text: # Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  """
  Utilities for requesting information for a gerrit server via https.
  
  https://gerrit-review.googlesource.com/Documentation/rest-api.html
  """
  
  import base64
  import contextlib
  import cookielib
  import httplib  # Still used for its constants.
  import json
  import logging
  import netrc
  import os
  import re
  import socket
  import stat
  import sys
  import tempfile
  import time
  import urllib
  import urlparse
  from cStringIO import StringIO
  
  import auth
  import gclient_utils
  import subprocess2
  from third_party import httplib2
  
  LOGGER = logging.getLogger()
  # With a starting sleep time of 1.5 seconds, 2^n exponential backoff, and seven
  # total tries, the sleep time between the first and last tries will be 94.5 sec.
  # TODO(crbug.com/881860): Lower this when crbug.com/877717 is fixed.
  TRY_LIMIT = 7
  
  
  # Controls the transport protocol used to communicate with gerrit.
  # This is parameterized primarily to enable GerritTestCase.
  GERRIT_PROTOCOL = 'https'
  
  
  class GerritError(Exception):
    """Exception class for errors commuicating with the gerrit-on-borg service."""
    def __init__(self, http_status, *args, **kwargs):
      super(GerritError, self).__init__(*args, **kwargs)
      self.http_status = http_status
      self.message = '(%d) %s' % (self.http_status, self.message)
  
  
  class GerritAuthenticationError(GerritError):
    """Exception class for authentication errors during Gerrit communication."""
  
  
  def _QueryString(params, first_param=None):
    """Encodes query parameters in the key:val[+key:val...] format specified here:
  
    https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#list-changes
    """
    q = [urllib.quote(first_param)] if first_param else []
    q.extend(['%s:%s' % (key, val) for key, val in params])
    return '+'.join(q)
  
  
  def GetConnectionObject(protocol=None):
    if protocol is None:
      protocol = GERRIT_PROTOCOL
    if protocol in ('http', 'https'):
      return httplib2.Http()
    else:
      raise RuntimeError(
          "Don't know how to work with protocol '%s'" % protocol)
  
  
  class Authenticator(object):
    """Base authenticator class for authenticator implementations to subclass."""
  
    def get_auth_header(self, host):
      raise NotImplementedError()
  
    @staticmethod
    def get():
      """Returns: (Authenticator) The identified Authenticator to use.
  
      Probes the local system and its environment and identifies the
      Authenticator instance to use.
      """
      # LUCI Context takes priority since it's normally present only on bots,
      # which then must use it.
      if LuciContextAuthenticator.is_luci():
        return LuciContextAuthenticator()
      if GceAuthenticator.is_gce():
        return GceAuthenticator()
      return CookiesAuthenticator()
  
  
  class CookiesAuthenticator(Authenticator):
    """Authenticator implementation that uses ".netrc" or ".gitcookies" for token.
  
    Expected case for developer workstations.
    """
  
    def __init__(self):
      self.netrc = self._get_netrc()
      self.gitcookies = self._get_gitcookies()
  
    @classmethod
    def get_new_password_url(cls, host):
      assert not host.startswith('http')
      # Assume *.googlesource.com pattern.
      parts = host.split('.')
      if not parts[0].endswith('-review'):
        parts[0] += '-review'
      return 'https://%s/new-password' % ('.'.join(parts))
  
    @classmethod
    def get_new_password_message(cls, host):
      assert not host.startswith('http')
      # Assume *.googlesource.com pattern.
      parts = host.split('.')
      if not parts[0].endswith('-review'):
        parts[0] += '-review'
      url = 'https://%s/new-password' % ('.'.join(parts))
      return 'You can (re)generate your credentials by visiting %s' % url
  
    @classmethod
    def get_netrc_path(cls):
      path = '_netrc' if sys.platform.startswith('win') else '.netrc'
      return os.path.expanduser(os.path.join('~', path))
  
