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stale_host_resolver.cc
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stale_host_resolver.cc
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// 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 "components/cronet/stale_host_resolver.h"
#include "base/callback_helpers.h"
#include "base/memory/ptr_util.h"
#include "base/metrics/histogram_macros.h"
#include "base/stl_util.h"
#include "base/timer/timer.h"
#include "base/values.h"
#include "net/base/net_errors.h"
#include "net/dns/dns_util.h"
#include "net/dns/host_resolver_impl.h"
namespace cronet {
namespace {
// Used in histograms; do not modify existing values.
enum RequestOutcome {
// Served from (valid) cache, hosts file, IP literal, etc.
SYNCHRONOUS = 0,
// Network responded; there was no usable stale data.
NETWORK_WITHOUT_STALE = 1,
// Network responded before stale delay; there was usable stale data.
NETWORK_WITH_STALE = 2,
// Stale data returned; network didn't respond before the stale delay.
STALE_BEFORE_NETWORK = 3,
// Request canceled; there was no usable stale data.
CANCELED_WITHOUT_STALE = 4,
// Request canceled; there was usable stale data.
CANCELED_WITH_STALE = 5,
MAX_REQUEST_OUTCOME
};
void RecordRequestOutcome(RequestOutcome outcome) {
UMA_HISTOGRAM_ENUMERATION("DNS.StaleHostResolver.RequestOutcome", outcome,
MAX_REQUEST_OUTCOME);
}
void RecordCacheSizes(size_t restored, size_t current) {
UMA_HISTOGRAM_COUNTS_1000("DNS.StaleHostResolver.RestoreSizeOnCacheMiss",
restored);
UMA_HISTOGRAM_COUNTS_1000("DNS.StaleHostResolver.SizeOnCacheMiss", current);
}
void RecordAddressListDelta(net::AddressListDeltaType delta) {
UMA_HISTOGRAM_ENUMERATION("DNS.StaleHostResolver.StaleAddressListDelta",
delta, net::MAX_DELTA_TYPE);
}
void RecordTimeDelta(base::TimeTicks network_time, base::TimeTicks stale_time) {
if (network_time <= stale_time) {
UMA_HISTOGRAM_LONG_TIMES_100("DNS.StaleHostResolver.NetworkEarly",
stale_time - network_time);
} else {
UMA_HISTOGRAM_LONG_TIMES_100("DNS.StaleHostResolver.NetworkLate",
network_time - stale_time);
}
}
bool StaleEntryIsUsable(const StaleHostResolver::StaleOptions& options,
const net::HostCache::EntryStaleness& entry) {
if (options.max_expired_time != base::TimeDelta() &&
entry.expired_by > options.max_expired_time) {
return false;
}
if (options.max_stale_uses > 0 && entry.stale_hits > options.max_stale_uses)
return false;
if (!options.allow_other_network && entry.network_changes > 0)
return false;
return true;
}
} // namespace
// A request made by the StaleHostResolver. May return fresh cached data,
// network data, or stale cached data.
class StaleHostResolver::RequestImpl {
public:
RequestImpl();
~RequestImpl();
// A callback for the caller to decide whether a stale entry is usable or not.
typedef base::Callback<bool(const net::HostCache::EntryStaleness&)>
StaleEntryUsableCallback;
// Starts the request. May call |usable_callback| inline if |resolver| returns
// stale data to let the caller decide whether the data is usable.
//
// Returns the result if the request finishes synchronously. Returns
// ERR_IO_PENDING and calls |result_callback| with the result if it finishes
// asynchronously (unless destroyed first).
//
// |addresses| must remain valid until the Request completes (synchronously or
// via |result_callback|) or is canceled by destroying the Request.
int Start(net::HostResolverImpl* resolver,
const RequestInfo& info,
net::RequestPriority priority,
net::AddressList* addresses,
const net::CompletionCallback& result_callback,
std::unique_ptr<net::HostResolver::Request>* out_req,
const net::NetLogWithSource& net_log,
const StaleEntryUsableCallback& usable_callback,
base::TimeDelta stale_delay);
void ChangeRequestPriority(net::RequestPriority priority);
private:
class Handle : public net::HostResolver::Request {
public:
Handle(RequestImpl* request) : request_(request) {}
~Handle() override { request_->OnHandleDestroyed(); }
void ChangeRequestPriority(net::RequestPriority priority) override {
request_->ChangeRequestPriority(priority);
}
private:
RequestImpl* request_;
};
bool have_network_request() const {
return network_request_.get() != nullptr;
}
bool have_stale_data() const {
return stale_error_ != net::ERR_DNS_CACHE_MISS;
}
bool have_returned() const { return result_callback_.is_null(); }
bool have_handle() const { return handle_ != nullptr; }
// Callback for |stale_timer_| that returns stale results.
void OnStaleDelayElapsed();
// Callback for network request that returns fresh results if the request
// hasn't already returned stale results, and completes the request.
