Add more logging when fetching layout test results.

third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py

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 import collections
+import logging
 import re
 import urllib2
 
 from webkitpy.common.memoized import memoized
 from webkitpy.common.net.layout_test_results import LayoutTestResults
 from webkitpy.common.net.network_transaction import NetworkTransaction
 
+_log = logging.getLogger(__name__)
 
 RESULTS_URL_BASE = 'https://storage.googleapis.com/chromium-layout-test-archives'
 
 
 class Build(collections.namedtuple('Build', ('builder_name', 'build_number'))):
     """Represents a combination of builder and build number.
 
     If build number is None, this represents the latest build
     for a given builder.
     """
@@ skipping 34 matching lines @@
     def fetch_retry_summary_json(self, build):
         """Fetches and returns the text of the archived retry_summary file.
 
         This file is expected to contain the results of retrying layout tests
         with and without a patch in a try job. It includes lists of tests
         that failed only with the patch ("failures"), and tests that failed
         both with and without ("ignored").
         """
         url_base = '%s/%s' % (self.builder_results_url_base(build.builder_name), build.build_number)
         return NetworkTransaction(return_none_on_404=True).run(
-            lambda: self._fetch_file(url_base, 'retry_summary.json'))
+            lambda: self.fetch_file(url_base, 'retry_summary.json'))
 
     def accumulated_results_url_base(self, builder_name):
         return self.builder_results_url_base(builder_name) + '/results/layout-test-results'
 
     @memoized
     def latest_layout_test_results(self, builder_name):
         return self.fetch_layout_test_results(self.accumulated_results_url_base(builder_name))
 
     @memoized
     def fetch_results(self, build):
         return self.fetch_layout_test_results(self.results_url(build.builder_name, build.build_number))
 
     @memoized
     def fetch_layout_test_results(self, results_url):
         """Returns a LayoutTestResults object for results fetched from a given URL."""
         results_file = NetworkTransaction(return_none_on_404=True).run(
-            lambda: self._fetch_file(results_url, 'failing_results.json'))
+            lambda: self.fetch_file(results_url, 'failing_results.json'))
+        if results_file is None:
+            _log.warning('Got 404 response from:\n%s/failing_results.json', results_url)
+            return None
         revision = NetworkTransaction(return_none_on_404=True).run(
-            lambda: self._fetch_file(results_url, 'LAST_CHANGE'))
-        if not revision:
-            results_file = None
+            lambda: self.fetch_file(results_url, 'LAST_CHANGE'))
+        if revision is None:
+            _log.warning('Got 404 response from:\n%s/LAST_CHANGE', results_url)
+            return None
         return LayoutTestResults.results_from_string(results_file, revision)
 
-    def _fetch_file(self, url_base, file_name):
+    def fetch_file(self, url_base, filename):
         # It seems this can return None if the url redirects and then returns 404.
         # FIXME: This could use Web instead of using urllib2 directly.
-        result = urllib2.urlopen('%s/%s' % (url_base, file_name))
+        result = urllib2.urlopen('%s/%s' % (url_base, filename))
         if not result:
             return None
         # urlopen returns a file-like object which sometimes works fine with str()
         # but sometimes is a addinfourl object.  In either case calling read() is correct.
         return result.read()
 
 
 def current_build_link(host):
     """Returns a link to the current job if running on buildbot, or None."""
     master_name = host.environ.get('BUILDBOT_MASTERNAME')
@@ skipping 15 matching lines @@
         there are only Builds with no build number, then one is kept; if there
         are Builds with build numbers, then the one with the highest build
         number is kept.
     """
     latest_builds = {}
     for build in builds:
         builder = build.builder_name
         if builder not in latest_builds or build.build_number > latest_builds[builder].build_number:
             latest_builds[builder] = build
     return sorted(latest_builds.values())