Transport modules
=================

Transport modules is a feature that allows different ways to connect to the server.
They may support different systems and/or different features.


File descriptors
================
If a module need to use a file descriptor it should use FD 3 and 4.
If more than two are needed, the module can try higher but that may be used
for other things in the future.


Configuration
=============
Additional configuration variables for a module should follow this naming scheme:
config_transport_transportname_variablename
Example:
config_transport_stunnel_path


Variables
=========
The module defines a variable called $transport_supports
It is a space separated list of supported features. Current ones:
 * ipv4  - Supports IPv4
 * ipv6  - Supports IPv6
 * nossl - Supports making non-SSL connections
 * ssl   - Supports SSL
 * bind  - Supports using a specific IP when connecting
This variable only needs to be set after transport_check_support has run


Functions
=========
The function names below should not be unique for the module like with
normal modules. You can only use one transport module at a time.


transport_check_support()
	Check if all the stuff needed to use this transport is available
	on this system.
	Return status:
		0 = Yes
		1 = No


transport_connect()
	Try to connect
	Return status:
		0 = Connection successful
		1 = Connection failed
	Parameters:
		$1 = Hostname/IP
		$2 = Port
		$3 = If 1 use SSL. If the module does not support it, just ignore it.
		$3 = IP to bind to if any and if supported
		     If the module does not support it, just ignore it.


transport_disconnect()
	Called to close connection
	Parameters:
		None
	Return status:
		Not checked.
	Notes:
		The module must handle this getting called even when not connected or when
		partly connected (it should clean up any program the module is running in
		the background on a ping time out for example).


transport_alive()
	Called to check if connection is still alive.
	Return status
		0 If connection is still alive.
		1 If it isn't alive.
	Notes:
		This function should be low overhead, it gets called quite often.



transport_read_line()
	Return a line in the variable $line.
	Return status:
		0 = Success
		1 = Connection has failed (timeout or whatever)
	Notes:
		The transport module should remove any trailing \r and/or \n (CR and/or LF)
		from the string before it returns it.


transport_write_line()
	Send a line
	Parameters:
		$* = send this
	Return status:
		Not checked.
	Notes:
		The transport module should add a \n (LF) to the end of the data it get.