void OnNetworkRequestComplete(int error);
void OnHandleDestroyed();
// Fills |*result_addresses_| if rv is OK and returns rv.
int HandleResult(int rv, const net::AddressList& addresses);
// Fills |*result_addresses_| if rv is OK and calls |result_callback_| with
// rv.
void ReturnResult(int rv, const net::AddressList& addresses);
void MaybeDeleteThis();
void RecordSynchronousRequest();
void RecordNetworkRequest(int error, bool returned_stale_data);
void RecordCanceledRequest();
// The address list passed into |Start()| to be filled in when the request
// returns.
net::AddressList* result_addresses_;
// The callback passed into |Start()| to be called when the request returns.
net::CompletionCallback result_callback_;
// Set when |result_callback_| is being called so |OnHandleDestroyed()|
// doesn't delete the request.
bool returning_result_;
// The error from the stale cache entry, if there was one.
// If not, net::ERR_DNS_CACHE_MISS.
int stale_error_;
// The address list from the stale cache entry, if there was one.
net::AddressList stale_addresses_;
// A timer that fires when the |Request| should return stale results, if the
// underlying network request has not finished yet.
base::OneShotTimer stale_timer_;
// The address list the underlying network request will fill in. (Can't be the
// one passed to |Start()|, or else the network request would overwrite stale
// results after they are returned.)
net::AddressList network_addresses_;
// The underlying network request, so the priority can be changed.
std::unique_ptr<net::HostResolver::Request> network_request_;
// Statistics used in histograms:
// Number of HostCache entries that were restored from prefs, recorded at the
// time the cache was checked.
size_t restore_size_;
// Current HostCache size at the time the cache was checked.
size_t current_size_;
// Handle that caller can use to cancel the request before it returns.
// Owned by the caller; cleared via |OnHandleDestroyed()| when destroyed.
Handle* handle_;
};
StaleHostResolver::RequestImpl::RequestImpl()
: result_addresses_(nullptr),
returning_result_(false),
stale_error_(net::ERR_DNS_CACHE_MISS),
restore_size_(0),
current_size_(0),
handle_(nullptr) {}
StaleHostResolver::RequestImpl::~RequestImpl() {}
int StaleHostResolver::RequestImpl::Start(
net::HostResolverImpl* resolver,
const RequestInfo& info,
net::RequestPriority priority,
net::AddressList* addresses,
const net::CompletionCallback& result_callback,
std::unique_ptr<net::HostResolver::Request>* out_req,
const net::NetLogWithSource& net_log,
const StaleEntryUsableCallback& usable_callback,
base::TimeDelta stale_delay) {
DCHECK(resolver);
DCHECK(addresses);
DCHECK(!result_callback.is_null());
DCHECK(out_req);
DCHECK(!usable_callback.is_null());
result_addresses_ = addresses;
restore_size_ = resolver->LastRestoredCacheSize();
current_size_ = resolver->CacheSize();
net::AddressList cache_addresses;
net::HostCache::EntryStaleness stale_info;
int cache_rv = resolver->ResolveStaleFromCache(info, &cache_addresses,
&stale_info, net_log);
// If it's a fresh cache hit (or literal), return it synchronously.
if (cache_rv != net::ERR_DNS_CACHE_MISS && !stale_info.is_stale()) {
RecordSynchronousRequest();
return HandleResult(cache_rv, cache_addresses);
}
result_callback_ = result_callback;
handle_ = new Handle(this);
*out_req = std::unique_ptr<net::HostResolver::Request>(handle_);
if (cache_rv == net::OK && usable_callback.Run(stale_info)) {
stale_error_ = cache_rv;
stale_addresses_ = cache_addresses;
// |stale_timer_| is deleted when the Request is deleted, so it's safe to
// use Unretained here.
base::Callback<void()> stale_callback =
base::Bind(&StaleHostResolver::RequestImpl::OnStaleDelayElapsed,
base::Unretained(this));
stale_timer_.Start(FROM_HERE, stale_delay, stale_callback);
}
// Don't check the cache again.
net::HostResolver::RequestInfo no_cache_info(info);
no_cache_info.set_allow_cached_response(false);
int network_rv = resolver->Resolve(
no_cache_info, priority, &network_addresses_,
base::Bind(&StaleHostResolver::RequestImpl::OnNetworkRequestComplete,
base::Unretained(this)),
&network_request_, net_log);
DCHECK_EQ(net::ERR_IO_PENDING, network_rv);
return net::ERR_IO_PENDING;
}
void StaleHostResolver::RequestImpl::ChangeRequestPriority(
net::RequestPriority priority) {
DCHECK(have_network_request());
network_request_->ChangeRequestPriority(priority);
}
void StaleHostResolver::RequestImpl::OnStaleDelayElapsed() {
DCHECK(!have_returned());
DCHECK(have_stale_data());
ReturnResult(stale_error_, stale_addresses_);
// The request needs to wait for both the network request to complete (to
// backfill the cache) and the caller to delete the handle before deleting
// itself.
