they are set below.
 704   context = PathContext(opts.archive, 0, 0, opts.official_builds, opts.aura)
 705   # Pick a starting point, try to get HEAD for this.
 706   if opts.bad:
 707     bad_rev = opts.bad
 708   else:
 709     bad_rev = '999.0.0.0'
 710     if not opts.official_builds:
 711       bad_rev = GetChromiumRevision(context.GetLastChangeURL())
 712
 713   # Find out when we were good.
 714   if opts.good:
 715     good_rev = opts.good
 716   else:
 717     good_rev = '0.0.0.0' if opts.official_builds else 0
 718
 719   if opts.official_builds:
 720     good_rev = LooseVersion(good_rev)
 721     bad_rev = LooseVersion(bad_rev)
 722   else:
 723     good_rev = int(good_rev)
 724     bad_rev = int(bad_rev)
 725
 726   if opts.times < 1:
 727     print('Number of times to run (%d) must be greater than or equal to 1.' %
 728           opts.times)
 729     parser.print_help()
 730     return 1
 731
 732   (min_chromium_rev, max_chromium_rev) = Bisect(
 733       opts.archive, opts.official_builds, opts.aura, good_rev, bad_rev,
 734       opts.times, opts.command, args, opts.profile)
 735
 736   # Get corresponding blink revisions.
 737   try:
 738     min_blink_rev = GetBlinkRevisionForChromiumRevision(min_chromium_rev)
 739     max_blink_rev = GetBlinkRevisionForChromiumRevision(max_chromium_rev)
 740   except Exception, e:
 741     # Silently ignore the failure.
 742     min_blink_rev, max_blink_rev = 0, 0
 743
 744   # We're done. Let the user know the results in an official manner.
 745   if good_rev > bad_rev:
 746     print DONE_MESSAGE_GOOD_MAX % (str(min_chromium_rev), str(max_chromium_rev))
 747   else:
 748     print DONE_MESSAGE_GOOD_MIN % (str(min_chromium_rev), str(max_chromium_rev))
 749
 750   if min_blink_rev != max_blink_rev:
 751     print 'BLINK CHANGELOG URL:'
 752     print '  ' + BLINK_CHANGELOG_URL % (max_blink_rev, min_blink_rev)
 753   print 'CHANGELOG URL:'
 754   if opts.official_builds:
 755     print OFFICIAL_CHANGELOG_URL % (min_chromium_rev, max_chromium_rev)
 756   else:
 757     print '  ' + CHANGELOG_URL % (min_chromium_rev, max_chromium_rev)
 758
 759 if __name__ == '__main__':
 760   sys.exit(main())