Action commands are a feature defined for the GCODE based RepRap communication protocol. To quote from the GCODE node of the RepRap wiki:
The RepRap machine may also send lines that look like this:
// This is some debugging or other information on a line on its own. It may be sent at any time.
Such lines will always be preceded by //.
On the latest version of Pronterface and [...] OctoPrint a special comment of the form:
// action:command
is allowed to be sent from the firmware[. T]he command can currently be pause, resume or disconnect which will execute those commands on the host. As this is also a comment other hosts will just ignored these commands.
OctoPrint out of the box supports handling of the above mentioned commands:
- pause
When this command is received from the printer, OctoPrint will pause streaming of a current print job just like if the "Pause" button had been clicked.
- resume
When this command is received from the printer, OctoPrint will resume streaming of a current print job just like if the "Resume" button had been clicked.
- disconnect
When this command is Received from the printer, OctoPrint will immediately disconnect from it.
Support for additional commands may be added by plugins by implementing a handler for the octoprint.comm.protocol.action <sec-plugins-hook-comm-protocol-action> hook.