Major addition to support DNS SRV resolution in PJSIP:

- added DNS asynchronous/caching resolver engine in
  PJLIB-UTIL (resolver.[hc])
- modified SIP resolver (sip_resolve.c) to properly
  perform DNS SRV/A resolution when DNS resolution is
  enabled.
- added dns_test.c in PJSIP-TEST for testing the SIP
  resolver.
- added nameserver configuration in PJSUA-LIB
- added "--nameserver" option in PJSUA.
- updated project/Makefiles and doxygen documentation.



git-svn-id: http://svn.pjsip.org/repos/pjproject/trunk@753 74dad513-b988-da41-8d7b-12977e46ad98

12 files changed, 1766 insertions, 71 deletions

diff --git a/pjsip/build/Makefile b/pjsip/build/Makefile
index 81c2cb2e..dad39451 100644
--- a/pjsip/build/Makefile
+++ b/pjsip/build/Makefile
@@ -88,7 +88,8 @@ export CC_OUT CC AR RANLIB HOST_MV HOST_RM HOST_RMDIR HOST_MKDIR OBJEXT LD LDOUT
 # Defines for building test application
 #
 export TEST_SRCDIR = ../src/test-pjsip
-export TEST_OBJS += dlg_core_test.o msg_err_test.o msg_logger.o msg_test.o \
+export TEST_OBJS += dlg_core_test.o dns_test.o msg_err_test.o \
+		    msg_logger.o msg_test.o \
 		    test.o transport_loop_test.o transport_tcp_test.o \
 		    transport_test.o transport_udp_test.o \
 		    tsx_basic_test.o tsx_bench.o tsx_uac_test.o \
diff --git a/pjsip/build/test_pjsip.dsp b/pjsip/build/test_pjsip.dsp
index 82f10ac3..27814458 100644
--- a/pjsip/build/test_pjsip.dsp
+++ b/pjsip/build/test_pjsip.dsp
@@ -93,6 +93,10 @@ SOURCE="..\src\test-pjsip\dlg_core_test.c"
 # End Source File

 # Begin Source File

 

+SOURCE="..\src\test-pjsip\dns_test.c"

+# End Source File

+# Begin Source File

+

 SOURCE="..\src\test-pjsip\main.c"

 # End Source File

 # Begin Source File

diff --git a/pjsip/include/pjsip/sip_config.h b/pjsip/include/pjsip/sip_config.h
index e4b402fb..420a2a01 100644
--- a/pjsip/include/pjsip/sip_config.h
+++ b/pjsip/include/pjsip/sip_config.h
@@ -199,6 +199,42 @@
 #endif
 
 
+/**
+ * This macro specifies whether full DNS resolution should be used.
+ * When enabled, #pjsip_resolve() will perform asynchronous DNS SRV and
+ * A (or AAAA, when IPv6 is supported) resolution to resolve the SIP
+ * domain.
+ *
+ * Note that even when this setting is enabled, asynchronous DNS resolution
+ * will only be done when application calls #pjsip_endpt_create_resolver(),
+ * configure the nameservers with #pj_dns_resolver_set_ns(), and configure
+ * the SIP endpoint's DNS resolver with #pjsip_endpt_set_resolver(). If
+ * these steps are not followed, the domain will be resolved with normal
+ * pj_gethostbyname() function.
+ *
+ * Turning off this setting will save the footprint by about 16KB, since
+ * it should also exclude dns.o and resolve.o from PJLIB-UTIL.
+ *
+ * Default: 1 (enabled)
+ */
+#ifndef PJSIP_HAS_RESOLVER
+#   define PJSIP_HAS_RESOLVER		1
+#endif
+
+
+/** 
+ * Maximum number of addresses returned by the resolver. The number here 
+ * will slightly affect stack usage, since each entry will occupy about
+ * 32 bytes of stack memory.
+ *
+ * Default: 8
+ */
+#ifndef PJSIP_MAX_RESOLVED_ADDRESSES
+#   define PJSIP_MAX_RESOLVED_ADDRESSES	    8
+#endif
+
+
+
 /* Endpoint. */
 #define PJSIP_MAX_TIMER_COUNT		(2*PJSIP_MAX_TSX_COUNT + 2*PJSIP_MAX_DIALOG_COUNT)
 #define PJSIP_POOL_LEN_ENDPT		(4000)
diff --git a/pjsip/include/pjsip/sip_endpoint.h b/pjsip/include/pjsip/sip_endpoint.h
index aed4d8a2..6e166090 100644
--- a/pjsip/include/pjsip/sip_endpoint.h
+++ b/pjsip/include/pjsip/sip_endpoint.h
@@ -275,12 +275,51 @@ PJ_DECL(pj_status_t) pjsip_endpt_create_tdata( pjsip_endpoint *endpt,
 					       pjsip_tx_data **p_tdata);
 
 /**
+ * Create the DNS resolver instance. Application creates the DNS
+ * resolver instance, set the nameserver to be used by the DNS
+ * resolver, then set the DNS resolver to be used by the endpoint
+ * by calling #pjsip_endpt_set_resolver().
+ *
+ * @param endpt		The SIP endpoint instance.
+ * @param p_resv	Pointer to receive the DNS resolver instance.
+ *
+ * @return		PJ_SUCCESS on success, or the appropriate error
+ *			code.
+ */
+PJ_DECL(pj_status_t) pjsip_endpt_create_resolver(pjsip_endpoint *endpt,
+						 pj_dns_resolver **p_resv);
+
+/**
+ * Set DNS resolver to be used by the SIP resolver. Application can set
+ * the resolver instance to NULL to disable DNS resolution (perhaps
+ * temporarily). When DNS resolver is disabled, the endpoint will resolve
+ * hostnames with the normal pj_gethostbyname() function.
+ *
+ * @param endpt		The SIP endpoint instance.
+ * @param resv		The resolver instance to be used by the SIP
+ *			endpoint.
+ *
+ * @return		PJ_SUCCESS on success, or the appropriate error
+ *			code.
+ */
+PJ_DECL(pj_status_t) pjsip_endpt_set_resolver(pjsip_endpoint *endpt,
+					      pj_dns_resolver *resv);
+
+/**
+ * Get the DNS resolver being used by the SIP resolver.
+ *
+ * @param endpt		The SIP endpoint instance.
+ *
+ * @return		The DNS resolver instance currently being used
+ *			by the SIP endpoint.
+ */
+PJ_DECL(pj_dns_resolver*) pjsip_endpt_get_resolver(pjsip_endpoint *endpt);
+
+/**
  * Asynchronously resolve a SIP target host or domain according to rule 
  * specified in RFC 3263 (Locating SIP Servers). When the resolving operation
  * has completed, the callback will be called.
  *
- * Note: at the moment we don't have implementation of RFC 3263 yet!
- *
  * @param endpt	    The endpoint instance.
  * @param pool	    The pool to allocate resolver job.
  * @param target    The target specification to be resolved.
diff --git a/pjsip/include/pjsip/sip_resolve.h b/pjsip/include/pjsip/sip_resolve.h
index 3ebface3..a71dd5b5 100644
--- a/pjsip/include/pjsip/sip_resolve.h
+++ b/pjsip/include/pjsip/sip_resolve.h
@@ -27,26 +27,141 @@
  */
 
 #include <pjsip/sip_types.h>
+#include <pjlib-util/resolver.h>
 #include <pj/sock.h>
 
