Construct a standard RDesk IPC message envelope

Builds the JSON envelope that both R and the JavaScript frontend use to exchange typed messages. Each envelope carries a unique ID, a message type string, a contract version, an arbitrary payload, and a millisecond-precision Unix timestamp.

Usage

rdesk_message(
  type,
  payload = list(),
  version = getOption("rdesk.ipc_version", "1.0")
)

Arguments

type

Character string. The message type / action name (e.g. "get_data").

payload

A named list representing the message data. Defaults to an empty list.

version

IPC contract version string. Defaults to the rdesk.ipc_version option (currently "1.0").

Value

A named list representing the standard JSON envelope. Pass this directly to jsonlite::toJSON() or to app$send().

Details

The envelope schema is:

  {
    "id":        "msg_<epoch_ms>_<random>",
    "type":      "<action_name>",
    "version":   "1.0",
    "payload":   { ... },
    "timestamp": <unix_seconds>
  }

Large payloads (above 1 MB) trigger a warning so developers notice performance-sensitive serialization early.

See also

rdesk_parse_message() for the corresponding deserializer.

Examples

# Construct a typed message with a simple payload
msg <- rdesk_message("get_data", list(filter = "cyl == 6"))
stopifnot(msg$type == "get_data")
stopifnot(msg$version == "1.0")
stopifnot(!is.null(msg$id))