NN_SENDMSG(3) nanomsg manual NN_SENDMSG(3)NAMEnn_sendmsg - fine-grained alternative to nn_send
SYNOPSIS
#include <nanomsg/nn.h>
int nn_sendmsg (int s, const struct nn_msghdr *msghdr, int flags);
DESCRIPTION
Sends data specified by msghdr parameter to socket s along with any
additional control data. msghdr structure should be nullified before
being used.
Structure nn_msghdr contains at least following members:
struct nn_iovec *msg_iov;
int msg_iovlen;
void *msg_control;
size_t msg_controllen;
msg_iov points to a scatter array of buffers to send. msg_iovlen
specifies the size of the array.
msg_control points to the buffer containing control information to be
associated with the message being sent. msg_controllen specifies the
length of the buffer. If there’s no control information to send,
msg_control should be set to NULL. For detailed discussion of how to
set control data check nn_cmsg(3) man page.
Structure nn_iovec defines one element in the scatter array (i.e. a
buffer to send to the socket) and contains following members:
void *iov_base;
size_t iov_len;
Alternatively, to send a buffer allocated by nn_allocmsg(3) function
set iov_base to point to the pointer to the buffer and iov_len to
NN_MSG constant. In this case a successful call to nn_sendmsg will
deallocate the buffer. Trying to deallocate it afterwards will result
in undefined behaviour. Also, scatter array in nn_msghdr structure can
contain only one element in this case.
To which of the peers will the message be sent to is determined by the
particular socket type.
The flags argument is a combination of the flags defined below:
NN_DONTWAIT
Specifies that the operation should be performed in non-blocking
mode. If the message cannot be sent straight away, the function
will fail with errno set to EAGAIN.
RETURN VALUE
If the function succeeds number of bytes in the message is returned.
Otherwise, -1 is returned and errno is set to to one of the values
defined below.
ERRORS
EINVAL
Either msghdr is NULL, there are multiple scatter buffers but
length is set to NN_MSG for one of them, or the sum of iov_len
values for the scatter buffers overflows size_t. These are early
checks and no pre-allocated message is freed in this case.
EMSGSIZE
msghdr→msg_iovlen is negative. This is an early check and no
pre-allocated message is freed in this case.
EFAULT
The supplied pointer for the pre-allocated message buffer or the
scatter buffer is NULL, or the length for the scatter buffer is 0.
EBADF
The provided socket is invalid.
ENOTSUP
The operation is not supported by this socket type.
EFSM
The operation cannot be performed on this socket at the moment
because socket is not in the appropriate state. This error may
occur with socket types that switch between several states.
EAGAIN
Non-blocking mode was requested and the message cannot be sent at
the moment.
EINTR
The operation was interrupted by delivery of a signal before the
message was sent.
ETIMEDOUT
Individual socket types may define their own specific timeouts. If
such timeout is hit this error will be returned.
ETERM
The library is terminating.
EXAMPLE
Usage of multiple scatter buffers:
struct nn_msghdr hdr;
struct nn_iovec iov [2];
iov [0].iov_base = "Hello";
iov [0].iov_len = 5;
iov [1].iov_base = "World";
iov [1].iov_len = 5;
memset (&hdr, 0, sizeof (hdr));
hdr.msg_iov = iov;
hdr.msg_iovlen = 2;
nn_sendmsg (s, &hdr, 0);
Usage of a single message:
void *msg;
struct nn_msghdr hdr;
struct nn_iovec iov;
msg = nn_allocmsg(12, 0);
strcpy(msg, "Hello World");
iov.iov_base = &msg;
iov.iov_len = NN_MSG;
memset (&hdr, 0, sizeof (hdr));
hdr.msg_iov = &iov;
hdr.msg_iovlen = 1;
nn_sendmsg (s, &hdr, 0);
SEE ALSOnn_send(3)nn_recvmsg(3)nn_allocmsg(3)nn_freemsg(3)nn_cmsg(3)nanomsg(7)AUTHORS
Martin Sustrik <sustrik@250bpm.com[1]>
NOTES
1. sustrik@250bpm.com
mailto:sustrik@250bpm.com
nanomsg Unknown 12/23/2015 NN_SENDMSG(3)