    @classmethod
    def _get_netrc(cls):
      # Buffer the '.netrc' path. Use an empty file if it doesn't exist.
      path = cls.get_netrc_path()
      if not os.path.exists(path):
        return netrc.netrc(os.devnull)
  
      st = os.stat(path)
      if st.st_mode & (stat.S_IRWXG | stat.S_IRWXO):
        print >> sys.stderr, (
            'WARNING: netrc file %s cannot be used because its file '
            'permissions are insecure.  netrc file permissions should be '
            '600.' % path)
      with open(path) as fd:
        content = fd.read()
  
      # Load the '.netrc' file. We strip comments from it because processing them
      # can trigger a bug in Windows. See crbug.com/664664.
      content = '\n'.join(l for l in content.splitlines()
                          if l.strip() and not l.strip().startswith('#'))
      with tempdir() as tdir:
        netrc_path = os.path.join(tdir, 'netrc')
        with open(netrc_path, 'w') as fd:
          fd.write(content)
        os.chmod(netrc_path, (stat.S_IRUSR | stat.S_IWUSR))
        return cls._get_netrc_from_path(netrc_path)
  
    @classmethod
    def _get_netrc_from_path(cls, path):
      try:
        return netrc.netrc(path)
      except IOError:
        print >> sys.stderr, 'WARNING: Could not read netrc file %s' % path
        return netrc.netrc(os.devnull)
      except netrc.NetrcParseError as e:
        print >> sys.stderr, ('ERROR: Cannot use netrc file %s due to a '
                              'parsing error: %s' % (path, e))
        return netrc.netrc(os.devnull)
  
    @classmethod
    def get_gitcookies_path(cls):
      if os.getenv('GIT_COOKIES_PATH'):
        return os.getenv('GIT_COOKIES_PATH')
      try:
        return subprocess2.check_output(
            ['git', 'config', '--path', 'http.cookiefile']).strip()
      except subprocess2.CalledProcessError:
        return os.path.join(os.environ['HOME'], '.gitcookies')
  
    @classmethod
    def _get_gitcookies(cls):
      gitcookies = {}
      path = cls.get_gitcookies_path()
      if not os.path.exists(path):
        return gitcookies
  
      try:
        f = open(path, 'rb')
      except IOError:
        return gitcookies
  
      with f:
        for line in f:
          try:
            fields = line.strip().split('\t')
            if line.strip().startswith('#') or len(fields) != 7:
              continue
            domain, xpath, key, value = fields[0], fields[2], fields[5], fields[6]
            if xpath == '/' and key == 'o':
              login, secret_token = value.split('=', 1)
              gitcookies[domain] = (login, secret_token)
          except (IndexError, ValueError, TypeError) as exc:
            LOGGER.warning(exc)
  
      return gitcookies
  
    def _get_auth_for_host(self, host):
      for domain, creds in self.gitcookies.iteritems():
        if cookielib.domain_match(host, domain):
          return (creds[0], None, creds[1])
      return self.netrc.authenticators(host)
  
    def get_auth_header(self, host):
      a = self._get_auth_for_host(host)
      if a:
        return 'Basic %s' % (base64.b64encode('%s:%s' % (a[0], a[2])))
      return None
  
    def get_auth_email(self, host):
      """Best effort parsing of email to be used for auth for the given host."""
      a = self._get_auth_for_host(host)
      if not a:
        return None
      login = a[0]
      # login typically looks like 'git-xxx.example.com'
      if not login.startswith('git-') or '.' not in login:
        return None
      username, domain = login[len('git-'):].split('.', 1)
      return '%s@%s' % (username, domain)
  
  
  # Backwards compatibility just in case somebody imports this outside of
  # depot_tools.
  NetrcAuthenticator = CookiesAuthenticator
  
  
  class GceAuthenticator(Authenticator):
    """Authenticator implementation that uses GCE metadata service for token.
    """
  
    _INFO_URL = 'http://metadata.google.internal'
    _ACQUIRE_URL = ('%s/computeMetadata/v1/instance/'
                    'service-accounts/default/token' % _INFO_URL)
    _ACQUIRE_HEADERS = {"Metadata-Flavor": "Google"}
  
