Ubuntu Manpage: nng_options - socket, dialer, listener, and pipe options

NAME

       nng_options - socket, dialer, listener, and pipe options

SYNOPSIS

           #include <nng/nng.h>

           #define NNG_OPT_SOCKNAME      "socket-name"
           #define NNG_OPT_RAW           "raw"
           #define NNG_OPT_PROTO         "protocol"
           #define NNG_OPT_PROTONAME     "protocol-name"
           #define NNG_OPT_PEER          "peer"
           #define NNG_OPT_PEERNAME      "peer-name"
           #define NNG_OPT_RECVBUF       "recv-buffer"
           #define NNG_OPT_SENDBUF       "send-buffer"
           #define NNG_OPT_RECVFD        "recv-fd"
           #define NNG_OPT_SENDFD        "send-fd"
           #define NNG_OPT_RECVTIMEO     "recv-timeout"
           #define NNG_OPT_SENDTIMEO     "send-timeout"
           #define NNG_OPT_LOCADDR       "local-address"
           #define NNG_OPT_REMADDR       "remote-address"
           #define NNG_OPT_URL           "url"
           #define NNG_OPT_MAXTTL        "ttl-max"
           #define NNG_OPT_RECVMAXSZ     "recv-size-max"
           #define NNG_OPT_RECONNMINT    "reconnect-time-min"
           #define NNG_OPT_RECONNMAXT    "reconnect-time-max"
           #define NNG_OPT_PEER_GID      "ipc:peer-gid"
           #define NNG_OPT_PEER_PID      "ipc:peer-pid"
           #define NNG_OPT_PEER_UID      "ipc:peer-uid"
           #define NNG_OPT_PEER_ZONEID   "ipc:peer-zoneid"

DESCRIPTION

This page documents the various standard options that can be set or retrieved on objects.

Sockets (nng_socket objects) use the functions nng_socket_get() and nng_socket_set() to
set and retrieve option values.

Dialers (nng_dialer objects) use the functions nng_dialer_get() and nng_dialer_set() to
set and retrieve option values.

Listeners (nng_listener objects) use the functions nng_listener_get() and
nng_listener_set() to set and retrieve option values.

Pipes (nng_pipe objects) can only retrieve option values using the nng_pipe_get()
function.

Other object types may have additional methods to access these options.

In addition to the options listed here, transports and protocols will generally have some
of their own options, which will be documented with the transport or protocol.

Generic Options
In the following list of options, the name of the option is supplied, along with the data
type of the underlying value.

Some options are only meaningful or supported in certain contexts; for example there is no
single meaningful address for a socket, since sockets can have multiple dialers and
endpoints associated with them. An attempt has been made to include details about such
restrictions in the description of the option.

NNG_OPT_LOCADDR
(nng_sockaddr) This read-only option may be used on listeners, dialers and connected
pipes, and represents the local address used for communication. NOTE: Not all
transports support this option, and some transports may support it on listeners but
not dialers.

When used on a TCP dialer, this option is used to configure the source IP address that
will be used when initiating outgoing connections. The specific port number will be
ignored, however, and the system will choose a random ephemeral port instead.

NNG_OPT_RAW

(bool) This read-only option indicates whether the socket is in raw mode. If true, the
socket is in raw mode, and if false the socket is in normal mode.

Raw mode sockets generally do not have any protocol-specific semantics applied to
them; instead the application is expected to perform such semantics itself. (For
example, in normal mode a rep socket would automatically copy message headers from a
received message to the corresponding reply, whereas in raw mode this is not done.)
See Raw Mode for more details.

NNG_OPT_RECONNMINT

(nng_duration) This is the minimum amount of time (milliseconds) to wait before
attempting to establish a connection after a previous attempt has failed. This can be
set on a socket, but it can also be overridden on an individual dialer. The option is
irrelevant for listeners.

NNG_OPT_RECONNMAXT

(nng_duration) This is the maximum amount of time (milliseconds) to wait before
attempting to establish a connection after a previous attempt has failed. If this is
non-zero, then the time between successive connection attempts will start at the value
of NNG_OPT_RECONNMINT, and grow exponentially, until it reaches this value. If this
value is zero, then no exponential back-off between connection attempts is done, and
each attempt will wait the time specified by NNG_OPT_RECONNMINT. This can be set on a
socket, but it can also be overridden on an individual dialer. The option is
irrelevant for listeners.

NNG_OPT_RECVBUF

(int) This is the depth of the socket’s receive buffer as a number of messages.
Messages received by a transport may be buffered until the application has accepted
them for delivery. This value must be an integer between 0 and 8192, inclusive. NOTE:
Not all protocols support buffering received messages. For example req can only deal
with a single reply at a time.

NNG_OPT_RECVFD

(int) This read-only option is used to obtain an integer file descriptor suitable for
use with poll() <http://pubs.opengroup.org/onlinepubs/7908799/xsh/poll.html>, select()
<http://pubs.opengroup.org/onlinepubs/7908799/xsh/select.html>, (or on Windows systems
WSAPoll()
<https://msdn.microsoft.com/en-us/library/windows/desktop/ms741669(v=vs.85).aspx>) and
similar functions. This descriptor will be readable when a message is available for
receiving on the socket. When no message is ready for receiving, then this file
descriptor will not be readable.