 PJ_BEGIN_DECL
 
 /**
- * @defgroup PJSIP_RESOLVE Server Resolution
+ * @defgroup PJSIP_RESOLVE SIP SRV Server Resolution (RFC 3263 - Locating SIP Servers)
  * @ingroup PJSIP_TRANSPORT
  * @brief Framework to resolve SIP servers based on RFC 3263.
  * @{
- * This is the server resolution framework, which is modelled after 
- * RFC 3263 - Locating SIP Servers document. The server resolution
+ * \section PJSIP_RESOLVE_FEATURES Features
+ *
+ * This is the SIP server resolution framework, which is modelled after 
+ * RFC 3263 - Locating SIP Servers document. The SIP server resolution
  * framework is asynchronous; callback will be called once the server 
  * address has been resolved (successfully or with errors).
+ *
+ * \subsection PJSIP_RESOLVE_CONFORMANT Conformance to RFC 3263
+ *
+ * The SIP server resolution framework is modelled after RFC 3263 (Locating 
+ * SIP Servers) document, and it provides a single function (#pjsip_resolve())
+ * to resolve a domain into actual IP addresses of the servers, by querying 
+ * DNS SRV record and DNS A record where necessary.
+ *
+ * The #pjsip_resolve() function performs the server resolution according
+ * to RFC 3263 with some additional fallback mechanisms, as follows:
+ *  - if the target name is an IP address, the callback will be called
+ *    immediately with the IP address. If port number was specified, this
+ *    port number will be used, otherwise the default port number for the
+ *    transport will be used (5060 for TCP/UDP, 5061 for TLS) if the transport
+ *    is specified. If the transport is not specified, UDP with port number
+ *    5060 will be used.
+ *  - if target name is not an IP address but it contains port number,
+ *    then the target name is resolved with DNS A (or AAAA, when IPv6 is
+ *    supported in the future) query, and the port is taken from the
+ *    port number argument. The callback will be called once the DNS A
+ *    resolution completes. If the DNS A resolution returns multiple IP
+ *    addresses, these IP addresses will be returned to the caller.
+ *  - if target name is not an IP address and port number is not specified,
+ *    DNS SRV resolution will be performed for the specified name and
+ *    transport type (or UDP when transport is not specified), 
+ *    then followed by DNS A (or AAAA, when IPv6 is supported)
+ *    resolution for each target in the SRV record. If DNS SRV
+ *    resolution returns error, DNS A (or AAAA) resolution will be
+ *    performed for the original target (it is assumed that the target domain
+ *    does not support SRV records). Upon successful completion, 
+ *    application callback will be called with each IP address of the
+ *    target selected based on the load-balancing and fail-over criteria
+ *    below.
+ *
+ * The above server resolution procedure differs from RFC 3263 in these
+ * regards:
+ *  - currently #pjsip_resolve() doesn't support DNS NAPTR record.
+ *  - if transport is not specified, it is assumed to be UDP (the proper
+ *    behavior is to query the NAPTR record, but we don't support this
+ *    yet).
+ *
+ *
+ * \subsection PJSIP_SIP_RESOLVE_FAILOVER_LOADBALANCE Load-Balancing and Fail-Over
+ *
+ * When multiple targets are returned in the DNS SRV response, server entries
+ * are selected based on the following rule (which is described in RFC 2782):
+ *  - targets will be sorted based on the priority first.
+ *  - for targets with the same priority, #pjsip_resolve() will select
+ *    only one target according to its weight. To select this one target,
+ *    the function associates running-sum for all targets, and generates 
+ *    a random number between zero and the total running-sum (inclusive).
+ *    The target selected is the first target with running-sum greater than
+ *    or equal to this random number.
+ *
+ * The above procedure will select one target for each priority, allowing
+ * application to fail-over to the next target when the previous target fails.
+ * These targets are returned in the #pjsip_server_addresses structure 
+ * argument of the callback. 
+ *
+ * \subsection PJSIP_SIP_RESOLVE_SIP_FEATURES SIP SRV Resolver Features
+ *
+ * Some features of the SIP resolver:
+ *  - DNS SRV entries are returned on sorted order based on priority 
+ *    to allow failover to the next appropriate server.
+ *  - The procedure in RFC 2782 is used to select server with the same
+ *    priority to load-balance the servers load.
+ *  - A single function (#pjsip_resolve()) performs all server resolution
+ *    works, from resolving the SRV records to getting the actual IP addresses
+ *    of the servers with DNS A (or AAAA) resolution.
+ *  - When multiple DNS SRV records are returned, parallel DNS A (or AAAA)
+ *    queries will be issued simultaneously.
+ *  - The PJLIB-UTIL DNS resolver provides additional functionality such as
+ *    response caching, query aggregation, parallel nameservers, fallback
+ *    nameserver, etc., which will be described below.
+ * 
+ *
+ * \subsection PJSIP_RESOLVE_DNS_FEATURES DNS Resolver Features
+ *
+ * The PJSIP server resolution framework uses PJLIB-UTIL DNS resolver engine
+ * for performing the asynchronous DNS request. The PJLIB-UTIL DNS resolver
+ * has some useful features, such as:
+ *  - queries are asynchronous with configurable timeout,
+ *  - query aggregation to combine multiple pending queries to the same
+ *    DNS target into a single DNS request (to save message round-trip and
+ *    processing),
+ *  - response caching with TTL negotiated between the minimum TTL found in
+ *    the response and the maximum TTL allowed in the configuration,
+ *  - multiple nameservers, with active nameserver is selected from nameserver
+ *    which provides the best response time,
+ *  - fallback nameserver, with periodic detection of which name servers are
+ *    active or down.
+ *  - etc.
+ *
+ * Please consult PJLIB-UTIL DNS resolver documentation for more details.
+ *
+ *
+ * \section PJSIP_RESOLVE_USING Using the Resolver
+ *
+ * To maintain backward compatibility, the resolver MUST be enabled manually.
+ * With the default settings, the resolver WILL NOT perform DNS SRV resolution,
+ * as it will just resolve the name with standard pj_gethostbyname() function.
+ *
+ * Application can enable the SRV resolver by creating the PJLIB-UTIL DNS 
+ * resolver with #pjsip_endpt_create_resolver(), configure the
+ * nameservers of the PJLIB-UTIL DNS resolver object by calling
+ * pj_dns_resolver_set_ns() function, and pass the DNS resolver object to 
+ * #pjsip_resolver_set_resolver() function.
+ *
+ * Once the resolver is set, it will be used automatically by PJSIP everytime
+ * PJSIP needs to send SIP request/response messages.
+ *
+ *
+ * \section PJSIP_RESOLVE_REFERENCE Reference
+ *
+ * Reference:
+ *  - RFC 2782: A DNS RR for specifying the location of services (DNS SRV)
+ *  - RFC 3263: Locating SIP Servers
  */
 
-/** 
- * Maximum number of addresses returned by the resolver. 
- */
-#define PJSIP_MAX_RESOLVED_ADDRESSES	8
-
 /**
  * The server addresses returned by the resolver.
  */
@@ -61,6 +176,12 @@ typedef struct pjsip_server_addresses
 	/** Preferable transport to be used to contact this address. */
 	pjsip_transport_type_e	type;
 
+	/** Server priority (the lower the higher the priority). */
+	unsigned		priority;
+
+	/** Server weight (the higher the more load it can handle). */
+	unsigned		weight;
+
 	/** The server's address. */
 	pj_sockaddr		addr;
 
@@ -85,15 +206,56 @@ typedef void pjsip_resolver_callback(pj_status_t status,
 				     const struct pjsip_server_addresses *addr);
 
 /**
- * Create resolver engine.
+ * Create SIP resolver engine. Note that this function is normally called
+ * internally by pjsip_endpoint instance.
+ *
+ * @param pf	    The Pool Factory.
+ * @param p_res	    Pointer to receive SIP resolver instance.
+ *
+ * @return	    PJ_SUCCESS when resolver can be successfully created.
+ */
+PJ_DECL(pj_status_t) pjsip_resolver_create(pj_pool_t *pool,
+					   pjsip_resolver_t **p_res);
+
+/**
+ * Set the DNS resolver instance of the SIP resolver engine. Before the
+ * DNS resolver is set, the SIP resolver will use standard pj_gethostbyname()
+ * to resolve addresses.
  *
- * @param pool	The Pool.
- * @return	The resolver engine.
+ * Note that application normally will use #pjsip_endpt_set_resolver() instead
+ * since it does not normally have access to the SIP resolver instance.
+ *
+ * @param res	    The SIP resolver engine.
+ * @param dns_res   The DNS resolver instance to be used by the SIP resolver.
+ *		    This argument can be NULL to reset the internal DNS
+ *		    instance.
+ *
+ * @return	    PJ_SUCCESS on success, or the appropriate error code.
+ */
+PJ_DECL(pj_status_t) pjsip_resolver_set_resolver(pjsip_resolver_t *res,
+						 pj_dns_resolver *dns_res);
+
+
+/**
+ * Get the DNS resolver instance of the SIP resolver engine. 
+ *
+ * Note that application normally will use #pjsip_endpt_get_resolver() instead
+ * since it does not normally have access to the SIP resolver instance.
+ *
+ * @param res	    The SIP resolver engine.
+ *
+ * @return	    The DNS resolver instance (may be NULL)
  */
-PJ_DECL(pjsip_resolver_t*) pjsip_resolver_create(pj_pool_t *pool);
+PJ_DECL(pj_dns_resolver*) pjsip_resolver_get_resolver(pjsip_resolver_t *res);
 
 /**
- * Destroy resolver engine.
+ * Destroy resolver engine. Note that this will also destroy the internal
+ * DNS resolver inside the engine. If application doesn't want the internal
+ * DNS resolver to be destroyed, it should set the internal DNS resolver
+ * to NULL before calling this function.
+ *
+ * Note that this function will normally called by the SIP endpoint instance
+ * when the SIP endpoint instance is destroyed.
  *
  * @param resolver The resolver.
  */
@@ -104,7 +266,8 @@ PJ_DECL(void) pjsip_resolver_destroy(pjsip_resolver_t *resolver);
  * specified in RFC 3263 (Locating SIP Servers). When the resolving operation
  * has completed, the callback will be called.
  *
- * Note: at the moment we don't have implementation of RFC 3263 yet!
+ * Note that application normally will use #pjsip_endpt_resolve() instead
+ * since it does not normally have access to the SIP resolver instance.
  *
  * @param resolver	The resolver engine.
  * @param pool		The pool to allocate resolver job.
@@ -114,7 +277,7 @@ PJ_DECL(void) pjsip_resolver_destroy(pjsip_resolver_t *resolver);
  */
 PJ_DECL(void) pjsip_resolve( pjsip_resolver_t *resolver,
 			     pj_pool_t *pool,
-			     pjsip_host_info *target,
+			     const pjsip_host_info *target,
 			     void *token,
 			     pjsip_resolver_callback *cb);
 
diff --git a/pjsip/include/pjsua-lib/pjsua.h b/pjsip/include/pjsua-lib/pjsua.h
index 9ded3f15..2b11df01 100644
--- a/pjsip/include/pjsua-lib/pjsua.h
+++ b/pjsip/include/pjsua-lib/pjsua.h
@@ -388,6 +388,20 @@ typedef struct pjsua_config
     unsigned	    thread_cnt;
 
     /**
+     * Number of nameservers. If no name server is configured, the SIP SRV
+     * resolution would be disabled, and domain will be resolved with
+     * standard pj_gethostbyname() function.
+     */
+    unsigned	    nameserver_count;
+
+    /**
+     * Array of nameservers to be used by the SIP resolver subsystem.
+     * The order of the name server specifies the priority (first name
+     * server will be used first, unless it is not reachable).
+     */
+    pj_str_t	    nameserver[4];
+
+    /**
      * Number of outbound proxies in the array.
      */
     unsigned	    outbound_proxy_cnt;
diff --git a/pjsip/src/pjsip/sip_endpoint.c b/pjsip/src/pjsip/sip_endpoint.c
index 1fa39831..571ee11c 100644
--- a/pjsip/src/pjsip/sip_endpoint.c
+++ b/pjsip/src/pjsip/sip_endpoint.c
@@ -484,8 +484,8 @@ PJ_DEF(pj_status_t) pjsip_endpt_create(pj_pool_factory *pf,
     }
 
     /* Create asynchronous DNS resolver. */
-    endpt->resolver = pjsip_resolver_create(endpt->pool);
-    if (!endpt->resolver) {
+    status = pjsip_resolver_create(endpt->pool, &endpt->resolver);
+    if (status != PJ_SUCCESS) {
 	PJ_LOG(4, (THIS_FILE, "Error creating resolver instance"));
 	goto on_error;
     }
@@ -926,6 +926,42 @@ PJ_DEF(pj_status_t) pjsip_endpt_create_tdata(  pjsip_endpoint *endpt,
 }
 
