Async SIP Routing with Kamailio and Node.js

Async SIP Routing with Kamailio and Node.js

Node.js-based external routing decision engine for Kamailio.

Overview

The aim is to show how to leverage evapi module to retrieve JSON-formatted routing information from external source, respectively a node.js application.

The module rtjson defines a format for JSON document that makes it straightforward to push new destinations for a SIP request. The module jansson is used to parse the JSON document in kamailio.cfg for fetching additional attributes that are relevant for processing.

SIP Routing

The routing JSON document format specified by the module rtjson allows SIP serial or parallel forking. The addresses for next hops are going to be computed by the node.js application, in this tutorial they are statically set, but they can be retrieved from a database system.

Serial and parallel forking are the basic mechanisms for forwarding SIP traffic:

serial forking - try several destinations one after the other, waiting for a final response on each try, stopping when one answered with 200ok or there is no other destination to try
parallel forking - try several destinations at once, stopping when one answered with 200ok and cancelling the other active branches, or when all branches responded with a negative response.

Leveraging the two routing mechanisms, one can implement various routing engine such as load balancer, least cost routing, group hunting, call forwarding (on no answer, busy, etc.). Kamailio has dedicated modules (e.g., dispatcher, lcr, …) to provide those features, but sometimes the logic behind deciding what is the best route to follow might not match existing components. Writing an application in nodejs might be faster or better integrated in the overall environment (e.g., when dealing with multiple nodes), than writing a new module in C. Obviously, the code written in C is always expected to run faster.

The tutorial here is aiming to offer a basic example, which should help building more complex external applications for deciding the SIP routing to be performed by Kamailio.

RTJSON Routing Document

The structure for RTJSON routing document is detailed at:

RTJSON Readme - Document Structure

Next is a partial example, with the attributes for one destination:

{
 "version": "1.0",
 "routing": "serial",
 "routes":
  [
   {
     "uri": "sip:127.0.0.1:5080",
     "dst_uri": "sip:127.0.0.1:5082",
     "path": "<sip:127.0.0.1:5084>, <sip:127.0.0.1:5086>",
     "socket": "udp:127.0.0.1:5060",
     "headers": {
       "from": {
         "display": "Alice",
         "uri": "sip:alice@wonderland.com"
       },
       "to": {
         "display": "Bob",
         "uri": "sip:bob@wonderland.com"
       },
       "extra": "X-Hdr-A: abc\r\nX-Hdr-B: bcd\r\n"
     },
     "branch_flags": 8,
     "fr_timer": 5000,
     "fr_inv_timer": 30000
   },
...
  ]
}

The routing field specify if Kamailio has to do serial or parallel forking. After that, the relevant routing information is an array of destinations stored in routes field.

Each destination corresponds to a SIP branch that is going to be created by Kamailio. For each branch can be specified values to set:

request uri
outbound proxy address (dst uri)
display name and uri for From/To headers
extra headers
retransmission and ringing timeouts
local socket or the path to be followed
branch flags

The example above results in: the request will be routed to sip:127.0.0.1:5080, via sip:127.0.0.1:5082, sip:127.0.0.1:5084, sip:127.0.0.1:5086; it will be sent using local socket udp:127.0.0.1:5060; From header display name will be set to Alice and From URI to sip:alice@wonderland.com; To header display name will be set to Bob and To URI to sip:alice@wonderland.com; branch flags will be updated with 8; retransmission will be done for 5000 milliseconds, waiting 30000 milliseconds while ringing.

EVAPI Processing

EVAPI is sort of generic framework to push events to external application from inside kamailio.cfg via TCP connections. It has the capability of suspending the processing of the SIP request until there is a response from the external application. By suspending the SIP request, other SIP messages can be processes, thus not blocking Kamailio while waiting for event response. This asynchronous mechanism enables high throughput for SIP routing.

Presentations

The presentation at Cluecon 2015 by Daniel-Constantin Mierla includes content about this tutorial:

Kamailio Config File

The tutorial should be used with Kamailio v4.3.1 or newer. The starting point is kamailio-basic.cfg, a simplified version of default kamailio.cfg, which is included in the installation from sources or packages and it is located in the same directory as kamailio.cfg.

To install Kamailio, you can use the tutorial available at:

http://www.kamailio.org/wiki/

To be easy to track changes, some parts that are no longer needed are still left in kamailio.cfg, being just inactive.

