res_pjsip: Add external PJSIP resolver implementation using core DNS API.

This change adds the following:

1. A query set implementation. This is an API that allows queries to be executed in parallel and once all have completed a callback is invoked.
2. Unit tests for the query set implementation.
3. An external PJSIP resolver which uses the DNS core API to do NAPTR, SRV, AAAA, and A lookups.

For the resolver it will do NAPTR, SRV, and AAAA/A lookups in parallel. If NAPTR or SRV
are available it will then do more queries. And so on. Preference is NAPTR > SRV > AAAA/A,
with IPv6 preferred over IPv4. For transport it will prefer TLS > TCP > UDP if no explicit
transport has been provided. Configured transports on the system are taken into account to
eliminate resolved addresses which have no hope of completing.

ASTERISK-24947 #close
Reported by: Joshua Colp

Change-Id: I56cb03ce4f9d3d600776f36928e0b3e379b5d71e

configure

@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.ac Revision: 432815 .
+# From configure.ac Revision.
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.69 for asterisk trunk.
 #
@@ -908,6 +908,10 @@ PBX_PORTAUDIO
 PORTAUDIO_DIR
 PORTAUDIO_INCLUDE
 PORTAUDIO_LIB
+PBX_PJSIP_EXTERNAL_RESOLVER
+PJSIP_EXTERNAL_RESOLVER_DIR
+PJSIP_EXTERNAL_RESOLVER_INCLUDE
+PJSIP_EXTERNAL_RESOLVER_LIB
 PBX_PJ_SSL_CERT_LOAD_FROM_FILES2
 PJ_SSL_CERT_LOAD_FROM_FILES2_DIR
 PJ_SSL_CERT_LOAD_FROM_FILES2_INCLUDE
@@ -10310,6 +10314,18 @@ PBX_PJ_SSL_CERT_LOAD_FROM_FILES2=0
 
 
 
+PJSIP_EXTERNAL_RESOLVER_DESCRIP="PJSIP External Resolver Support"
+PJSIP_EXTERNAL_RESOLVER_OPTION=pjsip
+PJSIP_EXTERNAL_RESOLVER_DIR=${PJPROJECT_DIR}
+
+PBX_PJSIP_EXTERNAL_RESOLVER=0
+
+
+
+
+
+
+
     PORTAUDIO_DESCRIP="PortAudio"
     PORTAUDIO_OPTION="portaudio"
     PBX_PORTAUDIO=0
@@ -24470,6 +24486,110 @@ fi
 
 
 
+if test "x${PBX_PJSIP_EXTERNAL_RESOLVER}" != "x1" -a "${USE_PJSIP_EXTERNAL_RESOLVER}" != "no"; then
+   pbxlibdir=""
+   # if --with-PJSIP_EXTERNAL_RESOLVER=DIR has been specified, use it.
+   if test "x${PJSIP_EXTERNAL_RESOLVER_DIR}" != "x"; then
+      if test -d ${PJSIP_EXTERNAL_RESOLVER_DIR}/lib; then
+         pbxlibdir="-L${PJSIP_EXTERNAL_RESOLVER_DIR}/lib"
+      else
+         pbxlibdir="-L${PJSIP_EXTERNAL_RESOLVER_DIR}"
+      fi
+   fi
+   pbxfuncname="pjsip_endpt_set_ext_resolver"
+   if test "x${pbxfuncname}" = "x" ; then   # empty lib, assume only headers
+      AST_PJSIP_EXTERNAL_RESOLVER_FOUND=yes
+   else
+      ast_ext_lib_check_save_CFLAGS="${CFLAGS}"
+      CFLAGS="${CFLAGS} $PJPROJECT_CFLAGS"
+      as_ac_Lib=`$as_echo "ac_cv_lib_pjsip_${pbxfuncname}" | $as_tr_sh`
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${pbxfuncname} in -lpjsip" >&5
+$as_echo_n "checking for ${pbxfuncname} in -lpjsip... " >&6; }
+if eval \${$as_ac_Lib+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lpjsip ${pbxlibdir} $PJPROJECT_LIBS $LIBS"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char ${pbxfuncname} ();
+int
+main ()
+{
+return ${pbxfuncname} ();
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  eval "$as_ac_Lib=yes"
+else
+  eval "$as_ac_Lib=no"
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+eval ac_res=\$$as_ac_Lib
+	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+if eval test \"x\$"$as_ac_Lib"\" = x"yes"; then :
+  AST_PJSIP_EXTERNAL_RESOLVER_FOUND=yes
+else
+  AST_PJSIP_EXTERNAL_RESOLVER_FOUND=no
+fi
+
+      CFLAGS="${ast_ext_lib_check_save_CFLAGS}"
+   fi
+
+   # now check for the header.
+   if test "${AST_PJSIP_EXTERNAL_RESOLVER_FOUND}" = "yes"; then
+      PJSIP_EXTERNAL_RESOLVER_LIB="${pbxlibdir} -lpjsip $PJPROJECT_LIBS"
+      # if --with-PJSIP_EXTERNAL_RESOLVER=DIR has been specified, use it.
+      if test "x${PJSIP_EXTERNAL_RESOLVER_DIR}" != "x"; then
+         PJSIP_EXTERNAL_RESOLVER_INCLUDE="-I${PJSIP_EXTERNAL_RESOLVER_DIR}/include"
+      fi
+      PJSIP_EXTERNAL_RESOLVER_INCLUDE="${PJSIP_EXTERNAL_RESOLVER_INCLUDE} $PJPROJECT_CFLAGS"
+      if test "xpjsip.h" = "x" ; then	# no header, assume found
+         PJSIP_EXTERNAL_RESOLVER_HEADER_FOUND="1"
+      else				# check for the header
+         ast_ext_lib_check_saved_CPPFLAGS="${CPPFLAGS}"
+         CPPFLAGS="${CPPFLAGS} ${PJSIP_EXTERNAL_RESOLVER_INCLUDE}"
+         ac_fn_c_check_header_mongrel "$LINENO" "pjsip.h" "ac_cv_header_pjsip_h" "$ac_includes_default"
+if test "x$ac_cv_header_pjsip_h" = xyes; then :
+  PJSIP_EXTERNAL_RESOLVER_HEADER_FOUND=1
+else
+  PJSIP_EXTERNAL_RESOLVER_HEADER_FOUND=0
+fi
+
+
+         CPPFLAGS="${ast_ext_lib_check_saved_CPPFLAGS}"
+      fi
+      if test "x${PJSIP_EXTERNAL_RESOLVER_HEADER_FOUND}" = "x0" ; then
+         PJSIP_EXTERNAL_RESOLVER_LIB=""
+         PJSIP_EXTERNAL_RESOLVER_INCLUDE=""
+      else
+         if test "x${pbxfuncname}" = "x" ; then		# only checking headers -> no library
+            PJSIP_EXTERNAL_RESOLVER_LIB=""
+         fi
+         PBX_PJSIP_EXTERNAL_RESOLVER=1
+         cat >>confdefs.h <<_ACEOF
+#define HAVE_PJSIP_EXTERNAL_RESOLVER 1
+_ACEOF
+
+      fi
+   fi
+fi
+
+
+
 
 if test "x${PBX_POPT}" != "x1" -a "${USE_POPT}" != "no"; then
    pbxlibdir=""