COREX Module

Daniel-Constantin Mierla

Edited by

Daniel-Constantin Mierla

Edited by

Muhammad Shahzad Shafi


Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. alias_subdomains (string)
3.2. network_io_intercept (int)
3.3. min_msg_len (int)
3.4. msg_avp (string)
4. Functions
4.1. append_branch([ uri, [ q ] ])
4.2. send_udp([ host [ :port ] ])
4.3. send_tcp([ host [ :port ] ])
4.4. send_data(uri, data)
4.5. sendx(uri, sock, data)
4.6. is_incoming()
4.7. msg_iflag_set(flagname)
4.8. msg_iflag_reset(flagname)
4.9. msg_iflag_is_set(flagname)
4.10. file_read(fpath, var)
4.11. file_write(fpath, content)
4.12. setxflag(flag)
4.13. isxflagset(flag)
4.14. resetxflag(flag)
4.15. set_send_socket(saddr)
4.16. set_recv_socket(saddr)
4.17. set_source_address(saddr)
4.18. via_add_srvid(flags)
4.19. via_add_xavp_params(flags)
5. RPC Commands
5.1. corex.debug
5.2. corex.list_sockets
5.3. corex.list_aliases
5.4. corex.shm_status
5.5. corex.shm_summary
5.6. corex.pkg_summary
6. Event Routes
6.1. event_route[network:msg]
7. Examples of Usage

List of Examples

1.1. Set alias_subdomains parameter
1.2. Set network_io_intercept parameter
1.3. Set min_msg_len parameter
1.4. Set msg_avp parameter
1.5. append_branch usage
1.6. send_udp usage
1.7. send_tcp usage
1.8. send_data usage
1.9. sendx usage
1.10. is_incoming usage
1.11. msg_iflag_set usage
1.12. msg_iflag_reset usage
1.13. msg_iflag_is_set usage
1.14. file_read usage
1.15. file_write usage
1.16. setxflag usage
1.17. isxflagset usage
1.18. resetxflag usage
1.19. set_send_socket usage
1.20. set_recv_socket usage
1.21. set_source_address usage
1.22. via_add_srvid usage
1.23. via_add_xavp_params usage
1.24. event_route[network:msg] use cases
1.25. Sample PERL code for do_compress and do_uncompress

Chapter 1. Admin Guide

1. Overview

This module provides reimplementation of a few very old functions that used to be in the core and supported only static string or integer parameters. The new versions bring support for dynamic parameters (allowing variables inside the parameters).

There are also brand new features, related to core internals, but controlled from configuration file or via control interfaces.

Contributions to this module must be done under the BSD license, to follow the requirements of the core contributions.

This module now also provides access to network input / output data through event_route[network:msg]. The raw data received from a remote host or about to be sent to a remote host is available in variable $mb. The script writer may manipulate this data and save the final result in an AVP defined by msg_avp module parameter. The content of this AVP will then be processed by SIP worker as normal, i.e. a received message will be parsed and sent to appropriate route block while a sent message is forwarded to remote host.

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • None.

2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

  • None

3. Parameters

3.1. alias_subdomains (string)

Register a domain and all its sub-domains to match the myself condition. It can be set many times. Its full format is: 'proto:domain:port', allowing to set restrictions on protocol and port as well. Protocol and port are optional.

Default value is NULL.

Example 1.1. Set alias_subdomains parameter

...
modparam("corex", "alias_subdomains", "kamailio.org")
modparam("corex", "alias_subdomains", "udp:sip-router.org:5060")
...

3.2. network_io_intercept (int)

If set to non-zero then raw data received from a remote host or about to be sent to a remote host is made available in event_route[network:msg]. The script writer may modify this and save to msg_avp, which will then be processed by SIP worker as normal.

Default value is 0, i.e. do not allow access to network io data.

Example 1.2. Set network_io_intercept parameter

...
modparam("corex", "network_io_intercept", 1)
...

3.3. min_msg_len (int)

Minimum content length of the packet to execute the event_route[network:msg]. This only works if network_io_intercept parameter is set to non-zero.

Default value is 0.

Example 1.3. Set min_msg_len parameter

...
modparam("corex", "min_msg_len", 32)
...

3.4. msg_avp (string)

AVP name to store modified content to be set in the packet. If not set in event_route[network:msg], then all changes are lost and original contents are used. This only works if network_io_intercept parameter is to set non-zero.

Default value is empty.

