In-browser DNS-based service discovery system

chrome/browser/local_discovery/service_discovery_client_impl.cc

+// 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 <utility>
+
+#include "base/logging.h"
+#include "base/memory/singleton.h"
+#include "base/message_loop_proxy.h"
+#include "base/stl_util.h"
+#include "chrome/browser/local_discovery/service_discovery_client_impl.h"
+#include "net/dns/dns_protocol.h"
+#include "net/dns/record_rdata.h"
+
+namespace local_discovery {
+
+ServiceDiscoveryClientImpl::ServiceDiscoveryClientImpl() {
+}
+
+ServiceDiscoveryClientImpl::~ServiceDiscoveryClientImpl() {
+}
+
+// static
+ServiceDiscoveryClientImpl* ServiceDiscoveryClientImpl::GetInstance() {
+  return Singleton<ServiceDiscoveryClientImpl>::get();
+}
+
+scoped_ptr<ServiceWatcher> ServiceDiscoveryClientImpl::CreateServiceWatcher(
+    const std::string& service_type,
+    ServiceWatcher::Delegate* delegate) {
+  return scoped_ptr<ServiceWatcher>(new ServiceWatcherImpl(
+      service_type,  delegate));
+}
+
+scoped_ptr<ServiceResolver> ServiceDiscoveryClientImpl::CreateServiceResolver(
+    const std::string& service_name,
+    const ServiceResolver::ResolveCompleteCallback& callback) {
+  return scoped_ptr<ServiceResolver>(new ServiceResolverImpl(
+      service_name, callback));
+}
+
+ServiceWatcherImpl::ServiceWatcherImpl(
+    const std::string& service_type,
+    ServiceWatcher::Delegate* delegate)
+    : service_type_(service_type), delegate_(delegate), started_(false) {
+}
+
+bool ServiceWatcherImpl::Start() {
+  DCHECK(!started_);
+  listener_ = net::MDnsClient::GetInstance()->CreateListener(
+      net::dns_protocol::kTypePTR, service_type_, this);
+  if (!listener_->Start())
+    return false;
+
+  started_ = true;
+  return true;
+}
+
+ServiceWatcherImpl::~ServiceWatcherImpl() {
+}
+
+void ServiceWatcherImpl::GetAvailableServices(
+    std::vector<std::string>* services) const {
+  DCHECK(started_);
+  DCHECK(services);
+  services->reserve(services_.size());
+  for (ServiceListenersMap::const_iterator i = services_.begin();
+       i != services_.end(); i++) {
+    services->push_back(i->first);
+  }
+}
+
+void ServiceWatcherImpl::DiscoverNewServices(bool force_update) {
+  DCHECK(started_);
+  if (force_update)
+    services_.clear();
+  CreateTransaction(true /*network*/, false /*cache*/, force_update,
+                    &transaction_network_);
+}
+
+void ServiceWatcherImpl::ReadCachedServices() {
+  DCHECK(started_);
+  CreateTransaction(false /*network*/, true /*cache*/, false /*force refresh*/,
+                    &transaction_cache_);
+}
+
+bool ServiceWatcherImpl::CreateTransaction(
+    bool network, bool cache, bool force_refresh,
+    scoped_ptr<net::MDnsTransaction>* transaction) {
+  int transaction_flags = 0;
+  if (network)
+    transaction_flags |= net::MDnsTransaction::QUERY_NETWORK;
+
+  if (cache)
+    transaction_flags |= net::MDnsTransaction::QUERY_CACHE;
+
+  // TODO(noamsml): Add flag for force_refresh when supported.
+
+  if (transaction_flags) {
+    *transaction = net::MDnsClient::GetInstance()->CreateTransaction(
+        net::dns_protocol::kTypePTR, service_type_, transaction_flags,
+        base::Bind(&ServiceWatcherImpl::OnTransactionResponse,
+                   base::Unretained(this), transaction));
+    return (*transaction)->Start();
+  }
+
+  return true;
+}
+
+std::string ServiceWatcherImpl::GetServiceType() const {
+  return listener_->GetName();
+}
+
+void ServiceWatcherImpl::OnRecordUpdate(
+    net::MDnsListener::UpdateType update,
+    const net::RecordParsed* record) {
+  DCHECK(started_);