 /*
+ * Create the DNS resolver instance. 
+ */
+PJ_DEF(pj_status_t) pjsip_endpt_create_resolver(pjsip_endpoint *endpt,
+						pj_dns_resolver **p_resv)
+{
+#if PJSIP_HAS_RESOLVER
+    PJ_ASSERT_RETURN(endpt && p_resv, PJ_EINVAL);
+    return pj_dns_resolver_create( endpt->pf, NULL, 0, endpt->timer_heap,
+				   endpt->ioqueue, p_resv);
+#else
+    PJ_UNUSED_ARG(endpt);
+    PJ_UNUSED_ARG(p_resv);
+    pj_assert(!"Resolver is disabled (PJSIP_HAS_RESOLVER==0)");
+    return PJ_EINVALIDOP;
+#endif
+}
+
+/*
+ * Set DNS resolver to be used by the SIP resolver.
+ */
+PJ_DEF(pj_status_t) pjsip_endpt_set_resolver( pjsip_endpoint *endpt,
+					      pj_dns_resolver *resv)
+{
+    return pjsip_resolver_set_resolver(endpt->resolver, resv);
+}
+
+/*
+ * Get the DNS resolver being used by the SIP resolver.
+ */
+PJ_DEF(pj_dns_resolver*) pjsip_endpt_get_resolver(pjsip_endpoint *endpt)
+{
+    PJ_ASSERT_RETURN(endpt, NULL);
+    return pjsip_resolver_get_resolver(endpt->resolver);
+}
+
+/*
  * Resolve
  */
 PJ_DEF(void) pjsip_endpt_resolve( pjsip_endpoint *endpt,
@@ -1036,6 +1072,13 @@ PJ_DEF(void) pjsip_endpt_dump( pjsip_endpoint *endpt, pj_bool_t detail )
 	       pj_pool_get_capacity(endpt->pool),
 	       pj_pool_get_used_size(endpt->pool)));
 
+    /* Resolver */
+#if PJSIP_HAS_RESOLVER
+    if (pjsip_endpt_get_resolver(endpt)) {
+	pj_dns_resolver_dump(pjsip_endpt_get_resolver(endpt), detail);
+    }
+#endif
+
     /* Transports. 
      */
     pjsip_tpmgr_dump_transports( endpt->transport_mgr );
diff --git a/pjsip/src/pjsip/sip_resolve.c b/pjsip/src/pjsip/sip_resolve.c
index 5b920be5..8f28f9e8 100644
--- a/pjsip/src/pjsip/sip_resolve.c
+++ b/pjsip/src/pjsip/sip_resolve.c
@@ -19,30 +19,141 @@
 #include <pjsip/sip_resolve.h>
 #include <pjsip/sip_transport.h>
 #include <pjsip/sip_errno.h>
-#include <pj/pool.h>
-#include <pj/ctype.h>
+#include <pjlib-util/errno.h>
+#include <pj/array.h>
 #include <pj/assert.h>
+#include <pj/ctype.h>
 #include <pj/log.h>
+#include <pj/pool.h>
+#include <pj/rand.h>
+#include <pj/string.h>
+
 
 #define THIS_FILE   "sip_resolve.c"
 
+#define ADDR_MAX_COUNT	    8
+
+struct naptr_target
+{
+    pj_str_t		    target_name;    /**< NAPTR target name. */
+    pjsip_transport_type_e  type;	    /**< Transport type.    */
+    unsigned		    order;	    /**< Order		    */
+    unsigned		    pref;	    /**< Preference.	    */
+};
+
+struct srv_target
+{
+    pjsip_transport_type_e  type;
+    pj_str_t		    target_name;
+    char		    target_buf[PJ_MAX_HOSTNAME];
+    unsigned		    port;
+    unsigned		    priority;
+    unsigned		    weight;
+    unsigned		    sum;
+    unsigned		    addr_cnt;
+    pj_in_addr		    addr[ADDR_MAX_COUNT];
+};
+
+struct query
+{
+    char		     objname[PJ_MAX_OBJ_NAME];
+
+    pjsip_resolver_t	    *resolver;	    /**< Resolver SIP instance.	    */
+    pj_dns_type		     dns_state;	    /**< DNS type being resolved.   */
+    void		    *token;
+    pjsip_resolver_callback *cb;
+    pj_dns_async_query	    *object;
+    pj_status_t		     last_error;
+
+    /* Original request: */
+    struct {
+	pjsip_host_info	     target;
+    } req;
+
+    /* NAPTR records: */
+    unsigned		     naptr_cnt;
+    struct naptr_target	     naptr[8];
+
+    /* SRV records and their resolved IP addresses: */
+    unsigned		     srv_cnt;
+    struct srv_target	     srv[PJSIP_MAX_RESOLVED_ADDRESSES];
+
+    /* Number of hosts in SRV records that the IP address has been resolved */
+    unsigned		     host_resolved;
+};
+
+
 struct pjsip_resolver_t
 {
-    void *dummy;
+    pj_dns_resolver *res;
+    unsigned	     job_id;
 };
 
-PJ_DEF(pjsip_resolver_t*) pjsip_resolver_create(pj_pool_t *pool)
+static void dns_callback(void *user_data,
+			 pj_status_t status,
+			 pj_dns_parsed_packet *response);
+
+
+/*
+ * Public API to create the resolver.
+ */
+PJ_DEF(pj_status_t) pjsip_resolver_create( pj_pool_t *pool,
+					   pjsip_resolver_t **p_res)
 {
     pjsip_resolver_t *resolver;
-    resolver = (pjsip_resolver_t*) pj_pool_calloc(pool, 1, sizeof(*resolver));
-    return resolver;
+
+    PJ_ASSERT_RETURN(pool && p_res, PJ_EINVAL);
+    resolver = pj_pool_zalloc(pool, sizeof(*resolver));
+    *p_res = resolver;
+
+    return PJ_SUCCESS;
+}
+
+
+/*
+ * Public API to set the DNS resolver instance for the SIP resolver.
+ */
+PJ_DEF(pj_status_t) pjsip_resolver_set_resolver(pjsip_resolver_t *res,
+						pj_dns_resolver *dns_res)
+{
+#if PJSIP_HAS_RESOLVER
+    res->res = dns_res;
+    return PJ_SUCCESS;
+#else
+    PJ_UNUSED_ARG(res);
+    PJ_UNUSED_ARG(dns_res);
+    pj_assert(!"Resolver is disabled (PJSIP_HAS_RESOLVER==0)");
+    return PJ_EINVALIDOP;
+#endif;
+}
+
+
+/*
+ * Public API to get the internal DNS resolver.
+ */
+PJ_DEF(pj_dns_resolver*) pjsip_resolver_get_resolver(pjsip_resolver_t *res)
+{
+    return res->res;
 }
 
+
+/*
+ * Public API to create destroy the resolver
+ */
 PJ_DEF(void) pjsip_resolver_destroy(pjsip_resolver_t *resolver)
 {
-    PJ_UNUSED_ARG(resolver);
+    if (resolver->res) {
+#if PJSIP_HAS_RESOLVER
+	pj_dns_resolver_destroy(resolver->res, PJ_FALSE);
+#endif
+	resolver->res = NULL;
+    }
 }
 
+/*
+ * Internal:
+ *  determine if an address is a valid IP address.
+ */
 static int is_str_ip(const pj_str_t *host)
 {
     const char *p = host->ptr;
@@ -58,29 +169,23 @@ static int is_str_ip(const pj_str_t *host)
     return 1;
 }
 
+
+/*
+ * This is the main function for performing server resolution.
+ */
 PJ_DEF(void) pjsip_resolve( pjsip_resolver_t *resolver,
 			    pj_pool_t *pool,
-			    pjsip_host_info *target,
+			    const pjsip_host_info *target,
 			    void *token,
 			    pjsip_resolver_callback *cb)
 {
-    struct pjsip_server_addresses svr_addr;
-    pj_status_t status;
+    pjsip_server_addresses svr_addr;
+    pj_status_t status = PJ_SUCCESS;
     int is_ip_addr;
+    struct query *query;
+    pj_str_t srv_name;
     pjsip_transport_type_e type = target->type;
 
-    PJ_UNUSED_ARG(resolver);
-    PJ_UNUSED_ARG(pool);
-
-    PJ_LOG(5,(THIS_FILE, "Resolving server '%.*s:%d' type=%s",
-			 target->addr.host.slen,
-			 target->addr.host.ptr,
-			 target->addr.port,
-			 pjsip_transport_get_type_name(type)));
-
-    /* We only do synchronous resolving at this moment. */
-    PJ_TODO(SUPPORT_RFC3263_SERVER_RESOLUTION)
-
     /* Is it IP address or hostname?. */
     is_ip_addr = is_str_ip(&target->addr.host);
 
@@ -109,50 +214,693 @@ PJ_DEF(void) pjsip_resolve( pjsip_resolver_t *resolver,
 	     */
 	    type = PJSIP_TRANSPORT_UDP;
 	}
+    }
+
+
+    /* If target is an IP address, or if resolver is not configured, 
+     * we can just finish the resolution now using pj_gethostbyname()
+     */
+    if (is_ip_addr || resolver->res == NULL) {
+
+	pj_in_addr ip_addr;
+	pj_uint16_t srv_port;
+
+	if (!is_ip_addr) {
+	    PJ_LOG(5,(THIS_FILE, 
+		      "DNS resolver not available, target '%.*s:%d' type=%s "
+		      "will be resolved with gethostbyname()",
+		      target->addr.host.slen,
+		      target->addr.host.ptr,
+		      target->addr.port,
+		      pjsip_transport_get_type_name(target->type)));
+	}
+
+	/* Set the port number if not specified. */
+	if (target->addr.port == 0) {
+	   srv_port = (pj_uint16_t)
+		      pjsip_transport_get_default_port_for_type(type);
+	} else {
+	   srv_port = (pj_uint16_t)target->addr.port;
+	}
+
+	/* This will eventually call pj_gethostbyname() if the host
+	 * is not an IP address.
+	 */
+	status = pj_sockaddr_in_init((pj_sockaddr_in*)&svr_addr.entry[0].addr,
+				      &target->addr.host, srv_port);
+	if (status != PJ_SUCCESS)
+	    goto on_error;
+
+	/* Call the callback. */
+	ip_addr = ((pj_sockaddr_in*)&svr_addr.entry[0].addr)->sin_addr;
+	PJ_LOG(5,(THIS_FILE, 
+		  "Target '%.*s:%d' type=%s resolved to "
+		  "'%s:%d' type=%s",
+		  (int)target->addr.host.slen,
+		  target->addr.host.ptr,
+		  target->addr.port,
+		  pjsip_transport_get_type_name(target->type),
+		  pj_inet_ntoa(ip_addr),
+		  srv_port,
+		  pjsip_transport_get_type_name(type)));
+	svr_addr.count = 1;
+	svr_addr.entry[0].priority = 0;
+	svr_addr.entry[0].weight = 0;
+	svr_addr.entry[0].type = type;
+	svr_addr.entry[0].addr_len = sizeof(pj_sockaddr_in);
+	(*cb)(status, token, &svr_addr);
 