    _cache_is_gce = None
    _token_cache = None
    _token_expiration = None
  
    @classmethod
    def is_gce(cls):
      if os.getenv('SKIP_GCE_AUTH_FOR_GIT'):
        return False
      if cls._cache_is_gce is None:
        cls._cache_is_gce = cls._test_is_gce()
      return cls._cache_is_gce
  
    @classmethod
    def _test_is_gce(cls):
      # Based on https://cloud.google.com/compute/docs/metadata#runninggce
      try:
        resp, _ = cls._get(cls._INFO_URL)
      except (socket.error, httplib2.ServerNotFoundError,
              httplib2.socks.HTTPError):
        # Could not resolve URL.
        return False
      return resp.get('metadata-flavor') == 'Google'
  
    @staticmethod
    def _get(url, **kwargs):
      next_delay_sec = 1
      for i in xrange(TRY_LIMIT):
        p = urlparse.urlparse(url)
        c = GetConnectionObject(protocol=p.scheme)
        resp, contents = c.request(url, 'GET', **kwargs)
        LOGGER.debug('GET [%s] #%d/%d (%d)', url, i+1, TRY_LIMIT, resp.status)
        if resp.status < httplib.INTERNAL_SERVER_ERROR:
          return (resp, contents)
  
        # Retry server error status codes.
        LOGGER.warn('Encountered server error')
        if TRY_LIMIT - i > 1:
          LOGGER.info('Will retry in %d seconds (%d more times)...',
                      next_delay_sec, TRY_LIMIT - i - 1)
          time.sleep(next_delay_sec)
          next_delay_sec *= 2
  
  
    @classmethod
    def _get_token_dict(cls):
      if cls._token_cache:
        # If it expires within 25 seconds, refresh.
        if cls._token_expiration < time.time() - 25:
          return cls._token_cache
  
      resp, contents = cls._get(cls._ACQUIRE_URL, headers=cls._ACQUIRE_HEADERS)
      if resp.status != httplib.OK:
        return None
      cls._token_cache = json.loads(contents)
      cls._token_expiration = cls._token_cache['expires_in'] + time.time()
      return cls._token_cache
  
    def get_auth_header(self, _host):
      token_dict = self._get_token_dict()
      if not token_dict:
        return None
      return '%(token_type)s %(access_token)s' % token_dict
  
  
  class LuciContextAuthenticator(Authenticator):
    """Authenticator implementation that uses LUCI_CONTEXT ambient local auth.
    """
  
    @staticmethod
    def is_luci():
      return auth.has_luci_context_local_auth()
  
    def __init__(self):
      self._access_token = None
      self._ensure_fresh()
  
    def _ensure_fresh(self):
      if not self._access_token or self._access_token.needs_refresh():
        self._access_token = auth.get_luci_context_access_token(
            scopes=' '.join([auth.OAUTH_SCOPE_EMAIL, auth.OAUTH_SCOPE_GERRIT]))
  
    def get_auth_header(self, _host):
      self._ensure_fresh()
      return 'Bearer %s' % self._access_token.token
  
  
  def CreateHttpConn(host, path, reqtype='GET', headers=None, body=None):
    """Opens an https connection to a gerrit service, and sends a request."""
    headers = headers or {}
    bare_host = host.partition(':')[0]
  
    a = Authenticator.get().get_auth_header(bare_host)
    if a:
      headers.setdefault('Authorization', a)
    else:
      LOGGER.debug('No authorization found for %s.' % bare_host)
  
    url = path
    if not url.startswith('/'):
      url = '/' + url
    if 'Authorization' in headers and not url.startswith('/a/'):
      url = '/a%s' % url
  
    if body:
      body = json.JSONEncoder().encode(body)
      headers.setdefault('Content-Type', 'application/json')
    if LOGGER.isEnabledFor(logging.DEBUG):
      LOGGER.debug('%s %s://%s%s' % (reqtype, GERRIT_PROTOCOL, host, url))
      for key, val in headers.iteritems():
        if key == 'Authorization':
          val = 'HIDDEN'
        LOGGER.debug('%s: %s' % (key, val))
      if body:
        LOGGER.debug(body)
    conn = GetConnectionObject()
    # HACK: httplib.Http has no such attribute; we store req_host here for later
    # use in ReadHttpResponse.
    conn.req_host = host
    conn.req_params = {
        'uri': urlparse.urljoin('%s://%s' % (GERRIT_PROTOCOL, host), url),
        'method': reqtype,
        'headers': headers,
        'body': body,
    }
    return conn
  
  
  def ReadHttpResponse(conn, accept_statuses=frozenset([200])):
    """Reads an http response from a connection into a string buffer.
  