+  if (record->type() == net::dns_protocol::kTypePTR) {
+    DCHECK(record->name() == GetServiceType());
+    const net::PtrRecordRdata* rdata = record->rdata<net::PtrRecordRdata>();
+
+    switch (update) {
+      case net::MDnsListener::RECORD_ADDED:
+        AddService(rdata->ptrdomain());
+        break;
+      case net::MDnsListener::RECORD_CHANGED:
+        NOTREACHED();
+        break;
+      case net::MDnsListener::RECORD_REMOVED:
+        RemoveService(rdata->ptrdomain());
+        break;
+    }
+  } else {
+    DCHECK(record->type() == net::dns_protocol::kTypeSRV ||
+           record->type() == net::dns_protocol::kTypeTXT);
+    DCHECK(services_.find(record->name()) != services_.end());
+
+    delegate_->OnServiceChanged(record->name());
+  }
+}
+
+void ServiceWatcherImpl::OnCachePurged() {
+  // Not yet implemented.
+}
+
+void ServiceWatcherImpl::OnTransactionResponse(
+    scoped_ptr<net::MDnsTransaction>* transaction,
+    net::MDnsTransaction::Result result,
+    const net::RecordParsed* record) {
+  DCHECK(started_);
+  if (result == net::MDnsTransaction::RESULT_RECORD) {
+    const net::PtrRecordRdata* rdata = record->rdata<net::PtrRecordRdata>();
+    DCHECK(rdata);
+    AddService(rdata->ptrdomain());
+  } else if (result == net::MDnsTransaction::RESULT_DONE) {
+    transaction->reset();
+  }
+
+  // Do nothing for NSEC records. It is an error for hosts to broadcast an NSEC
+  // record for PTR records on any name.
+}
+
+ServiceWatcherImpl::ServiceListeners::ServiceListeners(
+    const std::string& service_name,
+    ServiceWatcherImpl* watcher) {
+  srv_listener_ = net::MDnsClient::GetInstance()->CreateListener(
+      net::dns_protocol::kTypeSRV, service_name, watcher);
+  txt_listener_ = net::MDnsClient::GetInstance()->CreateListener(
+      net::dns_protocol::kTypeTXT, service_name, watcher);
+}
+
+ServiceWatcherImpl::ServiceListeners::~ServiceListeners() {
+}
+
+bool ServiceWatcherImpl::ServiceListeners::Start() {
+  if (!srv_listener_->Start())
+    return false;
+  return txt_listener_->Start();
+}
+
+void ServiceWatcherImpl::AddService(const std::string& service) {
+  DCHECK(started_);
+  std::pair<ServiceListenersMap::iterator, bool> found = services_.insert(
+      make_pair(service, static_cast<ServiceListeners*>(NULL)));
+  if (found.second) {  // Newly inserted.
+    found.first->second = linked_ptr<ServiceListeners>(
+        new ServiceListeners(service, this));
+    bool success = found.first->second->Start();
+    DCHECK(success);
+    delegate_->OnServiceStatusChanged(true, service);
+  }
+}
+
+void ServiceWatcherImpl::RemoveService(const std::string& service) {
+  DCHECK(started_);
+  ServiceListenersMap::iterator found = services_.find(service);
+  if (found != services_.end()) {
+    services_.erase(found);
+    delegate_->OnServiceStatusChanged(false, service);
+  }
+}
+
+void ServiceWatcherImpl::OnNsecRecord(const std::string& name,
+                                          unsigned rrtype) {
+  // Do nothing. It is an error for hosts to broadcast an NSEC record for PTR
+  // on any name.
+}
+
+ServiceResolverImpl::ServiceResolverImpl(
+    const std::string& service_name,
+    const ResolveCompleteCallback& callback)
+    : service_name_(service_name), callback_(callback),
+      is_resolving_(false), has_resolved_(false), metadata_resolved_(false),
+      address_resolved_(false), current_service_index_(0) {
+  services_[0].service_name = service_name_;
+  services_[1].service_name = service_name_;
+}
+
+bool ServiceResolverImpl::StartResolving() {
+  if (!CreateTxtTransaction())

