= 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 for nng

== SYNOPSIS

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

int nng_tcp_register(void);
----------

== DESCRIPTION

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

=== URI Format

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.  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`.

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.footnote:[This is a bug and will likely be fixed in the future.]

The special value of 0 (`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` structure, the actual structure is either
of type `nng_sockaddr_in` (for IPv4) or `nng_sockaddr_in6` (for IPv6).
These are `struct` types with the following definitions:

[source,c]
--------
#define NNG_AF_INET    3 <1>
#define NNG_AF_INET6   4
#define NNG_MAXADDRLEN 128

typedef struct {
    // ... <2>
    uint16_t sa_family;   // must be NNG_AF_INET
    uint16_t sa_port;     // TCP port number
    uint32_t sa_addr;
    // ...
} nng_sockaddr_in;

typedef struct {
    // ... <2>
    uint16_t sa_family;   // must be NNG_AF_INET6
    uint16_t sa_port;     // TCP port number
    uint8_t  sa_addr[16];
    // ...
} nng_sockaddr_in6;
--------
<1> The values of these macros may change, so applications
should avoid depending upon their values and instead use them symbolically.
<2> Other members may be present, but only those listed here
are suitable for application use.

The `sa_family` member will have the value `NNG_AF_INET` or `NNG_AF_INET6`.
The `sa_port` and `sa_addr` are the TCP port number and address, both in
network byte order (most significant byte is first).

=== Transport Options

The _tcp_ transport has no special
options.footnote:[Options for TCP keepalive, linger, and nodelay are planned.]
 
== SEE ALSO

<<nng#,nng(7)>>