+	/* Done. */
+	return;
     }
 
-    /* Set the port number if not specified. */
-    if (target->addr.port == 0) {
-	target->addr.port = pjsip_transport_get_default_port_for_type(type);
+    /* Target is not an IP address so we need to resolve it. */
+#if PJSIP_HAS_RESOLVER
+
+    /* Build the query state */
+    query = pj_pool_zalloc(pool, sizeof(struct query));
+    pj_ansi_snprintf(query->objname, sizeof(query->objname), "rsvjob%X",
+		     resolver->job_id++);
+    query->resolver = resolver;
+    query->token = token;
+    query->cb = cb;
+    query->req.target = *target;
+    pj_strdup(pool, &query->req.target.addr.host, &target->addr.host);
+
+    /* If port is not specified, start with SRV resolution
+     * (should be with NAPTR, but we'll do that later)
+     */
+    PJ_TODO(SUPPORT_DNS_NAPTR);
+
+    /* Build dummy NAPTR entry */
+    query->naptr_cnt = 1;
+    pj_bzero(&query->naptr[0], sizeof(query->naptr[0]));
+    query->naptr[0].order = 0;
+    query->naptr[0].pref = 0;
+    query->naptr[0].type = type;
+    query->naptr[0].target_name.ptr = 
+	pj_pool_alloc(pool, target->addr.host.slen + 12);
+
+    if (type == PJSIP_TRANSPORT_TLS)
+	pj_strcpy2(&query->naptr[0].target_name, "_sips._tcp.");
+    else if (type == PJSIP_TRANSPORT_TCP)
+	pj_strcpy2(&query->naptr[0].target_name, "_sip._tcp.");
+    else if (type == PJSIP_TRANSPORT_UDP)
+	pj_strcpy2(&query->naptr[0].target_name, "_sip._udp.");
+    else {
+	pj_assert(!"Unknown transport type");
+	pj_strcpy2(&query->naptr[0].target_name, "_sip._udp.");
     }
+    pj_strcat(&query->naptr[0].target_name, &target->addr.host);
+
+
+    /* Start DNS SRV or A resolution, depending on whether port is specified */
+    if (target->addr.port == 0) {
+	query->dns_state = PJ_DNS_TYPE_SRV;
+	srv_name = query->naptr[0].target_name;
 
-    /* Resolve hostname. */
-    if (!is_ip_addr) {
-	status = pj_sockaddr_in_init((pj_sockaddr_in*)&svr_addr.entry[0].addr, 
-				     &target->addr.host, 
-				     (pj_uint16_t)target->addr.port);
     } else {
-	status = pj_sockaddr_in_init((pj_sockaddr_in*)&svr_addr.entry[0].addr, 
-				      &target->addr.host, 
-				     (pj_uint16_t)target->addr.port);
+	/* Otherwise if port is specified, start with A (or AAAA) host 
+	 * resolution 
+	 */
+	query->dns_state = PJ_DNS_TYPE_A;
+
+	/* Since we don't perform SRV resolution, pretend that we'ee already
+	 * done so by inserting a dummy SRV record.
+	 */
+
+	query->srv_cnt = 1;
+	pj_bzero(&query->srv[0], sizeof(query->srv[0]));
+	query->srv[0].target_name = query->req.target.addr.host;
+	query->srv[0].type = type;
+	query->srv[0].port = query->req.target.addr.port;
+	query->srv[0].priority = 0;
+	query->srv[0].weight = 0;
+
+	srv_name = query->srv[0].target_name;
     }
 
+    /* Start the asynchronous query */
+    PJ_LOG(5, (query->objname, 
+	       "Starting async DNS %s query: target=%.*s, transport=%s, "
+	       "port=%d",
+	       pj_dns_get_type_name(query->dns_state),
+	       (int)srv_name.slen, srv_name.ptr,
+	       pjsip_transport_get_type_name(target->type),
+	       target->addr.port));
+
+    status = pj_dns_resolver_start_query(resolver->res, &srv_name, 
+				         query->dns_state, 0, &dns_callback,
+    					 query, &query->object);
+    if (status != PJ_SUCCESS)
+	goto on_error;
+
+    return;
+
+#else /* PJSIP_HAS_RESOLVER */
+    PJ_UNUSED_ARG(pool);
+    PJ_UNUSED_ARG(query);
+    PJ_UNUSED_ARG(srv_name);
+#endif /* PJSIP_HAS_RESOLVER */
+
+on_error:
     if (status != PJ_SUCCESS) {
 	char errmsg[PJ_ERR_MSG_SIZE];
 	PJ_LOG(4,(THIS_FILE, "Failed to resolve '%.*s'. Err=%d (%s)",
-			     target->addr.host.slen,
+			     (int)target->addr.host.slen,
 			     target->addr.host.ptr,
 			     status,
 			     pj_strerror(status,errmsg,sizeof(errmsg)).ptr));
-	(*cb)(status, token, &svr_addr);
+	(*cb)(status, token, NULL);
+	return;
+    }
+}
+
+/*
+ * The rest of the code should only get compiled when resolver is enabled
+ */
+#if PJSIP_HAS_RESOLVER
+
+#define SWAP(type,ptr1,ptr2)	if (ptr1 != ptr2) { \
+				  type tmp; \
+				  pj_memcpy(&tmp, ptr1, sizeof(type)); \
+				  pj_memcpy(ptr1, ptr2, sizeof(type)); \
+				  (ptr1)->target_name.ptr = (ptr1)->target_buf; \
+				  pj_memcpy(ptr2, &tmp, sizeof(type)); \
+				  (ptr2)->target_name.ptr = (ptr2)->target_buf; \
+				} else {}
+
+/* Build server entries in the query based on received SRV response */
+static void build_server_entries(struct query *query, 
+				 pj_dns_parsed_packet *response)
+{
+    unsigned i;
+    unsigned naptr_id;
+
+    /* Find NAPTR target which corresponds to this SRV target */
+    for (naptr_id=0; naptr_id < query->naptr_cnt; ++naptr_id) {
+	if (pj_stricmp(&query->naptr[naptr_id].target_name,
+		       &response->ans[0].name)==0)
+	    break;
+    }
+    if (naptr_id == query->naptr_cnt) {
+	PJ_LOG(4,(query->objname, 
+		  "Unable to find NAPTR record for SRV name %.*s!",
+		  (int)response->ans[0].name.slen, 
+		  response->ans[0].name.ptr));
 	return;
     }
 
-    /* Call the callback. */
-    PJ_LOG(5,(THIS_FILE, "Server resolved: '%.*s:%d' type=%s has %d entries, "
-			 "entry[0]=%s:%d type=%s",
-			 target->addr.host.slen,
-			 target->addr.host.ptr,
-			 target->addr.port,
-			 pjsip_transport_get_type_name(type),
-			 1,
-			 pj_inet_ntoa(((pj_sockaddr_in*)&svr_addr.entry[0].addr)->sin_addr),
-			 target->addr.port,
-			 pjsip_transport_get_type_name(type)));
-    svr_addr.count = (status == PJ_SUCCESS) ? 1 : 0;
-    svr_addr.entry[0].type = type;
-    svr_addr.entry[0].addr_len = sizeof(pj_sockaddr_in);
-    (*cb)(status, token, &svr_addr);
+
+    /* Save the Resource Records in DNS answer into SRV targets. */
+    query->srv_cnt = 0;
+    for (i=0; i<response->hdr.anscount && 
+	      query->srv_cnt < PJSIP_MAX_RESOLVED_ADDRESSES; ++i) 
+    {
+	pj_dns_parsed_rr *rr = &response->ans[i];
+	struct srv_target *srv = &query->srv[query->srv_cnt];
+
+	if (rr->type != PJ_DNS_TYPE_SRV) {
+	    PJ_LOG(4,(query->objname, 
+		      "Received non SRV answer for SRV query!"));
+	    continue;
+	}
+
+	if (rr->rdata.srv.target.slen > PJ_MAX_HOSTNAME) {
+	    PJ_LOG(4,(query->objname, "Hostname is too long!"));
+	    continue;
+	}
+
+	/* Build the SRV entry for RR */
+	pj_bzero(srv, sizeof(*srv));
+	pj_memcpy(srv->target_buf, rr->rdata.srv.target.ptr, 
+		  rr->rdata.srv.target.slen);
+	srv->target_name.ptr = srv->target_buf;
+	srv->target_name.slen = rr->rdata.srv.target.slen;
+	srv->type = query->naptr[naptr_id].type;
+	srv->port = rr->rdata.srv.port;
+	srv->priority = rr->rdata.srv.prio;
+	srv->weight = rr->rdata.srv.weight;
+	
+	++query->srv_cnt;
+    }
+
+    /* First pass: 
+     *	order the entries based on priority.
+     */
+    for (i=0; i<query->srv_cnt-1; ++i) {
+	unsigned min = i, j;
+	for (j=i+1; j<query->srv_cnt; ++j) {
+	    if (query->srv[j].priority < query->srv[min].priority)
+		min = j;
+	}
+	SWAP(struct srv_target, &query->srv[i], &query->srv[min]);
+    }
+
+    /* Second pass:
+     *	pick one host among hosts with the same priority, according
+     *	to its weight. The idea is when one server fails, client should
+     *	contact the next server with higher priority rather than contacting
+     *	server with the same priority as the failed one.
+     *
+     *  The algorithm for selecting server among servers with the same
+     *  priority is described in RFC 2782.
+     */
+    for (i=0; i<query->srv_cnt; ++i) {
+	unsigned j, count=1, sum;
+
+	/* Calculate running sum for servers with the same priority */
+	sum = query->srv[i].sum = query->srv[i].weight;
+	for (j=i+1; j<query->srv_cnt && 
+		    query->srv[j].priority == query->srv[i].priority; ++j)
+	{
+	    sum += query->srv[j].weight;
+	    query->srv[j].sum = sum;
+	    ++count;
+	}
+
+	if (count > 1) {
+	    unsigned r;
+
+	    /* Elect one random number between zero and the total sum of
+	     * weight (inclusive).
+	     */
+	    r = pj_rand() % (sum + 1);
+
+	    /* Select the first server which running sum is greater than or
+	     * equal to the random number.
+	     */
+	    for (j=i; j<i+count; ++j) {
+		if (query->srv[j].sum >= r)
+		    break;
+	    }
+
+	    /* Must have selected one! */
+	    pj_assert(j != i+count);
+
+	    /* Put this entry in front (of entries with same priority) */
+	    SWAP(struct srv_target, &query->srv[i], &query->srv[j]);
+
+	    /* Remove all other entries (of the same priority) */
+	    while (count > 1) {
+		pj_array_erase(query->srv, sizeof(struct srv_target), 
+			       query->srv_cnt, i+1);
+		--count;
+		--query->srv_cnt;
+	    }
+	}
+    }
+
+    /* Since we've been moving around SRV entries, update the pointers
+     * in target_name.
+     */
+    for (i=0; i<query->srv_cnt; ++i) {
+	query->srv[i].target_name.ptr = query->srv[i].target_buf;
+    }
+
+    /* Check for Additional Info section if A records are available, and
+     * fill in the IP address (so that we won't need to resolve the A 
+     * record with another DNS query). 
+     */
+    for (i=0; i<response->hdr.arcount; ++i) {
+	pj_dns_parsed_rr *rr = &response->arr[i];
+	unsigned j;
+
+	if (rr->type != PJ_DNS_TYPE_A)
+	    continue;
+
+	/* Yippeaiyee!! There is an "A" record! 
+	 * Update the IP address of the corresponding SRV record.
+	 */
+	for (j=0; j<query->srv_cnt; ++j) {
+	    if (pj_stricmp(&rr->name, &query->srv[j].target_name)==0) {
+		unsigned cnt = query->srv[j].addr_cnt;
+		query->srv[j].addr[cnt] = pj_inet_addr(&rr->rdata.a.ip_addr);
+		++query->srv[j].addr_cnt;
+		++query->host_resolved;
+		break;
+	    }
+	}
+
+	/* Not valid message; SRV entry might have been deleted in
+	 * server selection process.
+	 */
+	/*
+	if (j == query->srv_cnt) {
+	    PJ_LOG(4,(query->objname, 
+		      "Received DNS SRV answer with A record, but "
+		      "couldn't find matching name (name=%.*s)",
+		      (int)rr->name.slen,
+		      rr->name.ptr));
+	}
+	*/
+    }
+
+    /* Rescan again the name specified in the SRV record to see if IP
+     * address is specified as the target name (unlikely, but well, who 
+     * knows..).
+     */
+    for (i=0; i<query->srv_cnt; ++i) {
+	pj_in_addr addr;
+
+	if (query->srv[i].addr_cnt != 0) {
+	    /* IP address already resolved */
+	    continue;
+	}
+
+	if (pj_inet_aton(&query->srv[i].target_name, &addr) != 0) {
+	    query->srv[i].addr[query->srv[i].addr_cnt++] = addr;
+	    ++query->host_resolved;
+	}
+    }
+
+    /* Print resolved entries to the log */
+    PJ_LOG(5,(query->objname, 
+	      "SRV query for %.*s completed, "
+	      "%d of %d total entries selected%c",
+	      (int)query->naptr[naptr_id].target_name.slen,
+	      query->naptr[naptr_id].target_name.ptr,
+	      query->srv_cnt,
+	      response->hdr.anscount,
+	      (query->srv_cnt ? ':' : ' ')));
+
+    for (i=0; i<query->srv_cnt; ++i) {
+	const char *addr;
+
+	if (query->srv[i].addr_cnt != 0)
+	    addr = pj_inet_ntoa(query->srv[i].addr[0]);
+	else
+	    addr = "-";
+
+	PJ_LOG(5,(query->objname, 
+		  " %d: SRV %d %d %d %.*s (%s)",
+		  i, query->srv[i].priority, 
+		  query->srv[i].weight, 
+		  query->srv[i].port, 
+		  (int)query->srv[i].target_name.slen, 
+		  query->srv[i].target_name.ptr,
+		  addr));
+    }
 }
 