[gene, 2013/06/19 22:48:03]

Can result of the transaction arrive within this call?
If so, does it make sense to move is_resolving_, address_resolved_,
metadata_resolved_ initialization before starting transactions?

[Noam Samuel, 2013/06/19 23:53:29]

Done.

+    return false;
+  if (!CreateSrvTransaction())
+    return false;
+  is_resolving_ = true;
+  address_resolved_ = false;
+  metadata_resolved_ = false;
+  return true;
+}
+
+bool ServiceResolverImpl::IsResolving() const {
+  return is_resolving_;
+}
+
+bool ServiceResolverImpl::HasResolved() const {
+  return has_resolved_;
+}
+
+ServiceResolverImpl::~ServiceResolverImpl() {
+}
+
+bool ServiceResolverImpl::CreateTxtTransaction() {
+  txt_transaction_ = net::MDnsClient::GetInstance()->CreateTransaction(
+      net::dns_protocol::kTypeTXT, service_name_,
+      net::MDnsTransaction::SINGLE_RESULT | net::MDnsTransaction::QUERY_CACHE |
+      net::MDnsTransaction::QUERY_NETWORK,
+      base::Bind(&ServiceResolverImpl::TxtRecordTransactionResponse,
+                 AsWeakPtr()));
+  return txt_transaction_->Start();
+}
+
+// TODO(noamsml): quick-resolve for AAAA records.  Since A records tend to be in
+void ServiceResolverImpl::CreateATransaction() {
+  a_transaction_ = net::MDnsClient::GetInstance()->CreateTransaction(
+      net::dns_protocol::kTypeA,
+      staging_service()->address.host(),
+      net::MDnsTransaction::SINGLE_RESULT | net::MDnsTransaction::QUERY_CACHE,
+      base::Bind(&ServiceResolverImpl::ARecordTransactionResponse,
+                 AsWeakPtr()));
+  a_transaction_->Start();
+}
+
+bool ServiceResolverImpl::CreateSrvTransaction() {
+  srv_transaction_ = net::MDnsClient::GetInstance()->CreateTransaction(
+      net::dns_protocol::kTypeSRV, service_name_,
+      net::MDnsTransaction::SINGLE_RESULT | net::MDnsTransaction::QUERY_CACHE |
+      net::MDnsTransaction::QUERY_NETWORK,
+      base::Bind(&ServiceResolverImpl::SrvRecordTransactionResponse,
+                 AsWeakPtr()));
+  return srv_transaction_->Start();
+}
+
+std::string ServiceResolverImpl::GetName() const {
+  return service_name_;
+}
+
+void ServiceResolverImpl::SrvRecordTransactionResponse(
+    net::MDnsTransaction::Result status, const net::RecordParsed* record) {
+  srv_transaction_.reset();
+  if (status == net::MDnsTransaction::RESULT_RECORD) {
+    DCHECK(record);
+    staging_service()->address = RecordToAddress(record);
+    staging_service()->last_seen = record->time_created();
+    CreateATransaction();
+  } else {
+    txt_transaction_.reset();
+    srv_transaction_.reset();
+    a_transaction_.reset();
+    is_resolving_ = false;

[gene, 2013/06/19 22:48:03]

Do you need to reset address_resolved_ and metadata_resolved_ as well here?
You can have a separate function ServiceNotFound() in this case.

[Noam Samuel, 2013/06/19 23:53:29]

address_resolved_ and metadata_resolved_ are reset when the resolution starts
(in StartResolving). Moved to separate function.