The main concepts and changes are:

load evapi, jansson and rtjson modules
instead of routing to location service, request routing information from external application via evapi
add the routing blocks specific for evapi module
use jansson to investigate returned JSON document and take decision of what to do

Config Diff

The diff of the config file comparing with the default one:

kamailio-config.diff

--- kamailio-basic.cfg	2015-04-30 23:40:40.104096323 +0200
+++ kamailio-evapi-nodejs.cfg	2015-07-28 11:15:04.946928692 +0200
@@ -187,6 +187,10 @@
 loadmodule "debugger.so"
 #!endif
 
+loadmodule "evapi.so"
+loadmodule "jansson.so"
+loadmodule "rtjson.so"
+
 # ----------------- setting module-specific parameters ---------------
 
 
@@ -303,6 +307,10 @@
 modparam("debugger", "cfgtrace", 1)
 #!endif
 
+
+# ----- evapi params -----
+modparam("evapi", "bind_addr", "127.0.0.1:8448")
+
 ####### Routing Logic ########
 
 
@@ -311,6 +319,8 @@
 # - note: this is the same as route { ... }
 request_route {
 
+	sl_send_reply("100", "Trying right now");
+
 	# per request initial checks
 	route(REQINIT);
 
@@ -359,6 +369,9 @@
 	# handle registrations
 	route(REGISTRAR);
 
+	route(TOEVAPI);
+	exit;
+
 	if ($rU==$null) {
 		# request with no Username in RURI
 		sl_send_reply("484","Address Incomplete");
@@ -612,6 +625,7 @@
 # Manage outgoing branches
 branch_route[MANAGE_BRANCH] {
 	xdbg("new branch [$T_branch_idx] to $ru\n");
+	rtjson_update_branch();	
 	route(NATMANAGE);
 }
 
@@ -629,4 +643,62 @@
 	if (t_is_canceled()) {
 		exit;
 	}
+
+	if(rtjson_next_route()) {
+		t_on_branch("MANAGE_BRANCH");
+		t_on_failure("MANAGE_FAILURE");
+		route(RELAY);
+		exit;
+	}
+}
+
+event_route[evapi:connection-new] {
+	xlog("new connection from [$evapi(srcaddr):$evapi(srcport)]\n");
+	if($evapi(srcaddr)!="127.0.0.1") {
+		evapi_close();
+		exit;
+	}
+}
+
+event_route[evapi:connection-closed] {
+    xlog("connection closed by $evapi(srcaddr):$evapi(srcport)\n");
+}
+
+event_route[evapi:message-received] {
+    xlog("received [$evapi(msg)] from $evapi(srcaddr):$evapi(srcport)\n");
+    if($evapi(msg)=~"routing" && $evapi(msg)=~"tindex") {
+		jansson_get("xtra.tindex", "$evapi(msg)", "$var(tindex)");
+		jansson_get("xtra.tlabel", "$evapi(msg)", "$var(tlabel)");
+		$var(evmsg) = $evapi(msg);
+		xlog("L_INFO", "preparing to resume transaction for processing: $var(tindex) / $var(tlabel)\n");
+		t_continue("$var(tindex)", "$var(tlabel)", "EVAPIRESPONSE");
+    }
+}
+
+route[EVAPIRESPONSE] {
+	xlog("L_INFO", "resumed transaction for processing: $T(id_index) / $T(id_label)\n");
+	#if($var(evmsg)=~"location") {
+	#	send_reply("404", "No location yet");
+	#	exit;
+	#}
+	jansson_get("routing", "$var(evmsg)", "$var(routing)");
+	if($var(routing)=="location") {
+		route(LOCATION);
+		exit;
+	}
+	rtjson_init_routes("$var(evmsg)");
+	rtjson_push_routes();
+	t_on_branch("MANAGE_BRANCH");
+	t_on_failure("MANAGE_FAILURE");
+	route(RELAY);
+	exit;
+}
+
+route[TOEVAPI] {
+	evapi_async_relay("{\n \"event\": \"sip-routing\",\n"
+		" \"tindex\": $T(id_index), \"tlabel\": $T(id_label),"
+		" \"caller\": \"$fU\", \"callee\": \"$rU\"\n}");
+
+	xlog("L_INFO", "suspended transaction: $T(id_index) / $T(id_label)\n");
+	exit;
 }

