clovis: Identify prefetchable resources from dependencies and tracing.

tools/android/loading/prefetch_view.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.
+
+"""Models the effect of NoState Prefetch from a loading trace.

[blundell, 2016/03/21 10:07:18]

Nit: prefetch_view is a quite generic name. Maybe no_state_prefetch_view?

[blundell, 2016/03/21 10:22:04]

Also, let's provide a one-sentence description of nostate prefetch here and link
to this doc:

https://docs.google.com/document/d/16VCYGGWau483IMSxODpg5faZny1FJ6vNK2v-BuM5E...

[Benoit L, 2016/03/22 09:32:23]

This is intended to simulate prefetch in a generic way, not especially NoState
prefetch. So, what about:
- Keeping the name as is
- Adding the link to the design doc, citing it as an example?

+
+When executed as a script, takes a trace as a command-line arguments and shows
+how many requests were prefetched.
+"""
+
+import itertools
+import operator
+
+import loading_trace
+import request_dependencies_lens
+
+
+class PrefetchSimulationView(object):
+  """Simulates the effect of prefetching resources discoverable by the preload
+  scanner.
+  """
+  def __init__(self, trace, dependencies_lens):
+    """Initializes an instance of PrefetchSimulationView.
+
+    Args:
+      trace: (LoadingTrace) a loading trace.
+      dependencies_lens: (RequestDependencyLens) request dependencies.
+    """
+    self.trace = trace
+    self.dependencies_lens = dependencies_lens
+    self._resource_events = self.trace.tracing_track.Filter(
+        categories=set([u'blink.net']))
+    assert len(self._resource_events.GetEvents()) > 0,\
+            'Was the "blink.net" category enabled at trace collection time?"'
+
+  def ParserDiscoverableRequests(self, request, recurse=False):

[blundell, 2016/03/21 10:47:16]

Should/could this eventually be the same code that's used by sandwich to
determine which resources to stuff into the cache when doing its evaluation of
nostate prefetch?

[mattcary, 2016/03/21 10:54:44]

That's an interesting general question: should our model be based on the same
code, to maximize fidelity, or independent, to reduce the chance of making the
same implementation mistake twice?

For the immediate Q1 goals, though, I think we can keep them separate to
minimize thrashing and move quickly. The general question may take a while to
resolve.

[gabadie, 2016/03/21 12:55:45]

Fly by comment: Sandwich is currently simulating the HTMLPreloadScanner using
the exact same API, is taking care of the data protocol, but not the
GetRequestDependencies: 

https://code.google.com/p/chromium/codesearch#chromium/src/tools/android/load...

After having compared both implementation (that sadly looks both incomplete),
making them common could very much increase interests from both parties. I would
be happy to discuss a design of an extensible API that would let us write
different resources prefetching policies, and reuse them everywhere at will.

Basically, sandwich's need is to get a white-list of requests to keep their
resources into the cache.

+    """Returns a list of requests discovered by the parser from a given request.
+
+    Args:
+      request: (Request) Root request.
+
+    Returns:
+      [Request]
+    """
+    # TODO(lizeb): handle the recursive case.
+    assert not recurse
+    discoverable_requests = [request]
+    first_request = self.dependencies_lens.GetRedirectChain(request)[-1]
+    deps = self.dependencies_lens.GetRequestDependencies()
+    for (first, second, reason) in deps:
+      if first.request_id == first_request.request_id and reason == 'parser':
+        discoverable_requests.append(second)
+    return discoverable_requests
+
+  def ExpandRedirectChains(self, requests):
+    return list(itertools.chain.from_iterable(
+        [self.dependencies_lens.GetRedirectChain(r) for r in requests]))
+
+  def PreloadedRequests(self, request):
+    """Returns the requests that have been preloaded from a given request.
+
+    This list is the set of request that are:
+    - Discoverable by the parser
+    - Found in the trace log.
+
+    Before looking for dependencies, this follows the redirect chain.
+
+    Args:
+      request: (Request) Root request.
+
+    Returns:
+      A list of Request. Does not include the root request. This list is a
+      subset of the one returned by ParserDiscoverableRequests().
+    """
+    # Preload step events are emitted in ResourceFetcher::preloadStarted().
+    preload_step_events = filter(
+        lambda e:  e.args.get('step') == 'Preload',
+        self._resource_events.GetEvents())
+    preloaded_urls = set()
+    for preload_step_event in preload_step_events:
+      preload_event = self._resource_events.EventFromStep(preload_step_event)
+      if preload_event:
+        preloaded_urls.add(preload_event.args['url'])
+    parser_requests = self.ParserDiscoverableRequests(request)
+    preloaded_root_requests = filter(
+        lambda r: r.url in preloaded_urls, parser_requests)
+    # We can actually fetch the whole redirect chain.
+    return [request] + list(itertools.chain.from_iterable(
+        [self.dependencies_lens.GetRedirectChain(r)
+         for r in preloaded_root_requests]))
+
+
+def _PrintSummary(prefetch_view):
+  requests = prefetch_view.trace.request_track.GetEvents()
+  first_request = prefetch_view.trace.request_track.GetEvents()[0]
+  parser_requests = prefetch_view.ExpandRedirectChains(
+      prefetch_view.ParserDiscoverableRequests(first_request))
+  preloaded_requests = prefetch_view.ExpandRedirectChains(
+      prefetch_view.PreloadedRequests(first_request))
+  print '%d requests, %d parser from the main request, %d preloaded' % (
+      len(requests), len(parser_requests), len(preloaded_requests))
+
+
+def main(filename):
+  trace = loading_trace.LoadingTrace.FromJsonFile(filename)
+  dependencies_lens = request_dependencies_lens.RequestDependencyLens(trace)
+  prefetch_view = PrefetchSimulationView(trace, dependencies_lens)
+  _PrintSummary(prefetch_view)
+
+
+if __name__ == '__main__':
+  import sys
+  main(sys.argv[1])