Important
Applications should never attempt to read or write to the returned file
descriptor.

Important
This option is incompatible with nng_ctx contexts and should not be used on a
socket where they are in use.

Tip
While this option may help applications integrate into existing polling loops, it
is more efficient, and often easier, to use the asynchronous I/O objects instead.
See nng_aio_alloc().

NNG_OPT_RECVMAXSZ

(size_t) This is the maximum message size that the will be accepted from a remote
peer. If a peer attempts to send a message larger than this, then the message will be
discarded. If the value of this is zero, then no limit on message sizes is enforced.
This option exists to prevent certain kinds of denial-of-service attacks, where a
malicious agent can claim to want to send an extraordinarily large message, without
sending any data. This option can be set for the socket, but may be overridden for on
a per-dialer or per-listener basis.

Important
Applications on hostile networks should set this to a non-zero value to prevent
denial-of-service attacks.

Important
This option should be set before any listeners or dialers are added. Ideally this
option should be set on specific dialers or listeners; setting it on the socket
globally is deprecated behavior, and might not work in a future release, or might
only work for endpoints that have not yet been created. (Maximum receive sizes
might be negotiated during connection establishment for future transports, which
means that the option needs to be set before any connections are established.)

Note
Some transports may have further message size restrictions.

NNG_OPT_RECVTIMEO

(nng_duration) This is the socket receive timeout in milliseconds. When no message is
available for receiving at the socket for this period of time, receive operations will
fail with a return value of NNG_ETIMEDOUT.

NNG_OPT_REMADDR
(nng_sockaddr) This read-only option may be used on dialers and connected pipes, and
represents the address of a remote peer. Not all transports support this option.

NNG_OPT_SENDBUF

(int) This is the depth of the socket send buffer as a number of messages. Messages
sent by an application may be buffered by the socket until a transport is ready to
accept them for delivery. This value must be an integer between 0 and 8192, inclusive.

Note
Not all protocols support buffering sent messages. For example, req can only have
a single request outstanding at a time (per context).

NNG_OPT_SENDFD

This descriptor will be readable when the socket is able to accept a message for
sending without blocking. When the socket is no longer able to accept such messages
without blocking, the descriptor will not be readable.

Important
Applications should never attempt to read or write to the returned file
descriptor; use should be limited to polling system calls only.

Important
This option is incompatible with nng_ctx contexts and should not be used on a
socket where they are in use.

Tip
While this option may help applications integrate into existing polling loops, it
is more efficient, and often easier, to use the asynchronous I/O objects instead.
See nng_aio_alloc().

NNG_OPT_SENDTIMEO

(nng_duration) This is the socket send timeout in milliseconds. When a message cannot
be queued for delivery by the socket for this period of time (such as if send buffers
are full), the operation will fail with a return value of NNG_ETIMEDOUT.

NNG_OPT_SOCKNAME

(string) This the socket name. By default, this is a string corresponding to the value
of the socket. The string must fit within 64-bytes, including the terminating NUL
byte. The value is intended for application use, and is not used for anything in the
library itself.

NNG_OPT_MAXTTL
(int)

This is the maximum number of times a message may traverse across a nng_device()
forwarders. The intention here is to prevent forwarding loops in device chains. When
this is supported, it can have a value between 1 and 255, inclusive.

Note
Not all protocols support this option. Those that do generally have a default
value of 8.

Tip
Each node along a forwarding path may have its own value for the maximum
time-to-live, and performs its own checks before forwarding a message. Therefore
it is helpful if all nodes in the topology use the same value for this option.

NNG_OPT_URL

(string) This read-only option is used to obtain the URL with which a listener or
dialer was configured. Accordingly it can only be used with dialers, listeners, and
pipes.

Note
Some transports will canonify URLs before returning them to the application.

NNG_OPT_PROTO
(int) This read-only option is used to obtain the 16-bit number for the socket’s
protocol.

NNG_OPT_PEER
(int) This read-only option is used to obtain the 16-bit number of the peer protocol
for the socket.

NNG_OPT_PEER_GID
(uint64_t) This read-only option provides a connected peer’s primary group id, when
known. This is the effective group id of the peer when either the underlying listen()
or connect() calls were made, and is not forgeable. This option is generally only
available on POSIX systems, only on certain transports.

NNG_OPT_PEER_PID
(uint64_t) This read-only option provides the process id of the connected peer, when
known. This option is only available on certain platforms and transports.

Note
Applications should not assume that the process ID does not change, as it may be
possible for a process to pass a file descriptor between processes. However, it is
not possible for a nefarious application to forge the identity of a well-behaved
one using this method.

NNG_OPT_PEER_UID
(uint64_t) This read-only option provides a connected peer’s user id. This is the
effective user id of the peer when either the underlying listen() or connect() calls
were made, and cannot be forged. This option is generally only available on POSIX
systems, on certain transports.

NNG_OPT_PEER_ZONEID
(uint64_t) This read-only option provides a connected peer’s the zone id. Zones (and
this option) are only supported on Solaris and illumos systems, on select transports.

NNG_OPT_PEERNAME
(string) This read-only option is used to obtain the name of the peer protocol for the
socket.

NNG_OPT_PROTONAME
(string) This read-only option is used to obtain the name of the socket’s protocol.

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO