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With exception to the REST API and some other edge cases, all communication that happens between FarmBot users, devices, and systems is wrapped in a CeleryScript node.

A node is a specially formatted JSON document. It is a composable building block that can be nested and arranged to create trees of commands, similar to the way an abstract syntax tree is used to create programming languages.

Format

A CeleryScript node is comprised of:

  • A kind (string) that determines a node’s purpose.
  • An args object that contains key/value pairs (some of these values will be child nodes, others will be simple primitive values such as numbers). If a node requires a particular arg, it will always be present. There is no such thing as an optional arg in CeleryScript. This simplifies many aspects of the standard.
  • An optional body argument which, if defined, will contain a list of other CeleryScript nodes. A body will only ever contain CeleryScript nodes and will never contain primitive values such as strings or numbers.
  • An optional comment (string) field to aid developer readability.

Here is an example reboot node, which tells a device to restart the specified app:

reboot Celery Script node example:

{
    // THE "kind" ATTRIBUTE:
    // Every CS node MUST have a "kind" attribute.
    // This is the nodes name.
    // Legal "kind" types are listed here:
    // https://github.com/FarmBot/farmbot-js/blob/7044292a6591753b3edad3ed7bf3a8a08a41fac4/dist/corpus.d.ts#L418
    "kind": "reboot",

    // THE "args" (arguments) FIELD:
    // Every node has an "args" object. It is REQUIRED.
    // The arguments for a node will vary based on the "kind".
    "args": { package: "farmbot_os" },

    // THE "comment" FIELD:
    // You do not need to use this (or even include it), but you can if it is helpful.
    // We use comments for tracing and debugging.
    "comment": "Optional. Useful when debugging, but ignored by the system.",

    // THE "body" FIELD:
    // Not every node will have a body.
    // If a node does have a body, it will ONLY contain other celery script nodes.
    // Example: The body of a "sequence" node may contain a "move_relative" node.
    body: []
}

Some common CeleryScript nodes include:

  • move_relative, move_absolute
  • execute - Runs a sequence via the sequence_id arg.
  • rpc_request, rpc_ok, rpc_error - discussed later in this document.

Not every CeleryScript node represents a device command

Some nodes, such as the coordinate node, are used to represent data.

Available nodes

See also the corpus.d.ts file.

kind type also known as Description
assertion command   Command for assertion style automated testing (more info)
calibrate command find axis length Command for performing an axis calibration (find axis length)
change_ownership command   Transfers ownership of a FarmBot device from one web app account to another
channel      
check_updates command update Instructs FarmBot to check for (and install) software updates
coordinate      
emergency_lock command e-stop Emergency stops the FarmBot
emergency_unlock command unlock Unlocks the FarmBot from being emergency stopped
execute command execute sequence Command for executing a sequence (more info)
execute_script command    
explanation     Description of rpc_error
factory_reset command soft reset Instructs the FarmBot to factory reset
find_home command   Command for finding home along an axis
flash_firmware command   Instructs FarmBot to flash firmware to the microcontroller
home command move to home Command instructing FarmBot to go to the home position (this is different than finding home)
identifier      
if command   Allows FarmBot to evaluate if a condition is true or false and take a corresponding action
internal_entry_point      
internal_farm_event      
internal_regimen      
lua command   see lua documentation
move command   Command for moving FarmBot (more info)
move_absolute command move to Command for moving FarmBot to an absolute coordinate position (more info)
move_relative command   Command for moving FarmBot a relative amount from the current location (more info)
named_pin      
nothing      
pair      
parameter_application      
parameter_declaration      
point     Represents a point (location) in the farm designer map such as a plant, weed, point, or tool slot
point_group     A group of points (locations) in the farm designer map
power_off command shutdown Instructs FarmBot to shutdown completely
read_pin command read sensor Command for reading a pin (read sensor)
read_status command   Instructs FarmBot to send a status message with a full state tree
reboot command   Instructs FarmBot to reboot
rpc_error     Indicates that the request operation has failed
rpc_ok     Indicates that the request operation has succeeded
rpc_request     Requests the device do something
scope_declaration      
send_message command   Command for sending a message
sequence      
set_servo_angle command control servo Command for moving servo motors
set_user_env      
sync command   Instructs FarmBot to sync with the API
take_photo command   Instructs FarmBot to take a photo and upload it to the API
toggle_pin command toggle peripheral Command for toggling the state of a pin (toggle peripheral)
tool      
update_resource command mark as see documentation for mark as command
variable_declaration      
wait command   Command for waiting a time in milliseconds
write_pin command control peripheral Command for writing (control peripheral) a digital or analog value to a pin
zero command set home Command for setting the current location to zero (set home) along an axis

rpc_request

The CeleryScript specification defines three nodes used for real-time control of a device. These nodes are used extensively in the user interface for one-off commands, such as device position adjustments.

  • rpc_request - Initiated by a user (or occasionally, the REST API) when requesting the device do something. The desired action (eg: move_relative, reboot, etc..) is held in the body of this node.
  • rpc_ok - Sent by a device to an end user. Indicates that the request operation has succeeded.
  • rpc_error - Indicates that the request operation has failed. The body of an rpc_error will often contain a number of explanation nodes describing the circumstances of the failure.

What’s next?