Feature/mdnsresponder (#348)

Basic multicast-DNS service discovery responder

extras/mdnsresponder/mdnsresponder.h

@@ -0,0 +1,52 @@
+#ifndef __MDNSRESPONDER_H__
+#define __MDNSRESPONDER_H__
+
+/*
+ * Basic multicast DNS responder
+ * 
+ * Advertises the IP address, port, and characteristics of a service to other devices using multicast DNS on the same LAN,
+ * so they can find devices with addresses dynamically allocated by DHCP. See avahi, Bonjour, etc
+ * See RFC6762, RFC6763
+ *
+ * This sample code is in the public domain.
+ *
+ * by M J A Hamel 2016
+ */
+
+
+// Starts the mDNS responder task, call first
+void mdns_init();
+
+// Build and advertise an appropriate linked set of PTR/TXT/SRV/A records for the parameters provided
+// This is a simple canned way to build a set of records for a single service that will
+// be advertised whenever the device is given an IP address by WiFi
+
+typedef enum {
+    mdns_TCP,
+    mdns_UDP,
+    mdns_Browsable        // see RFC6763:11 - adds a standard record that lets browsers find the service without needing to know its name
+} mdns_flags;
+    
+void mdns_add_facility( const char* instanceName,   // Short user-friendly instance name, should NOT include serial number/MAC/etc
+                        const char* serviceName,    // Must be registered, _name, (see RFC6335 5.1 & 5.2)
+                        const char* addText,        // Should be <key>=<value>, or "" if unused (see RFC6763 6.3)
+                        mdns_flags  flags,          // TCP or UDP plus browsable
+                        u16_t       onPort,         // port number
+                        u32_t       ttl             // time-to-live, seconds
+                      );
+
+
+// Low-level RR builders for rolling your own
+void mdns_add_PTR(const char* rKey, u32_t ttl, const char* nameStr);
+void mdns_add_SRV(const char* rKey, u32_t ttl, u16_t rPort, const char* targname);
+void mdns_add_TXT(const char* rKey, u32_t ttl, const char* txtStr);
+void mdns_add_A  (const char* rKey, u32_t ttl, struct ip_addr addr);
+
+/* Sample usage, advertising a secure web service
+
+    mdns_init();
+    mdns_add_facility("Fluffy", "_https", "Zoom=1", mdns_TCP+mdns_Browsable, 443, 600);
+   
+*/
+
+#endif