WebSocket Module

Peter Dunkley

   Crocodile RCS Ltd

   Copyright © 2012 Crocodile RCS Ltd
     __________________________________________________________________

   Table of Contents

   1. Admin Guide

        1. Overview
        2. How it works

              2.1. Initiating a connection
              2.2. SIP message routing
              2.3. MSRP message routing

        3. Dependencies

              3.1. Kamailio Modules
              3.2. External Libraries or Applications

        4. Parameters

              4.1. keepalive_mechanism (integer)
              4.2. keepalive_timeout (integer)
              4.3. keepalive_processes (integer)
              4.4. keepalive_interval (integer)
              4.5. ping_application_data (string)
              4.6. sub_protocols (integer)

        5. Functions

              5.1. ws_handle_handshake()

        6. MI Commands

              6.1. ws.dump
              6.2. ws.close
              6.3. ws.ping
              6.4. ws.pong
              6.5. ws.disable
              6.6. ws.enable

        7. Event routes

              7.1. websocket:closed

   List of Examples

   1.1. event_route[xhttp:request]
   1.2. WebSocket SIP Routing
   1.3. Set keepalive_mechanism parameter
   1.4. Set keepalive_timeout parameter
   1.5. Set keepalive_processes parameter
   1.6. Set keepalive_interval parameter
   1.7. Set ping_application_data parameter
   1.8. Set sub_protocols parameter
   1.9. ws_handle_handshake usage

Chapter 1. Admin Guide

   Table of Contents

   1. Overview
   2. How it works

        2.1. Initiating a connection
        2.2. SIP message routing
        2.3. MSRP message routing

   3. Dependencies

        3.1. Kamailio Modules
        3.2. External Libraries or Applications

   4. Parameters

        4.1. keepalive_mechanism (integer)
        4.2. keepalive_timeout (integer)
        4.3. keepalive_processes (integer)
        4.4. keepalive_interval (integer)
        4.5. ping_application_data (string)
        4.6. sub_protocols (integer)

   5. Functions

        5.1. ws_handle_handshake()

   6. MI Commands

        6.1. ws.dump
        6.2. ws.close
        6.3. ws.ping
        6.4. ws.pong
        6.5. ws.disable
        6.6. ws.enable

   7. Event routes

        7.1. websocket:closed

1. Overview

   This module implements a WebSocket (RFC 6455) server and provides
   connection establishment (handshaking), management (including
   connection keep-alive), and framing for the SIP and MSRP WebSocket
   sub-protocols (draft-ietf-sipcore-sip-websocket and
   draft-pd-msrp-websocket).

   The module supports WebSockets (ws) and secure WebSockets (wss)

2. How it works

   2.1. Initiating a connection
   2.2. SIP message routing
   2.3. MSRP message routing

2.1. Initiating a connection

   A WebSocket connection is initiated with an HTTP GET. The xhttp module
   is used to handle this GET and call the Section 5.1, “
   ws_handle_handshake() ” exported function.

   event_route[xhttp:request] should perform some validation of the HTTP
   headers before calling Section 5.1, “ ws_handle_handshake() ”. The
   event_route can also be used to make sure the HTTP GET has the correct
   URI, perform HTTP authentication on the WebSocket connection, and check
   the Origin header (RFC 6454) to ensure a browser-based SIP UA or MSRP
   client has been downloaded from the correct location.

   Example 1.1. event_route[xhttp:request]
...
loadmodule "sl.so"
loadmodule "xhttp.so"
loadmodule "msrp.so"  # Only required if using MSRP over WebSockets
loadmodule "websocket.so"
...
event_route[xhttp:request] {
        set_reply_close();
        set_reply_no_connect();

        if ($Rp != 80
#!ifdef WITH_TLS
            && $Rp != 443
#!endif
        ) {

                xlog("L_WARN", "HTTP request received on $Rp\n");
                xhttp_reply("403", "Forbidden", "", "");
                exit;
        }

        xlog("L_DBG", "HTTP Request Received\n");

        if ($hdr(Upgrade)=~"websocket"
                        && $hdr(Connection)=~"Upgrade"
                        && $rm=~"GET") {

                # Validate Host - make sure the client is using the correct
                # alias for WebSockets
                if ($hdr(Host) == $null || !is_myself("sip:" + $hdr(Host))) {
                        xlog("L_WARN", "Bad host $hdr(Host)\n");
                        xhttp_reply("403", "Forbidden", "", "");
                        exit;
                }

                # Optional... validate Origin - make sure the client is from an
                # authorised website.  For example,
                #
                # if ($hdr(Origin) != "http://communicator.MY_DOMAIN"
                #     && $hdr(Origin) != "https://communicator.MY_DOMAIN") {
                #       xlog("L_WARN", "Unauthorised client $hdr(Origin)\n");
                #       xhttp_reply("403", "Forbidden", "", "");
                #       exit;
                # }

                # Optional... perform HTTP authentication

                # ws_handle_handshake() exits (no further configuration file
                # processing of the request) when complete.
                if (ws_handle_handshake())
                {
                        # Optional... cache some information about the
                        # successful connection
                        exit;
                }
        }

        xhttp_reply("404", "Not found", "", "");
}
...

