= nn_setsockopt(3compat)
//
// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
// Copyright 2018 Capitar IT Group BV <info@capitar.com>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

== NAME

nn_setsockopt - set socket option (compatible API)

== SYNOPSIS

[source,c]
----
#include <nanomsg/nn.h>

int nn_setsockopt(int sock, int level, int option, const void *val, size_t sz);
----

== DESCRIPTION

The `nn_setsockopt()` function sets a socket option on socket _sock_,
affecting the behavior of the socket.
The option set is determined by the _level_ and _option_.
The value of the option is set by _val_, and _sz_, which are pointers to
the actual value and the size of the value, respectively.

NOTE: This function is provided for API
<<nng_compat.3compat#,compatibility>> with legacy _libnanomsg_.
Consider using the relevant <<libnng.3#,modern API>> instead.

The _level_ determines whether the option is a generic socket option,
or is transport-specific.
The values possible for level are as follows:

[horizontal]
`NN_SOL_SOCKET`:: Generic socket option
`NN_IPC`:: Transport specific option for IPC.
`NN_TCP`:: Transport specific option for TCP.
`NN_WS`:: Transport specific option for WebSocket.

The following generic socket options are possible (all are of type `int` and
thus size 4, unless otherwise indicated.)

`NN_SNDBUF`::
Send buffer size in bytes.

NOTE: In _nng_ buffers are sized as a count of messages rather than
bytes, and so an attempt to estimate a conversion based upon a predetermined
message size of 1kB is made.
The value supplied is rouned up to the nearest value divisible by 1024, and
then divided by 1024 to convert to a message count.
Applications that have unusual message sizes may wish to adjust the value
used here accordingly.

`NN_RCVBUF`::
Receive buffer size in bytes.

NOTE: The same caveats for `NN_SNDBUF` apply here as well.

`NN_SNDTIMEO`::
Send time-out in milliseconds.
Send operations will fail with `ETIMEDOUT` if no message can be received
after this many milliseconds have transpired since the operation was started.
A value of -1 means that no timeout is applied.

`NN_RCVTIMEO`::
Receive time-out in milliseconds.
Receive operations will fail with `ETIMEDOUT` if no message can be received
after this many milliseconds have transpired since the operation was started.
A value of -1 means that no timeout is applied.

`NN_RCVMAXSIZE`::
Maximum receive size in bytes.
The socket will discard messages larger than this on receive.
The default, 1MB, is intended to prevent denial-of-service attacks.
The value -1 removes any limit.

`NN_RECONNECT_IVL`::
Reconnect interval in milliseconds.
After an outgoing connection is closed or fails, the socket will
automatically attempt to reconnect after this many milliseconds.
This is the starting value for the time, and is used in the first
reconnection attempt after a successful connection is made.
The default is 100.

`NN_RECONNECT_IVL_MAX`::
Maximum reconnect interval in milliseconds.
Subsequent reconnection attempts after a failed attempt are made at
exponentially increasing intervals (backoff), but the interval is
capped by this value.
If this value is smaller than `NN_RECONNECT_IVL`, then no exponential
backoff is performed, and each reconnect interval will be determined
solely by `NN_RECONNECT_IVL`.
The default is zero.

`NN_LINGER`::
This option is ignored, and exists only for compatibility.

NOTE: This option was unreliable in early releases of _libnanomsg_, and
is unsupported in _nng_ and recent _libnanomsg_ releases.
Applications needing assurance of message delivery should either include an
explicit notification (automatic with the `NN_REQ` protocol) or allow
sufficient time for the socket to drain before closing the socket or exiting.

`NN_SNDPRIO`::
This option is not implemented at this time.

`NN_RCVPRIO`::
This option is not implemented at this time.

`NN_IPV4ONLY`::
This option is not implemented at this time.

`NN_SOCKET_NAME`::
This option is a string, and represents the socket name.
It can be changed to help with identifying different sockets with
their different application-specific purposes.

`NN_MAXTTL`::
Maximum "`hops`" through proxies and devices a message may go through.
This value, if positive, provides some protection against forwarding loops in
<<nng_device.3#,device>> chains.

NOTE: Not all protocols offer this protection, so care should still be used
in configuring device forwarding.

The following option is available for `NN_REQ` sockets
using the `NN_REQ` level:

`NN_REQ_RESEND_IVL`::
Request retry interval in milliseconds.
If an `NN_REQ` socket does not receive a reply to a request within this
period of time, the socket will automatically resend the request.
The default value is 60000 (one minute).

The following options are available for `NN_SUB` sockets using the `NN_SUB` level:

`NN_SUB_SUBSCRIBE`::
Subscription topic, for `NN_SUB` sockets.
This sets a subscription topic.
When a message from a publisher arrives, it is compared against all
subscriptions.
If the first _sz_ bytes of the message are not identical to _val_,
then the message is silently discarded.

TIP: To receive all messages, subscribe to an empty topic (_sz_ equal to zero).

`NN_SUB_UNSUBSCRIBE`::
Removes a subscription topic that was earlier established.

The following option is available for `NN_SURVEYOR` sockets
using the `NN_SURVEYOR` level:

`NN_SURVEYOR_DEADLINE`::
Survey deadline in milliseconds for `NN_SURVEYOR` sockets.
After sending a survey message, the socket will only accept responses
from respondents for this long.
Any responses arriving after this expires are silently discarded.

In addition, the following transport specific options are offered:

`NN_IPC_SEC_ATTR`::
This `NN_IPC` option is not supported at this time.

`NN_IPC_OUTBUFSZ`::
This `NN_IPC` option is not supported at this time.

`NN_IPC_INBUFSZE`::
This `NN_IPC` option is not supported at this time.

`NN_TCP_NODELAY`::
This `NN_TCP` option is not supported at this time.

`NN_WS_MSG_TYPE`::
This `NN_WS` option is not supported, as _nng_ only supports binary messages
in this implementation.

== RETURN VALUES

This function returns zero on success, and -1 on failure.

== ERRORS

[horizontal]
`EBADF`:: The socket _sock_ is not an open socket.
`ENOMEM`:: Insufficient memory is available.
`ENOPROTOOPT`:: The level and/or option is invalid.
`EINVAL`:: The option, or the value passed, is invalid.
`ETERM`:: The library is shutting down.
`EACCES`:: The option cannot be changed.

== SEE ALSO

[.text-left]
<<nng_socket.5#,nng_socket(5)>>,
<<nn_close.3compat#,nn_close(3compat)>>,
<<nn_errno.3compat#,nn_errno(3compat)>>,
<<nn_getsockopt.3compat#,nn_getsockopt(3compat)>>,
<<nng_compat.3compat#,nng_compat(3compat)>>,
<<nng.7#,nng(7)>>