+    callback_.Run(MDnsStatusToRequestStatus(status), GetServiceDescription());
+  }
+}
+
+void ServiceResolverImpl::TxtRecordTransactionResponse(
+    net::MDnsTransaction::Result status, const net::RecordParsed* record) {
+  txt_transaction_.reset();
+  if (status == net::MDnsTransaction::RESULT_RECORD) {
+    DCHECK(record);
+    staging_service()->metadata = RecordToMetadata(record);
+  } else {
+    staging_service()->metadata = std::vector<std::string>();
+  }
+
+  metadata_resolved_ = true;
+  AlertCallbackIfReady();
+}
+
+void ServiceResolverImpl::ARecordTransactionResponse(
+    net::MDnsTransaction::Result status, const net::RecordParsed* record) {
+  a_transaction_.reset();
+
+  if (status == net::MDnsTransaction::RESULT_RECORD) {
+    DCHECK(record);
+    staging_service()->ip_address = RecordToIPAddress(record);
+  } else {
+    staging_service()->ip_address = net::IPAddressNumber();
+  }
+
+  address_resolved_ = true;
+  AlertCallbackIfReady();
+}
+
+void ServiceResolverImpl::AlertCallbackIfReady() {
+  if (metadata_resolved_ && address_resolved_) {
+    txt_transaction_.reset();
+    srv_transaction_.reset();
+    a_transaction_.reset();
+    has_resolved_ = true;
+    is_resolving_ = false;
+    current_service_index_ = (current_service_index_ + 1) % 2;
+    callback_.Run(STATUS_SUCCESS, GetServiceDescription());
+  }
+}
+
+const ServiceDescription& ServiceResolverImpl::GetServiceDescription() const {
+  return services_[current_service_index_];
+}
+
+ServiceResolver::RequestStatus ServiceResolverImpl::MDnsStatusToRequestStatus(
+    net::MDnsTransaction::Result status) const {
+  switch (status) {
+    case net::MDnsTransaction::RESULT_RECORD:
+      return ServiceResolver::STATUS_SUCCESS;
+    case net::MDnsTransaction::RESULT_NO_RESULTS:
+      return ServiceResolver::STATUS_TIMEOUT;
+    case net::MDnsTransaction::RESULT_NSEC:
+      return ServiceResolver::STATUS_KNOWN_NONEXISTENT;
+    case net::MDnsTransaction::RESULT_DONE:
+      NOTREACHED();

[Vitaly Buka (NO REVIEWS), 2013/06/19 22:51:24]

no default return value

[Noam Samuel, 2013/06/19 23:53:29]

Done.

+      return ServiceResolver::STATUS_TIMEOUT;
+  }
+}
+
+const std::vector<std::string>& ServiceResolverImpl::RecordToMetadata(
+    const net::RecordParsed* record) const {
+  DCHECK(record->type() == net::dns_protocol::kTypeTXT);
+  const net::TxtRecordRdata* txt_rdata = record->rdata<net::TxtRecordRdata>();
+  DCHECK(txt_rdata);
+  return txt_rdata->texts();
+}
+
+net::HostPortPair ServiceResolverImpl::RecordToAddress(
+    const net::RecordParsed* record) const {
+  DCHECK(record->type() == net::dns_protocol::kTypeSRV);
+  const net::SrvRecordRdata* srv_rdata = record->rdata<net::SrvRecordRdata>();
+  DCHECK(srv_rdata);
+  return net::HostPortPair(srv_rdata->target(), srv_rdata->port());
+}
+
+const net::IPAddressNumber& ServiceResolverImpl::RecordToIPAddress(
+    const net::RecordParsed* record) const {
+  DCHECK(record->type() == net::dns_protocol::kTypeA);
+  const net::ARecordRdata* a_rdata = record->rdata<net::ARecordRdata>();
+  DCHECK(a_rdata);
+  return a_rdata->address();
+}
+
+}  // namespace local_discovery