2.2. SIP message routing

   SIP over WebSockets uses invalid URIs in routing headers (Contact:,
   Record-Route:, and Via:) because a JavaScript stack running in a
   browser has no way to determine the local address from which the
   WebSocket connection is made. This means that the routing headers
   cannot be used for request or response routing in the normal manner.

   draft-ietf-sipcore-sip-websocket states that SIP WebSocket Clients and
   the SIP registrar should implement Outbound (RFC 5626) and Path (RFC
   3327) to enable requests and responses to be correctly routed. However,
   Kamailio does not currently support Outbound and it may not be possible
   to guarantee all SIP WebSocket clients will support Outbound and Path.

   The nathelper module functions (nat_uac_test(), fix_nated_register(),
   add_contact_alias(), and handle_ruri_alias()) and the Kamailio core
   force_rport() can be used to ensure correct routing of SIP WebSocket
   requests without using Outbound and Path.

   Example 1.2. WebSocket SIP Routing
...
loadmodule "sl.so"
loadmodule "tm.so"
...
loadmodule "websocket.so"
...
request_route {

        # per request initial checks
        route(REQINIT);

        if (nat_uac_test(64)) {
                # Do NAT traversal stuff for requests from a WebSocket
                # connection - even if it is not behind a NAT!
                # This won't be needed in the future if Kamailio and the
                # WebSocket client support Outbound and Path.
                force_rport();
                if (is_method("REGISTER"))
                        fix_nated_register();
                else {
                        if (!add_contact_alias()) {
                                xlog("L_ERR", "Error aliasing contact <$ct>\n");
                                sl_send_reply("400", "Bad Request");
                                exit;
                        }
                }
        }

        if (!is_method("REGISTER"))
                t_on_reply("WS_REPLY");
...
# Handle requests within SIP dialogs
route[WITHINDLG] {
        if (has_totag()) {
                # sequential request withing a dialog should
                # take the path determined by record-routing
                if (loose_route()) {
                        if ($du == "") {
                                if (!handle_ruri_alias()) {
                                        xlog("L_ERR", "Bad alias <$ru>\n");
                                        sl_send_reply("400", "Bad Request");
                                        exit;
                                }
                        }
                        route(RELAY);
                } else {
                        if ( is_method("ACK") ) {
...
onreply_route[WS_REPLY] {
        if (nat_uac_test(64)) {
                # Do NAT traversal stuff for replies to a WebSocket connection
                # - even if it is not behind a NAT!
                # This won't be needed in the future if Kamailio and the
                # WebSocket client support Outbound and Path.
                add_contact_alias();
        }
}
...

2.3. MSRP message routing

   MSRP over WebSocket clients create invalid local URIs for use in Path
   headers (From-Path: and To-Path:) because a JavaScript stack running in
   a browser has no way to determine the local address from which the
   WebSocket connection is made. This is OK because MSRP over WebSocket
   clients MUST use an MSRP relay and it is the MSRP relay's
   responsibility to select the correct connection to the client based on
   the MSRP URIs that it has created (and maintains a mapping for).

3. Dependencies

   3.1. Kamailio Modules
   3.2. External Libraries or Applications

3.1. Kamailio Modules

   The following module must be loaded before this module:
     * sl.

   The following modules are required to make proper use of this module:
     * nathelper.
     * tm.
     * xhttp.

   The following module is required to use the secure WebSocket (wss)
   scheme:
     * tls.

   The following module is required to support MSRP over WebSockets:
     * msrp.

3.2. External Libraries or Applications

   The following libraries must be installed before running Kamailio with
   this module loaded:
     * OpenSSL.
     * GNU libunistring.

4. Parameters

   4.1. keepalive_mechanism (integer)
   4.2. keepalive_timeout (integer)
   4.3. keepalive_processes (integer)
   4.4. keepalive_interval (integer)
   4.5. ping_application_data (string)
   4.6. sub_protocols (integer)

4.1. keepalive_mechanism (integer)

   The keep-alive mechanism to use for WebSocket connections.

