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.
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.
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 external pointer reference objects. When
receiving, mode 'serial' should be used as 'next' sends are fully
compatible.
req <- socket("req", listen = "tcp://127.0.0.1:6546")
rep <- socket("rep", dial = "tcp://127.0.0.1:6546")
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
close(req)
close(rep)