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nng_tcp(7) Manual Page

NAME

nng_tcp - TCP/IP transport for nng

SYNOPSIS

#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.

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.[1]

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:

#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.[2]

SEE ALSO

COPYRIGHT

Copyright 2017 Garrett D’Amore
Copyright 2017 Capitar IT Group BV

This document is supplied under the terms of the MIT License.

1. This is a bug and will likely be fixed in the future.
2. Options for TCP keepalive, linger, and nodelay are planned.