Skip to contents

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", "next"),
  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'] character value or integer equivalent - one of ‘serial’ (1L), ‘character’ (2L), ‘complex’ (3L), ‘double’ (4L), ‘integer’ (5L), ‘logical’ (6L), ‘numeric’ (7L), ‘raw’ (8L), or ‘string’ (9L). The default ‘serial’ means a serialised R object; for the other modes, received bytes are converted into the respective mode. ‘string’ is a faster option for length one character vectors.


[default 'serial'] character value or integer equivalent - one of ‘serial’ (1L) to send serialised R objects, ‘raw’ (2L) to send atomic vectors of any type as a raw byte vector, or ‘next’ (3L) - see ‘Send Modes’ section below.


[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'.


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.

Send Modes

The default mode ‘serial’ sends serialised R objects to ensure perfect reproducibility within R. When receiving, the corresponding mode ‘serial’ should be used.

Mode ‘raw’ sends atomic vectors of any type as a raw byte vector, and must be used when interfacing with external applications or raw system sockets, where R serialization is not in use. When receiving, the mode corresponding to the vector sent should be used.

Mode ‘next’ sends serialised R objects, with native extensions enabled by next_config. This configures custom serialization and unserialization functions for reference objects. When receiving, mode ‘serial’ should be used as ‘next’ sends are fully compatible.


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

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

send(ctxq, 2022, block = 100)
#> [1] 0
reply(ctxp, execute = function(x) x + 1, send_mode = "raw", timeout = 100)
#> [1] 0
recv(ctxq, mode = "double", block = 100)
#> [1] 2023

send(ctxq, 100, mode = "raw", block = 100)
#> [1] 0
reply(ctxp, recv_mode = "double", execute = log, base = 10, timeout = 100)
#> [1] 0
recv(ctxq, block = 100)
#> [1] 2