    Args:
      conn: An Http object created by CreateHttpConn above.
      accept_statuses: Treat any of these statuses as success. Default: [200]
                       Common additions include 204, 400, and 404.
    Returns: A string buffer containing the connection's reply.
    """
    sleep_time = 1.5
    for idx in range(TRY_LIMIT):
      response, contents = conn.request(**conn.req_params)
  
      # Check if this is an authentication issue.
      www_authenticate = response.get('www-authenticate')
      if (response.status in (httplib.UNAUTHORIZED, httplib.FOUND) and
          www_authenticate):
        auth_match = re.search('realm="([^"]+)"', www_authenticate, re.I)
        host = auth_match.group(1) if auth_match else conn.req_host
        reason = ('Authentication failed. Please make sure your .gitcookies file '
                  'has credentials for %s' % host)
        raise GerritAuthenticationError(response.status, reason)
  
      # If response.status < 500 then the result is final; break retry loop.
      # If the response is 404/409, it might be because of replication lag, so
      # keep trying anyway.
      if ((response.status < 500 and response.status not in [404, 409])
          or response.status in accept_statuses):
        LOGGER.debug('got response %d for %s %s', response.status,
                     conn.req_params['method'], conn.req_params['uri'])
        # If 404 was in accept_statuses, then it's expected that the file might
        # not exist, so don't return the gitiles error page because that's not the
        # "content" that was actually requested.
        if response.status == 404:
          contents = ''
        break
      # A status >=500 is assumed to be a possible transient error; retry.
      http_version = 'HTTP/%s' % ('1.1' if response.version == 11 else '1.0')
  
      # TODO(crbug/881860): remove this special 404 handling.
      if response.status == 404:
        LOGGER.warn(
            '404 NotFound error occurred while querying %s %s: %s\n'
            'NOTE: if see this while running `git cl upload`,\n'
            'consider reporting this to https://crbug.com/881860.\n'
            'Please, include response headers below:\n'
            '  %s\n',
            conn.req_params['method'], conn.req_params['uri'], response.reason,
            '\n  '.join(
                json.dumps(response, sort_keys=True, indent=2).splitlines()))
      else:
        LOGGER.warn('A transient error occurred while querying %s:\n'
                    '%s %s\n'
                    '%s %d %s\n',
                    conn.req_host,
                    conn.req_params['method'], conn.req_params['uri'],
                    http_version, response.status, response.reason)
  
      if TRY_LIMIT - idx > 1:
        LOGGER.info('Will retry in %d seconds (%d more times)...',
                    sleep_time, TRY_LIMIT - idx - 1)
        time.sleep(sleep_time)
        sleep_time = sleep_time * 2
    if response.status not in accept_statuses:
      if response.status in (401, 403):
        print('Your Gerrit credentials might be misconfigured. Try: \n'
              '  git cl creds-check')
      reason = '%s: %s' % (response.reason, contents)
      raise GerritError(response.status, reason)
    return StringIO(contents)
  
  
  def ReadHttpJsonResponse(conn, accept_statuses=frozenset([200])):
    """Parses an https response as json."""
    fh = ReadHttpResponse(conn, accept_statuses)
    # The first line of the response should always be: )]}'
    s = fh.readline()
    if s and s.rstrip() != ")]}'":
      raise GerritError(200, 'Unexpected json output: %s' % s)
    s = fh.read()
    if not s:
      return None
    return json.loads(s)
  
  
  def QueryChanges(host, params, first_param=None, limit=None, o_params=None,
                   start=None):
    """
    Queries a gerrit-on-borg server for changes matching query terms.
  