+
+/* Start DNS A record queries for all SRV records in the query structure */
+static pj_status_t resolve_hostnames(struct query *query)
+{
+    unsigned i;
+    pj_status_t err=PJ_SUCCESS, status;
+
+    query->dns_state = PJ_DNS_TYPE_A;
+    for (i=0; i<query->srv_cnt; ++i) {
+	PJ_LOG(5, (query->objname, 
+		   "Starting async DNS A query for %.*s",
+		   (int)query->srv[i].target_name.slen, 
+		   query->srv[i].target_name.ptr));
+
+	status = pj_dns_resolver_start_query(query->resolver->res,
+					     &query->srv[i].target_name,
+					     PJ_DNS_TYPE_A, 0,
+					     &dns_callback,
+					     query, NULL);
+	if (status != PJ_SUCCESS) {
+	    query->host_resolved++;
+	    err = status;
+	}
+    }
+    
+    return (query->host_resolved == query->srv_cnt) ? err : PJ_SUCCESS;
+}
+
+/* 
+ * This callback is called by PJLIB-UTIL DNS resolver when asynchronous
+ * query has completed (successfully or with error).
+ */
+static void dns_callback(void *user_data,
+			 pj_status_t status,
+			 pj_dns_parsed_packet *pkt)
+{
+    struct query *query = user_data;
+    unsigned i;
+
+    /* Proceed to next stage */
+
+    if (query->dns_state == PJ_DNS_TYPE_SRV) {
+
+	/* We are getting SRV response */
+
+	if (status == PJ_SUCCESS && pkt->hdr.anscount != 0) {
+	    /* Got SRV response, build server entry. If A records are available
+	     * in additional records section of the DNS response, save them too.
+	     */
+	    build_server_entries(query, pkt);
+
+	} else if (status != PJ_SUCCESS) {
+	    char errmsg[PJ_ERR_MSG_SIZE];
+	    unsigned naptr_id;
+
+	    /* Update query last error */
+	    query->last_error = status;
+
+	    /* Find which NAPTR target has not got SRV records */
+	    for (naptr_id=0; naptr_id < query->naptr_cnt; ++naptr_id) {
+		for (i=0; i<query->srv_cnt; ++i) {
+		    if (query->srv[i].type == query->naptr[naptr_id].type)
+			break;
+		}
+		if (i == query->srv_cnt)
+		    break;
+	    }
+	    if (naptr_id == query->naptr_cnt) {
+		/* Strangely all NAPTR records seem to already have SRV
+		 * records! This is quite unexpected, by anyway lets set
+		 * the naptr_id to zero just in case.
+		 */
+		pj_assert(!"Strange");
+		naptr_id = 0;
+
+	    }
+
+	    pj_strerror(status, errmsg, sizeof(errmsg));
+	    PJ_LOG(4,(query->objname, 
+		      "DNS SRV resolution failed for %.*s: %s", 
+		      (int)query->naptr[naptr_id].target_name.slen, 
+		      query->naptr[naptr_id].target_name.ptr,
+		      errmsg));
+	}
+
+	/* If we can't build SRV record, assume the original target is
+	 * an A record.
+	 */
+	if (query->srv_cnt == 0) {
+	    /* Looks like we aren't getting any SRV responses.
+	     * Resolve the original target as A record by creating a 
+	     * single "dummy" srv record and start the hostname resolution.
+	     */
+	    unsigned naptr_id;
+
+	    /* Find which NAPTR target has not got SRV records */
+	    for (naptr_id=0; naptr_id < query->naptr_cnt; ++naptr_id) {
+		for (i=0; i<query->srv_cnt; ++i) {
+		    if (query->srv[i].type == query->naptr[naptr_id].type)
+			break;
+		}
+		if (i == query->srv_cnt)
+		    break;
+	    }
+	    if (naptr_id == query->naptr_cnt) {
+		/* Strangely all NAPTR records seem to already have SRV
+		 * records! This is quite unexpected, by anyway lets set
+		 * the naptr_id to zero just in case.
+		 */
+		pj_assert(!"Strange");
+		naptr_id = 0;
+
+	    }
+
+	    PJ_LOG(4, (query->objname, 
+		       "DNS SRV resolution failed for %.*s, trying "
+		       "resolving A record for %.*s",
+		       (int)query->naptr[naptr_id].target_name.slen, 
+		       query->naptr[naptr_id].target_name.ptr,
+		       (int)query->req.target.addr.host.slen,
+		       query->req.target.addr.host.ptr));
+
+	    /* Create a "dummy" srv record using the original target */
+	    i = query->srv_cnt++;
+	    pj_bzero(&query->srv[i], sizeof(query->srv[i]));
+	    query->srv[i].target_name = query->req.target.addr.host;
+	    query->srv[i].type = query->naptr[naptr_id].type;
+	    query->srv[i].priority = 0;
+	    query->srv[i].weight = 0;
+
+	    query->srv[i].port = query->req.target.addr.port;
+	    if (query->srv[i].port == 0) {
+		query->srv[i].port = (pj_uint16_t)
+		 pjsip_transport_get_default_port_for_type(query->srv[i].type);
+	    }
+	} 
+	
+
+	/* Resolve server hostnames (DNS A record) for hosts which don't have
+	 * A record yet.
+	 */
+	if (query->host_resolved != query->srv_cnt) {
+	    status = resolve_hostnames(query);
+	    if (status != PJ_SUCCESS)
+		goto on_error;
+
+	    /* Must return now. Callback may have been called and query
+	     * may have been destroyed.
+	     */
+	    return;
+	}
+
+    } else if (query->dns_state == PJ_DNS_TYPE_A) {
+
+	/* Check that we really have answer */
+	if (status==PJ_SUCCESS && pkt->hdr.anscount != 0) {
+
+	    /* Update IP address of the corresponding hostname */
+	    for (i=0; i<query->srv_cnt; ++i) {
+		if (pj_stricmp(&pkt->ans[0].name, 
+			       &query->srv[i].target_name)==0) 
+		{
+		    break;
+		}
+	    }
+
+	    if (i == query->srv_cnt) {
+		PJ_LOG(4,(query->objname, 
+			  "Received answer to DNS A request with no matching "
+			  "SRV record! The unknown name is %.*s",
+			  (int)pkt->ans[0].name.slen, pkt->ans[0].name.ptr));
+	    } else {
+		unsigned j;
+
+		query->srv[i].addr[query->srv[i].addr_cnt++] =
+		    pj_inet_addr(&pkt->ans[0].rdata.a.ip_addr);
+
+		PJ_LOG(5,(query->objname, 
+			  "DNS A for %.*s: %.*s",
+			  (int)query->srv[i].target_name.slen, 
+			  query->srv[i].target_name.ptr,
+			  (int)pkt->ans[0].rdata.a.ip_addr.slen,
+			  pkt->ans[0].rdata.a.ip_addr.ptr));
+
+		/* Check for multiple IP addresses */
+		for (j=1; j<pkt->hdr.anscount && 
+			    query->srv[i].addr_cnt < ADDR_MAX_COUNT; ++j)
+		{
+		    query->srv[i].addr[query->srv[i].addr_cnt++] = 
+			pj_inet_addr(&pkt->ans[j].rdata.a.ip_addr);
+
+		    PJ_LOG(5,(query->objname, 
+			      "Additional DNS A for %.*s: %.*s",
+			      (int)query->srv[i].target_name.slen, 
+			      query->srv[i].target_name.ptr,
+			      (int)pkt->ans[j].rdata.a.ip_addr.slen,
+			      pkt->ans[j].rdata.a.ip_addr.ptr));
+		}
+	    }
+
+	} else if (status != PJ_SUCCESS) {
+	    char errmsg[PJ_ERR_MSG_SIZE];
+
+	    /* Update last error */
+	    query->last_error = status;
+
+	    /* Log error */
+	    pj_strerror(status, errmsg, sizeof(errmsg));
+	    PJ_LOG(4,(query->objname, "DNS A record resolution failed: %s", 
+		      errmsg));
+	}
+
+	++query->host_resolved;
+
+    } else {
+	pj_assert(!"Unexpected state!");
+	query->last_error = status = PJ_EINVALIDOP;
+	goto on_error;
+    }
+
+    /* Check if all hosts have been resolved */
+    if (query->host_resolved == query->srv_cnt) {
+	/* Got all answers, build server addresses */
+	pjsip_server_addresses svr_addr;
+
+	svr_addr.count = 0;
+	for (i=0; i<query->srv_cnt; ++i) {
+	    unsigned j;
+
+	    /* Do we have IP address for this server? */
+	    /* This log is redundant really.
+	    if (query->srv[i].addr_cnt == 0) {
+		PJ_LOG(5,(query->objname, 
+			  " SRV target %.*s:%d does not have IP address!",
+			  (int)query->srv[i].target_name.slen,
+			  query->srv[i].target_name.ptr,
+			  query->srv[i].port));
+		continue;
+	    }
+	    */
+
+	    for (j=0; j<query->srv[i].addr_cnt; ++j) {
+		unsigned idx = svr_addr.count;
+		pj_sockaddr_in *addr;
+
+		svr_addr.entry[idx].type = query->srv[i].type;
+		svr_addr.entry[idx].priority = query->srv[i].priority;
+		svr_addr.entry[idx].weight = query->srv[i].weight;
+		svr_addr.entry[idx].addr_len = sizeof(pj_sockaddr_in);
+	     
+		addr = (pj_sockaddr_in*)&svr_addr.entry[idx].addr;
+		pj_bzero(addr, sizeof(pj_sockaddr_in));
+		addr->sin_family = PJ_AF_INET;
+		addr->sin_addr = query->srv[i].addr[j];
+		addr->sin_port = pj_htons((pj_uint16_t)query->srv[i].port);
+
+		++svr_addr.count;
+	    }
+	}
+
+	PJ_LOG(5,(query->objname, 
+		  "Server resolution complete, %d server entry(s) found",
+		  svr_addr.count));
+
+
+	if (svr_addr.count > 0)
+	    status = PJ_SUCCESS;
+	else {
+	    status = query->last_error;
+	    if (status == PJ_SUCCESS)
+		status = PJLIB_UTIL_EDNSNOANSWERREC;
+	}
+
+	/* Call the callback */
+	(*query->cb)(status, query->token, &svr_addr);
+    }
+
+
+    return;
+
+on_error:
+    /* Check for failure */
+    if (status != PJ_SUCCESS) {
+	char errmsg[PJ_ERR_MSG_SIZE];
+	PJ_LOG(4,(query->objname, 
+		  "DNS %s record resolution error for '%.*s'."
+		  " Err=%d (%s)",
+		  pj_dns_get_type_name(query->dns_state),
+		  (int)query->req.target.addr.host.slen,
+		  query->req.target.addr.host.ptr,
+		  status,
+		  pj_strerror(status,errmsg,sizeof(errmsg)).ptr));
+	(*query->cb)(status, query->token, NULL);
+	return;
+    }
+}
+
+#endif	/* PJSIP_HAS_RESOLVER */
+
+
+
diff --git a/pjsip/src/pjsua-lib/pjsua_core.c b/pjsip/src/pjsua-lib/pjsua_core.c
index 6b39fdbb..b4f4325f 100644
--- a/pjsip/src/pjsua-lib/pjsua_core.c
+++ b/pjsip/src/pjsua-lib/pjsua_core.c
@@ -456,6 +456,45 @@ PJ_DEF(pj_status_t) pjsua_init( const pjsua_config *ua_cfg,
 	PJ_ASSERT_RETURN(status == PJ_SUCCESS, status);
     }
 
