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


  mode = c("serial", "character", "complex", "double", "integer", "logical", "numeric",
    "raw", "string"),
  block = NULL,
  n = 65536L



a Socket, Context or Stream.


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


[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.


[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.


The received data in the ‘mode’ specified.


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 an error occurred in unserialization or conversion of the message data to the specified mode, a raw vector will be returned instead to allow recovery (accompanied by a warning).


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

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

See also

recv_aio for asynchronous receive.


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

send(s1, data.frame(a = 1, b = 2))
#> [1] 0
res <- recv(s2)
#>   a b
#> 1 1 2
send(s1, data.frame(a = 1, b = 2))
#> [1] 0
#>   a b
#> 1 1 2

send(s1, c(1.1, 2.2, 3.3), mode = "raw")
#> [1] 0
res <- recv(s2, mode = "double", block = 100)
#> [1] 1.1 2.2 3.3
send(s1, "example message", mode = "raw")
#> [1] 0
recv(s2, mode = "character")
#> [1] "example message"


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)
#> [1] 0
recv(ctxp, block = 100)
#>   a b
#> 1 1 2

send(ctxq, c(1.1, 2.2, 3.3), mode = "raw", block = 100)
#> [1] 0
recv(ctxp, mode = "double", block = 100)
#> [1] 1.1 2.2 3.3