nn_getsockopt(3)
================

NAME
----
nn_getsockopt - retrieve a socket option


SYNOPSIS
--------
*#include <nanomsg/nn.h>*

*int nn_getsockopt (int 's', int 'level', int 'option', void '*optval', size_t '*optvallen');*

DESCRIPTION
-----------
Retrieves the value for the 'option'. The 'level' argument specifies
the protocol level at which the option resides. For generic socket-level options
use _NN_SOL_SOCKET_ level. For socket-type-specific options use socket type
for 'level' argument (e.g. _NN_SUB_). For transport-specific options use ID of
the transport as the 'level' argument (e.g. _NN_TCP_).

The value is stored in the buffer pointed to by 'optval' argument. Size of the
buffer is specified by the 'optvallen' argument. If the size of the option is
greater than size of the buffer, the value will be silently truncated.
Otherwise, the 'optvallen' will be modified to indicate the actual length of
the option.

_<nanomsg/nn.h>_ header defines generic socket-level options
(_NN_SOL_SOCKET_ level). The options are as follows:

*NN_DOMAIN*::
    Returns the domain constant as it was passed to _nn_socket()_.
*NN_PROTOCOL*::
    Returns the protocol constant as it was passed to _nn_socket()_.
*NN_LINGER*::
    Specifies how long should the socket try to send pending outbound messages
    after _nn_close()_ have been called, in milliseconds. Negative value means
    infinite linger. The type of the option is int. Default value
    is 1000 (1 second).
*NN_SNDBUF*::
    Size of the send buffer, in bytes. To prevent blocking for messages larger
    than the buffer, exactly one message may be buffered in addition to the data
    in the send buffer. The type of this option is int. Default value is 128kB.
*NN_RCVBUF*::
    Size of the receive buffer, in bytes. To prevent blocking for messages
    larger than the buffer, exactly one message may be buffered in addition
    to the data in the receive buffer. The type of this option is int. Default
    value is 128kB.
*NN_SNDTIMEO*::
    The timeout for send operation on the socket, in milliseconds. If message
    cannot be sent within the specified timeout, EAGAIN error is returned.
    Negative value means infinite timeout. The type of the option is int.
    Default value is -1.
*NN_RCVTIMEO*::
    The timeout for recv operation on the socket, in milliseconds. If message
    cannot be received within the specified timeout, EAGAIN error is returned.
    Negative value means infinite timeout. The type of the option is int.
    Default value is -1.
*NN_RECONNECT_IVL*::
    For connection-based transports such as TCP, this option specifies how
    long to wait, in milliseconds, when connection is broken before trying
    to re-establish it. Note that actual reconnect interval may be randomised
    to some extent to prevent severe reconnection storms. The type of the option
    is int. Default value is 100 (0.1 second).
*NN_RECONNECT_IVL_MAX*::
    This option is to be used only in addition to _NN_RECONNECT_IVL_ option.
    It specifies maximum reconnection interval. On each reconnect attempt,
    the previous interval is doubled until _NN_RECONNECT_IVL_MAX_ is reached.
    Value of zero means that no exponential backoff is performed and reconnect
    interval is based only on _NN_RECONNECT_IVL_. If _NN_RECONNECT_IVL_MAX_ is
    less than _NN_RECONNECT_IVL_, it is ignored. The type of the option is int.
    Default value is 0.
*NN_SNDPRIO*::
    Retrieves outbound priority currently set on the socket. This
    option has no effect on socket types that send messages to all the peers.
    However, if the socket type sends each message to a single peer
    (or a limited set of peers), peers with high priority take precedence
    over peers with low priority. The type of the option is int. Highest
    priority is 1, lowest priority is 16. Default value is 8.
*NN_RCVPRIO*::
    Sets inbound priority for endpoints subsequently added to the socket. This
    option has no effect on socket types that are not able to receive messages.
    When receiving a message, messages from peer with higher priority are
    received before messages from peer with lower priority. The type of the
    option is int. Highest priority is 1, lowest priority is 16. Default value
    is 8.
*NN_IPV4ONLY*::
    If set to 1, only IPv4 addresses are used. If set to 0, both IPv4 and IPv6
    addresses are used. The type of the option is int. Default value is 1.
*NN_SNDFD*::
    Retrieves a file descriptor that is readable when a message can be sent
    to the socket. The descriptor should be used only for polling and never
    read from or written to. The type of the option is same as the type of
    file descriptor on the platform. That is, int on POSIX-complaint platforms
    and SOCKET on Windows. The descriptor becomes invalid and should not be
    used any more once the socket is closed. This socket option is not available
    for unidirectional recv-only socket types.
*NN_RCVFD*::
    Retrieves a file descriptor that is readable when a message can be received
    from the socket. The descriptor should be used only for polling and never
    read from or written to. The type of the option is same as the type of
    file descriptor on the platform. That is, int on POSIX-complaint platforms
    and SOCKET on Windows. The descriptor becomes invalid and should not be
    used any more once the socket is closed. This socket option is not available
    for unidirectional send-only socket types.
*NN_SOCKET_NAME*::
    Socket name for error reporting and statistics. The type of the option
    is string. Default value is "socket.N" where N is socket integer.
    *This option is experimental, see linknanomsg:nn_env[7] for details*


RETURN VALUE
------------
If the function succeeds zero is returned. Otherwise, -1 is
returned and 'errno' is set to to one of the values defined below.


ERRORS
------
*EBADF*::
The provided socket is invalid.
*ENOPROTOOPT*::
The option is unknown at the level indicated.
*ETERM*::
The library is terminating.

EXAMPLE
-------

----
int linger;
size_t sz = sizeof (linger);
nn_getsockopt (s, NN_SOL_SOCKET, NN_LINGER, &linger, &sz);
----


SEE ALSO
--------
linknanomsg:nn_socket[3]
linknanomsg:nn_setsockopt[3]
linknanomsg:nanomsg[7]

AUTHORS
-------
Martin Sustrik <sustrik@250bpm.com>