= nng_tcp(7)
//
// 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

nng_tcp - TCP/IP transport

== SYNOPSIS

[source,c]
----
#include <nng/transport/tcp/tcp.h>

int nng_tcp_register(void);
----

== DESCRIPTION

(((transport, _tcp_)))
The ((_tcp_ transport)) provides communication support between
_nng_ sockets across a ((TCP/IP)) network.
Both IPv4 and IPv6 are supported when the underlying platform also supports it.

// We need to insert a reference to the nanomsg RFC.

=== Registration

The _nng_tcp_ transport is generally built-in to the _nng_ core, so
no extra steps to use it should be necessary.

=== URI Format

(((URI, `tcp://`)))
This transport uses URIs using the scheme `tcp://`, followed by
an IP address or hostname, followed by a colon and finally a
TCP port number.(((port number, TCP)))
For example, to contact port 80 on the localhost either of the following URIs
could be used: `tcp://127.0.0.1:80` or `tcp://localhost:80`.

A URI may be restricted to IPv6 using the scheme `tcp6://`, and may
be restricted to IPv4 using the scheme `tcp4://`.

NOTE: Specifying `tcp6://` may not prevent IPv4 hosts from being used with
IPv4-in-IPv6 addresses, particularly when using a wildcard hostname with
listeners.
The details of varies across operating systems.

NOTE: Both `tcp6://` and `tcp4://` are _nng_ extensions, and will not
be understood by other implementations such as _libnanomsg_.

TIP: We recommend using either numeric IP addresses, or names that are
specific to either IPv4 or IPv6 to prevent confusion and surprises.

When specifying IPv6 addresses, the address must be enclosed in
square brackets (`[]`) to avoid confusion with the final colon
separating the port.

For example, the same port 80 on the IPv6 loopback address (`::1`) would
be specified as `tcp://[::1]:80`.

NOTE: When using symbolic names, the name is resolved when the
name is first used. _nng_ won't become aware of changes in the
name resolution until restart,
usually.
(This is a bug and will likely be fixed in the future.)

The special value of 0 (`INADDR_ANY`)(((`INADDR_ANY`)))
can be used for a listener to indicate that it should listen on all
interfaces on the host.
A short-hand for this form is to either omit the address, or specify
the asterisk (`*`) character.
For example, the following three URIs are all equivalent,
and could be used to listen to port 9999 on the host:

  1. `tcp://0.0.0.0:9999`
  2. `tcp://*:9999`
  3. `tcp://:9999`

The entire URI must be less than `NNG_MAXADDRLEN` bytes long.

=== Socket Address

When using an `<<nng_sockaddr.5#,nng_sockaddr>>` structure,
the actual structure is either of type
`<<nng_sockaddr_in.5#,nng_sockaddr_in>>` (for IPv4) or
`<<nng_sockaddr_in6.5#,nng_sockaddr_in6>>` (for IPv6).

=== Transport Options

((`NNG_OPT_TCP_KEEPALIVE`))::

This option is used to configure TCP keep-alives.
The value is of type `bool`, and defaults to `false`.

((`NNG_OPT_TCP_NODELAY`))::

This option is used to configure Nagle's algorithm.
When enabled (`false`), the underlying TCP stream will attempt
to buffer and coalesce messages before sending them on, waiting
a short interval to improve buffering and reduce the overhead
caused by sending too-small messages.
This comes at a cost to latency, and is not recommended with modern
high speed networks.
The value is of type `bool` and defaults to `true`.

== SEE ALSO

[.text-left]
<<nng_sockaddr.5#,nng_sockaddr(5)>>,
<<nng_sockaddr_in.5#,nng_sockaddr_in(5)>>,
<<nng_sockaddr_in6.5#,nng_sockaddr_in6(5)>>,
<<nng.7#,nng(7)>>