nn_recv(3)

1NN_RECV(3)                       nanomsg 1.1.5                      NN_RECV(3)
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NAME

6       nn_recv - receive a message
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SYNOPSIS

9       #include <nanomsg/nn.h>
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11       int nn_recv (int s, void *buf, size_t len, int flags);
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DESCRIPTION

14       Receive a message from the socket s and store it in the buffer
15       referenced by the buf argument. Any bytes exceeding the length
16       specified by the len argument will be truncated.
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18       Alternatively, nanomsg can allocate the buffer for you. To do so, let
19       the buf parameter be a pointer to a void* variable (pointer to pointer)
20       to the receive buffer and set the len parameter to NN_MSG. If the call
21       is successful the user is responsible for deallocating the message
22       using the nn_freemsg(3) function.
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24       The flags argument is a combination of the flags defined below:
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26       NN_DONTWAIT
27           Specifies that the operation should be performed in non-blocking
28           mode. If the message cannot be received straight away, the function
29           will fail with errno set to EAGAIN.
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RETURN VALUE

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

37       EBADF
38           The provided socket is invalid.
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40       ENOTSUP
41           The operation is not supported by this socket type.
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43       EFSM
44           The operation cannot be performed on this socket at the moment
45           because socket is not in the appropriate state. This error may
46           occur with socket types that switch between several states.
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48       EAGAIN
49           Non-blocking mode was requested and there’s no message to receive
50           at the moment.
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52       EINTR
53           The operation was interrupted by delivery of a signal before the
54           message was received.
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56       ETIMEDOUT
57           Individual socket types may define their own specific timeouts. If
58           such timeout is hit this error will be returned.
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60       ETERM
61           The library is terminating.
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EXAMPLES

64       Receiving a message into a buffer allocated by the user
65           This example code will retrieve a message of either 100 bytes or
66           less. If a larger message was sent it will be truncated to 100
67           bytes.
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69           char buf [100];
70           nbytes = nn_recv (s, buf, sizeof (buf), 0);
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72       Receiving a message into a buffer allocated by nanomsg
73           The following will get a message from the pipe with a buffer
74           allocated by the system. It is large enough to accommodate the
75           entire message. This is a good way to get the entire message
76           without truncating if the size of the message is unknown. It is the
77           user’s responsibility to call nn_freemsg(3) after processing the
78           message.
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80           void *buf = NULL;
81           nbytes = nn_recv (s, &buf, NN_MSG, 0);
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83           if (nbytes < 0) {
84               /* handle error */
85               ...
86           }
87           else {
88               /* process message */
89               ...
90               nn_freemsg (buf);
91           }
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93       Note that this can be more efficient than manually allocating a buffer
94       since it is a zero-copy operation.
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AUTHORS

100       Martin Sustrik <sustrik@250bpm.com>
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104                                  2020-08-24                        NN_RECV(3)