Full Config

The full config file is:

kamailio.cfg

#!KAMAILIO
#
# Kamailio (OpenSER) SIP Server v4.3 - default configuration script
#     - web: http://www.kamailio.org
#     - git: http://sip-router.org
#
# Direct your questions about this file to: <sr-users@lists.sip-router.org>
#
# Refer to the Core CookBook at http://www.kamailio.org/wiki/
# for an explanation of possible statements, functions and parameters.
#
# Several features can be enabled using '#!define WITH_FEATURE' directives:
#
# *** To run in debug mode: 
#     - define WITH_DEBUG
#
# *** To enable mysql: 
#     - define WITH_MYSQL
#
# *** To enable authentication execute:
#     - enable mysql
#     - define WITH_AUTH
#     - add users using 'kamctl'
#
# *** To enable IP authentication execute:
#     - enable mysql
#     - enable authentication
#     - define WITH_IPAUTH
#     - add IP addresses with group id '1' to 'address' table
#
# *** To enable persistent user location execute:
#     - enable mysql
#     - define WITH_USRLOCDB
#
# *** To enable nat traversal execute:
#     - define WITH_NAT
#     - install RTPProxy: http://www.rtpproxy.org
#     - start RTPProxy:
#        rtpproxy -l _your_public_ip_ -s udp:localhost:7722
#     - option for NAT SIP OPTIONS keepalives: WITH_NATSIPPING
#
# *** To enable TLS support execute:
#     - adjust CFGDIR/tls.cfg as needed
#     - define WITH_TLS
#
# *** To enhance accounting execute:
#     - enable mysql
#     - define WITH_ACCDB
#     - add following columns to database
#!ifdef ACCDB_COMMENT
  ALTER TABLE acc ADD COLUMN src_user VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE acc ADD COLUMN src_domain VARCHAR(128) NOT NULL DEFAULT '';
  ALTER TABLE acc ADD COLUMN src_ip varchar(64) NOT NULL default '';
  ALTER TABLE acc ADD COLUMN dst_ouser VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE acc ADD COLUMN dst_user VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE acc ADD COLUMN dst_domain VARCHAR(128) NOT NULL DEFAULT '';
  ALTER TABLE missed_calls ADD COLUMN src_user VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE missed_calls ADD COLUMN src_domain VARCHAR(128) NOT NULL DEFAULT '';
  ALTER TABLE missed_calls ADD COLUMN src_ip varchar(64) NOT NULL default '';
  ALTER TABLE missed_calls ADD COLUMN dst_ouser VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE missed_calls ADD COLUMN dst_user VARCHAR(64) NOT NULL DEFAULT '';
  ALTER TABLE missed_calls ADD COLUMN dst_domain VARCHAR(128) NOT NULL DEFAULT '';
#!endif
 
####### Include Local Config If Exists #########
import_file "kamailio-local.cfg"
 
####### Defined Values #########
 
# *** Value defines - IDs used later in config
#!ifdef WITH_MYSQL
# - database URL - used to connect to database server by modules such
#       as: auth_db, acc, usrloc, a.s.o.
#!ifndef DBURL
#!define DBURL "mysql://kamailio:kamailiorw@localhost/kamailio"
#!endif
#!endif
#!define MULTIDOMAIN 0
 
# - flags
#   FLT_ - per transaction (message) flags
#	FLB_ - per branch flags
#!define FLT_ACC 1
#!define FLT_ACCMISSED 2
#!define FLT_ACCFAILED 3
#!define FLT_NATS 5
 
#!define FLB_NATB 6
#!define FLB_NATSIPPING 7
 
####### Global Parameters #########
 
### LOG Levels: 3=DBG, 2=INFO, 1=NOTICE, 0=WARN, -1=ERR
#!ifdef WITH_DEBUG
debug=4
log_stderror=yes
#!else
debug=2
log_stderror=no
#!endif
 
memdbg=5
memlog=5
 
log_facility=LOG_LOCAL0
 
fork=yes
children=4
 
/* uncomment the next line to disable TCP (default on) */
#disable_tcp=yes
 
/* uncomment the next line to disable the auto discovery of local aliases
   based on reverse DNS on IPs (default on) */
#auto_aliases=no
 
/* add local domain aliases */
#alias="sip.mydomain.com"
 
