IPv6 / IPv4 address parser in C

A small C library for parsing, formatting, and comparing IP addresses, with no dynamic allocation. Supports IPv6 and IPv4, CIDR masks, ports, zone IDs, and IPv4 embedded in IPv6. JavaScript bindings are available through WebAssembly.

Try it in your browser · IPv6 introduction · Releases

Usage

The parser reads an address into a structure. The formatter converts it back to text, including any IPv6 mask, zone ID, or port.

flowchart TD
    input["Address string"] -->|ipv6_from_str| address["ipv6_address_full_t"]
    address -->|ipv6_to_str| output["Formatted string"]

Loading

#include "ipv6.h"
#include <stdio.h>
#include <string.h>

int main(void) {
    const char *input = "[2001:db8::1/64]:8080";
    ipv6_address_full_t addr = {0};
    char output[IPV6_STRING_SIZE];

    if (!ipv6_from_str(input, strlen(input), &addr)) {
        return 1;
    }

    ipv6_to_str(&addr, output, sizeof(output));
    puts(output);  // [2001:db8::1/64]:8080
    return 0;
}

Zone IDs reference the original input string; keep it alive while using the parsed address. See the C API reference for diagnostics, field flags, and comparison options.

Build

Requires CMake and a C/C++ toolchain. From the repository root:

cmake -S . -B build
cmake --build build --config Release
cmake --install build --config Release

This builds a static library by default. Use -DBUILD_SHARED_LIBS=ON for a shared library. The installation guide covers CMake integration, pkg-config, and package managers.

JavaScript

npm install ipv6-parse

const ipv6 = require('ipv6-parse');

async function main() {
    const addr = await ipv6.parse('2001:db8::1');
    console.log(addr.formatted); // 2001:db8::1
}

main().catch(console.error);

See the JavaScript guide for synchronous parsing and browser usage, or the TypeScript guide for typed examples.

Development

To build and run the native tests:

cmake -S . -B build -DIPV6_PARSE_LIBRARY_ONLY=OFF
cmake --build build --config Release
ctest --test-dir build --build-config Release --output-on-failure

Contributing · Testing and benchmarks · MIT license