Introduce new mDNS API, add mDNS client example

tutorials/udp/mdns-client/Makefile

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+PROG ?= example                   # Program we are building
+DELETE = rm -rf                   # Command to remove files
+OUT ?= -o $(PROG)                 # Compiler argument for output file
+SOURCES = main.c mongoose.c       # Source code files
+CFLAGS = -W -Wall -Wextra -g -I.  # Build options
+
+# Mongoose build options. See https://mongoose.ws/documentation/#build-options
+CFLAGS_MONGOOSE += -DMG_ENABLE_MDNS=1 -DMG_ENABLE_LINES
+
+ifeq ($(OS),Windows_NT)   # Windows settings. Assume MinGW compiler. To use VC: make CC=cl CFLAGS=/MD OUT=/Feprog.exe
+  PROG ?= example.exe           # Use .exe suffix for the binary
+  CC = gcc                      # Use MinGW gcc compiler
+  CFLAGS += -lws2_32            # Link against Winsock library
+  DELETE = cmd /C del /Q /F /S  # Command prompt command to delete files
+  OUT ?= -o $(PROG)             # Build output
+endif
+
+all: $(PROG)              # Default target. Build and run program
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): $(SOURCES)       # Build program from sources
+	$(CC) $(SOURCES) $(CFLAGS) $(CFLAGS_MONGOOSE) $(CFLAGS_EXTRA) $(OUT)
+
+clean:                    # Cleanup. Delete built program and all build artifacts
+	$(DELETE) $(PROG) *.o *.obj *.exe *.dSYM

tutorials/udp/mdns-client/main.c

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+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+
+#include "mongoose.h"
+
+char s_theone[] = "Server.local";
+
+static void mdns_ev_handler(struct mg_connection *c, int ev, void *ev_data) {
+  if (ev == MG_EV_MDNS_RESP) {  // is this the one ?
+    struct mg_mdns_resp *resp = (struct mg_mdns_resp *) ev_data;
+    if (mg_strcasecmp(mg_str(s_theone), resp->name) == 0)
+      MG_INFO(("%.*s is: %M", resp->name.len, resp->name.buf, mg_print_ip, &resp->addr));
+  }
+  (void) c;
+}
+
+int main(void) {
+  uint32_t response_ip = inet_addr("192.168.69.11");
+  struct mg_mgr mgr;
+  static struct mg_connection *c;
+  mg_log_set(MG_LL_DEBUG);  // Set log level
+  mg_mgr_init(&mgr);        // Initialise event manager
+
+  // Desired name must NOT have any dots in it, nor a domain
+  c = mg_mdns_listen(&mgr, mdns_ev_handler, "Mongoose");  // Start mDNS server
+  if (c == NULL) return 1;
+  // if not using our built-in TCP/IP stack, pass the IP address you want to
+  // use as a response, this depends on your underlying TCP/IP stack and number
+  // of interfaces available
+  memcpy(c->data, &response_ip, sizeof(response_ip));
+  if (!mg_mdns_query(c, s_theone, MG_DNS_RTYPE_A)) return 1;
+
+  for (;;) mg_mgr_poll(&mgr, 1000);  // Event loop
+
+  mg_mgr_free(&mgr);
+  return 0;
+}

tutorials/udp/mdns-client/mongoose.c

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+../../../mongoose.c

tutorials/udp/mdns-client/mongoose.h

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+../../../mongoose.h