DCHECK(have_network_request());
}
void StaleHostResolver::RequestImpl::OnNetworkRequestComplete(int error) {
DCHECK(have_network_request());
network_request_.reset();
RecordNetworkRequest(error, /* returned_stale_data = */ have_returned());
if (!have_returned()) {
if (have_stale_data())
stale_timer_.Stop();
ReturnResult(error, network_addresses_);
}
if (!have_handle())
delete this;
}
void StaleHostResolver::RequestImpl::OnHandleDestroyed() {
DCHECK(have_handle());
handle_ = nullptr;
// If the caller deletes the handle *before* the request has returned, treat
// it as a cancel.
if (!have_returned()) {
network_request_.reset();
result_callback_ = net::CompletionCallback();
RecordCanceledRequest();
}
if (!returning_result_ && !have_handle() && !have_network_request())
delete this;
}
int StaleHostResolver::RequestImpl::HandleResult(
int rv,
const net::AddressList& addresses) {
DCHECK(result_addresses_);
if (rv == net::OK)
*result_addresses_ = addresses;
result_addresses_ = nullptr;
return rv;
}
void StaleHostResolver::RequestImpl::ReturnResult(
int rv,
const net::AddressList& addresses) {
DCHECK(result_callback_);
returning_result_ = true;
base::ResetAndReturn(&result_callback_).Run(HandleResult(rv, addresses));
returning_result_ = false;
}
void StaleHostResolver::RequestImpl::RecordSynchronousRequest() {
RecordRequestOutcome(SYNCHRONOUS);
}
void StaleHostResolver::RequestImpl::RecordNetworkRequest(
int error,
bool returned_stale_data) {
if (have_stale_data())
RecordTimeDelta(base::TimeTicks::Now(), stale_timer_.desired_run_time());
if (returned_stale_data && stale_error_ == net::OK && error == net::OK) {
RecordAddressListDelta(
FindAddressListDeltaType(stale_addresses_, network_addresses_));
}
if (returned_stale_data) {
RecordRequestOutcome(STALE_BEFORE_NETWORK);
} else if (have_stale_data()) {
RecordRequestOutcome(NETWORK_WITH_STALE);
RecordCacheSizes(restore_size_, current_size_);
} else {
RecordRequestOutcome(NETWORK_WITHOUT_STALE);
}
}
void StaleHostResolver::RequestImpl::RecordCanceledRequest() {
if (have_stale_data())
RecordRequestOutcome(CANCELED_WITH_STALE);
else
RecordRequestOutcome(CANCELED_WITHOUT_STALE);
}
StaleHostResolver::StaleOptions::StaleOptions()
: delay(),
max_expired_time(),
allow_other_network(false),
max_stale_uses(0) {}
StaleHostResolver::StaleHostResolver(
std::unique_ptr<net::HostResolverImpl> inner_resolver,
const StaleOptions& stale_options)
: inner_resolver_(std::move(inner_resolver)), options_(stale_options) {
DCHECK_LE(0, stale_options.max_expired_time.InMicroseconds());
DCHECK_LE(0, stale_options.max_stale_uses);
}
StaleHostResolver::~StaleHostResolver() {}
int StaleHostResolver::Resolve(const RequestInfo& info,
net::RequestPriority priority,
net::AddressList* addresses,
const net::CompletionCallback& callback,
std::unique_ptr<Request>* out_req,
const net::NetLogWithSource& net_log) {
StaleHostResolver::RequestImpl::StaleEntryUsableCallback usable_callback =
base::Bind(&StaleEntryIsUsable, options_);
RequestImpl* request = new RequestImpl();
int rv =
request->Start(inner_resolver_.get(), info, priority, addresses, callback,
out_req, net_log, usable_callback, options_.delay);
if (rv != net::ERR_IO_PENDING)
delete request;
return rv;
}
int StaleHostResolver::ResolveFromCache(const RequestInfo& info,
net::AddressList* addresses,
const net::NetLogWithSource& net_log) {
return inner_resolver_->ResolveFromCache(info, addresses, net_log);
}
int StaleHostResolver::ResolveStaleFromCache(
const RequestInfo& info,
net::AddressList* addresses,
net::HostCache::EntryStaleness* stale_info,
const net::NetLogWithSource& net_log) {
return inner_resolver_->ResolveStaleFromCache(info, addresses, stale_info,
net_log);
}
bool StaleHostResolver::HasCached(
base::StringPiece hostname,
net::HostCache::Entry::Source* source_out,
net::HostCache::EntryStaleness* stale_out) const {
return inner_resolver_->HasCached(hostname, source_out, stale_out);
}
void StaleHostResolver::SetDnsClientEnabled(bool enabled) {
inner_resolver_->SetDnsClientEnabled(enabled);
}
net::HostCache* StaleHostResolver::GetHostCache() {
return inner_resolver_->GetHostCache();
}
std::unique_ptr<base::Value> StaleHostResolver::GetDnsConfigAsValue() const {
return inner_resolver_->GetDnsConfigAsValue();
}
} // namespace net