/* uncomment and configure the following line if you want Kamailio to 
   bind on a specific interface/port/proto (default bind on all available) */
#listen=udp:10.0.0.10:5060
 
/* port to listen to
 * - can be specified more than once if needed to listen on many ports */
port=5060
 
#!ifdef WITH_TLS
enable_tls=yes
#!endif
 
# life time of TCP connection when there is no traffic
# - a bit higher than registration expires to cope with UA behind NAT
tcp_connection_lifetime=3605
 
####### Modules Section ########
 
# set paths to location of modules (to sources or installation folders)
#!ifdef WITH_SRCPATH
mpath="modules"
#!else
mpath="/usr/local/lib/kamailio/modules/"
#!endif
 
#!ifdef WITH_MYSQL
loadmodule "db_mysql.so"
#!endif
 
loadmodule "mi_fifo.so"
loadmodule "kex.so"
loadmodule "corex.so"
loadmodule "tm.so"
loadmodule "tmx.so"
loadmodule "sl.so"
loadmodule "rr.so"
loadmodule "pv.so"
loadmodule "maxfwd.so"
loadmodule "usrloc.so"
loadmodule "registrar.so"
loadmodule "textops.so"
loadmodule "siputils.so"
loadmodule "xlog.so"
loadmodule "sanity.so"
loadmodule "ctl.so"
loadmodule "cfg_rpc.so"
loadmodule "mi_rpc.so"
loadmodule "acc.so"
 
#!ifdef WITH_AUTH
loadmodule "auth.so"
loadmodule "auth_db.so"
#!ifdef WITH_IPAUTH
loadmodule "permissions.so"
#!endif
#!endif
 
#!ifdef WITH_NAT
loadmodule "nathelper.so"
loadmodule "rtpproxy.so"
#!endif
 
#!ifdef WITH_TLS
loadmodule "tls.so"
#!endif
 
#!ifdef WITH_DEBUG
loadmodule "debugger.so"
#!endif
 
loadmodule "evapi.so"
loadmodule "jansson.so"
loadmodule "rtjson.so"
 
# ----------------- setting module-specific parameters ---------------
 
 
# ----- mi_fifo params -----
#modparam("mi_fifo", "fifo_name", "/var/run/kamailio/kamailio_fifo")
 
# ----- ctl params -----
#modparam("ctl", "binrpc", "unix:/var/run/kamailio/kamailio_ctl")
 
# ----- tm params -----
# auto-discard branches from previous serial forking leg
modparam("tm", "failure_reply_mode", 3)
# default retransmission timeout: 30sec
modparam("tm", "fr_timer", 30000)
# default invite retransmission timeout after 1xx: 120sec
modparam("tm", "fr_inv_timer", 120000)
 
 
# ----- rr params -----
# add value to ;lr param to cope with most of the UAs
modparam("rr", "enable_full_lr", 1)
# do not append from tag to the RR (no need for this script)
modparam("rr", "append_fromtag", 0)
 
 
# ----- registrar params -----
modparam("registrar", "method_filtering", 1)
/* uncomment the next line to disable parallel forking via location */
# modparam("registrar", "append_branches", 0)
/* uncomment the next line not to allow more than 10 contacts per AOR */
#modparam("registrar", "max_contacts", 10)
# max value for expires of registrations
modparam("registrar", "max_expires", 3600)
# set it to 1 to enable GRUU
modparam("registrar", "gruu_enabled", 0)
 
 
# ----- acc params -----
/* what special events should be accounted ? */
modparam("acc", "early_media", 0)
modparam("acc", "report_ack", 0)
modparam("acc", "report_cancels", 0)
/* by default ww do not adjust the direct of the sequential requests.
   if you enable this parameter, be sure the enable "append_fromtag"
   in "rr" module */
modparam("acc", "detect_direction", 0)
/* account triggers (flags) */
modparam("acc", "log_flag", FLT_ACC)
modparam("acc", "log_missed_flag", FLT_ACCMISSED)
modparam("acc", "log_extra", 
	"src_user=$fU;src_domain=$fd;src_ip=$si;"
	"dst_ouser=$tU;dst_user=$rU;dst_domain=$rd")
modparam("acc", "failed_transaction_flag", FLT_ACCFAILED)
/* enhanced DB accounting */
#!ifdef WITH_ACCDB
modparam("acc", "db_flag", FLT_ACC)
modparam("acc", "db_missed_flag", FLT_ACCMISSED)
modparam("acc", "db_url", DBURL)
modparam("acc", "db_extra",
	"src_user=$fU;src_domain=$fd;src_ip=$si;"
	"dst_ouser=$tU;dst_user=$rU;dst_domain=$rd")
#!endif
 