Example 1.4. Set msg_avp parameter

...
modparam("corex", "msg_avp", "$avp(msg)")
...

4. Functions

4.1.  append_branch([ uri, [ q ] ])

Append a new branch to the destination set, useful to build the set of destination addresses for parallel forking or redirect replies.

Both parameters are optional, If no uri parameter is provided, then the address from request URI (r-uri) is used to build the new branch.

Meaning of the parameters is as follows:

  • uri - SIP address of the branch to be used as R-URI in the outgoing request.

  • q - the Q value to set the priority of the branch based on Contact address specifications

This function can be used from REQUEST_ROUTE or FAILURE_ROUTE.

Example 1.5. append_branch usage

...
    append_branch();
    append_branch("$avp(uri)", "0.5");
...

4.2.  send_udp([ host [ :port ] ])

Send the original SIP message to a specific destination in stateless mode. No changes are applied to received message, no Via header is added. Host can be an IP address or hostname. Port is optional and defaults to 5060. Used protocol: UDP.

The parameter is optional and defaults to the destination URI from the SIP message if left out. Otherwise it's a string parameter (supporting pseudo-variables) in format "hostname" or "hostname:port", where hostname" can also be a numeric IP address.

This function can be used from REQUEST_ROUTE or FAILURE_ROUTE.

Example 1.6. send_udp usage

...
	send_udp();
	send_udp("10.20.15.10");
	send_udp("sip.example.com:5070");
	send_udp("$var(res)");
...

4.3.  send_tcp([ host [ :port ] ])

This function is identical to send_udp() described above, except that it sends the SIP message using the TCP protocol instead of UDP.

Example 1.7. send_tcp usage

...
	send_tcp();
	send_tcp("10.20.15.10");
	send_tcp("sip.example.com:5070");
	send_tcp("$var(res)");
...

4.4.  send_data(uri, data)

Send the data to address specified by uri. Both parameters can contain pseudo-variables. The uri parameter has to be a valid SIP URI. The data parameter can by any arbitrary content.

This function can be used from ANY_ROUTE.

Example 1.8. send_data usage

...
	send_data("sip:example.com:5070;transport=sctp", "Message at $Ts");
...

4.5.  sendx(uri, sock, data)

Send the data to address specified by uri using a specific local socket. All parameters can contain pseudo-variables. The uri parameter has to be a valid SIP URI. The sock parameter has to be a valid socket specifier (like values assigned to $fs). The data parameter can by any arbitrary content.

This function can be used from ANY_ROUTE.

Example 1.9. sendx usage

...
sendx("sip:example.com:5070;transport=sctp", "sctp:2.3.4.5:5060", "Message at $Ts");
...

4.6.  is_incoming()

Returns true if contents of message buffer $mb are the data received from remote host, otherwise false indicating that the contents of $mb are data that is about to be sent out to remote host. This only works if network_io_intercept parameter is set to non-zero.

This function can be used from event_route[network:msg].

Example 1.10. is_incoming usage

...
event_route[network:msg] {
    if (is_incoming()) {
        xlog("L_INFO", "Received message '$mb' \n");
        $avp(msg) = $mb;
    } else {
        xlog("L_INFO", "Sending message '$mb' \n");
        $avp(msg) = $mb;
    };
}
...

4.7.  msg_iflag_set(flagname)

Set internal SIP message flag. The parameter flagname can be: USE_UAC_FROM, USE_UAC_TO or UAC_AUTH.

This functions should not be used in configuration file for (re)setting the internal flags, those are done by various functions internally, however, in very particular cases they might be useful (e.g., changing From/To via textops functions).

This function can be used from ANY_ROUTE.

Example 1.11. msg_iflag_set usage

...
    msg_iflag_set("UAC_AUTH");
...

4.8.  msg_iflag_reset(flagname)

Reset the internal flag given as parameter.

This function can be used from ANY_ROUTE.

Example 1.12. msg_iflag_reset usage

...
    msg_iflag_reset("UAC_AUTH");
...

4.9.  msg_iflag_is_set(flagname)

Test if the internal flag given as parameter is set.

This function can be used from ANY_ROUTE.

Example 1.13. msg_iflag_is_set usage

...
    if(msg_iflag_is_set("UAC_AUTH")) { ... }
...

4.10.  file_read(fpath, var)

Read content of a text file into a variable.

This function can be used from ANY_ROUTE.

Example 1.14. file_read usage

...
if(file_read("/tmp/data.txt", "$var(data)")) { ... }
...

