illumos: manual page: sendmsg.3socket

SEND(3SOCKET) Sockets Library Functions SEND(3SOCKET)

NAME

send, sendto, sendmsg - send a message from a socket

SYNOPSIS

cc [ flag... ] file... -lsocket -lnsl [ library... ]
#include <sys/types.h>
#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, int tolen);

ssize_t sendmsg(int s, const struct msghdr *msg, int flags);

DESCRIPTION

The send(), sendto(), and sendmsg() functions are used to transmit a
message to another transport end-point. The send() function can be used
only when the socket is in a connected state. See connect(3SOCKET). The
sendto() and sendmsg() functions can be used at any time. The s socket is
created with socket(3SOCKET).

The address of the target is supplied by to with a tolen parameter used
to specify the size. The length of the message is supplied by the len
parameter. For socket types such as SOCK_DGRAM and SOCK_RAW that require
atomic messages, the error EMSGSIZE is returned and the message is not
transmitted when it is too long to pass atomically through the underlying
protocol. The same restrictions do not apply to SOCK_STREAM sockets.

A return value -1 indicates locally detected errors. It does not imply a
delivery failure.

If the socket does not have enough buffer space available to hold a
message, the send() function blocks the message, unless the socket has
been placed in non-blocking I/O mode (see fcntl(2)). The select(3C) or
poll(2) call can be used to determine when it is possible to send more
data.

The flags parameter is formed from the bitwise OR of zero or more of the
following:

MSG_OOB
Send out-of-band data on sockets that support this
notion. The underlying protocol must also support out-
of-band data. Only SOCK_STREAM sockets created in the
AF_INET or the AF_INET6 address family support out-of-
band data.

MSG_DONTROUTE
The SO_DONTROUTE option is turned on for the duration of
the operation. It is used only by diagnostic or routing
programs.

MSG_NOSIGNAL
Don't generate the SIGPIPE signal when a stream-oriented
socket is no longer connected.

The sendmsg() function call uses a msghdr structure defined in
<sys/socket.h> to minimize the number of directly supplied parameters.

RETURN VALUES

Upon successful completion, these functions return the number of bytes
sent. Otherwise, they return -1 and set errno to indicate the error.

ERRORS

In addition to the errors documented below, an asynchronous error
generated by the underlying socket protocol may be returned. For the full
list of errors, please see the corresponding socket protocol manual page.
For example, for a list of TCP errors, please see tcp(4P).

The send(), sendto(), and sendmsg() functions return errors under the
following conditions:

EBADF
s is not a valid file descriptor.

ECONNRESET
The s argument refers to a connection oriented socket and
the connection was forcibly closed by the peer and is no
longer valid. I/O can no longer be performed to filedes.

EINTR
The operation was interrupted by delivery of a signal
before any data could be buffered to be sent.

EMSGSIZE
The message is too large to be sent all at once (as the
socket requires), or the msg_iovlen member of the msghdr
structure pointed to by message is less than or equal to
0 or is greater than {IOV_MAX}.

ENOMEM
Insufficient memory is available to complete the
operation.

ENOSR
Insufficient STREAMS resources are available for the
operation to complete.

ENOTSOCK
s is not a socket.

EWOULDBLOCK
The socket is marked non-blocking and the requested
operation would block. EWOULDBLOCK is also returned when
sufficient memory is not immediately available to
allocate a suitable buffer. In such a case, the operation
can be retried later.

ECONNREFUSED
The requested connection was refused by the peer. For
connected IPv4 and IPv6 datagram sockets, this indicates
that the system received an ICMP Destination Port
Unreachable message from the peer in response to some
prior transmission.

The send() and sendto() functions return errors under the following
conditions:

EINVAL
The len argument overflows a ssize_t.

Inconsistent port attributes for system call.

The sendto() function returns errors under the following conditions:

EINVAL
The value specified for the tolen parameter is not the size of
a valid address for the specified address family.

EISCON
A destination address was specified and the socket is already
connected.

The sendmsg() function returns errors under the following conditions:

EINVAL
The msg_iovlen member of the msghdr structure pointed to by msg
is less than or equal to 0, or the sum of the iov_len values in
the msg_iov array overflows a ssize_t.

One of the iov_len values in the msg_iov array member of the
msghdr structure pointed to by msg is negative, or the sum of
the iov_len values in the msg_iov array overflows a ssize_t.

msg_iov contents are inconsistent with port attributes.

The send() function returns errors under the following conditions:

EPIPE
The socket is shut down for writing, or the socket is
connection-mode and is no longer connected. In the latter case,
if the socket is of type SOCK_STREAM, the SIGPIPE signal is
generated to the calling thread unless the MSG_NOSIGNAL flag is
set.