 
# ----- usrloc params -----
/* enable DB persistency for location entries */
#!ifdef WITH_USRLOCDB
modparam("usrloc", "db_url", DBURL)
modparam("usrloc", "db_mode", 2)
modparam("usrloc", "use_domain", MULTIDOMAIN)
#!endif
 
 
# ----- auth_db params -----
#!ifdef WITH_AUTH
modparam("auth_db", "db_url", DBURL)
modparam("auth_db", "calculate_ha1", yes)
modparam("auth_db", "password_column", "password")
modparam("auth_db", "load_credentials", "")
modparam("auth_db", "use_domain", MULTIDOMAIN)
 
# ----- permissions params -----
#!ifdef WITH_IPAUTH
modparam("permissions", "db_url", DBURL)
modparam("permissions", "db_mode", 1)
#!endif
 
#!endif
 
 
#!ifdef WITH_NAT
# ----- rtpproxy params -----
modparam("rtpproxy", "rtpproxy_sock", "udp:127.0.0.1:7722")
 
# ----- nathelper params -----
modparam("nathelper", "natping_interval", 30)
modparam("nathelper", "ping_nated_only", 1)
modparam("nathelper", "sipping_bflag", FLB_NATSIPPING)
modparam("nathelper", "sipping_from", "sip:pinger@kamailio.org")
 
# params needed for NAT traversal in other modules
modparam("nathelper|registrar", "received_avp", "$avp(RECEIVED)")
modparam("usrloc", "nat_bflag", FLB_NATB)
#!endif
 
 
#!ifdef WITH_TLS
# ----- tls params -----
modparam("tls", "config", "/usr/local/etc/kamailio/tls.cfg")
#!endif
 
#!ifdef WITH_DEBUG
# ----- debugger params -----
modparam("debugger", "cfgtrace", 1)
#!endif
 
 
# ----- evapi params -----
modparam("evapi", "bind_addr", "127.0.0.1:8448")
 
####### Routing Logic ########
 
 
# Main SIP request routing logic
# - processing of any incoming SIP request starts with this route
# - note: this is the same as route { ... }
request_route {
 
	sl_send_reply("100", "Trying right now");
 
	# per request initial checks
	route(REQINIT);
 
	# NAT detection
	route(NATDETECT);
 
	# CANCEL processing
	if (is_method("CANCEL")) {
		if (t_check_trans()) {
			route(RELAY);
		}
		exit;
	}
 
	# handle requests within SIP dialogs
	route(WITHINDLG);
 
	### only initial requests (no To tag)
 
	# handle retransmissions
	if(t_precheck_trans()) {
		t_check_trans();
		exit;
	}
	t_check_trans();
 
	# authentication
	route(AUTH);
 
	# record routing for dialog forming requests (in case they are routed)
	# - remove preloaded route headers
	remove_hf("Route");
	if (is_method("INVITE|SUBSCRIBE"))
		record_route();
 
	# account only INVITEs
	if (is_method("INVITE")) {
		setflag(FLT_ACC); # do accounting
	}
 
	# dispatch requests to foreign domains
	route(SIPOUT);
 
	### requests for my local domains
 
	# handle registrations
	route(REGISTRAR);
 
	route(TOEVAPI);
	exit;
 
	if ($rU==$null) {
		# request with no Username in RURI
		sl_send_reply("484","Address Incomplete");
		exit;
	}
 