    Args:
      params: A list of key:value pairs for search parameters, as documented
          here (e.g. ('is', 'owner') for a parameter 'is:owner'):
          https://gerrit-review.googlesource.com/Documentation/user-search.html#search-operators
      first_param: A change identifier
      limit: Maximum number of results to return.
      start: how many changes to skip (starting with the most recent)
      o_params: A list of additional output specifiers, as documented here:
          https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#list-changes
    Returns:
      A list of json-decoded query results.
    """
    # Note that no attempt is made to escape special characters; YMMV.
    if not params and not first_param:
      raise RuntimeError('QueryChanges requires search parameters')
    path = 'changes/?q=%s' % _QueryString(params, first_param)
    if start:
      path = '%s&start=%s' % (path, start)
    if limit:
      path = '%s&n=%d' % (path, limit)
    if o_params:
      path = '%s&%s' % (path, '&'.join(['o=%s' % p for p in o_params]))
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GenerateAllChanges(host, params, first_param=None, limit=500,
                         o_params=None, start=None):
    """
    Queries a gerrit-on-borg server for all the changes matching the query terms.
  
    WARNING: this is unreliable if a change matching the query is modified while
      this function is being called.
  
    A single query to gerrit-on-borg is limited on the number of results by the
    limit parameter on the request (see QueryChanges) and the server maximum
    limit.
  
    Args:
      params, first_param: Refer to QueryChanges().
      limit: Maximum number of requested changes per query.
      o_params: Refer to QueryChanges().
      start: Refer to QueryChanges().
  
    Returns:
      A generator object to the list of returned changes.
    """
    already_returned = set()
    def at_most_once(cls):
      for cl in cls:
        if cl['_number'] not in already_returned:
          already_returned.add(cl['_number'])
          yield cl
  
    start = start or 0
    cur_start = start
    more_changes = True
  
    while more_changes:
      # This will fetch changes[start..start+limit] sorted by most recently
      # updated. Since the rank of any change in this list can be changed any time
      # (say user posting comment), subsequent calls may overalp like this:
      #   > initial order ABCDEFGH
      #   query[0..3]  => ABC
      #   > E get's updated. New order: EABCDFGH
      #   query[3..6] => CDF   # C is a dup
      #   query[6..9] => GH    # E is missed.
      page = QueryChanges(host, params, first_param, limit, o_params,
                          cur_start)
      for cl in at_most_once(page):
        yield cl
  
      more_changes = [cl for cl in page if '_more_changes' in cl]
      if len(more_changes) > 1:
        raise GerritError(
            200,
            'Received %d changes with a _more_changes attribute set but should '
            'receive at most one.' % len(more_changes))
      if more_changes:
        cur_start += len(page)
  
    # If we paged through, query again the first page which in most circumstances
    # will fetch all changes that were modified while this function was run.
    if start != cur_start:
      page = QueryChanges(host, params, first_param, limit, o_params, start)
      for cl in at_most_once(page):
        yield cl
  
  
  def MultiQueryChanges(host, params, change_list, limit=None, o_params=None,
                        start=None):
    """Initiate a query composed of multiple sets of query parameters."""
    if not change_list:
      raise RuntimeError(
          "MultiQueryChanges requires a list of change numbers/id's")
    q = ['q=%s' % '+OR+'.join([urllib.quote(str(x)) for x in change_list])]
    if params:
      q.append(_QueryString(params))
    if limit:
      q.append('n=%d' % limit)
    if start:
      q.append('S=%s' % start)
    if o_params:
      q.extend(['o=%s' % p for p in o_params])
    path = 'changes/?%s' % '&'.join(q)
    try:
      result = ReadHttpJsonResponse(CreateHttpConn(host, path))
    except GerritError as e:
      msg = '%s:\n%s' % (e.message, path)
      raise GerritError(e.http_status, msg)
    return result
  
  
  def GetGerritFetchUrl(host):
    """Given a gerrit host name returns URL of a gerrit instance to fetch from."""
    return '%s://%s/' % (GERRIT_PROTOCOL, host)
  
  
  def GetChangePageUrl(host, change_number):
    """Given a gerrit host name and change number, return change page url."""
    return '%s://%s/#/c/%d/' % (GERRIT_PROTOCOL, host, change_number)
  
