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.
Arguments
- context
a Context.
- execute
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 ‘...’.- recv_mode
[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.
- send_mode
[default 'serial'] character value or integer equivalent - either ‘serial’ (1L) to send serialised R objects, or ‘raw’ (2L) to send atomic vectors of any type as a raw byte vector.
- timeout
[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'.
Details
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. Custom serialization and unserialization
functions for reference objects may be enabled by the function
serial_config.
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.
Examples
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)