	# user location service
	route(LOCATION);
}
 
 
route[RELAY] {
	# enable additional event routes for forwarded requests
	# - serial forking, RTP relaying handling, a.s.o.
	if (is_method("INVITE|BYE|SUBSCRIBE|UPDATE")) {
		if(!t_is_set("branch_route")) t_on_branch("MANAGE_BRANCH");
	}
	if (is_method("INVITE|SUBSCRIBE|UPDATE")) {
		if(!t_is_set("onreply_route")) t_on_reply("MANAGE_REPLY");
	}
	if (is_method("INVITE")) {
		if(!t_is_set("failure_route")) t_on_failure("MANAGE_FAILURE");
	}
 
	if (!t_relay()) {
		sl_reply_error();
	}
	exit;
}
 
# Per SIP request initial checks
route[REQINIT] {
#!ifdef WITH_ANTIFLOOD
	# flood dection from same IP and traffic ban for a while
	# be sure you exclude checking trusted peers, such as pstn gateways
	# - local host excluded (e.g., loop to self)
	if(src_ip!=myself) {
		if($sht(ipban=>$si)!=$null) {
			# ip is already blocked
			xdbg("request from blocked IP - $rm from $fu (IP:$si:$sp)\n");
			exit;
		}
		if (!pike_check_req()) {
			xlog("L_ALERT","ALERT: pike blocking $rm from $fu (IP:$si:$sp)\n");
			$sht(ipban=>$si) = 1;
			exit;
		}
	}
	if($ua =~ "friendly-scanner") {
		sl_send_reply("200", "OK");
		exit;
	}
#!endif
 
	if (!mf_process_maxfwd_header("10")) {
		sl_send_reply("483","Too Many Hops");
		exit;
	}
 
	if(is_method("OPTIONS") && uri==myself && $rU==$null) {
		sl_send_reply("200","Keepalive");
		exit;
	}
 
	if(!sanity_check("1511", "7")) {
		xlog("Malformed SIP message from $si:$sp\n");
		exit;
	}
}
 
# Handle requests within SIP dialogs
route[WITHINDLG] {
	if (!has_totag()) return;
 
	# sequential request withing a dialog should
	# take the path determined by record-routing
	if (loose_route()) {
		route(DLGURI);
		if (is_method("BYE")) {
			setflag(FLT_ACC); # do accounting ...
			setflag(FLT_ACCFAILED); # ... even if the transaction fails
		}
		else if ( is_method("ACK") ) {
			# ACK is forwarded statelessy
			route(NATMANAGE);
		}
		else if ( is_method("NOTIFY") ) {
			# Add Record-Route for in-dialog NOTIFY as per RFC 6665.
			record_route();
		}
		route(RELAY);
		exit;
	}
	if ( is_method("ACK") ) {
		if ( t_check_trans() ) {
			# no loose-route, but stateful ACK;
			# must be an ACK after a 487
			# or e.g. 404 from upstream server
			route(RELAY);
			exit;
		} else {
			# ACK without matching transaction ... ignore and discard
			exit;
		}
	}
	sl_send_reply("404", "Not here");
	exit;
}
 
# Handle SIP registrations
route[REGISTRAR] {
	if (!is_method("REGISTER")) return;
	if(isflagset(FLT_NATS)) {
		setbflag(FLB_NATB);
#!ifdef WITH_NATSIPPING
		# do SIP NAT pinging
		setbflag(FLB_NATSIPPING);
#!endif
	}
	if (!save("location"))
		sl_reply_error();
 
	exit;
}
 
# User location service
route[LOCATION] {
	if (!lookup("location")) {
		$var(rc) = $rc;
		t_newtran();
		switch ($var(rc)) {
			case -1:
			case -3:
				send_reply("404", "Not Found");
				exit;
			case -2:
				send_reply("405", "Method Not Allowed");
				exit;
		}
	}
 
	# when routing via usrloc, log the missed calls also
	if (is_method("INVITE")) {
		setflag(FLT_ACCMISSED);
	}
 
	route(RELAY);
	exit;
}
 
 
# IP authorization and user uthentication
route[AUTH] {
#!ifdef WITH_AUTH
 
#!ifdef WITH_IPAUTH
	if((!is_method("REGISTER")) && allow_source_address()) {
		# source IP allowed
		return;
	}
#!endif
 
	if (is_method("REGISTER") || from_uri==myself) {
		# authenticate requests
		if (!auth_check("$fd", "subscriber", "1")) {
			auth_challenge("$fd", "0");
			exit;
		}
		# user authenticated - remove auth header
		if(!is_method("REGISTER|PUBLISH"))
			consume_credentials();
	}
	# if caller is not local subscriber, then check if it calls
	# a local destination, otherwise deny, not an open relay here
	if (from_uri!=myself && uri!=myself) {
		sl_send_reply("403","Not relaying");
		exit;
	}
 
