GCP2.0 Device: mDNS basics

cloud_print/gcp20/prototype/dns_sd.cc

Index: cloud_print/gcp20/prototype/dns_sd.cc
diff --git a/cloud_print/gcp20/prototype/dns_sd.cc b/cloud_print/gcp20/prototype/dns_sd.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e51de03a8bdcc9e2bed57c8c782f7bf5f67f271a
--- /dev/null
+++ b/cloud_print/gcp20/prototype/dns_sd.cc
@@ -0,0 +1,186 @@
+// Copyright 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 "cloud_print/gcp20/prototype/dns_sd.h"
+
+#include <string.h>
+
+#include "base/basictypes.h"
+#include "net/base/big_endian.h"
+#include "net/base/net_util.h"
+#include "net/dns/dns_protocol.h"
+
+namespace {
+
+const char* kDefaultIpAddressMulticast = "224.0.0.251";
+const uint16 kDefaultPortMulticast = 5353;
+
+// TODO(maksymb): Add possibility to set constants via command line arguments
+const uint32 kDefaultTTL = 60*60;  // in seconds
+
+}  // namespace
+
+DnsSd::DnsSd(): is_online_(false) {
+  // Do nothing
+}
+
+DnsSd::~DnsSd() {
+  Shutdown();
+}
+
+bool DnsSd::Start() {
+  if (is_online_)
+    return true;
+
+  if (!BindSocket())
+    return false;
+
+  LOG(INFO) << "DNS server started";
+
+  SendAnnouncement(kDefaultTTL);
+
+  is_online_ = true;
+  return true;
+}
+
+void DnsSd::Update() {
+  if (!is_online_)
+    return;
+
+  SendAnnouncement(kDefaultTTL);
+}
+
+void DnsSd::Shutdown() {
+  if (!is_online_)
+    return;
+
+  SendAnnouncement(0);  // ttl is 0
+  socket_->Close();
+  is_online_ = false;
+  LOG(INFO) << "DNS server stopped";
+}
+
+bool DnsSd::BindSocket() {

[gene, 2013/06/06 00:13:51]

BindSocket -> CreateSocket ?

[maksymb, 2013/06/06 01:52:46]

Done.

+  net::IPAddressNumber local_ip_any;
+  bool success = net::ParseIPLiteralToNumber("0.0.0.0", &local_ip_any);
+  DCHECK(success);
+
+  net::IPAddressNumber multicast_dns_ip_address;
+  success = net::ParseIPLiteralToNumber(kDefaultIpAddressMulticast,
+                                        &multicast_dns_ip_address);
+  DCHECK(success);
+
+
+  socket_.reset(new net::UDPSocket(net::DatagramSocket::DEFAULT_BIND,
+                                   net::RandIntCallback(),
+                                   NULL,
+                                   net::NetLog::Source()));
+
+  net::IPEndPoint local_address = net::IPEndPoint(local_ip_any,
+                                                  kDefaultPortMulticast);
+  multicast_address_ = net::IPEndPoint(multicast_dns_ip_address,
+                                       kDefaultPortMulticast);
+
+  socket_->AllowAddressReuse();
+
+  int status = socket_->Bind(local_address);
+  if (status < 0)
+    return false;
+
+  socket_->SetMulticastLoopbackMode(false);
+  status = socket_->JoinGroup(multicast_dns_ip_address);
+
+  if (status < 0)
+    return false;
+
+  DCHECK(socket_->is_connected());
+
+  return true;
+}
+
+bool DnsSd::CheckPendingQueries() {
+  // write code
+  return false;
+}
+
+void DoNothing(int /*var*/) {
+  // Do nothing
+}
+
+void DnsSd::SendAnnouncement(uint32 ttl) {
+  // Create a message with allocated space for header.
+  scoped_ptr<std::vector<uint8> > message(
+    new std::vector<uint8>(sizeof(net::dns_protocol::Header)));
+
+  // These variables will be autimaticaly calculated in |Append*| methods.
+  question_count_ = 0;

[gene, 2013/06/06 00:13:51]

I think it is better not to make question_count_ and answers_count_ as members.
Since you have not implement any AppendXXX functions, I suggest you remove them
from the class declaration.

[maksymb, 2013/06/06 01:52:46]

Done.

+  answers_count_ = 0;
+
+  // AppendSrv(ttl, message.get());
+  // AppendPtr(ttl, message.get());
+  // AppendTxt(ttl, message.get());
+  // AppendA(ttl, message.get());
+  UpdateHeader(false/*no question*/, message.get());

[gene, 2013/06/06 00:13:51]

It is better to create header here, or pass all parameters necessary to create
header in the message

[maksymb, 2013/06/06 01:52:46]

Cleared. Created temporary dump. 

+
+

[gene, 2013/06/06 00:13:51]

extra empty line

[maksymb, 2013/06/06 01:52:46]

Done.

+  // Preparing for sending
+  scoped_refptr<net::IOBufferWithSize> buffer =
+    new net::IOBufferWithSize(message.get()->size());
+  memcpy(buffer.get()->data(), message.get()->data(), message.get()->size());
+
+  // Create empty callback (we don't need it at all) and send packet
+  net::CompletionCallback callback = base::Bind(DoNothing);
+  socket_->SendTo(buffer.get(),
+                  buffer.get()->size(),
+                  multicast_address_,
+                  callback);
+
+  LOG(INFO) << "Announcement was sent with TTL: " << ttl;
+}
+
+void DnsSd::UpdateHeader(bool is_question, std::vector<uint8>* message) {
+  net::dns_protocol::Header header;
+  header.id = 0;
+  header.flags = 0;  // setting flags is below
+  header.qdcount = question_count_;
+  header.ancount = answers_count_;
+  header.nscount = 0;
+  header.arcount = 0;
+
+  // Setting flags
+  header.flags = 0;
+  if (is_question)
+    header.flags |= net::dns_protocol::kFlagResponse;
+
+  // Putting into message (place for header already should be allocated)
+  net::BigEndianWriter writer(message->data(), message->size());
+  bool success = writer.WriteU16(header.id) &&
+                 writer.WriteU16(header.flags) &&
+                 writer.WriteU16(header.qdcount) &&
+                 writer.WriteU16(header.ancount) &&
+                 writer.WriteU16(header.nscount) &&
+                 writer.WriteU16(header.arcount);
+  DCHECK(success);
+}
+
+void DnsSd::AppendSrv(uint32 /*ttl*/, std::vector<uint8>* /* message*/) {
+  ++answers_count_;
+// write code

[gene, 2013/06/06 00:13:51]

"// write code" -> "NOTIMPLEMENTED();  // implement this"

[maksymb, 2013/06/06 01:52:46]

Done.

+}
+
+void DnsSd::AppendPtr(uint32 /*ttl*/, std::vector<uint8>* /* message*/) {
+  ++answers_count_;
+// write code
+}
+
+void DnsSd::AppendTxt(uint32 /*ttl*/, std::vector<uint8>* /* message*/) {
+  ++answers_count_;
+// write code
+}
+
+void DnsSd::AppendA(uint32 /*ttl*/, std::vector<uint8>* /* message*/) {
+  ++answers_count_;
+// write code
+}
+