nn_recvmsg(3)

1NN_RECVMSG(3)                    nanomsg 1.1.5                   NN_RECVMSG(3)
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NAME

6       nn_recvmsg - fine-grained alternative to nn_recv
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SYNOPSIS

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

14       Receives a message from socket s into buffers specified by msghdr
15       parameter along with any additional control data. msghdr parameter
16       should be nullified before 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 gather array of buffers to fill in. msg_iovlen
26       specifies the size of the array.
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28       msg_control points to the buffer to hold control information
29       associated with the received message. msg_controllen specifies the
30       length of the buffer. If the control information should not be
31       retrieved, set msg_control parameter to NULL. For detailed discussion
32       of how to parse the control information check nn_cmsg(3) man page.
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34       Structure nn_iovec defines one element in the gather array (a buffer to
35       be filled in by message data) and contains following members:
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37           void *iov_base;
38           size_t iov_len;
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40       Alternatively, nanomsg library can allocate the buffer for you. To do
41       so, let the iov_base point to void* variable to receive the buffer and
42       set iov_len to NN_MSG. After successful completion user is responsible
43       for deallocating the message using nn_freemsg(3) function. Gather array
44       in nn_msghdr structure can contain only one element in this case.
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46       The flags argument is a combination of the flags defined below:
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48       NN_DONTWAIT
49           Specifies that the operation should be performed in non-blocking
50           mode. If the message cannot be received straight away, the function
51           will fail with errno set to EAGAIN.
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RETURN VALUE

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

59       EBADF
60           The provided socket is invalid.
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62       ENOTSUP
63           The operation is not supported by this socket type.
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65       EFSM
66           The operation cannot be performed on this socket at the moment
67           because socket is not in the appropriate state. This error may
68           occur with socket types that switch between several states.
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70       EAGAIN
71           Non-blocking mode was requested and there’s no message to receive
72           at the moment.
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74       EINTR
75           The operation was interrupted by delivery of a signal before the
76           message was received.
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78       ETIMEDOUT
79           Individual socket types may define their own specific timeouts. If
80           such timeout is hit this error will be returned.
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82       ETERM
83           The library is terminating.
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EXAMPLE

86           struct nn_msghdr hdr;
87           struct nn_iovec iov [2];
88           char buf0 [4];
89           char buf1 [2];
90           iov [0].iov_base = buf0;
91           iov [0].iov_len = sizeof (buf0);
92           iov [1].iov_base = buf1;
93           iov [1].iov_len = sizeof (buf1);
94           memset (&hdr, 0, sizeof (hdr));
95           hdr.msg_iov = iov;
96           hdr.msg_iovlen = 2;
97           nn_recvmsg (s, &hdr, 0);
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AUTHORS

104       Martin Sustrik <sustrik@250bpm.com>
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108                                  2021-07-22                     NN_RECVMSG(3)