UUID Generation (Version 4 & 7)

This repository provides a simple implementation of UUID Version 4 and UUID Version 7, based on RFC 9562 (a draft revision of RFC 4122). Note that this code is not production-ready and is intended primarily for learning or demonstration.

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Overview

1. uuid_v4()
   Generates a Version 4 UUID (random-based).

   • Clears the upper 4 bits of byte 6, then sets them to 0x4 (Version 4).
   • Clears the upper 2 bits of byte 8, then sets them to 10 (RFC 4122 variant).

2. uuid_v7()
   Generates a Version 7 UUID (time-ordered + randomness).

   • Uses a 48-bit millisecond Unix epoch timestamp (bits 0–47), stored in the first 6 bytes in big-endian order.
   • Sets the version nibble (0x7) in byte 6.
   • Sets the variant bits (10) in byte 8.

3. uuid_to_string(const struct UUID *uuid, char *out)
   Converts the 128-bit UUID (stored in uuid->bytes) into a standard UUID string format (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).

Important Note

• This code uses arc4random_buf for randomness, which may not be available on all platforms without extra libraries (e.g., libbsd on some Linux systems).
• Replace it with another secure random method (e.g. getrandom(), /dev/urandom) if needed.

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Example Usage

#include "uuid.h"
#include <stdio.h>

int main(void) {
    // Generate a Version 4 UUID
    UUID v4 = uuid_v4();

    // Generate a Version 7 UUID
    UUID v7 = uuid_v7();

    // Convert to string
    char buf[37];  // 36 chars + null terminator

    uuid_to_string(&v4, buf);
    printf("Version 4 UUID: %s\n", buf);

    uuid_to_string(&v7, buf);
    printf("Version 7 UUID: %s\n", buf);

    return 0;
}