Implement DNS-SD publishing of KISS over TCP service on Linux and Mac

This allows client applications to locate the IP addresses and the port of
the KISS TCP service, allowing the end user to just select a Dire Wolf from
a list instead of trying to guess its dynamic IP address and typing it in
manually.  This is especially convenient on mobile devices.

On Linux, the standard Avahi daemon is used via dbus and the avahi-client
library.  Building with it requires installing the development header
package; README.md is updated accordingly.

On Mac, the MacOS dnssd API is used:
https://developer.apple.com/documentation/dnssd?language=objc

I don't have Windows, but more recent Windows 10 builds apparently have
a working DNS-SD mDNS implementation that can be used on 64-bit builds.

Author: hessu

CMakeLists.txt

@@ -156,6 +156,10 @@ elseif(APPLE)
   set(CMAKE_MACOSX_RPATH ON)
   message(STATUS "RPATH support: ${CMAKE_MACOSX_RPATH}")
 
+  # just blindly enable dns-sd
+  set(USE_MACOS_DNSSD ON)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DUSE_MACOS_DNSSD")
+
 elseif (WIN32)
   if(NOT VS2015 AND NOT VS2017)
     message(FATAL_ERROR "You must use Microsoft Visual Studio 2015 or 2017 as compiler")
@@ -276,6 +280,11 @@ if(LINUX)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DUSE_CM108")
   endif()
 
+  find_package(Avahi)
+  if(AVAHI_CLIENT_FOUND)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DUSE_AVAHI_CLIENT")
+  endif()
+
 elseif (NOT WIN32 AND NOT CYGWIN)
   find_package(Portaudio REQUIRED)
   if(PORTAUDIO_FOUND)

README.md

@@ -131,15 +131,17 @@ On Debian / Ubuntu / Raspbian / Raspberry Pi OS:
     sudo apt-get install cmake
     sudo apt-get install libasound2-dev
     sudo apt-get install libudev-dev
+    sudo apt-get install libavahi-client-dev
 
 Or on Red Hat / Fedora / CentOS:
 
-	sudo yum install git
-	sudo yum install gcc
-	sudo yum install gcc-c++
-	sudo yum install make
+    sudo yum install git
+    sudo yum install gcc
+    sudo yum install gcc-c++
+    sudo yum install make
     sudo yum install alsa-lib-devel
     sudo yum install libudev-devel
+    sudo yum install avahi-devel
 
 CentOS 6 & 7 currently have cmake 2.8 but we need 3.1 or later.
 First you need to enable the EPEL repository.  Add a symlink if you don't already have the older version and want to type cmake rather than cmake3.

cmake/modules/FindAvahi.cmake

@@ -0,0 +1,19 @@
+
+find_library(AVAHI_COMMON_LIBRARY NAMES avahi-common PATHS ${PC_AVAHI_CLIENT_LIBRARY_DIRS})
+if(AVAHI_COMMON_LIBRARY)
+    set(AVAHI_COMMON_FOUND TRUE)
+endif()
+
+find_library(AVAHI_CLIENT_LIBRARY NAMES avahi-client PATHS ${PC_AVAHI_CLIENT_LIBRARY_DIRS})
+if(AVAHI_CLIENT_LIBRARY)
+    set(AVAHI_CLIENT_FOUND TRUE)
+endif()
+
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(AVAHI DEFAULT_MSG AVAHI_COMMON_FOUND AVAHI_CLIENT_FOUND)
+
+if (AVAHI_FOUND)
+    set(AVAHI_INCLUDE_DIRS ${AVAHI_UI_INCLUDE_DIR})
+    set(AVAHI_LIBRARIES ${AVAHI_COMMON_LIBRARY} ${AVAHI_CLIENT_LIBRARY})
+endif()
+
+mark_as_advanced(AVAHI_INCLUDE_DIRS AVAHI_LIBRARIES)

