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.

Note

This option is deprecated. Use the nng_socket_raw function instead.

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.

Note

This option is deprecated. Use the nng_socket_proto_id function instead.

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

Note

This option is deprecated. Use the nng_socket_peer_id function instead.

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.

Note

This option is deprecated. Use the nng_socket_peer_name function instead.

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

Note

This option is deprecated. Use the nng_socket_proto_name function instead.

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO