xs_getsockopt(3)
================


NAME
----

xs_getsockopt - get Crossroads socket option


SYNOPSIS
--------
*int xs_getsockopt (void '*socket', int 'option_name', void '*option_value', size_t '*option_len');*


DESCRIPTION
-----------
The _xs_getsockopt()_ function shall retrieve the value for the option
specified by the 'option_name' argument for the Crossroads socket pointed to by
the 'socket' argument, and store it in the buffer pointed to by the
'option_value' argument. The 'option_len' argument is the size in bytes of the
buffer pointed to by 'option_value'; upon successful completion
_xs_getsockopt()_ shall modify the 'option_len' argument to indicate the actual
size of the option value stored in the buffer.

The following options can be retrieved with the _xs_getsockopt()_ function:


XS_TYPE: Retrieve socket type
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_TYPE' option shall retrieve the socket type for the specified
'socket'.  The socket type is specified at socket creation time and
cannot be modified afterwards.

[horizontal]
Option value type:: int
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: all


XS_RCVMORE: More message data parts to follow
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RCVMORE' option shall return True (1) if the message part last
received from the 'socket' was a data part with more parts to follow. If there
are no data parts to follow, this option shall return False (0).

Refer to linkxs:xs_send[3] and linkxs:xs_recv[3] for a detailed description
of multi-part messages.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: N/A
Applicable socket types:: all


XS_SNDHWM: Retrieves high water mark for outbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_SNDHWM' option shall return the high water mark for outbound messages
on the specified 'socket'. The high water mark is a hard limit on the maximum
number of outstanding messages the library shall queue in memory for any single
peer that the specified 'socket' is communicating with.

If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, the library shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in linkxs:xs_socket[3] for details on the exact action taken for each socket
type.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 1000
Applicable socket types:: all


XS_RCVHWM: Retrieve high water mark for inbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RCVHWM' option shall return the high water mark for inbound messages on
the specified 'socket'. The high water mark is a hard limit on the maximum
number of outstanding messages the library shall queue in memory for any single
peer that the specified 'socket' is communicating with.

If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, the library shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in linkxs:xs_socket[3] for details on the exact action taken for each socket
type.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 1000
Applicable socket types:: all


XS_AFFINITY: Retrieve I/O thread affinity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_AFFINITY' option shall retrieve the I/O thread affinity for newly
created connections on the specified 'socket'.

Affinity determines which threads from the Crossroads I/O thread pool associated
with the socket's _context_ shall handle newly created connections.  A value of
zero specifies no affinity, meaning that work shall be distributed fairly among
all I/O threads in the thread pool. For non-zero values, the lowest bit
corresponds to thread 1, second lowest bit to thread 2 and so on.  For example,
a value of 3 specifies that subsequent connections on 'socket' shall be handled
exclusively by I/O threads 1 and 2.

See also linkxs:xs_init[3] for details on allocating the number of I/O
threads for a specific _context_.

[horizontal]
Option value type:: uint64_t
Option value unit:: N/A (bitmap)
Default value:: 0
Applicable socket types:: N/A

XS_IDENTITY: Set socket identity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_IDENTITY' option shall retrieve the identity of the specified 'socket'.
Socket identity is used only by request/reply pattern. Namely, it can be used
in tandem with a 'XS_XREP' socket to route messages to the peer with specific
identity.

Identity should be at least one byte and at most 255 bytes long. Identities
starting with binary zero are reserved for use by Crossroads infrastructure.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: NULL
Applicable socket types:: all


XS_RATE: Retrieve multicast data rate
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RATE' option shall retrieve the maximum send or receive data rate for
multicast transports using the specified 'socket'.

[horizontal]
Option value type:: int
Option value unit:: kilobits per second
Default value:: 100
Applicable socket types:: all, when using multicast transports


XS_RECOVERY_IVL: Get multicast recovery interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RECOVERY_IVL' option shall retrieve the recovery interval for
multicast transports using the specified 'socket'.  The recovery interval
determines the maximum time in milliseconds that a receiver can be absent from a
multicast group before unrecoverable data loss will occur.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 10000
Applicable socket types:: all, when using multicast transports


XS_SNDBUF: Retrieve kernel transmit buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_SNDBUF' option shall retrieve the underlying kernel transmit buffer
size for the specified 'socket'. A value of zero means that the OS default is
in effect. For details refer to your operating system documentation for the
'SO_SNDBUF' socket option.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


XS_RCVBUF: Retrieve kernel receive buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RCVBUF' option shall retrieve the underlying kernel receive buffer
size for the specified 'socket'. A value of zero means that the OS default is
in effect. For details refer to your operating system documentation for the
'SO_RCVBUF' socket option.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


XS_LINGER: Retrieve linger period for socket shutdown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_LINGER' option shall retrieve the linger period for the specified
'socket'.  The linger period determines how long pending messages which have
yet to be sent to a peer shall linger in memory after a socket is closed with
linkxs:xs_close[3], and further affects the termination of the socket's
context with linkxs:xs_term[3]. The following outlines the different
behaviours:

* The default value of '-1' specifies an infinite linger period. Pending
  messages shall not be discarded after a call to _xs_close()_; attempting to
  terminate the socket's context with _xs_term()_ shall block until all
  pending messages have been sent to a peer.

* The value of '0' specifies no linger period. Pending messages shall be
  discarded immediately when the socket is closed with _xs_close()_.

* Positive values specify an upper bound for the linger period in milliseconds.
  Pending messages shall not be discarded after a call to _xs_close()_;
  attempting to terminate the socket's context with _xs_term()_ shall block
  until either all pending messages have been sent to a peer, or the linger
  period expires, after which any pending messages shall be discarded.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


XS_RECONNECT_IVL: Retrieve reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RECONNECT_IVL' option shall retrieve the initial reconnection interval
for the specified 'socket'.  The reconnection interval is the period the library
shall wait between attempts to reconnect disconnected peers when using
connection-oriented transports.

NOTE: The reconnection interval may be randomized by the library to prevent
reconnection storms in topologies with a large number of peers per socket.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports


XS_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_RECONNECT_IVL_MAX' option shall retrieve the maximum reconnection
interval for the specified 'socket'.  This is the maximum period the library
shall wait between attempts to reconnect. On each reconnect attempt, the
previous interval shall be doubled untill XS_RECONNECT_IVL_MAX is reached. This
allows for exponential backoff strategy. Default value means no exponential
backoff is  performed and reconnect interval calculations are only based on
XS_RECONNECT_IVL.

NOTE:  Values less than XS_RECONNECT_IVL will be ignored.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 0 (only use XS_RECONNECT_IVL)
Applicable socket types:: all, only for connection-oriented transport


XS_BACKLOG: Retrieve maximum length of the queue of outstanding connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_BACKLOG' option shall retrieve the maximum length of the queue of
outstanding peer connections for the specified 'socket'; this only applies to
connection-oriented transports. For details refer to your operating system
documentation for the 'listen' function.

[horizontal]
Option value type:: int
Option value unit:: connections
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports


XS_MAXMSGSIZE: Maximum acceptable inbound message size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The option shall retrieve limit for the inbound messages. If a peer sends
a message larger than XS_MAXMSGSIZE it is disconnected.

[horizontal]
Option value type:: uint64_t
Option value unit:: bytes
Default value:: 2^64-1
Applicable socket types:: all


XS_MULTICAST_HOPS: Maximum network hops for multicast packets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The option shall retrieve time-to-live used for outbound multicast packets.
The default of 1 means that the multicast packets don't leave the local network.

[horizontal]
Option value type:: int
Option value unit:: network hops
Default value:: 1
Applicable socket types:: all, when using multicast transports


XS_RCVTIMEO: Maximum time before a socket operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieve the timeout for recv operation on the socket.  If the value is `0`,
_xs_recv(3)_ will return immediately, with a EAGAIN error if there is no
message to receive. If the value is `-1`, it will block until a message is
available. For all other values, it will wait for a message for that amount
of time before returning with an EAGAIN error.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


XS_SNDTIMEO: Maximum time before a socket operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieve the timeout for send operation on the socket. If the value is `0`,
_xs_send(3)_ will return immediately, with a EAGAIN error if the message
cannot be sent. If the value is `-1`, it will block until the message is sent.
For all other values, it will try to send the message for that amount of time
before returning with an EAGAIN error.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


XS_IPV4ONLY: Retrieve IPv4-only socket override status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieve the underlying native socket type.  A value of `1` will use IPv4
sockets, while the value of `0` will use IPv6 sockets. An IPv6 socket
lets applications connect to and accept connections from both IPv4 and IPv6
hosts.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 1 (true)
Applicable socket types:: all, when using TCP transport.


