Cronet: Use stale DNS cache entries experimentally.

net/dns/stale_host_resolver.cc

+// 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.
+
+#include "net/dns/stale_host_resolver.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/timer/timer.h"
+#include "base/values.h"
+#include "net/base/net_errors.h"
+#include "net/dns/dns_util.h"
+
+namespace net {
+
+namespace {
+
+bool StaleEntryIsUsable(const StaleHostResolver::StaleOptions& options,
+                        const HostCache::StaleEntryInfo& entry) {
+  if (options.max_expired_time != base::TimeDelta()) {
+    if (entry.expired_by > options.max_expired_time)

[Ryan Sleevi, 2016/04/26 02:25:36]

Can't you condense these conditionals?

[Julia Tuttle, 2016/04/27 14:50:26]

Done.

+      return false;
+  }
+  if (options.max_stale_uses > 0u) {
+    if (entry.stale_hits > options.max_stale_uses)
+      return false;
+  }
+  if (!options.allow_other_network) {
+    if (entry.network_changes > 0u)
+      return false;
+  }
+  return true;
+}
+
+}  // namespace
+
+// Used in histograms; please only insert new entries before MAX.
+enum RequestOutcome {
+  // Served from (valid) cache, hosts file, IP literal, etc.
+  SYNCHRONOUS,
+  // Network responded; there was no usable stale data.
+  NETWORK_WITHOUT_STALE,
+  // Network responded before stale delay; there was usable stale data.
+  NETWORK_WITH_STALE,
+  // Stale data returned; network didn't respond before the stale delay.
+  STALE_BEFORE_NETWORK,
+  // Request canceled; there was no usable stale data.
+  CANCELED_WITHOUT_STALE,
+  // Request canceled; there was usable stale data.
+  CANCELED_WITH_STALE,
+  MAX_REQUEST_OUTCOME
+};
+
+void HistogramRequestOutcome(RequestOutcome outcome) {
+  UMA_HISTOGRAM_ENUMERATION("DNS.StaleHostResolverRequestOutcome", outcome,
+                            MAX_REQUEST_OUTCOME);
+}
+
+void HistogramStaleDelta(AddressListDeltaType delta) {
+  UMA_HISTOGRAM_ENUMERATION("DNS.StaleHostResolverStaleDelta", delta,
+                            MAX_DELTA_TYPE);
+}
+
+class StaleHostResolver::Request {

[Ryan Sleevi, 2016/04/26 02:25:36]

Document (throughout)?

I'd like to suggest it may make it more readable to separate the definition and
declaration here, so you can one-pass read what the interface is for
StaleHostResolver::Request, and then see the actual implementation.

[Julia Tuttle, 2016/04/27 14:50:26]

Done.

+ public:
+  Request(AddressList* addresses,
+          const CompletionCallback& callback,
+          const BoundNetLog& net_log)
+      : addresses_(addresses),
+        callback_(callback),
+        net_log_(net_log),
+        network_handle_(nullptr) {
+    DCHECK(!callback_.is_null());
+  }
+
+  typedef base::Callback<bool(const HostCache::StaleEntryInfo&)>
+      StaleEntryUsableCallback;
+
+  int Start(HostResolver* resolver,
+            const RequestInfo& info,
+            RequestPriority priority,
+            const StaleEntryUsableCallback& usable_callback,
+            base::TimeDelta stale_delay) {
+    HostCache::StaleEntryInfo stale_info;
+    int rv = resolver->ResolveStale(info, priority, &network_addresses_,
+                                    network_callback(), &network_handle_,
+                                    &stale_error_, &stale_addresses_,
+                                    &stale_info, net_log_);
+    if (rv != ERR_IO_PENDING) {
+      *addresses_ = network_addresses_;
+      delete this;
+      HistogramRequestOutcome(SYNCHRONOUS);
+      return rv;
+    }
+
+    if (stale_error_ != ERR_DNS_CACHE_MISS && usable_callback.Run(stale_info))
+      stale_timer_.Start(FROM_HERE, stale_delay, stale_callback());
+    else
+      stale_addresses_.clear();
+
+    return ERR_IO_PENDING;
+  }
+
+  void Cancel(HostResolver* resolver) {
+    DCHECK(!returned_stale_response());
+    DCHECK(network_handle_);
+    resolver->CancelRequest(network_handle_);
+    if (stale_timer_.IsRunning())
+      HistogramRequestOutcome(CANCELED_WITH_STALE);
+    else
+      HistogramRequestOutcome(CANCELED_WITHOUT_STALE);
+    delete this;
+  }
+
+  void OnStaleDelayElapsed() {
+    DCHECK(!returned_stale_response());
+    callback_.Run(HandleResponse(stale_error_, stale_addresses_));
+    HistogramRequestOutcome(STALE_BEFORE_NETWORK);
+    callback_.Reset();
+  }
+
+  void OnNetworkRequestComplete(int error) {
+    if (!returned_stale_response()) {
+      callback_.Run(HandleResponse(error, network_addresses_));
+      if (stale_timer_.IsRunning())
+        HistogramRequestOutcome(NETWORK_WITH_STALE);
+      else
+        HistogramRequestOutcome(NETWORK_WITHOUT_STALE);
+    }
+    if (returned_stale_response() && stale_error_ == OK && error == OK) {
+      HistogramStaleDelta(
+          FindAddressListDeltaType(stale_addresses_, network_addresses_));
+    }
+    delete this;
+  }
+
+ private:
+  int HandleResponse(int rv, const AddressList& addresses) {
+    if (rv == OK)
+      *addresses_ = addresses;
+    return rv;
+  }
+
+  bool returned_stale_response() { return callback_.is_null(); }
+
+  base::Callback<void()> stale_callback() {
+    return base::Bind(&StaleHostResolver::Request::OnStaleDelayElapsed,
+                      base::Unretained(this));
+  }
+
+  CompletionCallback network_callback() {
+    return base::Bind(&StaleHostResolver::Request::OnNetworkRequestComplete,
+                      base::Unretained(this));
+  }
+
+  AddressList* addresses_;
+  CompletionCallback callback_;
+  BoundNetLog net_log_;
+
+  int stale_error_;
+  AddressList stale_addresses_;
+  base::OneShotTimer stale_timer_;
+
+  AddressList network_addresses_;
+  HostResolver::RequestHandle network_handle_;
+};
+
+StaleHostResolver::StaleHostResolver(
+    std::unique_ptr<HostResolver> inner_resolver,
+    const StaleOptions& stale_options)
+    : resolver_(std::move(inner_resolver)), options_(stale_options) {}
+
+StaleHostResolver::~StaleHostResolver() {}
+
+int StaleHostResolver::Resolve(const RequestInfo& info,
+                               RequestPriority priority,
+                               AddressList* addresses,
+                               const CompletionCallback& callback,
+                               RequestHandle* out_req,
+                               const BoundNetLog& net_log) {
+  Request* request = new Request(addresses, callback, net_log);
+  int rv =
+      request->Start(resolver_.get(), info, priority,
+                     base::Bind(&StaleEntryIsUsable, options_), options_.delay);
+  if (rv == ERR_IO_PENDING && out_req)
+    *out_req = reinterpret_cast<RequestHandle>(request);
+  return rv;
+}
+
+void StaleHostResolver::CancelRequest(RequestHandle req_handle) {
+  Request* request = reinterpret_cast<Request*>(req_handle);
+  DCHECK(request);
+  request->Cancel(resolver_.get());
+}
+
+int StaleHostResolver::ResolveFromCache(const RequestInfo& info,
+                                        AddressList* addresses,
+                                        const BoundNetLog& net_log) {
+  return resolver_->ResolveFromCache(info, addresses, net_log);
+}
+
+int StaleHostResolver::ResolveStaleFromCache(
+    const RequestInfo& info,
+    AddressList* addresses,
+    HostCache::StaleEntryInfo* stale_info,
+    const BoundNetLog& net_log) {
+  return resolver_->ResolveStaleFromCache(info, addresses, stale_info, net_log);
+}
+
+void StaleHostResolver::SetDnsClientEnabled(bool enabled) {
+  resolver_->SetDnsClientEnabled(enabled);
+}
+
+HostCache* StaleHostResolver::GetHostCache() {
+  return resolver_->GetHostCache();
+}
+
+std::unique_ptr<base::Value> StaleHostResolver::GetDnsConfigAsValue() const {
+  return resolver_->GetDnsConfigAsValue();
+}
+
+}  // namespace net