4.11.  file_write(fpath, content)

Write content of parameter to a text file.

This function can be used from ANY_ROUTE.

Example 1.15. file_write usage

...
if(file_write("/tmp/data.txt", "Data is: $var(data)")) { ... }
...

4.12. setxflag(flag)

Set the extended message (transaction) flag.

Meaning of the parameters is as follows:

  • flag - the index of the flag to be set. Can be integer or pseudo-variable with integer value (range 0-63).

This function can be used from ANY_ROUTE.

Example 1.16. setxflag usage

...
setxflag("1");
...
$var(flag) = 11;
setxflag("$var(flag)");
...

4.13. isxflagset(flag)

Return true of the extended message (transaction) flag is set.

Meaning of the parameters is as follows:

  • flag - the index of the flag to be tested. Can be integer or pseudo-variable with integer value (range 0-63).

This function can be used from ANY_ROUTE.

Example 1.17. isxflagset usage

...
if(isxflagset("1"))
{
    ...
}
...

4.14. resetxflag(flag)

Reset the extended message (transaction) flag.

Meaning of the parameters is as follows:

  • flag - the index of the flag to be reset. Can be integer or pseudo-variable with integer value (range 0-63).

This function can be used from ANY_ROUTE.

Example 1.18. resetxflag usage

...
resetxflag("1");
...

4.15. set_send_socket(saddr)

Set the socket for sending out.

Meaning of the parameters is as follows:

  • saddr - the address of the local socket (listen address). Can be a static string or contain pseudo-variable.

This function can be used from ANY_ROUTE.

Example 1.19. set_send_socket usage

...
set_send_socket("udp:127.0.0.1:5060");
...

4.16. set_recv_socket(saddr)

Switch local socket used for receiving the message.

Meaning of the parameters is as follows:

  • saddr - the address of the local socket (listen address). Can be a static string or contain pseudo-variable.

This function can be used from ANY_ROUTE.

Example 1.20. set_recv_socket usage

...
set_recv_socket("udp:127.0.0.1:5060");
...

4.17. set_source_address(saddr)

Set the source address for the message.

Meaning of the parameters is as follows:

  • saddr - the source address in socket format. Can be a static string or contain pseudo-variable.

This function can be used from ANY_ROUTE.

Example 1.21. set_source_address usage

...
set_source_address("udp:127.0.0.1:5080");
...

4.18. via_add_srvid(flags)

Control if srvid parameter is added or not to local Via. If yes, the value is server_id, added only if it is different than 0.

Meaning of the parameters is as follows:

  • flags: 1 - add srvid parameter; 0 - do not add srvid parameter.

This function can be used from ANY_ROUTE.

Example 1.22. via_add_srvid usage

...
via_add_srv("1");
...

4.19. via_add_xavp_params(flags)

Control if fields of the xavp with the name specified by xavp_via_params global parameter are added or not to local Via.

Meaning of the parameters is as follows:

  • flags: 1 - add xavp parameters; 0 - do not add xavp parameters.

This function can be used from ANY_ROUTE.

Example 1.23. via_add_xavp_params usage

...
via_add_xavp_params("1");
...

5. RPC Commands

5.1.  corex.debug

Set or get the global log level (the value for global parameter 'debug'). To set the debug, provide an integer parameter. If no parameter is provided, then the current value is returned.

Example:

		kamcmd corex.debug
		kamcmd corex.debug 2

5.2.  corex.list_sockets

Print the list of sockets the application is listening on.

Example:

		kamcmd corex.list_sockets

5.3.  corex.list_aliases

Print the list of hostname aliases used to match the myself condition.

Example:

		kamcmd corex.list_aliases

5.4.  corex.shm_status

Trigger shm status dump to syslog.

Example:

		kamcmd corex.shm_status

5.5.  corex.shm_summary

Trigger shm summary dump to syslog.

Example:

		kamcmd corex.shm_summary

5.6.  corex.pkg_summary

Trigger pkg summary dump to syslog for a specific pid or process index. It has two parameters: first to specify what matching type is desired (can be 'pid' or 'idx'); second to specify the value for desired match.

The dump is happening when the selected process is doing a runtime handling (e.g., processing a sip message).

Example:

		kamcmd corex.pkg_summary pid 2345
		kamcmd corex.pkg_summary idx 1

6. Event Routes

6.1.  event_route[network:msg]

Event route block to be executed when new data is received from network or the data that is about to be sent to a remote host by a SIP worker process.

The kamailio script writer can check which type of data triggered this event route using is_incoming method.

After executing of this event route, if msg_avp was defined and set then its value is used for further processing, otherwise, original value of $mb is used. If message was received from remote host, then it is parsed and proceeds to appropriate route. Otherwise if message set to send out, then is sent to remote host per configured SIP timers in config script.

Please note this event route is meant to prepare the message for on-wire communication, e.g. to do custom encryption or decryption, compression/decompression etc. of the message sent to or received from remote host. Therefore, except text operations, no module functions or pseudo variables are available in this event route.

7. Examples of Usage

To use network event_route[network:msg] the remote SIP UA must also implement and understand the encoding / decoding done in this event route. It is up to Kamailio config script writer to define and implement how encoding and decoding is done. Any language module such as app_perl or app_lua can be called in in event_route[network:msg] to implement desired logic.

The most simple use case is to compress the SIP packet on-wire. As SIP is a text based protocol, so it is highly compressable. Using this module, one can compress entire SIP message, including headers and message body before sending it to remote host using any compression algorithm of choice, thus saving significant bandwidth on mobile data networks.

A useful case is to use this function between SIP edge proxy and SIP application server. The SIP messages received from end-user at SIP edge proxy may be decrypted and sent to SIP application server at remote location unencrypted, where they are processed as normal. One the way back, the messages received from SIP application server at edge proxy can be encrypted before being sent to actual destination. The edge proxy can check whether received message came from end-user or SIP application server by using simple regular expressions.

Another use case is to implement a virtual HTTP tunnel for SIP messages. The SIP client app can convert SIP message to binary e.g. by doing XOR, Base64 etc., then prepend some fake HTTP headers to make it look like an HTTP request before sending it to kamailio over SIP TCP socket. At kamailio, the fake headers are removed and data is decoded back to normal SIP and processed per config script logic. For the data that is to be sent to SIP client app, one can prepend fake HTTP reply headers to encoded data before sending it to client app.

More advance use cases may involve custom encryption algorithms such as ITV encryption algorithm, https://github.com/mshary/itv

For example, the client app running on Android or iPhone, may send device UUID along with ITV key, encrypted using RSA or AES256 with pre-shared secret, as first packet, which is set as cookie by server in e.g. memcache. This cookie is referred by client app in each next packet, so server can retrieve encryption key from cache and use that for decryption. Same can be done for server at client app side, so messages encrypted by server can be decrypted at client app.

Next is a basic usage example where encoding and decoding is done using PERL,

Example 1.24. event_route[network:msg] use cases

...
loadmodule "app_perl.so"
loadmodule "corex.so"
...
# ----- app_perl params -----
modparam("app_perl", "filename", "/usr/local/etc/kamailio/custom_compress.pl")
modparam("app_perl", "modpath", "/usr/local/lib64/kamailio/perl")

# ----- corex params -----
modparam("corex", "network_io_intercept", 32)
modparam("corex", "min_msg_len", 32)
modparam("corex", "msg_avp", "$avp(msg)")
...
event_route[network:msg] {
	if (is_incoming()) {
		if (perl_exec_simple("do_uncompress", "" + $mb + "")) {
			xlog("L_INFO", "Received message '$avp(msg)' \n");
		} else {
			xlog("L_INFO", "Received message '$mb' \n");
			$avp(msg) = $mb;
		};
	} else {
		xlog("L_INFO", "Sending message '$mb' \n");
		if (!perl_exec_simple("do_compress", "" + $mb + "")) {
			$avp(msg) = $mb;
		};
	};
}
...

Example 1.25. Sample PERL code for do_compress and do_uncompress

...
use strict;
use warnings;
use IO::Compress::Gzip qw(gzip $GzipError) ;
use IO::Uncompress::Gunzip qw(gunzip $GunzipError) ;

sub do_compress() {
	my $input = shift;
	my $output;

	gzip \$input => \$output
		or eval {
			Kamailio::log(L_WARN, "GZIP failed: $GzipError\n");
			$output = $input;
		};

	Kamailio::AVP::add("msg", $output);
}

sub do_uncompress() {
	my $input = shift;
	my $output;

	gunzip \$input => \$output
		or eval {
			Kamailio::log(L_WARN, "GUNZIP failed: $GzipError\n");
			$output = $input;
		};

	Kamailio::AVP::add("msg", $output);
}
...