#!endif
	return;
}
 
# Caller NAT detection
route[NATDETECT] {
#!ifdef WITH_NAT
	force_rport();
	if (nat_uac_test("19")) {
		if (is_method("REGISTER")) {
			fix_nated_register();
		} else {
			if(is_first_hop())
				set_contact_alias();
		}
		setflag(FLT_NATS);
	}
#!endif
	return;
}
 
# RTPProxy control
route[NATMANAGE] {
#!ifdef WITH_NAT
	if (is_request()) {
		if(has_totag()) {
			if(check_route_param("nat=yes")) {
				setbflag(FLB_NATB);
			}
		}
	}
	if (!(isflagset(FLT_NATS) || isbflagset(FLB_NATB)))
		return;
 
	rtpproxy_manage("co");
 
	if (is_request()) {
		if (!has_totag()) {
			if(t_is_branch_route()) {
				add_rr_param(";nat=yes");
			}
		}
	}
	if (is_reply()) {
		if(isbflagset(FLB_NATB)) {
			set_contact_alias();
		}
	}
#!endif
	return;
}
 
# URI update for dialog requests
route[DLGURI] {
#!ifdef WITH_NAT
	if(!isdsturiset()) {
		handle_ruri_alias();
	}
#!endif
	return;
}
 
# Routing to foreign domains
route[SIPOUT] {
	if (uri==myself) return;
 
	append_hf("P-hint: outbound\r\n");
	route(RELAY);
	exit;
}
 
# Manage outgoing branches
branch_route[MANAGE_BRANCH] {
	xdbg("new branch [$T_branch_idx] to $ru\n");
	rtjson_update_branch();	
	route(NATMANAGE);
}
 
# Manage incoming replies
onreply_route[MANAGE_REPLY] {
	xdbg("incoming reply\n");
	if(status=~"[12][0-9][0-9]")
		route(NATMANAGE);
}
 
# Manage failure routing cases
failure_route[MANAGE_FAILURE] {
	route(NATMANAGE);
 
	if (t_is_canceled()) {
		exit;
	}
 
	if(rtjson_next_route()) {
		t_on_branch("MANAGE_BRANCH");
		t_on_failure("MANAGE_FAILURE");
		route(RELAY);
		exit;
	}
}
 
event_route[evapi:connection-new] {
	xlog("new connection from [$evapi(srcaddr):$evapi(srcport)]\n");
	if($evapi(srcaddr)!="127.0.0.1") {
		evapi_close();
		exit;
	}
}
 
event_route[evapi:connection-closed] {
    xlog("connection closed by $evapi(srcaddr):$evapi(srcport)\n");
}
 
event_route[evapi:message-received] {
    xlog("received [$evapi(msg)] from $evapi(srcaddr):$evapi(srcport)\n");
    if($evapi(msg)=~"routing" && $evapi(msg)=~"tindex") {
		jansson_get("xtra.tindex", "$evapi(msg)", "$var(tindex)");
		jansson_get("xtra.tlabel", "$evapi(msg)", "$var(tlabel)");
		$var(evmsg) = $evapi(msg);
		xlog("L_INFO", "preparing to resume transaction for processing: $var(tindex) / $var(tlabel)\n");
		t_continue("$var(tindex)", "$var(tlabel)", "EVAPIRESPONSE");
    }
}
 
route[EVAPIRESPONSE] {
	xlog("L_INFO", "resumed transaction for processing: $T(id_index) / $T(id_label)\n");
	#if($var(evmsg)=~"location") {
	#	send_reply("404", "No location yet");
	#	exit;
	#}
	jansson_get("routing", "$var(evmsg)", "$var(routing)");
	if($var(routing)=="location") {
		route(LOCATION);
		exit;
	}
	rtjson_init_routes("$var(evmsg)");
	rtjson_push_routes();
	t_on_branch("MANAGE_BRANCH");
	t_on_failure("MANAGE_FAILURE");
	route(RELAY);
	exit;
}
 
route[TOEVAPI] {
	evapi_async_relay("{\n \"event\": \"sip-routing\",\n"
		" \"tindex\": $T(id_index), \"tlabel\": $T(id_label),"
		" \"caller\": \"$fU\", \"callee\": \"$rU\"\n}");
 
	xlog("L_INFO", "suspended transaction: $T(id_index) / $T(id_label)\n");
	exit;
}

Node.js Application

The installation of node.js is documented on the project website:

http://nodejs.org

A simple sample application is shown next example. It connects to Kamailio's EVAPI socket, waiting for messages with json content serialized as netstring. There response will contain two destinations built with static values (sip:127.0.0.1:5080 and sip:127.0.0.1:5090), again serialazed as netstring.

