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| 1 # Copyright 2016 The Chromium Authors. All rights reserved. |
| 2 # Use of this source code is governed by a BSD-style license that can be |
| 3 # found in the LICENSE file. |
| 4 |
| 5 """Models the effect of prefetching resources from a loading trace. |
| 6 |
| 7 For example, this can be used to evaluate NoState Prefetch |
| 8 (https://goo.gl/B3nRUR). |
| 9 |
| 10 When executed as a script, takes a trace as a command-line arguments and shows |
| 11 how many requests were prefetched. |
| 12 """ |
| 13 |
| 14 import itertools |
| 15 import operator |
| 16 |
| 17 import loading_trace |
| 18 import request_dependencies_lens |
| 19 |
| 20 |
| 21 class PrefetchSimulationView(object): |
| 22 """Simulates the effect of prefetching resources discoverable by the preload |
| 23 scanner. |
| 24 """ |
| 25 def __init__(self, trace, dependencies_lens): |
| 26 """Initializes an instance of PrefetchSimulationView. |
| 27 |
| 28 Args: |
| 29 trace: (LoadingTrace) a loading trace. |
| 30 dependencies_lens: (RequestDependencyLens) request dependencies. |
| 31 """ |
| 32 self.trace = trace |
| 33 self.dependencies_lens = dependencies_lens |
| 34 self._resource_events = self.trace.tracing_track.Filter( |
| 35 categories=set([u'blink.net'])) |
| 36 assert len(self._resource_events.GetEvents()) > 0,\ |
| 37 'Was the "blink.net" category enabled at trace collection time?"' |
| 38 |
| 39 def ParserDiscoverableRequests(self, request, recurse=False): |
| 40 """Returns a list of requests discovered by the parser from a given request. |
| 41 |
| 42 Args: |
| 43 request: (Request) Root request. |
| 44 |
| 45 Returns: |
| 46 [Request] |
| 47 """ |
| 48 # TODO(lizeb): handle the recursive case. |
| 49 assert not recurse |
| 50 discoverable_requests = [request] |
| 51 first_request = self.dependencies_lens.GetRedirectChain(request)[-1] |
| 52 deps = self.dependencies_lens.GetRequestDependencies() |
| 53 for (first, second, reason) in deps: |
| 54 if first.request_id == first_request.request_id and reason == 'parser': |
| 55 discoverable_requests.append(second) |
| 56 return discoverable_requests |
| 57 |
| 58 def ExpandRedirectChains(self, requests): |
| 59 return list(itertools.chain.from_iterable( |
| 60 [self.dependencies_lens.GetRedirectChain(r) for r in requests])) |
| 61 |
| 62 def PreloadedRequests(self, request): |
| 63 """Returns the requests that have been preloaded from a given request. |
| 64 |
| 65 This list is the set of request that are: |
| 66 - Discoverable by the parser |
| 67 - Found in the trace log. |
| 68 |
| 69 Before looking for dependencies, this follows the redirect chain. |
| 70 |
| 71 Args: |
| 72 request: (Request) Root request. |
| 73 |
| 74 Returns: |
| 75 A list of Request. Does not include the root request. This list is a |
| 76 subset of the one returned by ParserDiscoverableRequests(). |
| 77 """ |
| 78 # Preload step events are emitted in ResourceFetcher::preloadStarted(). |
| 79 preload_step_events = filter( |
| 80 lambda e: e.args.get('step') == 'Preload', |
| 81 self._resource_events.GetEvents()) |
| 82 preloaded_urls = set() |
| 83 for preload_step_event in preload_step_events: |
| 84 preload_event = self._resource_events.EventFromStep(preload_step_event) |
| 85 if preload_event: |
| 86 preloaded_urls.add(preload_event.args['url']) |
| 87 parser_requests = self.ParserDiscoverableRequests(request) |
| 88 preloaded_root_requests = filter( |
| 89 lambda r: r.url in preloaded_urls, parser_requests) |
| 90 # We can actually fetch the whole redirect chain. |
| 91 return [request] + list(itertools.chain.from_iterable( |
| 92 [self.dependencies_lens.GetRedirectChain(r) |
| 93 for r in preloaded_root_requests])) |
| 94 |
| 95 |
| 96 def _PrintSummary(prefetch_view): |
| 97 requests = prefetch_view.trace.request_track.GetEvents() |
| 98 first_request = prefetch_view.trace.request_track.GetEvents()[0] |
| 99 parser_requests = prefetch_view.ExpandRedirectChains( |
| 100 prefetch_view.ParserDiscoverableRequests(first_request)) |
| 101 preloaded_requests = prefetch_view.ExpandRedirectChains( |
| 102 prefetch_view.PreloadedRequests(first_request)) |
| 103 print '%d requests, %d parser from the main request, %d preloaded' % ( |
| 104 len(requests), len(parser_requests), len(preloaded_requests)) |
| 105 |
| 106 |
| 107 def main(filename): |
| 108 trace = loading_trace.LoadingTrace.FromJsonFile(filename) |
| 109 dependencies_lens = request_dependencies_lens.RequestDependencyLens(trace) |
| 110 prefetch_view = PrefetchSimulationView(trace, dependencies_lens) |
| 111 _PrintSummary(prefetch_view) |
| 112 |
| 113 |
| 114 if __name__ == '__main__': |
| 115 import sys |
| 116 main(sys.argv[1]) |
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