Raise Exception if GetHTTPResponses() called multiple times

tools/chrome_proxy/webdriver/common.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import argparse
 import json
 import logging
 import os
 import re
 import socket
@@ skipping 109 matching lines @@
   This class is the tool that is used by every integration test to interact with
   the Chromium browser and validate proper functionality. This class sits on top
   of the Selenium Chrome Webdriver with added utility and helper functions for
   Chrome-Proxy. This class should be used with Python's 'with' operator.
 
   Attributes:
     _flags: A Namespace object from the call to ParseFlags()
     _driver: A reference to the driver object from the Chrome Driver library.
     _chrome_args: A set of string arguments to start Chrome with.
     _url: The string URL that Chrome will navigate to for this test.
+    _has_logs: Boolean flag set when a page is loaded and cleared when logs are
+      fetched.
   """
 
   def __init__(self):
     self._flags = ParseFlags()
     self._driver = None
     self._chrome_args = set()
     self._url = ''
     self._logger = GetLogger(name='TestDriver')
+    self._has_logs = False
 
   def __enter__(self):
     return self
 
   def __exit__(self, exc_type, exc_value, tb):
     if self._driver:
       self._StopDriver()
 
   def _OverrideChromeArgs(self):
     """Overrides any given arguments in the code with those given on the command
@@ skipping 128 matching lines @@
     if (len(urlparse.urlparse(url).netloc) == 0 and
         len(urlparse.urlparse(url).scheme) == 0):
       self._logger.warn('Invalid URL: "%s". Did you forget to prepend '
         '"http://"? See RFC 1808 for more information', url)
     if not self._driver:
       self._StartDriver()
     self._driver.set_page_load_timeout(timeout)
     self._logger.debug('Set page load timeout to %f seconds', timeout)
     self._driver.get(self._url)
     self._logger.debug('Loaded page %s', url)
+    self._has_logs = True
 
   def ExecuteJavascript(self, script, timeout=30):
     """Executes the given javascript in the browser's current page in an
     anonymous function.
 
     If you expect a result and don't get one, try adding a return statement or
     using ExecuteJavascriptStatement() below.
 
     Args:
       script: A string of Javascript code.
@@ skipping 52 matching lines @@
     while not result and total_waited_time < timeout:
       time.sleep(poll_interval)
       total_waited_time += poll_interval
       result = self.ExecuteJavascriptStatement(expression)
     if not result:
       self._logger.error('%s not true after %f seconds' % (expression, timeout))
       raise Exception('%s not true after %f seconds' % (expression, timeout))
     return result
 
   def GetPerformanceLogs(self, method_filter=r'Network\.responseReceived'):
-    """Returns all logged Performance events from Chrome.
+    """Returns all logged Performance events from Chrome. Raises an Exception if
+    no pages have been loaded since the last time this function was called.
 
     Args:
       method_filter: A regex expression to match the method of logged events
         against. Only logs who's method matches the regex will be returned.
     Returns:
       Performance logs as a list of dicts, since the last time this function was
       called.
     """
+    if not self._has_logs:
+      raise Exception('No pages loaded since last Network log query!')
     all_messages = []
     for log in self._driver.execute('getLog', {'type': 'performance'})['value']:
       message = json.loads(log['message'])['message']
       self._logger.debug('Got Performance log: %s', log['message'])
       if re.match(method_filter, message['method']):
         all_messages.append(message)
     self._logger.info('Got %d performance logs with filter method=%s',
       len(all_messages), method_filter)
+    self._has_logs = False
     return all_messages
 
   def GetHTTPResponses(self, include_favicon=False, skip_domainless_pages=True):
     """Parses the Performance Logs and returns a list of HTTPResponse objects.
 
     Use caution when calling this function  multiple times. Only responses
     since the last time this function was called are returned (or since Chrome
-    started, whichever is later).
+    started, whichever is later). An Exception will be raised if no page was
+    loaded since the last time this function was called.
 
     Args:
       include_favicon: A bool that if True will include responses for favicons.
       skip_domainless_pages: If True, only responses with a net_loc as in RFC
         1808 will be included. Pages such as about:blank will be skipped.
     Returns:
       A list of HTTPResponse objects, each representing a single completed HTTP
       transaction by Chrome.
     """
     def MakeHTTPResponse(log_dict):
@@ skipping 172 matching lines @@
     for test_suite in test_suite_iter:
       for test_case in test_suite:
         for test in test_case:
           # Drop the file name in the form <filename>.<classname>.<methodname>
           test_id = test.id()[test.id().find('.') + 1:]
           if re.match(test_filter_re, test_id):
             tests.addTest(test)
     testRunner = unittest.runner.TextTestRunner(verbosity=2,
       failfast=flags.failfast, buffer=(not flags.disable_buffer))
     testRunner.run(tests)