Note

   If nathelper is only being used for WebSocket connections then
   nathelper NAT pinging is not required. If nathelper is used for
   WebSocket connections and TCP/TLS aliasing/NAT-traversal then WebSocket
   keep-alives are not required.

     * 0 - no WebSocket keep-alives
     * 1 - Ping WebSocket keep-alives
     * 2 - Pong WebSocket keep-alives

   Default value is 1.

   Example 1.3. Set keepalive_mechanism parameter
...
modparam("websocket", "keepalive_mechanism", 0)
...

4.2. keepalive_timeout (integer)

   The time (in seconds) after which to send a keep-alive on idle
   WebSocket connections.

   Default value is 180.

   Example 1.4. Set keepalive_timeout parameter
...
modparam("websocket", "keepalive_timeout", 30)
...

4.3. keepalive_processes (integer)

   The number of processes to start to perform WebSocket connection
   keep-alives.

   Default value is 1.

   Example 1.5. Set keepalive_processes parameter
...
modparam("websocket", "keepalive_processes", 2)
...

4.4. keepalive_interval (integer)

   The number of seconds between each keep-alice process run

   Default value is 1.

   Example 1.6. Set keepalive_interval parameter
...
modparam("websocket", "keepalive_interval", 2)
...

4.5. ping_application_data (string)

   The application data to use in keep-alive Ping and Pong frames.

   Default value is Kamailio Server: header content

   Example 1.7. Set ping_application_data parameter
...
modparam("websocket", "ping_application_data", "WebSockets rock")
...

4.6. sub_protocols (integer)

   A bitmap that allows you to control the sub-protocols supported by the
   WebSocket server.
     * 1 - sip (draft-ietf-sipcore-sip-websocket)
     * 2 - msrp (draft-pd-msrp-websocket) - msrp.so must be loaded before
       websocket.so

   Default value is 1 when msrp.so is not loaded 3 when msrp.so is loaded.

   Example 1.8. Set sub_protocols parameter
...
modparam("websocket", "sub_protocols", 2)
...

5. Functions

   5.1. ws_handle_handshake()

5.1.  ws_handle_handshake()

   This function checks an HTTP GET request for the required headers and
   values, and (if successful) upgrades the connection from HTTP to
   WebSocket.

   This function can be used from ANY_ROUTE (but will only work in
   event_route[xhttp:request]).

Note

   This function returns 0, stopping all further processing of the
   request, when there is a problem.

   Example 1.9. ws_handle_handshake usage
...
ws_handle_handshake();
...

6. MI Commands

   6.1. ws.dump
   6.2. ws.close
   6.3. ws.ping
   6.4. ws.pong
   6.5. ws.disable
   6.6. ws.enable

6.1. ws.dump

   Provides the details of the first 50 WebSocket connections.

   Name: ws.dump

   Parameters:
     * order (optional) - “id_hash”, “used_desc”, or “used_asc”.

Note

   If no parameter is provided id_hash order is used.

   MI FIFO Command Format:
                        :ws.dump:fifo_reply
                        used_asc
                        _empty_line_

6.2. ws.close

   Starts the close handshake for the specified WebSocket connection.

   Name: ws.close

   Parameters:
     * id - WebSocket connection ID.

   MI FIFO Command Format:
                        :ws.close:fifo_reply
                        1
                        _empty_line_

6.3. ws.ping

   Sends a Ping frame on the specified WebSocket connection.

   Name: ws.ping

   Parameters:
     * id - WebSocket connection ID.

   MI FIFO Command Format:
                        :ws.ping:fifo_reply
                        1
                        _empty_line_

6.4. ws.pong

   Sends a Pong frame on the specified WebSocket connection.

   Name: ws.pong

   Parameters:
     * id - WebSocket connection ID.

   MI FIFO Command Format:
                        :ws.pong:fifo_reply
                        1
                        _empty_line_

6.5. ws.disable

   Disables WebSockets preventing new connections from being established.

   Name: ws.disable

   Parameters: none

   MI FIFO Command Format:
                        :ws.disable:fifo_reply
                        _empty_line_

6.6. ws.enable

   Enables WebSockets allowing new connections to be established.

Note

   WebSockets are enabled at start-up.

   Name: ws.enable

   Parameters: none

   MI FIFO Command Format:
                        :ws.enable:fifo_reply
                        _empty_line_

7. Event routes

   7.1. websocket:closed

7.1.  websocket:closed

   When defined, the module calls event_route[websocket:closed] when a
   connection closes. The connection may be identified using the the $si
   and $sp pseudo-variables.
...
event_route[websocket:closed] {
        xlog("L_INFO", "WebSocket connection from $si:$sp has closed\n");
}
...
