nn_sendmsg(3)

1NN_SENDMSG(3)                    nanomsg 1.1.5                   NN_SENDMSG(3)
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NAME

6       nn_sendmsg - fine-grained alternative to nn_send
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SYNOPSIS

9       #include <nanomsg/nn.h>
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11       int nn_sendmsg (int s, const struct nn_msghdr *msghdr, int flags);
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DESCRIPTION

14       Sends data specified by msghdr parameter to socket s along with any
15       additional control data. msghdr structure should be nullified before
16       being used.
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18       Structure nn_msghdr contains at least following members:
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20           struct nn_iovec *msg_iov;
21           int msg_iovlen;
22           void *msg_control;
23           size_t msg_controllen;
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25       msg_iov points to a scatter array of buffers to send. msg_iovlen
26       specifies the size of the array.
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28       msg_control points to the buffer containing control information to be
29       associated with the message being sent. msg_controllen specifies the
30       length of the buffer. If there’s no control information to send,
31       msg_control should be set to NULL. For detailed discussion of how to
32       set control data check nn_cmsg(3) man page.
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34       Structure nn_iovec defines one element in the scatter array (i.e. a
35       buffer to send to the socket) and contains following members:
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37           void *iov_base;
38           size_t iov_len;
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40       Alternatively, to send a buffer allocated by nn_allocmsg(3) function
41       set iov_base to point to the pointer to the buffer and iov_len to
42       NN_MSG constant. In this case a successful call to nn_sendmsg will
43       deallocate the buffer. Trying to deallocate it afterwards will result
44       in undefined behaviour. Also, scatter array in nn_msghdr structure can
45       contain only one element in this case.
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47       To which of the peers will the message be sent to is determined by the
48       particular socket type.
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50       The flags argument is a combination of the flags defined below:
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52       NN_DONTWAIT
53           Specifies that the operation should be performed in non-blocking
54           mode. If the message cannot be sent straight away, the function
55           will fail with errno set to EAGAIN.
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RETURN VALUE

58       If the function succeeds number of bytes in the message is returned.
59       Otherwise, -1 is returned and errno is set to to one of the values
60       defined below.
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ERRORS

63       EINVAL
64           Either msghdr is NULL, there are multiple scatter buffers but
65           length is set to NN_MSG for one of them, or the sum of iov_len
66           values for the scatter buffers overflows size_t. These are early
67           checks and no pre-allocated message is freed in this case.
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69       EMSGSIZE
70           msghdr→msg_iovlen is negative. This is an early check and no
71           pre-allocated message is freed in this case.
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73       EFAULT
74           The supplied pointer for the pre-allocated message buffer or the
75           scatter buffer is NULL, or the length for the scatter buffer is 0.
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77       EBADF
78           The provided socket is invalid.
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80       ENOTSUP
81           The operation is not supported by this socket type.
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83       EFSM
84           The operation cannot be performed on this socket at the moment
85           because socket is not in the appropriate state. This error may
86           occur with socket types that switch between several states.
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88       EAGAIN
89           Non-blocking mode was requested and the message cannot be sent at
90           the moment.
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92       EINTR
93           The operation was interrupted by delivery of a signal before the
94           message was sent.
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96       ETIMEDOUT
97           Individual socket types may define their own specific timeouts. If
98           such timeout is hit this error will be returned.
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100       ETERM
101           The library is terminating.
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EXAMPLE

104       Usage of multiple scatter buffers:
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106           struct nn_msghdr hdr;
107           struct nn_iovec iov [2];
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109           iov [0].iov_base = "Hello";
110           iov [0].iov_len = 5;
111           iov [1].iov_base = "World";
112           iov [1].iov_len = 5;
113           memset (&hdr, 0, sizeof (hdr));
114           hdr.msg_iov = iov;
115           hdr.msg_iovlen = 2;
116           nn_sendmsg (s, &hdr, 0);
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118       Usage of a single message:
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120           void *msg;
121           struct nn_msghdr hdr;
122           struct nn_iovec iov;
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124           msg = nn_allocmsg(12, 0);
125           strcpy(msg, "Hello World");
126           iov.iov_base = &msg;
127           iov.iov_len = NN_MSG;
128           memset (&hdr, 0, sizeof (hdr));
129           hdr.msg_iov = &iov;
130           hdr.msg_iovlen = 1;
131           nn_sendmsg (s, &hdr, 0);
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AUTHORS

138       Martin Sustrik <sustrik@250bpm.com>
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142                                  2021-01-26                     NN_SENDMSG(3)