XS_FD: Retrieve file descriptor associated with the socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_FD' option shall retrieve the file descriptor associated with the
specified 'socket'. The returned file descriptor can be used to integrate the
socket into an existing event loop; the library shall signal any pending
events on the socket in an _edge-triggered_ fashion by making the file
descriptor become ready for reading.

NOTE: The ability to read from the returned file descriptor does not
necessarily indicate that messages are available to be read from, or can be
written to, the underlying socket; applications must retrieve the actual event
state with a subsequent retrieval of the 'XS_EVENTS' option.

NOTE: The returned file descriptor is also used internally by the 'xs_send'
and 'xs_recv' functions. As the descriptor is edge triggered, applications
must update the state of 'XS_EVENTS' after each invocation of 'xs_send'
or 'xs_recv'.To be more explicit: after calling 'xs_send' the socket may
become readable (and vice versa) without triggering a read event on the
file descriptor.

CAUTION: The returned file descriptor is intended for use with a 'poll' or
similar system call only. Applications must never attempt to read or write data
to it directly, neither should they try to close it.

[horizontal]
Option value type:: int on POSIX systems, SOCKET on Windows
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: all


XS_EVENTS: Retrieve socket event state
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'XS_EVENTS' option shall retrieve the event state for the specified
'socket'.  The returned value is a bit mask constructed by OR'ing a combination
of the following event flags:

*XS_POLLIN*::
Indicates that at least one message may be received from the specified socket
without blocking.

*XS_POLLOUT*::
Indicates that at least one message may be sent to the specified socket without
blocking.

The combination of a file descriptor returned by the 'XS_FD' option being
ready for reading but no actual events returned by a subsequent retrieval of
the 'XS_EVENTS' option is valid; applications should simply ignore this case
and restart their polling operation/event loop.

[horizontal]
Option value type:: int
Option value unit:: N/A (flags)
Default value:: N/A
Applicable socket types:: all


XS_KEEPALIVE: Enable transport keepalives
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When set to `1`, this option enables use of protocol keepalives on the
'socket', if supported by the underlying transport protocol.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: all, when using TCP transport.


XS_SURVEY_TIMEOUT: Retrieve deadline for the survey
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Specifies how long to wait for responses to the survey. After the interval
expires, any firther calls to xs_recv() will return EAGAIN error. All the
responses received later on will be silently discarded. Value of -1 means
infinite.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: XS_SURVEYOR


RETURN VALUE
------------
The _xs_getsockopt()_ function shall return zero if successful. Otherwise it
shall return `-1` and set 'errno' to one of the values defined below.


ERRORS
------
*EINVAL*::
The requested option _option_name_ is unknown, or the requested _option_len_ or
_option_value_ is invalid, or the size of the buffer pointed to by
_option_value_, as specified by _option_len_, is insufficient for storing the
option value.
*ETERM*::
The 'context' associated with the specified 'socket' was terminated.
*ENOTSOCK*::
The provided 'socket' was invalid.
*EINTR*::
The operation was interrupted by delivery of a signal.


EXAMPLE
-------
.Retrieving the high water mark for outgoing messages
----
/* Retrieve high water mark into sndhwm */
int sndhwm;
size_t sndhwm_size = sizeof (sndhwm);
rc = xs_getsockopt (socket, XS_SNDHWM, &sndhwm, &sndhwm_size);
assert (rc == 0);
----


SEE ALSO
--------
linkxs:xs_setsockopt[3]
linkxs:xs_socket[3]
linkxs:xs[7]


AUTHORS
-------
The Crossroads documentation was written by Martin Sustrik <sustrik@250bpm.com>
and Martin Lucina <martin@lucina.net>.