src/CMakeLists.txt

@@ -96,6 +96,12 @@ if(LINUX)
       cm108.c
       )
   endif()
+  if(AVAHI_CLIENT_FOUND)
+    list(APPEND direwolf_SOURCES
+      dns_sd_common.c
+      dns_sd_avahi.c
+      )
+  endif()
   elseif(WIN32 OR CYGWIN) # windows
     list(APPEND direwolf_SOURCES
       audio_win.c
@@ -111,6 +117,12 @@ if(LINUX)
     list(APPEND direwolf_SOURCES
       audio_portaudio.c
       )
+    if(USE_MACOS_DNSSD)
+      list(APPEND direwolf_SOURCES
+        dns_sd_common.c
+        dns_sd_macos.c
+        )
+    endif()
 endif()
 
 add_executable(direwolf
@@ -127,6 +139,7 @@ target_link_libraries(direwolf
   ${ALSA_LIBRARIES}
   ${UDEV_LIBRARIES}
   ${PORTAUDIO_LIBRARIES}
+  ${AVAHI_LIBRARIES}
   )
 
 if(WIN32 OR CYGWIN)

src/config.c

@@ -856,6 +856,8 @@ void config_init (char *fname, struct audio_s *p_audio_config,
 	p_misc_config->enable_kiss_pt = 0;				/* -p option */
 	p_misc_config->kiss_copy = 0;
 
+	p_misc_config->dns_sd_enabled = 1;
+
 	/* Defaults from http://info.aprs.net/index.php?title=SmartBeaconing */
 
 	p_misc_config->sb_configured = 0;	/* TRUE if SmartBeaconing is configured. */
@@ -4564,6 +4566,43 @@ void config_init (char *fname, struct audio_s *p_audio_config,
 	  }
 
 
+/*
+ * DNSSD 		- Enable or disable (1/0) dns-sd, DNS Service Discovery announcements
+ * DNSSDNAME            - Set DNS-SD service name, defaults to "Dire Wolf on <hostname>"
+ */
+
+	  else if (strcasecmp(t, "DNSSD") == 0) {
+	    int n;
+	    t = split(NULL,0);
+	    if (t == NULL) {
+	      text_color_set(DW_COLOR_ERROR);
+	      dw_printf ("Line %d: Missing integer value for DNSSD command.\n", line);
+	      continue;
+	    }
+	    n = atoi(t);
+	    if (n == 0 || n == 1) {
+	      p_misc_config->dns_sd_enabled = n;
+	    } else {
+	      p_misc_config->dns_sd_enabled = 0;
+	      text_color_set(DW_COLOR_ERROR);
+	      dw_printf ("Line %d: Invalid integer value for DNSSD. Disabling dns-sd.\n", line);
+	    }
+	  }
+
+	  else if (strcasecmp(t, "DNSSDNAME") == 0) {
+	    t = split(NULL, 1);
+	    if (t == NULL) {
+	      text_color_set(DW_COLOR_ERROR);
+	      dw_printf ("Line %d: Missing service name for DNSSDNAME.\n", line);
+	      continue;
+	    }
+	    else {
+	      strlcpy(p_misc_config->dns_sd_name, t, sizeof(p_misc_config->dns_sd_name));
+	    }
+	  }
+
+
+
 /*
  * GPSNMEA		- Device name for reading from GPS receiver.
  */

src/config.h

@@ -88,6 +88,9 @@ struct misc_config_s {
 
 	char log_path[80];	/* Either directory or full file name depending on above. */
 
+	int dns_sd_enabled;	/* DNS Service Discovery announcement enabled. */
+	char dns_sd_name[64];	/* Name announced on dns-sd; defaults to "Dire Wolf on <hostname>" */
+
 	int sb_configured;	/* TRUE if SmartBeaconing is configured. */
 	int sb_fast_speed;	/* MPH */
 	int sb_fast_rate;	/* seconds */

src/direwolf.c

@@ -125,6 +125,7 @@
 #include "dtime_now.h"
 #include "fx25.h"
 #include "dwsock.h"
+#include "dns_sd_dw.h"
 
 
 //static int idx_decoded = 0;
@@ -944,6 +945,11 @@ int main (int argc, char *argv[])
 	server_init (&audio_config, &misc_config);
 	kissnet_init (&misc_config);
 
+#if (USE_AVAHI_CLIENT|USE_MACOS_DNSSD)
+	if (misc_config.kiss_port > 0 && misc_config.dns_sd_enabled)
+	  dns_sd_announce(&misc_config);
+#endif
+
 /*
  * Create a pseudo terminal and KISS TNC emulator.
  */