SEND(2) SEND(2)
send, sendto, sendmsg - send a message from a socket
#include <sys/types.h>
#include <sys/socket.h>
int send(int s, const void *msg, int len, int flags);
int sendto(int s, const void *msg, int len, int flags,
struct sockaddr *to, int tolen);
int sendmsg(int s, const struct msghdr *msg, int flags);
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 when the socket is unconnected.
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, then the error EMSGSIZE
is returned, and the message is not transmitted.
Usually no indication of failure to deliver is implicit in a send.
Return values of -1 indicate some locally detected errors. Connected
datagram sockets may receive error indications from a previous send.
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) 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 0x1 /* process out-of-band data */
#define MSG_DONTROUTE 0x4 /* bypass routing,
use direct interface */
#define MSG_DONT_BRKPG 0x100 /* don't break up pages for send */
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_DONTROUTE is usually used only by
diagnostic or routing programs. MSG_DONT_BRKPG is used to allow the
user, on a per send basis to stop page flipping and the break up of large
memory pages to 16k. This can be done automatically for all large pages
transfers by setting the mtune/bsd/ip_nolgpg_brkup variable. NOTE that
setting this can have a negative effect on performance.
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SEND(2) SEND(2)
See recv(2) for a description of the msghdr structure.
The call returns the number of characters sent, or -1 if an error
occurred.
[EBADF] An invalid descriptor was specified.
[ENOTSOCK] The argument s is not a socket.
[EFAULT] An invalid user space address was specified for a
parameter.
[EMSGSIZE] The socket requires that message be sent atomically,
and the size of the message to be sent made this
impossible.
[EWOULDBLOCK] The socket is marked non-blocking and the requested
operation would block.
[ENOBUFS] The system was unable to allocate an internal buffer.
The operation may succeed when buffers become
available.
[ENOBUFS] The output queue for a network interface was full.
This generally indicates that the interface has
stopped sending, but may be caused by transient
congestion.
[ECONNREFUSED] The remote port was invalid when using the send call
on a connected datagram socket.
[EISCONN] A sendto or sendmsg call was used on a connected
socket.
[EACCES] The requested operation specified a broadcast address
as the destination but the SO_BROADCAST socket option
was not enabled (see setsockopt(2)).
[EHOSTUNREACH] The remote host was unreachable via the network.
[ENETUNREACH] The remote network is unknown to the routing system.
[EHOSTDOWN] The remote host was determined to be down, possibly
due to a failure to resolve its MAC-level address
(see arp(7P)).
fcntl(2), recv(2), select(2), getsockopt(2), socket(2), write(2)
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SEND(2) SEND(2)
ABI-compliant versions of the above call can be obtained from
libsocket.so.
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