Jay MahendruProgram ManagerDNS-SD API

Discovering Devices or Services over the Local Network

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Agenda

What is DNS-SD?RegistrationDiscovery & ResolutionConnectionCode SampleResources

• Uses standard DNS records to register and discover other services (device or app) on the local network

• Works in conjunction with mDNS, allowing devices to communicate with each other, without the need for a unicast server

DNS Service Discovery (DNS-SD)

DNS-SD enables easy discovery of other services on the local network

• Advertise app to others on the network• Service Name Format: <Instance Name>.<Service

Type>.<Domain>• Instance Name: Human-readable name (such as “Simple Chat

App”)• Service Type: Combination of the protocol name + transport(such

as _sca._tcp)• Domain: Standard DNS domain, such as microsoft.com

• Can also specify text attributes:• Max Concurrent Users; 20• Locale; En-US

Registration

• Are there any instances of _sca._tcp on the local domain?• Yes:

1. JayM._sca._tcp.local2. KaylenW._sca._tcp.local

• Resolve:1. 124.169.26.15 (IP), 1010 (Port); Max Concurrent Users = 20; Locale

= En-US2. 124.169.26.16 (IP), 1010 (Port); Max Concurrent Users = 20; Locale

= En-US

Discovery & Resolution

• Use the resolved port number and hostname for connecting to the app• Can use a number of methods such as the

Modern Sockets API

Connect

async void RegisterService() { // Create a listening socket to watch for incoming connections from other apps StreamSocketListener listener = new StreamSocketListener();

// We can pass an actual port number here or one will get assigned automatically await listener.BindServiceNameAsync("");

// Create a DNS-SD Service Instance DnssdServiceInstance chatServ = new DnssdServiceInstance("SimpleChatApp._sca._tcp.local.", null);

// Can add optional text attributes (key-val pairs) as well chatServ.TextAttributes.Add("MaxConcurrentUsers", "20"); chatServ.TextAttributes.Add("Locale", "En-US");

// Register Service var registrationResult = await chatServ.RegisterStreamSocketListenerAsync(listener);}

Sample Code – Service Registration

Sample Code – Service Discovery & Resolution• Use the Windows.Devices.Enumeration API to discover the DNS-SD services

// Devices.Enumeration API requires a GUID for each discovery type (such as DNS-SD, Bluetooth etc.)public static Guid DnsSdProtocol = new Guid("{4526e8c1-8aac-4153-9b16-55e86ada0e54}");

// Filter results by domain and service namestring queryString = "System.Devices.AepService.ProtocolId:={" + DnsSdProtocol + "} AND " + "System.Devices.Dnssd.Domain:=\"local\" AND System.Devices.Dnssd.ServiceName:=\"_sca._tcp\"";

// Start a watcher with the query string, and request other properties (discover & resolve)var watcher = DeviceInformation.CreateWatcher(queryString, new String[] { "System.Devices.Dnssd.HostName", "System.Devices.Dnssd.ServiceName", "System.Devices.Dnssd.TextAttributes", "System.Devices.IpAddress"}, DeviceInformationKind.AssociationEndpointService);

// Add callback to watcher watcher.Added += ConnectToService;

watcher.Start();

Sample Code – Connectivityasync void ConnectToService(DeviceWatcher sender, DeviceInformation args){ // The IpAddress property contains a list of strings representing IP literals var ipAddresses = args["System.Devices.IpAddress"] as string[]; var remoteAddress = new HostName(ipAddresses[0]);

// The PortNumber property gives us the port on which the service is advertised (UInt16) var remotePort = args["System.Devices.Dnssd.PortNumber"]. ToString(); var streamSock = new StreamSocket();

// The TextAttributes property contains a list of the text attributes added, such as // Max Concurrent Users = 20; Locale = En-US var textAttrs = args["TextAttributes"] as string[];

// Connect to the other app instance await streamSock.ConnectAsync(remoteAddress, remotePort);}

• MSDN Documentation & Sample App:• http://aka.ms/dnssdapi• Check out the sample app and create your own service discovery app!

Resources

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