+    /* If nameserver is configured, create DNS resolver instance and
+     * set it to be used by SIP resolver.
+     */
+    if (ua_cfg->nameserver_count) {
+#if PJSIP_HAS_RESOLVER
+	pj_dns_resolver *resv;
+	unsigned i;
+
+	/* Create DNS resolver */
+	status = pjsip_endpt_create_resolver(pjsua_var.endpt, &resv);
+	PJ_ASSERT_RETURN(status == PJ_SUCCESS, status);
+
+	/* Configure nameserver for the DNS resolver */
+	status = pj_dns_resolver_set_ns(resv, ua_cfg->nameserver_count,
+					ua_cfg->nameserver, NULL);
+	if (status != PJ_SUCCESS) {
+	    pjsua_perror(THIS_FILE, "Error setting nameserver", status);
+	    return status;
+	}
+
+	/* Set this DNS resolver to be used by the SIP resolver */
+	status = pjsip_endpt_set_resolver(pjsua_var.endpt, resv);
+	if (status != PJ_SUCCESS) {
+	    pjsua_perror(THIS_FILE, "Error setting DNS resolver", status);
+	    return status;
+	}
+
+	/* Print nameservers */
+	for (i=0; i<ua_cfg->nameserver_count; ++i) {
+	    PJ_LOG(4,(THIS_FILE, "Nameserver %.*s added",
+		      (int)ua_cfg->nameserver[i].slen,
+		      ua_cfg->nameserver[i].ptr));
+	}
+#else
+	PJ_LOG(2,(THIS_FILE, 
+		  "DNS resolver is disabled (PJSIP_HAS_RESOLVER==0)"));
+#endif
+    }
+
     /* Init SIP UA: */
 
