set sockaddr_un.sun_len on the systems that have sockaddr.sa_len.

If your system has sa_len but is not BSD-derived, define HAVE_SA_LEN=1
on mrbgem.rake or build_config.rb.

mrbgems/mruby-socket/mrbgem.rake

@@ -4,6 +4,7 @@ MRuby::Gem::Specification.new('mruby-socket') do |spec|
   spec.summary = 'standard socket class'
 
   spec.cc.include_paths << "#{build.root}/src"
+  #spec.cc.defines << "HAVE_SA_LEN=0"
 
   # If Windows, use winsock
   if ( /mswin|mingw|win32/ =~ RUBY_PLATFORM ) then

mrbgems/mruby-socket/src/socket.c

@@ -19,6 +19,7 @@
 #else
   #include <sys/types.h>
   #include <sys/socket.h>
+  #include <sys/param.h>
   #include <sys/un.h>
   #include <netinet/in.h>
   #include <netinet/tcp.h>
@@ -42,6 +43,14 @@
 
 #include "mruby/ext/io.h"
 
+#if !defined(HAVE_SA_LEN)
+#if (defined(BSD) && (BSD >= 199006))
+#define HAVE_SA_LEN  1
+#else
+#define HAVE_SA_LEN  0
+#endif
+#endif
+
 #define E_SOCKET_ERROR             (mrb_class_get(mrb, "SocketError"))
 
 #if !defined(mrb_cptr)
@@ -695,6 +704,9 @@ mrb_socket_sockaddr_un(mrb_state *mrb, mrb_value klass)
   }
   s = mrb_str_buf_new(mrb, sizeof(struct sockaddr_un));
   sunp = (struct sockaddr_un *)RSTRING_PTR(s);
+#if HAVE_SA_LEN
+  sunp->sun_len = sizeof(struct sockaddr_un);
+#endif
   sunp->sun_family = AF_UNIX;
   memcpy(sunp->sun_path, RSTRING_PTR(path), RSTRING_LEN(path));
   sunp->sun_path[RSTRING_LEN(path)] = '\0';