docs: subtypes

Author: richardschneider

README.md

@@ -21,6 +21,7 @@ service or service instance.
 - Detects new and/or removed network interfaces
 - Supports multicasting on multiple network interfaces
 - Supports reverse address mapping
+- Supports service subtypes (features)
 - Handles legacy unicast queries, see #61
 
 ## Getting started

doc/articles/subtype.md

@@ -0,0 +1,38 @@
+# Subtypes
+
+Subtypes are used to define features implemented by a service instance. See
+[RFC 6763 - 7.1 Selective Instance Enumeration (Subtypes)](https://tools.ietf.org/html/rfc6763#section-7.1) for the details. 
+
+
+## Finding service instances
+
+[QueryServiceInstances](xref:Makaretu.Dns.ServiceDiscovery.QueryServiceInstances*) is used to find the
+all the instances of a service with a specific feature. 
+The [ServiceInstanceDiscovered](xref:Makaretu.Dns.ServiceDiscovery.ServiceInstanceDiscovered) event is raised 
+each time a service instance is discovered.
+
+```csharp
+using Makaretu.Dns;
+
+var sd = new ServiceDiscovery();
+sd.ServiceInstanceDiscovered += (s, e) =>
+{
+    Console.WriteLine($"service instance '{e.ServiceInstanceName}'");
+};
+sd.QueryServiceInstances("_myservice", "apiv2");
+```
+
+## Advertising
+
+Create a [ServiceProfile](xref:Makaretu.Dns.ServiceProfile) with a feature
+and then [Advertise](xref:Makaretu.Dns.ServiceDiscovery.Advertise*) it.  Any queries for the service or 
+service instance will be answered with information from the profile.
+
+```csharp
+using Makaretu.Dns;
+
+var profile = new ServiceProfile("x", "_myservice._udp", 1024);
+profile.Subtypes.Add("apiv2");
+var sd = new ServiceDiscovery();
+sd.Advertise(profile);
+```

doc/articles/toc.yml

@@ -4,5 +4,8 @@
   href: ms.md
 - name: Service Discovery
   href: sd.md
+  items:
+    - name: Subtypes
+      href: subtype.md
 - name: Class Reference
   href: ../api/Makaretu.Dns.yml