= nng_tcp(7)
//
// Copyright 2019 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
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

This transport is generally built-in to the core of _NNG_, 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 this varies across operating systems.

NOTE: Both `tcp6://` and `tcp4://` are specific to _NNG_, and might not
be understood by other implementations.

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`.

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 xref:nng_sockaddr.5.adoc[`nng_sockaddr`] structure,
the actual structure is either of type
xref:nng_sockaddr_in.5.adoc[`nng_sockaddr_in`] (for IPv4) or
xref:nng_sockaddr_in6.5.adoc[`nng_sockaddr_in6`] (for IPv6).

=== Transport Options

The following transport options are supported by this transport,
where supported by the underlying platform.

* xref:nng_options.5.adoc#NNG_OPT_LOCADDR[`NNG_OPT_LOCADDR`]
* xref:nng_options.5.adoc#NNG_OPT_REMADDR[`NNG_OPT_REMADDR`]
* xref:nng_tcp_options.5.adoc#NNG_OPT_TCP_KEEPALIVE[`NNG_OPT_TCP_KEEPALIVE`]
* xref:nng_tcp_options.5.adoc#NNG_OPT_TCP_NODELAY[`NNG_OPT_TCP_NODELAY`]
* xref:nng_options.5.adoc#NNG_OPT_URL[`NNG_OPT_URL`]


== SEE ALSO

[.text-left]
xref:nng_options.5.adoc[nng_options(5)],
xref:nng_sockaddr.5.adoc[nng_sockaddr(5)],
xref:nng_sockaddr_in.5.adoc[nng_sockaddr_in(5)],
xref:nng_sockaddr_in6.5.adoc[nng_sockaddr_in6(5)],
xref:nng_tcp_options.5.adoc[nng_tcp_options(5)],
xref:nng.7.adoc[nng(7)]