  
  def GetChangeUrl(host, change):
    """Given a gerrit host name and change id, return an url for the change."""
    return '%s://%s/a/changes/%s' % (GERRIT_PROTOCOL, host, change)
  
  
  def GetChange(host, change):
    """Query a gerrit server for information about a single change."""
    path = 'changes/%s' % change
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GetChangeDetail(host, change, o_params=None):
    """Query a gerrit server for extended information about a single change."""
    path = 'changes/%s/detail' % change
    if o_params:
      path += '?%s' % '&'.join(['o=%s' % p for p in o_params])
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GetChangeCommit(host, change, revision='current'):
    """Query a gerrit server for a revision associated with a change."""
    path = 'changes/%s/revisions/%s/commit?links' % (change, revision)
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GetChangeCurrentRevision(host, change):
    """Get information about the latest revision for a given change."""
    return QueryChanges(host, [], change, o_params=('CURRENT_REVISION',))
  
  
  def GetChangeRevisions(host, change):
    """Get information about all revisions associated with a change."""
    return QueryChanges(host, [], change, o_params=('ALL_REVISIONS',))
  
  
  def GetChangeReview(host, change, revision=None):
    """Get the current review information for a change."""
    if not revision:
      jmsg = GetChangeRevisions(host, change)
      if not jmsg:
        return None
      elif len(jmsg) > 1:
        raise GerritError(200, 'Multiple changes found for ChangeId %s.' % change)
      revision = jmsg[0]['current_revision']
    path = 'changes/%s/revisions/%s/review'
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GetChangeComments(host, change):
    """Get the line- and file-level comments on a change."""
    path = 'changes/%s/comments' % change
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def AbandonChange(host, change, msg=''):
    """Abandon a gerrit change."""
    path = 'changes/%s/abandon' % change
    body = {'message': msg} if msg else {}
    conn = CreateHttpConn(host, path, reqtype='POST', body=body)
    return ReadHttpJsonResponse(conn)
  
  
  def RestoreChange(host, change, msg=''):
    """Restore a previously abandoned change."""
    path = 'changes/%s/restore' % change
    body = {'message': msg} if msg else {}
    conn = CreateHttpConn(host, path, reqtype='POST', body=body)
    return ReadHttpJsonResponse(conn)
  
  
  def SubmitChange(host, change, wait_for_merge=True):
    """Submits a gerrit change via Gerrit."""
    path = 'changes/%s/submit' % change
    body = {'wait_for_merge': wait_for_merge}
    conn = CreateHttpConn(host, path, reqtype='POST', body=body)
    return ReadHttpJsonResponse(conn)
  
  
  def HasPendingChangeEdit(host, change):
    conn = CreateHttpConn(host, 'changes/%s/edit' % change)
    try:
      ReadHttpResponse(conn)
    except GerritError as e:
      # 204 No Content means no pending change.
      if e.http_status == 204:
        return False
      raise
    return True
  
  
  def DeletePendingChangeEdit(host, change):
    conn = CreateHttpConn(host, 'changes/%s/edit' % change, reqtype='DELETE')
    # On success, gerrit returns status 204; if the edit was already deleted it
    # returns 404.  Anything else is an error.
    ReadHttpResponse(conn, accept_statuses=[204, 404])
  
  
  def SetCommitMessage(host, change, description, notify='ALL'):
    """Updates a commit message."""
    assert notify in ('ALL', 'NONE')
    path = 'changes/%s/message' % change
    body = {'message': description, 'notify': notify}
    conn = CreateHttpConn(host, path, reqtype='PUT', body=body)
    try:
      ReadHttpResponse(conn, accept_statuses=[200, 204])
    except GerritError as e:
      raise GerritError(
          e.http_status,
          'Received unexpected http status while editing message '
          'in change %s' % change)
  
  
  def GetReviewers(host, change):
    """Get information about all reviewers attached to a change."""
    path = 'changes/%s/reviewers' % change
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def GetReview(host, change, revision):
    """Get review information about a specific revision of a change."""
    path = 'changes/%s/revisions/%s/review' % (change, revision)
    return ReadHttpJsonResponse(CreateHttpConn(host, path))
  
