SYNOPSIS
#include <nng/nng.h>
#define NNG_OPT_TCP_NODELAY "tcp-nodelay"
#define NNG_OPT_TCP_KEEPALIVE "tcp-keepalive"
#define NNG_OPT_TCP_BOUND_PORT "tcp-bound-port"DESCRIPTION
This page documents the various standard options that can be set or retrieved on objects using TCP in the nng library.
The option names should always be used by their symbolic definitions.
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, or may have other access restrictions. An attempt has been made to include details about such restrictions in the description of the option.
The following options are generally application to objects making use of TCP/IP communications.
TCP Options
NNG_OPT_TCP_NODELAY-
(
bool) This option is used to disable (or enable) the use of Nagle’s algorithm for TCP connections.This setting may apply to transports that are built on top of TCP. See the transport documentation for each transport for details. When
true(the default), messages are sent immediately by the underlying TCP stream without waiting to gather more data.When
false, Nagle’s algorithm is enabled, and the TCP stream may wait briefly in attempt to coalesce messages. Nagle’s algorithm is useful on low-bandwidth connections to reduce overhead, but it comes at a cost to latency.When used on a dialer or a listener, the value affects how newly created connections will be configured.
NNG_OPT_TCP_KEEPALIVE-
(
bool) This option is used to enable the sending of keep-alive messages on the underlying TCP stream. This option isfalseby default.This setting may apply to transports that are built on top of TCP. See the transport documentation for each transport for details. When enabled, if no messages are seen for a period of time, then a zero length TCP message is sent with the ACK flag set in an attempt to tickle some traffic from the peer. If none is still seen (after some platform-specific number of retries and timeouts), then the remote peer is presumed dead, and the connection is closed.
When used on a dialer or a listener, the value affects how newly created connections will be configured.
This option has two purposes. First, it can be used to detect dead peers on an otherwise quiescent network. Second, it can be used to keep connection table entries in NAT and other middleware from being expiring due to lack of activity.
NNG_OPT_TCP_BOUND_PORT-
(
int) This option is available on listeners, after the listern has bound to a port, and provides the port bound to in native byte order. This is most useful when using a listener with an ephemeral port (configured by using port 0 at configuration time), as it allows the caller to determine the actual ephemeral port that was chosen by the system. While the value is of typeint, it will be a legal TCP port number, that is a value between 1 and 65535, inclusive.
Inherited Options
Generally, the following option values are also available for TCP objects, when appropriate for the context: