#!/usr/bin/python

"""
Copyright 2013 Google Inc.

Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.

HTTP server for our HTML rebaseline viewer.
"""

# System-level imports
import argparse
import BaseHTTPServer
import json
import logging
import os
import posixpath
import re
import shutil
import socket
import subprocess
import thread
import threading
import time
import urllib
import urlparse

# Must fix up PYTHONPATH before importing from within Skia
import fix_pythonpath  # pylint: disable=W0611

# Imports from within Skia
from py.utils import gs_utils
import buildbot_globals
import gm_json

# Imports from local dir
#
# pylint: disable=C0301
# Note: we import results under a different name, to avoid confusion with the
# Server.results() property. See discussion at
# https://codereview.chromium.org/195943004/diff/1/gm/rebaseline_server/server.py#newcode44
# pylint: enable=C0301
import compare_configs
import compare_rendered_pictures
import compare_to_expectations
import download_actuals
import imagediffdb
import imagepairset
import results as results_mod

PATHSPLIT_RE = re.compile('/([^/]+)/(.+)')

# A simple dictionary of file name extensions to MIME types. The empty string
# entry is used as the default when no extension was given or if the extension
# has no entry in this dictionary.
MIME_TYPE_MAP = {'': 'application/octet-stream',
                 'html': 'text/html',
                 'css': 'text/css',
                 'png': 'image/png',
                 'js': 'application/javascript',
                 'json': 'application/json'
                 }

# Keys that server.py uses to create the toplevel content header.
# NOTE: Keep these in sync with static/constants.js
KEY__EDITS__MODIFICATIONS = 'modifications'
KEY__EDITS__OLD_RESULTS_HASH = 'oldResultsHash'
KEY__EDITS__OLD_RESULTS_TYPE = 'oldResultsType'

DEFAULT_ACTUALS_DIR = results_mod.DEFAULT_ACTUALS_DIR
DEFAULT_GM_SUMMARIES_BUCKET = download_actuals.GM_SUMMARIES_BUCKET
DEFAULT_JSON_FILENAME = download_actuals.DEFAULT_JSON_FILENAME
DEFAULT_PORT = 8888

PARENT_DIRECTORY = os.path.dirname(os.path.realpath(__file__))
TRUNK_DIRECTORY = os.path.dirname(os.path.dirname(PARENT_DIRECTORY))

# Directory, relative to PARENT_DIRECTORY, within which the server will serve
# out static files.
STATIC_CONTENTS_SUBDIR = 'static'
# All of the GENERATED_*_SUBDIRS are relative to STATIC_CONTENTS_SUBDIR
GENERATED_HTML_SUBDIR = 'generated-html'
GENERATED_IMAGES_SUBDIR = 'generated-images'
GENERATED_JSON_SUBDIR = 'generated-json'

# Directives associated with various HTTP GET requests.
GET__LIVE_RESULTS = 'live-results'
GET__PRECOMPUTED_RESULTS = 'results'
GET__PREFETCH_RESULTS = 'prefetch'
GET__STATIC_CONTENTS = 'static'

# Parameters we use within do_GET_live_results() and do_GET_prefetch_results()
LIVE_PARAM__DOWNLOAD_ONLY_DIFFERING = 'downloadOnlyDifferingImages'
LIVE_PARAM__SET_A_DIR = 'setADir'
LIVE_PARAM__SET_A_SECTION = 'setASection'
LIVE_PARAM__SET_B_DIR = 'setBDir'
LIVE_PARAM__SET_B_SECTION = 'setBSection'

# How often (in seconds) clients should reload while waiting for initial
# results to load.
RELOAD_INTERVAL_UNTIL_READY = 10

_GM_SUMMARY_TYPES = [
    results_mod.KEY__HEADER__RESULTS_FAILURES,
    results_mod.KEY__HEADER__RESULTS_ALL,
]
# If --compare-configs is specified, compare these configs.
CONFIG_PAIRS_TO_COMPARE = [('8888', 'gpu')]

# SKP results that are available to compare.
#
# TODO(stephana): We don't actually want to maintain this list of platforms.
# We are just putting them in here for now, as "convenience" links for testing
# SKP diffs.
# Ultimately, we will depend on buildbot steps linking to their own diffs on
# the shared rebaseline_server instance.
_SKP_BASE_GS_URL = 'gs://' + buildbot_globals.Get('skp_summaries_bucket')
_SKP_BASE_REPO_URL = (
    compare_rendered_pictures.REPO_URL_PREFIX + posixpath.join(
        'expectations', 'skp'))
_SKP_PLATFORMS = [
    'Test-Mac10.8-MacMini4.1-GeForce320M-x86_64-Debug',
    'Test-Ubuntu12-ShuttleA-GTX660-x86-Release',
]

_HTTP_HEADER_CONTENT_LENGTH = 'Content-Length'
_HTTP_HEADER_CONTENT_TYPE = 'Content-Type'

_SERVER = None   # This gets filled in by main()


def _run_command(args, directory):
  """Runs a command and returns stdout as a single string.

  Args:
    args: the command to run, as a list of arguments
    directory: directory within which to run the command

  Returns: stdout, as a string

  Raises an Exception if the command failed (exited with nonzero return code).
  """
  logging.debug('_run_command: %s in directory %s' % (args, directory))
  proc = subprocess.Popen(args, cwd=directory,
                          stdout=subprocess.PIPE,
                          stderr=subprocess.PIPE)
  (stdout, stderr) = proc.communicate()
  if proc.returncode is not 0:
    raise Exception('command "%s" failed in dir "%s": %s' %
                    (args, directory, stderr))
  return stdout


def _get_routable_ip_address():
  """Returns routable IP address of this host (the IP address of its network
     interface that would be used for most traffic, not its localhost
     interface).  See http://stackoverflow.com/a/166589 """
  sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  sock.connect(('8.8.8.8', 80))
  host = sock.getsockname()[0]
  sock.close()
  return host


def _create_index(file_path, config_pairs):
  """Creates an index file linking to all results available from this server.

  Prior to https://codereview.chromium.org/215503002 , we had a static
  index.html within our repo.  But now that the results may or may not include
  config comparisons, index.html needs to be generated differently depending
  on which results are included.

  TODO(epoger): Instead of including raw HTML within the Python code,
  consider restoring the index.html file as a template and using django (or
  similar) to fill in dynamic content.

  Args:
    file_path: path on local disk to write index to; any directory components
               of this path that do not already exist will be created
    config_pairs: what pairs of configs (if any) we compare actual results of
  """
  dir_path = os.path.dirname(file_path)
  if not os.path.isdir(dir_path):
    os.makedirs(dir_path)
  with open(file_path, 'w') as file_handle:
    file_handle.write(
        '<!DOCTYPE html><html>'
        '<head><title>rebaseline_server</title></head>'
        '<body><ul>')

    if _GM_SUMMARY_TYPES:
      file_handle.write('<li>GM Expectations vs Actuals</li><ul>')
      for summary_type in _GM_SUMMARY_TYPES:
        file_handle.write(
            '\n<li><a href="/{static_directive}/view.html#/view.html?'
            'resultsToLoad=/{results_directive}/{summary_type}">'
            '{summary_type}</a></li>'.format(
                results_directive=GET__PRECOMPUTED_RESULTS,
                static_directive=GET__STATIC_CONTENTS,
                summary_type=summary_type))
      file_handle.write('</ul>')

    if config_pairs:
      file_handle.write(
          '\n<li>Comparing configs within actual GM results</li><ul>')
      for config_pair in config_pairs:
        file_handle.write('<li>%s vs %s:' % config_pair)
        for summary_type in _GM_SUMMARY_TYPES:
          file_handle.write(
              ' <a href="/%s/view.html#/view.html?'
              'resultsToLoad=/%s/%s/%s-vs-%s_%s.json">%s</a>' % (
                  GET__STATIC_CONTENTS, GET__STATIC_CONTENTS,
                  GENERATED_JSON_SUBDIR, config_pair[0], config_pair[1],
                  summary_type, summary_type))
        file_handle.write('</li>')
      file_handle.write('</ul>')

    if _SKP_PLATFORMS:
      file_handle.write('\n<li>Rendered SKPs:<ul>')
      for builder in _SKP_PLATFORMS:
        file_handle.write(
            '\n<li><a href="../live-view.html#live-view.html?%s">' %
            urllib.urlencode({
                LIVE_PARAM__SET_A_SECTION:
                    gm_json.JSONKEY_EXPECTEDRESULTS,
                LIVE_PARAM__SET_A_DIR:
                    posixpath.join(_SKP_BASE_REPO_URL, builder),
                LIVE_PARAM__SET_B_SECTION:
                    gm_json.JSONKEY_ACTUALRESULTS,
                LIVE_PARAM__SET_B_DIR:
                    posixpath.join(_SKP_BASE_GS_URL, builder),
            }))
        file_handle.write('expected vs actuals on %s</a></li>' % builder)
      file_handle.write(
          '\n<li><a href="../live-view.html#live-view.html?%s">' %
          urllib.urlencode({
              LIVE_PARAM__SET_A_SECTION:
                  gm_json.JSONKEY_ACTUALRESULTS,
              LIVE_PARAM__SET_A_DIR:
                  posixpath.join(_SKP_BASE_GS_URL, _SKP_PLATFORMS[0]),
              LIVE_PARAM__SET_B_SECTION:
                  gm_json.JSONKEY_ACTUALRESULTS,
              LIVE_PARAM__SET_B_DIR:
                  posixpath.join(_SKP_BASE_GS_URL, _SKP_PLATFORMS[1]),
          }))
      file_handle.write('actuals on %s vs %s</a></li>' % (
          _SKP_PLATFORMS[0], _SKP_PLATFORMS[1]))
      file_handle.write('</li>')

    file_handle.write('\n</ul></body></html>')


class Server(object):
  """ HTTP server for our HTML rebaseline viewer. """

  def __init__(self,
               actuals_dir=DEFAULT_ACTUALS_DIR,
               json_filename=DEFAULT_JSON_FILENAME,
               gm_summaries_bucket=DEFAULT_GM_SUMMARIES_BUCKET,
               port=DEFAULT_PORT, export=False, editable=True,
               reload_seconds=0, config_pairs=None, builder_regex_list=None,
               boto_file_path=None,
               imagediffdb_threads=imagediffdb.DEFAULT_NUM_WORKER_THREADS):
    """
    Args:
      actuals_dir: directory under which we will check out the latest actual
          GM results
      json_filename: basename of the JSON summary file to load for each builder
      gm_summaries_bucket: Google Storage bucket to download json_filename
          files from; if None or '', don't fetch new actual-results files
          at all, just compare to whatever files are already in actuals_dir
      port: which TCP port to listen on for HTTP requests
      export: whether to allow HTTP clients on other hosts to access this server
      editable: whether HTTP clients are allowed to submit new GM baselines
          (SKP baseline modifications are performed using an entirely different
          mechanism, not affected by this parameter)
      reload_seconds: polling interval with which to check for new results;
          if 0, don't check for new results at all
      config_pairs: List of (string, string) tuples; for each tuple, compare
          actual results of these two configs.  If None or empty,
          don't compare configs at all.
      builder_regex_list: List of regular expressions specifying which builders
          we will process. If None, process all builders.
      boto_file_path: Path to .boto file giving us credentials to access
          Google Storage buckets; if None, we will only be able to access
          public GS buckets.
      imagediffdb_threads: How many threads to spin up within imagediffdb.
    """
    self._actuals_dir = actuals_dir
    self._json_filename = json_filename
    self._gm_summaries_bucket = gm_summaries_bucket
    self._port = port
    self._export = export
    self._editable = editable
    self._reload_seconds = reload_seconds
    self._config_pairs = config_pairs or []
    self._builder_regex_list = builder_regex_list
    self.truncate_results = False

    if boto_file_path:
      self._gs = gs_utils.GSUtils(boto_file_path=boto_file_path)
    else:
      self._gs = gs_utils.GSUtils()

    _create_index(
        file_path=os.path.join(
            PARENT_DIRECTORY, STATIC_CONTENTS_SUBDIR, GENERATED_HTML_SUBDIR,
            "index.html"),
        config_pairs=config_pairs)

    # Reentrant lock that must be held whenever updating EITHER of:
    # 1. self._results
    # 2. the expected or actual results on local disk
    self.results_rlock = threading.RLock()

    # Create a single ImageDiffDB instance that is used by all our differs.
    self._image_diff_db = imagediffdb.ImageDiffDB(
        gs=self._gs,
        storage_root=os.path.join(
            PARENT_DIRECTORY, STATIC_CONTENTS_SUBDIR,
            GENERATED_IMAGES_SUBDIR),
        num_worker_threads=imagediffdb_threads)

    # This will be filled in by calls to update_results()
    self._results = None

  @property
  def results(self):
    """ Returns the most recently generated results, or None if we don't have
    any valid results (update_results() has not completed yet). """
    return self._results

  @property
  def image_diff_db(self):
    """ Returns reference to our ImageDiffDB object."""
    return self._image_diff_db

  @property
  def gs(self):
    """ Returns reference to our GSUtils object."""
    return self._gs

  @property
  def is_exported(self):
    """ Returns true iff HTTP clients on other hosts are allowed to access
    this server. """
    return self._export

  @property
  def is_editable(self):
    """ True iff HTTP clients are allowed to submit new GM baselines.

    TODO(epoger): This only pertains to GM baselines; SKP baselines are
    editable whenever expectations vs actuals are shown.
    Once we move the GM baselines to use the same code as the SKP baselines,
    we can delete this property.
    """
    return self._editable

  @property
  def reload_seconds(self):
    """ Returns the result reload period in seconds, or 0 if we don't reload
    results. """
    return self._reload_seconds

  def update_results(self, invalidate=False):
    """ Create or update self._results, based on the latest expectations and
    actuals.

    We hold self.results_rlock while we do this, to guarantee that no other
    thread attempts to update either self._results or the underlying files at
    the same time.

    Args:
      invalidate: if True, invalidate self._results immediately upon entry;
                  otherwise, we will let readers see those results until we
                  replace them
    """
    with self.results_rlock:
      if invalidate:
        self._results = None
      if self._gm_summaries_bucket:
        logging.info(
            'Updating GM result summaries in %s from gm_summaries_bucket %s ...'
            % (self._actuals_dir, self._gm_summaries_bucket))

        # Clean out actuals_dir first, in case some builders have gone away
        # since we last ran.
        if os.path.isdir(self._actuals_dir):
          shutil.rmtree(self._actuals_dir)

        # Get the list of builders we care about.
        all_builders = download_actuals.get_builders_list(
            summaries_bucket=self._gm_summaries_bucket)
        if self._builder_regex_list:
          matching_builders = []
          for builder in all_builders:
            for regex in self._builder_regex_list:
              if re.match(regex, builder):
                matching_builders.append(builder)
                break  # go on to the next builder, no need to try more regexes
        else:
          matching_builders = all_builders

        # Download the JSON file for each builder we care about.
        #
        # TODO(epoger): When this is a large number of builders, we would be
        # better off downloading them in parallel!
        for builder in matching_builders:
          self._gs.download_file(
              source_bucket=self._gm_summaries_bucket,
              source_path=posixpath.join(builder, self._json_filename),
              dest_path=os.path.join(self._actuals_dir, builder,
                                     self._json_filename),
              create_subdirs_if_needed=True)

      # We only update the expectations dir if the server was run with a
      # nonzero --reload argument; otherwise, we expect the user to maintain
      # her own expectations as she sees fit.
      #
      # Because the Skia repo is hosted using git, and git does not
      # support updating a single directory tree, we have to update the entire
      # repo checkout.
      #
      # Because Skia uses depot_tools, we have to update using "gclient sync"
      # instead of raw git commands.
      #
      # TODO(epoger): Fetch latest expectations in some other way.
      # Eric points out that our official documentation recommends an
      # unmanaged Skia checkout, so "gclient sync" will not bring down updated
      # expectations from origin/master-- you'd have to do a "git pull" of
      # some sort instead.
      # However, the live rebaseline_server at
      # http://skia-tree-status.appspot.com/redirect/rebaseline-server (which
      # is probably the only user of the --reload flag!) uses a managed
      # checkout, so "gclient sync" works in that case.
      # Probably the best idea is to avoid all of this nonsense by fetching
      # updated expectations into a temp directory, and leaving the rest of
      # the checkout alone.  This could be done using "git show", or by
      # downloading individual expectation JSON files from
      # skia.googlesource.com .
      if self._reload_seconds:
        logging.info(
            'Updating expected GM results in %s by syncing Skia repo ...' %
            compare_to_expectations.DEFAULT_EXPECTATIONS_DIR)
        _run_command(['gclient', 'sync'], TRUNK_DIRECTORY)

      self._results = compare_to_expectations.ExpectationComparisons(
          image_diff_db=self._image_diff_db,
          actuals_root=self._actuals_dir,
          diff_base_url=posixpath.join(
              os.pardir, STATIC_CONTENTS_SUBDIR, GENERATED_IMAGES_SUBDIR),
          builder_regex_list=self._builder_regex_list)

      json_dir = os.path.join(
          PARENT_DIRECTORY, STATIC_CONTENTS_SUBDIR, GENERATED_JSON_SUBDIR)
      if not os.path.isdir(json_dir):
        os.makedirs(json_dir)

      for config_pair in self._config_pairs:
        config_comparisons = compare_configs.ConfigComparisons(
            configs=config_pair,
            actuals_root=self._actuals_dir,
            generated_images_root=os.path.join(
                PARENT_DIRECTORY, STATIC_CONTENTS_SUBDIR,
                GENERATED_IMAGES_SUBDIR),
            diff_base_url=posixpath.join(
                os.pardir, GENERATED_IMAGES_SUBDIR),
            builder_regex_list=self._builder_regex_list)
        for summary_type in _GM_SUMMARY_TYPES:
          gm_json.WriteToFile(
              config_comparisons.get_packaged_results_of_type(
                  results_type=summary_type),
              os.path.join(
                  json_dir, '%s-vs-%s_%s.json' % (
                      config_pair[0], config_pair[1], summary_type)))

  def _result_loader(self, reload_seconds=0):
    """ Call self.update_results(), either once or periodically.

    Params:
      reload_seconds: integer; if nonzero, reload results at this interval
          (in which case, this method will never return!)
    """
    self.update_results()
    logging.info('Initial results loaded. Ready for requests on %s' % self._url)
    if reload_seconds:
      while True:
        time.sleep(reload_seconds)
        self.update_results()

  def run(self):
    arg_tuple = (self._reload_seconds,)  # start_new_thread needs a tuple,
                                         # even though it holds just one param
    thread.start_new_thread(self._result_loader, arg_tuple)

    if self._export:
      server_address = ('', self._port)
      host = _get_routable_ip_address()
      if self._editable:
        logging.warning('Running with combination of "export" and "editable" '
                        'flags.  Users on other machines will '
                        'be able to modify your GM expectations!')
    else:
      host = '127.0.0.1'
      server_address = (host, self._port)
    # pylint: disable=W0201
    http_server = BaseHTTPServer.HTTPServer(server_address, HTTPRequestHandler)
    self._url = 'http://%s:%d' % (host, http_server.server_port)
    logging.info('Listening for requests on %s' % self._url)
    http_server.serve_forever()


class HTTPRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
  """ HTTP request handlers for various types of queries this server knows
      how to handle (static HTML and Javascript, expected/actual results, etc.)
  """
  def do_GET(self):
    """
    Handles all GET requests, forwarding them to the appropriate
    do_GET_* dispatcher.

    If we see any Exceptions, return a 404.  This fixes http://skbug.com/2147
    """
    try:
      logging.debug('do_GET: path="%s"' % self.path)
      if self.path == '' or self.path == '/' or self.path == '/index.html' :
        self.redirect_to('/%s/%s/index.html' % (
            GET__STATIC_CONTENTS, GENERATED_HTML_SUBDIR))
        return
      if self.path == '/favicon.ico' :
        self.redirect_to('/%s/favicon.ico' % GET__STATIC_CONTENTS)
        return

      # All requests must be of this form:
      #   /dispatcher/remainder
      # where 'dispatcher' indicates which do_GET_* dispatcher to run
      # and 'remainder' is the remaining path sent to that dispatcher.
      (dispatcher_name, remainder) = PATHSPLIT_RE.match(self.path).groups()
      dispatchers = {
          GET__LIVE_RESULTS: self.do_GET_live_results,
          GET__PRECOMPUTED_RESULTS: self.do_GET_precomputed_results,
          GET__PREFETCH_RESULTS: self.do_GET_prefetch_results,
          GET__STATIC_CONTENTS: self.do_GET_static,
      }
      dispatcher = dispatchers[dispatcher_name]
      dispatcher(remainder)
    except:
      self.send_error(404)
      raise

  def do_GET_precomputed_results(self, results_type):
    """ Handle a GET request for part of the precomputed _SERVER.results object.

    Args:
      results_type: string indicating which set of results to return;
            must be one of the results_mod.RESULTS_* constants
    """
    logging.debug('do_GET_precomputed_results: sending results of type "%s"' %
                  results_type)
    # Since we must make multiple calls to the ExpectationComparisons object,
    # grab a reference to it in case it is updated to point at a new
    # ExpectationComparisons object within another thread.
    #
    # TODO(epoger): Rather than using a global variable for the handler
    # to refer to the Server object, make Server a subclass of
    # HTTPServer, and then it could be available to the handler via
    # the handler's .server instance variable.
    results_obj = _SERVER.results
    if results_obj:
      response_dict = results_obj.get_packaged_results_of_type(
          results_type=results_type, reload_seconds=_SERVER.reload_seconds,
          is_editable=_SERVER.is_editable, is_exported=_SERVER.is_exported)
    else:
      now = int(time.time())
      response_dict = {
          imagepairset.KEY__ROOT__HEADER: {
              results_mod.KEY__HEADER__SCHEMA_VERSION: (
                  results_mod.VALUE__HEADER__SCHEMA_VERSION),
              results_mod.KEY__HEADER__IS_STILL_LOADING: True,
              results_mod.KEY__HEADER__TIME_UPDATED: now,
              results_mod.KEY__HEADER__TIME_NEXT_UPDATE_AVAILABLE: (
                  now + RELOAD_INTERVAL_UNTIL_READY),
          },
      }
    self.send_json_dict(response_dict)

  def _get_live_results_or_prefetch(self, url_remainder, prefetch_only=False):
    """ Handle a GET request for live-generated image diff data.

    Args:
      url_remainder: string indicating which image diffs to generate
      prefetch_only: if True, the user isn't waiting around for results
    """
    param_dict = urlparse.parse_qs(url_remainder)
    download_all_images = (
        param_dict.get(LIVE_PARAM__DOWNLOAD_ONLY_DIFFERING, [''])[0].lower()
        not in ['1', 'true'])
    setA_dirs = param_dict[LIVE_PARAM__SET_A_DIR]
    setB_dirs = param_dict[LIVE_PARAM__SET_B_DIR]
    setA_section = self._validate_summary_section(
        param_dict.get(LIVE_PARAM__SET_A_SECTION, [None])[0])
    setB_section = self._validate_summary_section(
        param_dict.get(LIVE_PARAM__SET_B_SECTION, [None])[0])

    # If the sets show expectations vs actuals, always show expectations on
    # the left (setA).
    if ((setA_section == gm_json.JSONKEY_ACTUALRESULTS) and
        (setB_section == gm_json.JSONKEY_EXPECTEDRESULTS)):
      setA_dirs, setB_dirs = setB_dirs, setA_dirs
      setA_section, setB_section = setB_section, setA_section

    # Are we comparing some actuals against expectations stored in the repo?
    # If so, we can allow the user to submit new baselines.
    is_editable = (
        (setA_section == gm_json.JSONKEY_EXPECTEDRESULTS) and
        (setA_dirs[0].startswith(compare_rendered_pictures.REPO_URL_PREFIX)) and
        (setB_section == gm_json.JSONKEY_ACTUALRESULTS))

    results_obj = compare_rendered_pictures.RenderedPicturesComparisons(
        setA_dirs=setA_dirs, setB_dirs=setB_dirs,
        setA_section=setA_section, setB_section=setB_section,
        image_diff_db=_SERVER.image_diff_db,
        diff_base_url='/static/generated-images',
        gs=_SERVER.gs, truncate_results=_SERVER.truncate_results,
        prefetch_only=prefetch_only, download_all_images=download_all_images)
    if prefetch_only:
      self.send_response(200)
    else:
      self.send_json_dict(results_obj.get_packaged_results_of_type(
          results_type=results_mod.KEY__HEADER__RESULTS_ALL,
          is_editable=is_editable))

  def do_GET_live_results(self, url_remainder):
    """ Handle a GET request for live-generated image diff data.

    Args:
      url_remainder: string indicating which image diffs to generate
    """
    logging.debug('do_GET_live_results: url_remainder="%s"' % url_remainder)
    self._get_live_results_or_prefetch(
        url_remainder=url_remainder, prefetch_only=False)

  def do_GET_prefetch_results(self, url_remainder):
    """ Prefetch image diff data for a future do_GET_live_results() call.

    Args:
      url_remainder: string indicating which image diffs to generate
    """
    logging.debug('do_GET_prefetch_results: url_remainder="%s"' % url_remainder)
    self._get_live_results_or_prefetch(
        url_remainder=url_remainder, prefetch_only=True)

  def do_GET_static(self, path):
    """ Handle a GET request for a file under STATIC_CONTENTS_SUBDIR .
    Only allow serving of files within STATIC_CONTENTS_SUBDIR that is a
    filesystem sibling of this script.

    Args:
      path: path to file (within STATIC_CONTENTS_SUBDIR) to retrieve
    """
    # Strip arguments ('?resultsToLoad=all') from the path
    path = urlparse.urlparse(path).path

    logging.debug('do_GET_static: sending file "%s"' % path)
    static_dir = os.path.realpath(os.path.join(
        PARENT_DIRECTORY, STATIC_CONTENTS_SUBDIR))
    full_path = os.path.realpath(os.path.join(static_dir, path))
    if full_path.startswith(static_dir):
      self.send_file(full_path)
    else:
      logging.error(
          'Attempted do_GET_static() of path [%s] outside of static dir [%s]'
          % (full_path, static_dir))
      self.send_error(404)

  def do_POST(self):
    """ Handles all POST requests, forwarding them to the appropriate
        do_POST_* dispatcher. """
    # All requests must be of this form:
    #   /dispatcher
    # where 'dispatcher' indicates which do_POST_* dispatcher to run.
    logging.debug('do_POST: path="%s"' % self.path)
    normpath = posixpath.normpath(self.path)
    dispatchers = {
      '/edits': self.do_POST_edits,
    }
    try:
      dispatcher = dispatchers[normpath]
      dispatcher()
      self.send_response(200)
    except:
      self.send_error(404)
      raise

  def do_POST_edits(self):
    """ Handle a POST request with modifications to GM expectations, in this
    format:

    {
      KEY__EDITS__OLD_RESULTS_TYPE: 'all',  # type of results that the client
                                            # loaded and then made
                                            # modifications to
      KEY__EDITS__OLD_RESULTS_HASH: 39850913, # hash of results when the client
                                              # loaded them (ensures that the
                                              # client and server apply
                                              # modifications to the same base)
      KEY__EDITS__MODIFICATIONS: [
        # as needed by compare_to_expectations.edit_expectations()
        ...
      ],
    }

    Raises an Exception if there were any problems.
    """
    if not _SERVER.is_editable:
      raise Exception('this server is not running in --editable mode')

    content_type = self.headers[_HTTP_HEADER_CONTENT_TYPE]
    if content_type != 'application/json;charset=UTF-8':
      raise Exception('unsupported %s [%s]' % (
          _HTTP_HEADER_CONTENT_TYPE, content_type))

    content_length = int(self.headers[_HTTP_HEADER_CONTENT_LENGTH])
    json_data = self.rfile.read(content_length)
    data = json.loads(json_data)
    logging.debug('do_POST_edits: received new GM expectations data [%s]' %
                  data)

    # Update the results on disk with the information we received from the
    # client.
    # We must hold _SERVER.results_rlock while we do this, to guarantee that
    # no other thread updates expectations (from the Skia repo) while we are
    # updating them (using the info we received from the client).
    with _SERVER.results_rlock:
      oldResultsType = data[KEY__EDITS__OLD_RESULTS_TYPE]
      oldResults = _SERVER.results.get_results_of_type(oldResultsType)
      oldResultsHash = str(hash(repr(
          oldResults[imagepairset.KEY__ROOT__IMAGEPAIRS])))
      if oldResultsHash != data[KEY__EDITS__OLD_RESULTS_HASH]:
        raise Exception('results of type "%s" changed while the client was '
                        'making modifications. The client should reload the '
                        'results and submit the modifications again.' %
                        oldResultsType)
      _SERVER.results.edit_expectations(data[KEY__EDITS__MODIFICATIONS])

    # Read the updated results back from disk.
    # We can do this in a separate thread; we should return our success message
    # to the UI as soon as possible.
    thread.start_new_thread(_SERVER.update_results, (True,))

  def redirect_to(self, url):
    """ Redirect the HTTP client to a different url.

    Args:
      url: URL to redirect the HTTP client to
    """
    self.send_response(301)
    self.send_header('Location', url)
    self.end_headers()

  def send_file(self, path):
    """ Send the contents of the file at this path, with a mimetype based
        on the filename extension.

    Args:
      path: path of file whose contents to send to the HTTP client
    """
    # Grab the extension if there is one
    extension = os.path.splitext(path)[1]
    if len(extension) >= 1:
      extension = extension[1:]

    # Determine the MIME type of the file from its extension
    mime_type = MIME_TYPE_MAP.get(extension, MIME_TYPE_MAP[''])

    # Open the file and send it over HTTP
    if os.path.isfile(path):
      with open(path, 'rb') as sending_file:
        self.send_response(200)
        self.send_header('Content-type', mime_type)
        self.end_headers()
        self.wfile.write(sending_file.read())
    else:
      self.send_error(404)

  def send_json_dict(self, json_dict):
    """ Send the contents of this dictionary in JSON format, with a JSON
        mimetype.

    Args:
      json_dict: dictionary to send
    """
    self.send_response(200)
    self.send_header('Content-type', 'application/json')
    self.end_headers()
    json.dump(json_dict, self.wfile)

  def _validate_summary_section(self, section_name):
    """Validates the section we have been requested to read within JSON summary.

    Args:
      section_name: which section of the JSON summary file has been requested

    Returns: the validated section name

    Raises: Exception if an invalid section_name was requested.
    """
    if section_name not in compare_rendered_pictures.ALLOWED_SECTION_NAMES:
      raise Exception('requested section name "%s" not in allowed list %s' % (
          section_name, compare_rendered_pictures.ALLOWED_SECTION_NAMES))
    return section_name


def main():
  logging.basicConfig(format='%(asctime)s %(levelname)s %(message)s',
                      datefmt='%m/%d/%Y %H:%M:%S',
                      level=logging.INFO)
  parser = argparse.ArgumentParser()
  parser.add_argument('--actuals-dir',
                    help=('Directory into which we will check out the latest '
                          'actual GM results. If this directory does not '
                          'exist, it will be created. Defaults to %(default)s'),
                    default=DEFAULT_ACTUALS_DIR)
  parser.add_argument('--boto',
                    help=('Path to .boto file giving us credentials to access '
                          'Google Storage buckets. If not specified, we will '
                          'only be able to access public GS buckets (and thus '
                          'won\'t be able to download SKP images).'),
                    default='')
  # TODO(epoger): Before https://codereview.chromium.org/310093003 ,
  # when this tool downloaded the JSON summaries from skia-autogen,
  # it had an --actuals-revision the caller could specify to download
  # actual results as of a specific point in time.  We should add similar
  # functionality when retrieving the summaries from Google Storage.
  parser.add_argument('--builders', metavar='BUILDER_REGEX', nargs='+',
                      help=('Only process builders matching these regular '
                            'expressions.  If unspecified, process all '
                            'builders.'))
  parser.add_argument('--compare-configs', action='store_true',
                      help=('In addition to generating differences between '
                            'expectations and actuals, also generate '
                            'differences between these config pairs: '
                            + str(CONFIG_PAIRS_TO_COMPARE)))
  parser.add_argument('--editable', action='store_true',
                      help=('Allow HTTP clients to submit new GM baselines; '
                            'SKP baselines can be edited regardless of this '
                            'setting.'))
  parser.add_argument('--export', action='store_true',
                      help=('Instead of only allowing access from HTTP clients '
                            'on localhost, allow HTTP clients on other hosts '
                            'to access this server.  WARNING: doing so will '
                            'allow users on other hosts to modify your '
                            'GM expectations, if combined with --editable.'))
  parser.add_argument('--gm-summaries-bucket',
                    help=('Google Cloud Storage bucket to download '
                          'JSON_FILENAME files from. '
                          'Defaults to %(default)s ; if set to '
                          'empty string, just compare to actual-results '
                          'already found in ACTUALS_DIR.'),
                    default=DEFAULT_GM_SUMMARIES_BUCKET)
  parser.add_argument('--json-filename',
                    help=('JSON summary filename to read for each builder; '
                          'defaults to %(default)s.'),
                    default=DEFAULT_JSON_FILENAME)
  parser.add_argument('--port', type=int,
                      help=('Which TCP port to listen on for HTTP requests; '
                            'defaults to %(default)s'),
                      default=DEFAULT_PORT)
  parser.add_argument('--reload', type=int,
                      help=('How often (a period in seconds) to update the '
                            'results.  If specified, both expected and actual '
                            'results will be updated by running "gclient sync" '
                            'on your Skia checkout as a whole.  '
                            'By default, we do not reload at all, and you '
                            'must restart the server to pick up new data.'),
                      default=0)
  parser.add_argument('--threads', type=int,
                      help=('How many parallel threads we use to download '
                            'images and generate diffs; defaults to '
                            '%(default)s'),
                      default=imagediffdb.DEFAULT_NUM_WORKER_THREADS)
  parser.add_argument('--truncate', action='store_true',
                      help=('FOR TESTING ONLY: truncate the set of images we '
                            'process, to speed up testing.'))
  args = parser.parse_args()
  if args.compare_configs:
    config_pairs = CONFIG_PAIRS_TO_COMPARE
  else:
    config_pairs = None

  global _SERVER
  _SERVER = Server(actuals_dir=args.actuals_dir,
                   json_filename=args.json_filename,
                   gm_summaries_bucket=args.gm_summaries_bucket,
                   port=args.port, export=args.export, editable=args.editable,
                   reload_seconds=args.reload, config_pairs=config_pairs,
                   builder_regex_list=args.builders, boto_file_path=args.boto,
                   imagediffdb_threads=args.threads)
  if args.truncate:
    _SERVER.truncate_results = True
  _SERVER.run()


if __name__ == '__main__':
  main()