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// Copyright (c) 2013 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/mdns_cache.h"
#include <algorithm>
#include <tuple>
#include <utility>
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "net/dns/public/dns_protocol.h"
#include "net/dns/record_parsed.h"
#include "net/dns/record_rdata.h"
// TODO(noamsml): Recursive CNAME closure (backwards and forwards).
namespace net {
namespace {
constexpr size_t kDefaultEntryLimit = 100'000;
} // namespace
// The effective TTL given to records with a nominal zero TTL.
// Allows time for hosts to send updated records, as detailed in RFC 6762
// Section 10.1.
static const unsigned kZeroTTLSeconds = 1;
MDnsCache::Key::Key(unsigned type,
const std::string& name,
const std::string& optional)
: type_(type),
name_lowercase_(base::ToLowerASCII(name)),
optional_(optional) {}
MDnsCache::Key::Key(const MDnsCache::Key& other) = default;
MDnsCache::Key& MDnsCache::Key::operator=(const MDnsCache::Key& other) =
default;
MDnsCache::Key::~Key() = default;
bool MDnsCache::Key::operator<(const MDnsCache::Key& other) const {
return std::tie(name_lowercase_, type_, optional_) <
std::tie(other.name_lowercase_, other.type_, other.optional_);
}
bool MDnsCache::Key::operator==(const MDnsCache::Key& key) const {
return type_ == key.type_ && name_lowercase_ == key.name_lowercase_ &&
optional_ == key.optional_;
}
// static
MDnsCache::Key MDnsCache::Key::CreateFor(const RecordParsed* record) {
return Key(record->type(),
record->name(),
GetOptionalFieldForRecord(record));
}
MDnsCache::MDnsCache() : entry_limit_(kDefaultEntryLimit) {}
MDnsCache::~MDnsCache() = default;
const RecordParsed* MDnsCache::LookupKey(const Key& key) {
auto found = mdns_cache_.find(key);
if (found != mdns_cache_.end()) {
return found->second.get();
}
return nullptr;
}
MDnsCache::UpdateType MDnsCache::UpdateDnsRecord(
std::unique_ptr<const RecordParsed> record) {
Key cache_key = Key::CreateFor(record.get());
// Ignore "goodbye" packets for records not in cache.
if (record->ttl() == 0 && mdns_cache_.find(cache_key) == mdns_cache_.end())
return NoChange;
base::Time new_expiration = GetEffectiveExpiration(record.get());
if (next_expiration_ != base::Time())
new_expiration = std::min(new_expiration, next_expiration_);
std::pair<RecordMap::iterator, bool> insert_result =
mdns_cache_.insert(std::make_pair(cache_key, nullptr));
UpdateType type = NoChange;
if (insert_result.second) {
type = RecordAdded;
} else {
if (record->ttl() != 0 &&
!record->IsEqual(insert_result.first->second.get(), true)) {
type = RecordChanged;
}
}
insert_result.first->second = std::move(record);
next_expiration_ = new_expiration;
return type;
}
void MDnsCache::CleanupRecords(
base::Time now,
const RecordRemovedCallback& record_removed_callback) {
base::Time next_expiration;
// TODO(crbug.com/946688): Make overfill pruning more intelligent than a bulk
// clearing of everything.
bool clear_cache = IsCacheOverfilled();
// We are guaranteed that |next_expiration_| will be at or before the next
// expiration. This allows clients to eagrely call CleanupRecords with
// impunity.
if (now < next_expiration_ && !clear_cache)
return;
for (auto i = mdns_cache_.begin(); i != mdns_cache_.end();) {
base::Time expiration = GetEffectiveExpiration(i->second.get());
if (clear_cache || now >= expiration) {
record_removed_callback.Run(i->second.get());
i = mdns_cache_.erase(i);
} else {
if (next_expiration == base::Time() || expiration < next_expiration) {
next_expiration = expiration;
}
++i;
}
}
next_expiration_ = next_expiration;
}
void MDnsCache::FindDnsRecords(unsigned type,
const std::string& name,
std::vector<const RecordParsed*>* results,
base::Time now) const {
DCHECK(results);
results->clear();
const std::string name_lowercase = base::ToLowerASCII(name);
auto i = mdns_cache_.lower_bound(Key(type, name, ""));
for (; i != mdns_cache_.end(); ++i) {
if (i->first.name_lowercase() != name_lowercase ||
(type != 0 && i->first.type() != type)) {
break;
}
const RecordParsed* record = i->second.get();
// Records are deleted only upon request.
if (now >= GetEffectiveExpiration(record)) continue;
results->push_back(record);
}
}
std::unique_ptr<const RecordParsed> MDnsCache::RemoveRecord(
const RecordParsed* record) {
Key key = Key::CreateFor(record);
auto found = mdns_cache_.find(key);
if (found != mdns_cache_.end() && found->second.get() == record) {
std::unique_ptr<const RecordParsed> result = std::move(found->second);
mdns_cache_.erase(key);
return result;
}
return std::unique_ptr<const RecordParsed>();
}
bool MDnsCache::IsCacheOverfilled() const {
return mdns_cache_.size() > entry_limit_;
}
// static
std::string MDnsCache::GetOptionalFieldForRecord(const RecordParsed* record) {
switch (record->type()) {
case PtrRecordRdata::kType: {
const PtrRecordRdata* rdata = record->rdata<PtrRecordRdata>();
return rdata->ptrdomain();
}
default: // Most records are considered unique for our purposes
return "";
}
}
// static
base::Time MDnsCache::GetEffectiveExpiration(const RecordParsed* record) {
base::TimeDelta ttl;
if (record->ttl()) {
ttl = base::TimeDelta::FromSeconds(record->ttl());
} else {
ttl = base::TimeDelta::FromSeconds(kZeroTTLSeconds);
}
return record->time_created() + ttl;
}
} // namespace net
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