send(),
sendto(), and
sendmsg() are used to transmit a message to another socket.
send() may be used only when the socket is in a
connected state, while
sendto() and
sendmsg() may be used at any time.
The address of the target is given by
to with
tolen specifying its size. The length of the message is given by
len. If the message is too long to pass atomically through the underlying protocol, the error
EMSGSIZE is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a
send(). Locally detected errors are indicated by a return value of -1.
If no messages space is available at the socket to hold the message to be transmitted, then
send() normally blocks, unless the socket has been placed in non-blocking I/O mode. The
select(2) or
poll(2) call may be used to determine when it is possible to send more data.
The
flags parameter may include one or more of the following:
#define MSG_OOB 0x0001 /* process out-of-band data */
#define MSG_PEEK 0x0002 /* peek at incoming message */
#define MSG_DONTROUTE 0x0004 /* bypass routing, use direct interface */
#define MSG_EOR 0x0008 /* data completes record */
#define MSG_NOSIGNAL 0x0400 /* do not generate SIGPIPE on EOF */
The flag
MSG_OOB is used to send “out-of-band” data on sockets that support this notion (e.g.
SOCK_STREAM); the underlying protocol must also support “out-of-band” data.
MSG_EOR is used to indicate a record mark for protocols which support the concept.
MSG_DONTROUTE is usually used only by diagnostic or routing programs.
See
recv(2) for a description of the
msghdr structure.
MSG_NOSIGNAL is used to prevent
SIGPIPE generation when writing a socket that may be closed.