     /* Initialize transaction layer: */
diff --git a/pjsip/src/test-pjsip/dns_test.c b/pjsip/src/test-pjsip/dns_test.c
new file mode 100644
index 00000000..a088e5d9
--- /dev/null
+++ b/pjsip/src/test-pjsip/dns_test.c
@@ -0,0 +1,596 @@
+/* $Id$ */
+/* 
+ * Copyright (C) 2003-2006 Benny Prijono <benny@prijono.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
+ */
+#include "test.h"
+#include <pjsip.h>
+#include <pjlib.h>
+#include <pjlib-util.h>
+
+/* For logging purpose. */
+#define THIS_FILE   "dns_test.c"
+
+struct result
+{
+    pj_status_t		    status;
+    pjsip_server_addresses  servers;
+};
+
+
+static void cb(pj_status_t status,
+	       void *token,
+	       const struct pjsip_server_addresses *addr)
+{
+    struct result *result = token;
+
+    result->status = status;
+    if (status == PJ_SUCCESS)
+	pj_memcpy(&result->servers, addr, sizeof(*addr));
+}
+
+
+static void add_dns_entries(pj_dns_resolver *resv)
+{
+    /* Inject DNS SRV entry */
+    pj_dns_parsed_packet pkt;
+    pj_dns_parsed_rr ans[4];
+    pj_dns_parsed_rr ar[5];
+    unsigned i;
+
+    /*
+     * This is answer to SRV query to "example.com" domain, and
+     * the answer contains full reference to the A records of
+     * the server. The full DNS records is :
+
+     _sip._udp.example.com 3600 IN SRV 0 0  5060 sip01.example.com.
+     _sip._udp.example.com 3600 IN SRV 0 20 5060 sip02.example.com.
+     _sip._udp.example.com 3600 IN SRV 0 10 5060 sip03.example.com.
+     _sip._udp.example.com 3600 IN SRV 1 0  5060 sip04.example.com.
+     
+     sip01.example.com. 3600 IN A       1.1.1.1
+     sip02.example.com. 3600 IN A       2.2.2.2
+     sip03.example.com. 3600 IN A       3.3.3.3
+     sip04.example.com. 3600 IN A       4.4.4.4
+     
+     ; Additionally, add A record for "example.com"
+     example.com.	3600 IN A       5.5.5.5
+
+     */
+    pj_bzero(&pkt, sizeof(pkt));
+    pj_bzero(ans, sizeof(ans));
+    pj_bzero(ar, sizeof(ar));
+
+    pkt.hdr.flags = PJ_DNS_SET_QR(1);
+    pkt.hdr.anscount = PJ_ARRAY_SIZE(ans);
+    pkt.hdr.arcount = 0;
+    pkt.ans = ans;
+    pkt.arr = ar;
+
+    ans[0].name = pj_str("_sip._udp.example.com");
+    ans[0].type = PJ_DNS_TYPE_SRV;
+    ans[0].dnsclass = PJ_DNS_CLASS_IN;
+    ans[0].ttl = 3600;
+    ans[0].rdata.srv.prio = 0;
+    ans[0].rdata.srv.weight = 0;
+    ans[0].rdata.srv.port = 5060;
+    ans[0].rdata.srv.target = pj_str("sip01.example.com");
+
+    ans[1].name = pj_str("_sip._udp.example.com");
+    ans[1].type = PJ_DNS_TYPE_SRV;
+    ans[1].dnsclass = PJ_DNS_CLASS_IN;
+    ans[1].ttl = 3600;
+    ans[1].rdata.srv.prio = 0;
+    ans[1].rdata.srv.weight = 20;
+    ans[1].rdata.srv.port = 5060;
+    ans[1].rdata.srv.target = pj_str("sip02.example.com");
+
+    ans[2].name = pj_str("_sip._udp.example.com");
+    ans[2].type = PJ_DNS_TYPE_SRV;
+    ans[2].dnsclass = PJ_DNS_CLASS_IN;
+    ans[2].ttl = 3600;
+    ans[2].rdata.srv.prio = 0;
+    ans[2].rdata.srv.weight = 10;
+    ans[2].rdata.srv.port = 5060;
+    ans[2].rdata.srv.target = pj_str("sip03.example.com");
+
+    ans[3].name = pj_str("_sip._udp.example.com");
+    ans[3].type = PJ_DNS_TYPE_SRV;
+    ans[3].dnsclass = PJ_DNS_CLASS_IN;
+    ans[3].ttl = 3600;
+    ans[3].rdata.srv.prio = 1;
+    ans[3].rdata.srv.weight = 0;
+    ans[3].rdata.srv.port = 5060;
+    ans[3].rdata.srv.target = pj_str("sip04.example.com");
+
+    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+
+    ar[0].name = pj_str("sip01.example.com");
+    ar[0].type = PJ_DNS_TYPE_A;
+    ar[0].dnsclass = PJ_DNS_CLASS_IN;
+    ar[0].ttl = 3600;
+    ar[0].rdata.a.ip_addr = pj_str("1.1.1.1");
+
+    ar[1].name = pj_str("sip02.example.com");
+    ar[1].type = PJ_DNS_TYPE_A;
+    ar[1].dnsclass = PJ_DNS_CLASS_IN;
+    ar[1].ttl = 3600;
+    ar[1].rdata.a.ip_addr = pj_str("2.2.2.2");
+
+    ar[2].name = pj_str("sip03.example.com");
+    ar[2].type = PJ_DNS_TYPE_A;
+    ar[2].dnsclass = PJ_DNS_CLASS_IN;
+    ar[2].ttl = 3600;
+    ar[2].rdata.a.ip_addr = pj_str("3.3.3.3");
+
+    ar[3].name = pj_str("sip04.example.com");
+    ar[3].type = PJ_DNS_TYPE_A;
+    ar[3].dnsclass = PJ_DNS_CLASS_IN;
+    ar[3].ttl = 3600;
+    ar[3].rdata.a.ip_addr = pj_str("4.4.4.4");
+
+    ar[4].name = pj_str("example.com");
+    ar[4].type = PJ_DNS_TYPE_A;
+    ar[4].dnsclass = PJ_DNS_CLASS_IN;
+    ar[4].ttl = 3600;
+    ar[4].rdata.a.ip_addr = pj_str("5.5.5.5");
+
+    /* 
+     * Create individual A records for all hosts in "example.com" domain.
+     */
+    for (i=0; i<PJ_ARRAY_SIZE(ar); ++i) {
+	pj_bzero(&pkt, sizeof(pkt));
+	pkt.hdr.anscount = 1;
+	pkt.hdr.flags = PJ_DNS_SET_QR(1);
+	pkt.ans = &ar[i];
+
+	pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+    }
+
+    /* 
+     * Simulate DNS error response by creating these answers.
+     * Sample of invalid SRV records: _sip._udp.sip01.example.com.
+     */
+    for (i=0; i<PJ_ARRAY_SIZE(ans); ++i) {
+	pj_dns_parsed_query q;
+	char buf[128];
+	char *services[] = { "_sip._udp.", "_sip._tcp.", "_sips._tcp."};
+	unsigned j;
+
+	for (j=0; j<PJ_ARRAY_SIZE(services); ++j) {
+	    q.dnsclass = PJ_DNS_CLASS_IN;
+	    q.type = PJ_DNS_TYPE_SRV;
+
+	    q.name.ptr = buf;
+	    pj_bzero(buf, sizeof(buf));
+	    pj_strcpy2(&q.name, services[j]);
+	    pj_strcat(&q.name, &ans[i].rdata.srv.target);
+
+	    pj_bzero(&pkt, sizeof(pkt));
+	    pkt.hdr.qdcount = 1;
+	    pkt.hdr.flags = PJ_DNS_SET_QR(1) |
+			    PJ_DNS_SET_RCODE(PJ_DNS_RCODE_NXDOMAIN);
+	    pkt.q = &q;
+	    
+	    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+	}
+    }
+
+
+    /*
+     * ANOTHER DOMAIN.
+     *
+     * This time we let SRV and A get answered in different DNS
+     * query.
+     */
+
+    /* The "domain.com" DNS records (note the different the port):
+
+	_sip._tcp.domain.com 3600 IN SRV 1 0 50060 sip06.domain.com.
+	_sip._tcp.domain.com 3600 IN SRV 2 0 50060 sip07.domain.com.
+
+	sip06.domain.com. 3600 IN A       6.6.6.6
+	sip07.domain.com. 3600 IN A       7.7.7.7
+     */
+
+    pj_bzero(&pkt, sizeof(pkt));
+    pj_bzero(&ans, sizeof(ans));
+    pkt.hdr.flags = PJ_DNS_SET_QR(1);
+    pkt.hdr.anscount = 2;
+    pkt.ans = ans;
+
+    /* Add the SRV records, with reverse priority (to test that sorting
+     * works.
+     */
+    ans[0].name = pj_str("_sip._tcp.domain.com");
+    ans[0].type = PJ_DNS_TYPE_SRV;
+    ans[0].dnsclass = PJ_DNS_CLASS_IN;
+    ans[0].ttl = 3600;
+    ans[0].rdata.srv.prio = 2;
+    ans[0].rdata.srv.weight = 0;
+    ans[0].rdata.srv.port = 50060;
+    ans[0].rdata.srv.target = pj_str("SIP07.DOMAIN.COM");
+
+    ans[1].name = pj_str("_sip._tcp.domain.com");
+    ans[1].type = PJ_DNS_TYPE_SRV;
+    ans[1].dnsclass = PJ_DNS_CLASS_IN;
+    ans[1].ttl = 3600;
+    ans[1].rdata.srv.prio = 1;
+    ans[1].rdata.srv.weight = 0;
+    ans[1].rdata.srv.port = 50060;
+    ans[1].rdata.srv.target = pj_str("SIP06.DOMAIN.COM");
+
+    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+
+    /* From herein there is only one answer */
+    pkt.hdr.anscount = 1;
+
+    /* Add a single SRV for UDP */
+    ans[0].name = pj_str("_sip._udp.domain.com");
+    ans[0].type = PJ_DNS_TYPE_SRV;
+    ans[0].dnsclass = PJ_DNS_CLASS_IN;
+    ans[0].ttl = 3600;
+    ans[0].rdata.srv.prio = 0;
+    ans[0].rdata.srv.weight = 0;
+    ans[0].rdata.srv.port = 50060;
+    ans[0].rdata.srv.target = pj_str("SIP06.DOMAIN.COM");
+
+    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+
+
+    /* Add the A record for sip06.domain.com */
+    ans[0].name = pj_str("sip06.domain.com");
+    ans[0].type = PJ_DNS_TYPE_A;
+    ans[0].dnsclass = PJ_DNS_CLASS_IN;
+    ans[0].ttl = 3600;
+    ans[0].rdata.a.ip_addr = pj_str("6.6.6.6");
+
+    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+
+    /* Add the A record for sip07.domain.com */
+    ans[0].name = pj_str("sip07.domain.com");
+    ans[0].type = PJ_DNS_TYPE_A;
+    ans[0].dnsclass = PJ_DNS_CLASS_IN;
+    ans[0].ttl = 3600;
+    ans[0].rdata.a.ip_addr = pj_str("7.7.7.7");
+
+    pj_dns_resolver_add_entry( resv, &pkt, PJ_FALSE);
+}
+
+
+/*
+ * Perform server resolution where the results are expected to
+ * come in strict order.
+ */
+static int test_resolve(const char *title,
+			pj_pool_t *pool,
+			pjsip_transport_type_e type,
+			char *name,
+			int port,
+			pjsip_server_addresses *ref)
+{
+    pjsip_host_info dest;
+    struct result result;
+
+    PJ_LOG(3,(THIS_FILE, " test_resolve(): %s", title));
+
+    dest.type = type;
+    dest.flag = pjsip_transport_get_flag_from_type(type);
+    dest.addr.host = pj_str(name);
+    dest.addr.port = port;
+
+    result.status = 0x12345678;
+
+    pjsip_endpt_resolve(endpt, pool, &dest, &result, &cb);
+
+    while (result.status == 0x12345678) {
+	int i = 0;
+	pj_time_val timeout = { 1, 0 };
+	pjsip_endpt_handle_events(endpt, &timeout);
+	if (i == 1)
+	    pj_dns_resolver_dump(pjsip_endpt_get_resolver(endpt), PJ_TRUE);
+    }
+
+    if (result.status != PJ_SUCCESS) {
+	app_perror("  pjsip_endpt_resolve() error", result.status);
+	return result.status;
+    }
+
+    if (ref) {
+	unsigned i;
+
+	if (ref->count != result.servers.count) {
+	    PJ_LOG(3,(THIS_FILE, "  test_resolve() error 10: result count mismatch"));
+	    return 10;
+	}
+	
+	for (i=0; i<ref->count; ++i) {
+	    pj_sockaddr_in *ra = (pj_sockaddr_in *)&ref->entry[i].addr;
+	    pj_sockaddr_in *rb = (pj_sockaddr_in *)&result.servers.entry[i].addr;
+
+	    if (ra->sin_addr.s_addr != rb->sin_addr.s_addr) {
+		PJ_LOG(3,(THIS_FILE, "  test_resolve() error 20: IP address mismatch"));
+		return 20;
+	    }
+	    if (ra->sin_port != rb->sin_port) {
+		PJ_LOG(3,(THIS_FILE, "  test_resolve() error 30: port mismatch"));
+		return 30;
+	    }
+	    if (ref->entry[i].addr_len != result.servers.entry[i].addr_len) {
+		PJ_LOG(3,(THIS_FILE, "  test_resolve() error 40: addr_len mismatch"));
+		return 40;
+	    }
+	    if (ref->entry[i].type != result.servers.entry[i].type) {
+		PJ_LOG(3,(THIS_FILE, "  test_resolve() error 50: transport type mismatch"));
+		return 50;
+	    }
+	}
+    }
+
+    return PJ_SUCCESS;
+}
+
+/*
+ * Perform round-robin/load balance test.
+ */
+static int round_robin_test(pj_pool_t *pool)
+{
+    enum { COUNT = 400, PCT_ALLOWANCE = 5 };
+    unsigned i;
+    struct server_hit
+    {
+	char *ip_addr;
+	unsigned percent;
+	unsigned hits;
+    } server_hit[] =
+    {
+	{ "1.1.1.1", 3,  0 },
+	{ "2.2.2.2", 65, 0 },
+	{ "3.3.3.3", 32, 0 },
+	{ "4.4.4.4", 0,  0 }
+    };
+
+    PJ_LOG(3,(THIS_FILE, " Performing round-robin/load-balance test.."));
+
+    /* Do multiple resolve request to "example.com".
+     * The resolver should select the server based on the weight proportion
+     * the the servers in the SRV entry.
+     */
+    for (i=0; i<COUNT; ++i) {
+	pjsip_host_info dest;
+	struct result result;
+	unsigned j;
+
+	dest.type = PJSIP_TRANSPORT_UDP;
+	dest.flag = pjsip_transport_get_flag_from_type(PJSIP_TRANSPORT_UDP);
+	dest.addr.host = pj_str("example.com");
+	dest.addr.port = 0;
+
+	result.status = 0x12345678;
+
+	pjsip_endpt_resolve(endpt, pool, &dest, &result, &cb);
+
+	while (result.status == 0x12345678) {
+	    int i = 0;
+	    pj_time_val timeout = { 1, 0 };
+	    pjsip_endpt_handle_events(endpt, &timeout);
+	    if (i == 1)
+		pj_dns_resolver_dump(pjsip_endpt_get_resolver(endpt), PJ_TRUE);
+	}
+
+	/* Find which server was "hit" */
+	for (j=0; j<PJ_ARRAY_SIZE(server_hit); ++j) {
+	    pj_str_t tmp;
+	    pj_in_addr a1;
+	    pj_sockaddr_in *a2;
+
+	    tmp = pj_str(server_hit[j].ip_addr);
+	    a1 = pj_inet_addr(&tmp);
+	    a2 = (pj_sockaddr_in*) &result.servers.entry[0].addr;
+
+	    if (a1.s_addr == a2->sin_addr.s_addr) {
+		server_hit[j].hits++;
+		break;
+	    }
+	}
+
+	if (j == PJ_ARRAY_SIZE(server_hit)) {
+	    PJ_LOG(1,(THIS_FILE, "..round_robin_test() error 10: returned address mismatch"));
+	    return 10;
+	}
+    }
+
+    /* Print the actual hit rate */
+    for (i=0; i<PJ_ARRAY_SIZE(server_hit); ++i) {
+	PJ_LOG(3,(THIS_FILE, " ..Server %s: weight=%d%%, hit %d%% times",
+		  server_hit[i].ip_addr, server_hit[i].percent,
+		  (server_hit[i].hits * 100) / COUNT));
+    }
+
+    /* Compare the actual hit with the weight proportion */
+    for (i=0; i<PJ_ARRAY_SIZE(server_hit); ++i) {
+	int actual_pct = (server_hit[i].hits * 100) / COUNT;
+
+	if (actual_pct + PCT_ALLOWANCE < (int)server_hit[i].percent ||
+	    actual_pct - PCT_ALLOWANCE > (int)server_hit[i].percent)
+	{
+	    PJ_LOG(1,(THIS_FILE, 
+		      "..round_robin_test() error 20: "
+		      "hit rate difference for server %s (%d%%) is more than "
+		      "tolerable allowance (%d%%)",
+		      server_hit[i].ip_addr, 
+		      actual_pct - server_hit[i].percent, 
+		      PCT_ALLOWANCE));
+	    return 20;
+	}
+    }
+
+    PJ_LOG(3,(THIS_FILE, 
+	      " Load balance test success, hit-rate is "
+	      "within %d%% allowance", PCT_ALLOWANCE));
+    return PJ_SUCCESS;
+}
+
+
+#define C(expr)	    status = expr; \
+		    if (status != PJ_SUCCESS) app_perror(THIS_FILE, "Error", status);
+
+static void add_ref(pjsip_server_addresses *r,
+		    pjsip_transport_type_e type,
+		    char *addr,
+		    int port)
+{
+    pj_sockaddr_in *a;
+    pj_str_t tmp;
+
+    r->entry[r->count].type = type;
+    r->entry[r->count].priority = 0;
+    r->entry[r->count].weight = 0;
+    r->entry[r->count].addr_len = sizeof(pj_sockaddr_in);
+
+    a = (pj_sockaddr_in *)&r->entry[r->count].addr;
+    a->sin_family = PJ_AF_INET;
+    tmp = pj_str(addr);
+    a->sin_addr = pj_inet_addr(&tmp);
+    a->sin_port = pj_htons((pj_uint16_t)port);
+
+    r->count++;
+}
+
+static void create_ref(pjsip_server_addresses *r,
+		       pjsip_transport_type_e type,
+		       char *addr,
+		       int port)
+{
+    r->count = 0;
+    add_ref(r, type, addr, port);
+}
+
+
+/*
+ * Main test entry.
+ */
+int resolve_test(void)
+{
+    pj_pool_t *pool;
+    pj_dns_resolver *resv;
+    pj_str_t nameserver;
+    pj_uint16_t port = 5353;
+    pj_status_t status;
+
+    pool = pjsip_endpt_create_pool(endpt, NULL, 4000, 4000);
+
+    status = pjsip_endpt_create_resolver(endpt, &resv);
+
+    nameserver = pj_str("192.168.0.106");
+    pj_dns_resolver_set_ns(resv, 1, &nameserver, &port);
+    pjsip_endpt_set_resolver(endpt, resv);
+
+    add_dns_entries(resv);
+
+    /* These all should be resolved as IP addresses (DNS A query) */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_UDP, "1.1.1.1", 5060);
+	status = test_resolve("IP address without transport and port", pool, PJSIP_TRANSPORT_UNSPECIFIED, "1.1.1.1", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -100;
+    }
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_UDP, "1.1.1.1", 5060);
+	status = test_resolve("IP address with explicit port", pool, PJSIP_TRANSPORT_UNSPECIFIED, "1.1.1.1", 5060, &ref);
+	if (status != PJ_SUCCESS)
+	    return -110;
+    }
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_TCP, "1.1.1.1", 5060);
+	status = test_resolve("IP address without port (TCP)", pool, PJSIP_TRANSPORT_TCP,"1.1.1.1", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -120;
+    }
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_TLS, "1.1.1.1", 5061);
+	status = test_resolve("IP address without port (TLS)", pool, PJSIP_TRANSPORT_TLS, "1.1.1.1", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -130;
+    }
+
+    /* This should be resolved as DNS A record (because port is present) */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_UDP, "5.5.5.5", 5060);
+	status = test_resolve("domain name with port should resolve to A record", pool, PJSIP_TRANSPORT_UNSPECIFIED, "example.com", 5060, &ref);
+	if (status != PJ_SUCCESS)
+	    return -140;
+    }
+
+    /* This will fail to be resolved as SRV, resolver should fallback to 
+     * resolving to A record.
+     */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_UDP, "2.2.2.2", 5060);
+	status = test_resolve("failure with SRV fallback to A record", pool, PJSIP_TRANSPORT_UNSPECIFIED, "sip02.example.com", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -150;
+    }
+
+    /* Same as above, but explicitly for TLS. */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_TLS, "2.2.2.2", 5061);
+	status = test_resolve("failure with SRV fallback to A record (for TLS)", pool, PJSIP_TRANSPORT_TLS, "sip02.example.com", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -150;
+    }
+
+    /* Standard DNS SRV followed by A recolution */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_UDP, "6.6.6.6", 50060);
+	status = test_resolve("standard SRV resolution", pool, PJSIP_TRANSPORT_UNSPECIFIED, "domain.com", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -155;
+    }
+
+    /* Standard DNS SRV followed by A recolution (explicit transport) */
+    {
+	pjsip_server_addresses ref;
+	create_ref(&ref, PJSIP_TRANSPORT_TCP, "6.6.6.6", 50060);
+	add_ref(&ref, PJSIP_TRANSPORT_TCP, "7.7.7.7", 50060);
+	status = test_resolve("standard SRV resolution with explicit transport (TCP)", pool, PJSIP_TRANSPORT_TCP, "domain.com", 0, &ref);
+	if (status != PJ_SUCCESS)
+	    return -160;
+    }
+
+
+    /* Round robin/load balance test */
+    if (round_robin_test(pool) != 0)
+	return -170;
+
+    /* Timeout test */
+    {
+	status = test_resolve("timeout test", pool, PJSIP_TRANSPORT_UNSPECIFIED, "an.invalid.address", 0, NULL);
+	if (status == PJ_SUCCESS)
+	    return -150;
+    }
+
+    return 0;
+}
+
diff --git a/pjsip/src/test-pjsip/test.c b/pjsip/src/test-pjsip/test.c
index 502f049b..c7566bb2 100644
--- a/pjsip/src/test-pjsip/test.c
+++ b/pjsip/src/test-pjsip/test.c
@@ -20,6 +20,7 @@
 
