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


send(con, data, mode = c("serial", "raw", "next"), block = NULL)



a Socket, Context or Stream.


an object (a vector, if mode = ‘raw’).


[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. For Streams, ‘raw’ is the only option and this argument is ignored.


[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.


Integer exit code (zero on success).


For Sockets and Contexts: the default behaviour is non-blocking with block = FALSE. This will return immediately with an error if the message could not be queued for sending. Certain protocol / transport combinations may limit the number of messages that can be queued if they have yet to be received.

For Streams: the default behaviour is blocking with block = TRUE. This will wait until the send has completed. Set a timeout 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 small positive value for block rather than FALSE.

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.

See also

send_aio for asynchronous send.


pub <- socket("pub", dial = "inproc://nanonext")

send(pub, data.frame(a = 1, b = 2))
#> [1] 0
send(pub, c(10.1, 20.2, 30.3), mode = "raw", block = 100)
#> [1] 0


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

ctx <- context(req)
send(ctx, data.frame(a = 1, b = 2), block = 100)
#> [1] 0

msg <- recv_aio(rep, timeout = 100)
send(ctx, c(1.1, 2.2, 3.3), mode = "raw", block = 100)
#> [1] 0