SEND(2) | System Calls Manual | SEND(2) |
send
, sendto
,
sendmsg
— send a message
from a socket
#include
<sys/socket.h>
ssize_t
send
(int
s, const void *msg,
size_t len,
int flags);
ssize_t
sendto
(int
s, const void *msg,
size_t len,
int flags,
const struct sockaddr
*to, socklen_t
tolen);
ssize_t
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 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) system calls may be
used to determine when it is possible to send more data.
The flags parameter may include one or more of the following:
MSG_DONTROUTE
MSG_DONTWAIT
MSG_EOR
MSG_NOSIGNAL
SIGPIPE
MSG_OOB
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_NOSIGNAL
is used to request not to send the
SIGPIPE
signal if an attempt to send is made on a
socket that is shut down for writing or no longer connected.
See recv(2) for a description of the msghdr structure.
The call returns the number of characters sent, or -1 if an error occurred.
send
(), sendto
(),
and sendmsg
() fail if:
EBADF
]ENOTSOCK
]EFAULT
]EMSGSIZE
]EAGAIN
]MSG_DONTWAIT
flag is set and the requested
operation would block.ENOBUFS
]ENOBUFS
]EACCES
]SO_BROADCAST
is not set on the socket and a
broadcast address was given as the destination.EHOSTUNREACH
]EINVAL
]EHOSTDOWN
]ENETDOWN
]ECONNREFUSED
]ENOPROTOOPT
]EDESTADDRREQ
]EPIPE
]MSG_NOSIGNAL
flag is set.In addition, send
() and
sendto
() may return the following error:
EINVAL
]SSIZE_MAX
.sendto
() and
sendmsg
() may return the following errors:
EADDRNOTAVAIL
]EAFNOSUPPORT
]EISCONN
]sendmsg
() may return the following
errors:
EINVAL
]EMSGSIZE
]IOV_MAX
.EMFILE
]fcntl(2), getsockopt(2), poll(2), recv(2), select(2), socket(2), write(2), CMSG_DATA(3)
The send
(),
sendto
(), and sendmsg
()
functions conform to IEEE Std 1003.1-2008
(“POSIX.1”). The MSG_DONTWAIT
and MSG_NOSIGNAL
flags are extensions to that
specification.
The send
() function call appeared in
4.1cBSD.
January 11, 2019 | OpenBSD-6.7 |