 #include "test.h"
 #include <pjlib.h>
+#include <pjlib-util.h>
 #include <pjsip.h>
 
 #define THIS_FILE   "test.c"
@@ -240,6 +241,11 @@ int test_main(void)
 	return rc;
     }
 
+    if ((rc=pjlib_util_init()) != PJ_SUCCESS) {
+	app_perror("pj_init", rc);
+	return rc;
+    }
+
     status = init_report();
     if (status != PJ_SUCCESS)
 	return status;
@@ -311,6 +317,10 @@ int test_main(void)
     DO_TEST(transport_tcp_test());
 #endif
 
+#if INCLUDE_RESOLVE_TEST
+    DO_TEST(resolve_test());
+#endif
+
 
 #if INCLUDE_TSX_TEST
     status = pjsip_udp_transport_start(endpt, NULL, NULL, 1,  &tp);
diff --git a/pjsip/src/test-pjsip/test.h b/pjsip/src/test-pjsip/test.h
index fc0901c1..bc8db5e4 100644
--- a/pjsip/src/test-pjsip/test.h
+++ b/pjsip/src/test-pjsip/test.h
@@ -38,7 +38,7 @@ extern pjsip_endpoint *endpt;
 
 #define INCLUDE_MESSAGING_GROUP	    0
 #define INCLUDE_TRANSPORT_GROUP	    0
-#define INCLUDE_TSX_GROUP	    1
+#define INCLUDE_TSX_GROUP	    0
 
 /*
  * Include tests that normally would fail under certain gcc
@@ -56,6 +56,7 @@ extern pjsip_endpoint *endpt;
 #define INCLUDE_UDP_TEST	INCLUDE_TRANSPORT_GROUP
 #define INCLUDE_LOOP_TEST	INCLUDE_TRANSPORT_GROUP
 #define INCLUDE_TCP_TEST	INCLUDE_TRANSPORT_GROUP
+#define INCLUDE_RESOLVE_TEST	1
 #define INCLUDE_TSX_TEST	INCLUDE_TSX_GROUP
 
 
@@ -69,6 +70,7 @@ int tsx_bench(void);
 int transport_udp_test(void);
 int transport_loop_test(void);
 int transport_tcp_test(void);
+int resolve_test(void);
 
 struct tsx_test_param
 {