5.1.2 Out-of-Band Processing

It is possible to compile the server to recognize an out-of-band prefix for input lines. This is a string that the server will check for at the beginning of every unflushed line of input from a connection, regardless of whether or not a player is logged in and regardless of whether or not reading tasks are waiting for input on that connection.

If a given line of input begins with the defined out-of-band prefix (`#$#' by default), then it is not treated as a normal command or given as input to any reading task. Instead, the line is parsed into a list of words in the usual way and those words are given as the arguments in a call to $do_out_of_band_command().

If this verb does not exist or is not executable, the line in question will be completely ignored.

For example, with the default out-of-band prefix, the line of input

#$#mcp-client-set-type fancy

would result in the following call being made in a new server task:

$do_out_of_band_command("#$#mcp-client-set-type", "fancy")

During the call to $do_out_of_band_command(), the variable player is set to the object number representing the player associated with the connection from which the input line came. Of course, if that connection has not yet logged in, the object number will be negative. Also, the variable argstr will have as its value the unparsed input line as received on the network connection.

Out-of-band commands are intended for use by advanced client programs that may generate asynchronous events of which the server must be notified. Since the client cannot, in general, know the state of the player's connection (logged-in or not, reading task or not), out-of-band commands provide the only reliable client-to-server communications channel.