Receive data over a connection (Socket, Context or Stream).

recv(
  con,
  mode = c("serial", "character", "complex", "double", "integer", "logical", "numeric",
    "raw"),
  block = NULL,
  keep.raw = FALSE,
  ...,
  n = 65536L
)

Arguments

con

a Socket, Context or Stream.

mode

[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. For Streams, 'serial' is not an option and the default is 'character'.

block

[default NULL] which applies the connection default (see section 'Blocking' below). Specify logical TRUE to block until successful or FALSE to return immediately even if unsuccessful (e.g. if no connection is available), or else an integer value specifying the maximum time to block in milliseconds, after which the operation will time out.

keep.raw

[default FALSE] logical flag whether to keep and return the received raw vector along with the converted data.

...

not used.

n

[default 65536L] applicable to Streams only, the maximum number of bytes to receive. Can be an over-estimate, but note that a buffer of this size is reserved.

Value

Depending on the value of 'keep.raw': if TRUE, a named list of 2 elements - 'raw' containing the received raw vector and 'data' containing the converted object, or if FALSE, the converted object.

Details

In case of an error, an integer 'errorValue' is returned (to be distiguishable from an integer message value). This can be verified using is_error_value.

If the raw message was successfully received but an error occurred in unserialisation or data conversion (for example if the incorrect mode was specified), the received raw vector will always be returned to allow for the data to be recovered.

Blocking

For Sockets: the default behaviour is non-blocking with block = FALSE. This will return immediately with an error if no messages are available.

For Contexts and Streams: the default behaviour is blocking with block = TRUE. This will wait until a message is received. Set a timeout in this case to ensure that the function returns under all scenarios. As the underlying implementation uses an asynchronous send with a wait, it is recommended to set a positive integer value for block rather than FALSE.

Examples

s1 <- socket("pair", listen = "inproc://nanonext")
s2 <- socket("pair", dial = "inproc://nanonext")

send(s1, data.frame(a = 1, b = 2))
res <- recv(s2)
res
#>   a b
#> 1 1 2
send(s1, data.frame(a = 1, b = 2), echo = FALSE)
recv(s2, keep.raw = FALSE)
#>   a b
#> 1 1 2

send(s1, c(1.1, 2.2, 3.3), mode = "raw")
res <- recv(s2, mode = "double", block = 100)
res
#> [1] 1.1 2.2 3.3
send(s1, "example message", mode = "raw", echo = FALSE)
recv(s2, mode = "character", keep.raw = FALSE)
#> [1] "example message"

close(s1)
close(s2)

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

ctxq <- context(req)
ctxp <- context(rep)
send(ctxq, data.frame(a = 1, b = 2), block = 100)
recv(ctxp, block = 100)
#>   a b
#> 1 1 2

send(ctxq, c(1.1, 2.2, 3.3), mode = "raw", block = 100)
recv(ctxp, mode = "double", block = 100)
#> [1] 1.1 2.2 3.3

close(req)
close(rep)