The API can be used to interact with FluidNC via HTTP and WebSocket protocol.
In the curl examples below, ${FLUIDNC_FQDN} should be replace with your FluidNC address (for example: fluidnc.home or 192.168.1.162
If you connect via a websocket (on $http/port +1, e.g. 81), you have a streaming connection to FluidNC that behaves just like serial. You send newline-delimited lines just like you would over serial, and get back the same ok or error responses. Flow control is the same as for serial, as documented on the plain old Grbl wiki.
A web socket can be opened to listen to messages emitted by FluidNC
curl ws://$(FLUIDNC_FQDN):81
This will upload file file.yaml to the ESP32 localfs (flash) with the name /config.yaml
curl -F "file=@/path/to/local/file.yaml;filename=/config.yaml" http://${FLUIDNC_FQDN}/files
This will upload file file.gcode to the SD card with the name /test.yaml
curl -F "file=@/path/to/local/file.gcode;filename=/test.gcode" http://${FLUIDNC_FQDN}/upload