  
  def AddReviewers(host, change, reviewers=None, ccs=None, notify=True,
                   accept_statuses=frozenset([200, 400, 422])):
    """Add reviewers to a change."""
    if not reviewers and not ccs:
      return None
    if not change:
      return None
    reviewers = frozenset(reviewers or [])
    ccs = frozenset(ccs or [])
    path = 'changes/%s/revisions/current/review' % change
  
    body = {
      'drafts': 'KEEP',
      'reviewers': [],
      'notify': 'ALL' if notify else 'NONE',
    }
    for r in sorted(reviewers | ccs):
      state = 'REVIEWER' if r in reviewers else 'CC'
      body['reviewers'].append({
       'reviewer': r,
       'state': state,
       'notify': 'NONE',  # We handled `notify` argument above.
     })
  
    conn = CreateHttpConn(host, path, reqtype='POST', body=body)
    # Gerrit will return 400 if one or more of the requested reviewers are
    # unprocessable. We read the response object to see which were rejected,
    # warn about them, and retry with the remainder.
    resp = ReadHttpJsonResponse(conn, accept_statuses=accept_statuses)
  
    errored = set()
    for result in resp.get('reviewers', {}).itervalues():
      r = result.get('input')
      state = 'REVIEWER' if r in reviewers else 'CC'
      if result.get('error'):
        errored.add(r)
        LOGGER.warn('Note: "%s" not added as a %s' % (r, state.lower()))
    if errored:
      # Try again, adding only those that didn't fail, and only accepting 200.
      AddReviewers(host, change, reviewers=(reviewers-errored),
                   ccs=(ccs-errored), notify=notify, accept_statuses=[200])
  
  
  def RemoveReviewers(host, change, remove=None):
    """Remove reveiewers from a change."""
    if not remove:
      return
    if isinstance(remove, basestring):
      remove = (remove,)
    for r in remove:
      path = 'changes/%s/reviewers/%s' % (change, r)
      conn = CreateHttpConn(host, path, reqtype='DELETE')
      try:
        ReadHttpResponse(conn, accept_statuses=[204])
      except GerritError as e:
        raise GerritError(
            e.http_status,
            'Received unexpected http status while deleting reviewer "%s" '
            'from change %s' % (r, change))
  
  
  def SetReview(host, change, msg=None, labels=None, notify=None, ready=None):
    """Set labels and/or add a message to a code review."""
    if not msg and not labels:
      return
    path = 'changes/%s/revisions/current/review' % change
    body = {'drafts': 'KEEP'}
    if msg:
      body['message'] = msg
    if labels:
      body['labels'] = labels
    if notify is not None:
      body['notify'] = 'ALL' if notify else 'NONE'
    if ready:
      body['ready'] = True
    conn = CreateHttpConn(host, path, reqtype='POST', body=body)
    response = ReadHttpJsonResponse(conn)
    if labels:
      for key, val in labels.iteritems():
        if ('labels' not in response or key not in response['labels'] or
            int(response['labels'][key] != int(val))):
          raise GerritError(200, 'Unable to set "%s" label on change %s.' % (
              key, change))
  