To read more about nestring format, see:

https://en.wikipedia.org/wiki/Netstring

Node.js application:

kanapi.js

var net = require('net');
 
var HOST = '127.0.0.1';
var PORT = 8448;
 
var client = new net.Socket();
 
client.connect(PORT, HOST, function() {
 
	console.log('CONNECTING TO: ' + HOST + ':' + PORT);
 
});
 
client.on('connect', function(data) {
	console.log('CONNECTED TO: ' + HOST + ':' + PORT);
	// Write a message to the socket as soon as the client is connected, the server will receive it as message from the client 
	// client.write('I am the node.js SIP routing engine');
	kanapi_send_response('{ "version": "1.0", "client": "kanapi.js", "akey": "1q2w3e4r" }');
});
 
client.on('error', function(e) {
    if(e.code == 'ECONNREFUSED') {
        console.log('Is the server running at ' + PORT + '?');
 
        setTimeout(function() {
            client.connect(PORT, HOST, function(){
                // console.log('CONNECTING TO: ' + HOST + ':' + PORT + ' (*)');
            });
        }, 4000);
 
        console.log('Timeout for 5 seconds before trying port:' + PORT + ' again');
 
    }   
});
 
// Add a 'data' event handler for the client socket
// data is what the server sent to this socket
client.on('data', function(data) {
 
	console.log('RECEIVED DATA: ' + data);
	kanapi_handle_request(data);
 
	// Close the client socket completely
	// client.destroy();
 
});
 
// Add a 'close' event handler for the client socket
client.on('close', function() {
	console.log('Connection closed');
});
 
function kanapi_handle_request(data) {
    var size, strings, jdoc;
	var re = /^\+?[1-9]\d{1,14}$/;
	var response = {};
 
    size = 0;
    strings = [];
 
    data = new Buffer(data || '', null);
 
    for(var i = 0; i < data.length; i++) {
        var offset, c;
 
        c = data[i];
 
        if (c === 58) {
            offset = i + 1;
            size = parseInt(data.toString(null, size, i));
            strings.push(data.slice(offset, offset + size));
            i += size + 1;
            size += offset + 1;
            continue;
        }
    }
 
    console.log('[' + strings + '] <----: [' + data + ']');
 
	jdoc = JSON.parse(strings);
 
	console.log('json: [' + JSON.stringify(jdoc) + ']');
	if(jdoc.event != 'sip-routing') {
		return kanapi_send_response('{ "version": "1.0", "routing": "none" }');
	}
 
	console.log('caller: [' + jdoc.caller + ']');
	console.log('callee: [' + jdoc.callee + ']');
 
    response.version="1.0";
    response.xtra = {};
    response.xtra.tindex=jdoc.tindex;
    response.xtra.tlabel=jdoc.tlabel;
 
    if(re.test(jdoc.callee)) {
    	// e.164 number - send to gateway
    	response.routing = "serial";
    	//response.routing = "parallel";
    	response.routes = [];
    	response.routes[0] = {};
    	response.routes[0].uri = "sip:127.0.0.1:5080";
    	response.routes[0].headers = {};
    	response.routes[0].headers.extra = "X-Hdr-A: abc\r\nX-Hdr-B: bcd\r\n";
    	response.routes[1] = {};
    	response.routes[1].uri = "sip:127.0.0.1:5090";
    	response.routes[1].headers = {};
    	response.routes[1].headers.extra = "X-Hdr-C: cde\r\nX-Hdr-D: def\r\n";
	} else {
		// expect local extension - send to location
    	response.routing = "location";
	}
	return kanapi_send_response(JSON.stringify(response));
}
 
function kanapi_send_response(data) {
    var buffer;
 
    data = new Buffer(data || '', null);
 
    buffer = Buffer.concat([new Buffer(data.length + ':', null), data, new Buffer(',', null)]);
 
    console.log('[' + data + '] :----> [' + buffer + ']');
 
	client.write(buffer.toString('ascii'));
    return buffer;
}

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