Implements an executor/server for the rep node of the req/rep protocol. Awaits data, applies an arbitrary specified function, and returns the result to the caller/client.

  recv_mode = c("serial", "character", "complex", "double", "integer", "logical",
    "numeric", "raw"),
  send_mode = c("serial", "raw"),
  timeout = NULL,



a Context.


a function which takes the received (converted) data as its first argument. Can be an anonymous function of the form function(x) do(x). Additional arguments can also be passed in through '...'.


[default 'serial'] mode of vector to be received - one of 'serial', 'character', 'complex', 'double', 'integer', 'logical', 'numeric', or 'raw'. The default 'serial' means a serialised R object, for the other modes, the raw vector received will be converted into the respective mode.


[default 'serial'] whether data will be sent serialized or as a raw vector. Use 'serial' for sending and receiving within R to ensure perfect reproducibility. Use 'raw' for sending vectors of any type (will be converted to a raw byte vector for sending) - essential when interfacing with external applications.


[default NULL] integer value in milliseconds or NULL, which applies a socket-specific default, usually the same as no timeout. Note that this applies to receiving the request. The total elapsed time would also include performing 'execute' on the received data. The timeout then also applies to sending the result (in the event that the requestor has become unavailable since sending the request).


additional arguments passed to the function specified by 'execute'.


Invisibly, an integer exit code (zero on success).


Receive will block while awaiting a message to arrive and is usually the desired behaviour. Set a timeout to allow the function to return if no data is forthcoming.

In the event of an error in either processing the messages or in evaluation of the function with respect to the data, a nul byte 00 (or serialized nul byte) will be sent in reply to the client to signal an error. This is to be distinguishable from a possible return value. is_nul_byte can be used to test for a nul byte.


req <- socket("req", listen = "tcp://")
rep <- socket("rep", dial = "tcp://")

ctxq <- context(req)
ctxp <- context(rep)

send(ctxq, 2022, block = 100, echo = FALSE)
reply(ctxp, execute = function(x) x + 1, send_mode = "raw", timeout = 100)
recv(ctxq, mode = "double", block = 100, keep.raw = FALSE)
#> [1] 2023

send(ctxq, 100, mode = "raw", block = 100, echo = FALSE)
reply(ctxp, recv_mode = "double", execute = log, base = 10, timeout = 100)
recv(ctxq, block = 100, keep.raw = FALSE)
#> [1] 2