  
  def ResetReviewLabels(host, change, label, value='0', message=None,
                        notify=None):
    """Reset the value of a given label for all reviewers on a change."""
    # This is tricky, because we want to work on the "current revision", but
    # there's always the risk that "current revision" will change in between
    # API calls.  So, we check "current revision" at the beginning and end; if
    # it has changed, raise an exception.
    jmsg = GetChangeCurrentRevision(host, change)
    if not jmsg:
      raise GerritError(
          200, 'Could not get review information for change "%s"' % change)
    value = str(value)
    revision = jmsg[0]['current_revision']
    path = 'changes/%s/revisions/%s/review' % (change, revision)
    message = message or (
        '%s label set to %s programmatically.' % (label, value))
    jmsg = GetReview(host, change, revision)
    if not jmsg:
      raise GerritError(200, 'Could not get review information for revison %s '
                     'of change %s' % (revision, change))
    for review in jmsg.get('labels', {}).get(label, {}).get('all', []):
      if str(review.get('value', value)) != value:
        body = {
            'drafts': 'KEEP',
            'message': message,
            'labels': {label: value},
            'on_behalf_of': review['_account_id'],
        }
        if notify:
          body['notify'] = notify
        conn = CreateHttpConn(
            host, path, reqtype='POST', body=body)
        response = ReadHttpJsonResponse(conn)
        if str(response['labels'][label]) != value:
          username = review.get('email', jmsg.get('name', ''))
          raise GerritError(200, 'Unable to set %s label for user "%s"'
                         ' on change %s.' % (label, username, change))
    jmsg = GetChangeCurrentRevision(host, change)
    if not jmsg:
      raise GerritError(
          200, 'Could not get review information for change "%s"' % change)
    elif jmsg[0]['current_revision'] != revision:
      raise GerritError(200, 'While resetting labels on change "%s", '
                     'a new patchset was uploaded.' % change)
  
  
  def CreateGerritBranch(host, project, branch, commit):
    """
    Create a new branch from given project and commit
    https://gerrit-review.googlesource.com/Documentation/rest-api-projects.html#create-branch
  
    Returns:
      A JSON with 'ref' key
    """
    path = 'projects/%s/branches/%s' % (project, branch)
    body = {'revision': commit}
    conn = CreateHttpConn(host, path, reqtype='PUT', body=body)
    response = ReadHttpJsonResponse(conn, accept_statuses=[201])
    if response:
      return response
    raise GerritError(200, 'Unable to create gerrit branch')
  
  
  def GetGerritBranch(host, project, branch):
    """
    Get a branch from given project and commit
    https://gerrit-review.googlesource.com/Documentation/rest-api-projects.html#get-branch
  
    Returns:
      A JSON object with 'revision' key
    """
    path = 'projects/%s/branches/%s' % (project, branch)
    conn = CreateHttpConn(host, path, reqtype='GET')
    response = ReadHttpJsonResponse(conn)
    if response:
      return response
    raise GerritError(200, 'Unable to get gerrit branch')
  
  
  def GetAccountDetails(host, account_id='self'):
    """Returns details of the account.
  
    If account_id is not given, uses magic value 'self' which corresponds to
    whichever account user is authenticating as.
  
    Documentation:
      https://gerrit-review.googlesource.com/Documentation/rest-api-accounts.html#get-account
    """
    if account_id != 'self':
      account_id = int(account_id)
    conn = CreateHttpConn(host, '/accounts/%s' % account_id)
    return ReadHttpJsonResponse(conn)
  
  
  def PercentEncodeForGitRef(original):
    """Apply percent-encoding for strings sent to gerrit via git ref metadata.
  
    The encoding used is based on but stricter than URL encoding (Section 2.1
    of RFC 3986). The only non-escaped characters are alphanumerics, and
    'SPACE' (U+0020) can be represented as 'LOW LINE' (U+005F) or
    'PLUS SIGN' (U+002B).
  
    For more information, see the Gerrit docs here:
  
    https://gerrit-review.googlesource.com/Documentation/user-upload.html#message
    """
    safe = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 '
    encoded = ''.join(c if c in safe else '%%%02X' % ord(c) for c in original)
  
    # spaces are not allowed in git refs; gerrit will interpret either '_' or
    # '+' (or '%20') as space. Use '_' since that has been supported the longest.
    return encoded.replace(' ', '_')
  
  
  @contextlib.contextmanager
  def tempdir():
    tdir = None
    try:
      tdir = tempfile.mkdtemp(suffix='gerrit_util')
      yield tdir
    finally:
      if tdir:
        gclient_utils.rmtree(tdir)
  
  
  def ChangeIdentifier(project, change_number):
    """Returns change identifier "project~number" suitable for |chagne| arg of
    this module API.
  
    Such format is allows for more efficient Gerrit routing of HTTP requests,
    comparing to specifying just change_number.
    """
    assert int(change_number)
    return '%s~%s' % (urllib.quote(project, safe=''), change_number)
  