github.com/rogpeppe/fastuuid v1.2.0: Hex128

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify github.com/rogpeppe/fastuuid.Hex128 in pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0
Demonstrate these symbols/APIs:
  - github.com/rogpeppe/fastuuid.Hex128

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:71d3e02de0a55091a91b0210a1ce0a602702c088f990519264f13053921bf629","contract":["fastuuid.Hex128 encodes a 24-byte UUID array into a 36-character RFC-4122 V4 string","fastuuid.Hex128 sets hyphens at positions 8, 13, 18, and 23 with version 4 and variant RFC-4122 bits","fastuuid.Hex128 produces distinct outputs for distinct 24-byte inputs from Generator.Next","fastuuid.ValidHex128 accepts fastuuid.Hex128 output and rejects invalid lengths, uppercase hex, or non-hex inputs"],"goal":"verify github.com/rogpeppe/fastuuid.Hex128 in pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0","kind":"HOW","packages":["pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0"],"schemaVersion":1,"symbols":["github.com/rogpeppe/fastuuid.Hex128"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0","symbols":["github.com/rogpeppe/fastuuid.Hex128"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/rogpeppe/fastuuid v1.2.0

github.com/rogpeppe/fastuuid v1.2.0 h1:Ppwyp6VYCF1nvBTXL3trRso7mXMlRrw9ooo375wvi2s=
github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=

package main

import (
	"fmt"
	"log"

	"github.com/rogpeppe/fastuuid"
)

func main() {
	gen, err := fastuuid.NewGenerator()
	if err != nil {
		log.Fatalf("failed to initialize fastuuid generator: %v", err)
	}

	rawUUID := gen.Next()
	formattedUUID := fastuuid.Hex128(rawUUID)

	fmt.Printf("Raw UUID bytes: %x\n", rawUUID)
	fmt.Printf("Formatted RFC-4122 V4 UUID: %s\n", formattedUUID)

	if !fastuuid.ValidHex128(formattedUUID) {
		log.Fatalf("validation failed for UUID: %s", formattedUUID)
	}
	fmt.Println("UUID validated successfully.")
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/rogpeppe/fastuuid.Hex128 in pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0"
  ],
  "symbols": [
    "github.com/rogpeppe/fastuuid.Hex128"
  ]
}

package main

import (
	"fmt"
	"os"

	"github.com/rogpeppe/fastuuid"
)

func main() {
	// Assertion 1: fastuuid.Hex128 encodes a 24-byte UUID array into a 36-character RFC-4122 V4 string
	{
		gen, err := fastuuid.NewGenerator()
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: NewGenerator error: %v\n", err)
			os.Exit(1)
		}
		raw := gen.Next()
		encoded := fastuuid.Hex128(raw)
		if len(encoded) != 36 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: length expected 36, got %d\n", len(encoded))
			os.Exit(1)
		}
		if !fastuuid.ValidHex128(encoded) {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: ValidHex128 failed on %s\n", encoded)
			os.Exit(1)
		}
	}

	// Assertion 2: fastuuid.Hex128 sets hyphens at positions 8, 13, 18, and 23 with version 4 and variant RFC-4122 bits
	{
		gen := fastuuid.MustNewGenerator()
		raw := gen.Next()
		encoded := fastuuid.Hex128(raw)

		if encoded[8] != '-' || encoded[13] != '-' || encoded[18] != '-' || encoded[23] != '-' {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: incorrect hyphen delimiters in %s\n", encoded)
			os.Exit(1)
		}

		if encoded[14] != '4' {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: version character is not '4' in %s\n", encoded)
			os.Exit(1)
		}

		variantChar := encoded[19]
		if variantChar != '8' && variantChar != '9' && variantChar != 'a' && variantChar != 'b' {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: variant character invalid (%c) in %s\n", variantChar, encoded)
			os.Exit(1)
		}
	}

	// Assertion 3: fastuuid.Hex128 produces distinct outputs for distinct 24-byte inputs from Generator.Next
	{
		gen := fastuuid.MustNewGenerator()
		seen := make(map[string]bool)
		for i := 0; i < 500; i++ {
			raw := gen.Next()
			encoded := fastuuid.Hex128(raw)
			if seen[encoded] {
				fmt.Fprintf(os.Stderr, "assertion 3 failed: duplicate Hex128 output at iteration %d\n", i)
				os.Exit(1)
			}
			seen[encoded] = true
		}
	}

	// Assertion 4: fastuuid.ValidHex128 accepts fastuuid.Hex128 output and rejects invalid lengths, uppercase hex, or non-hex inputs
	{
		gen := fastuuid.MustNewGenerator()
		validStr := fastuuid.Hex128(gen.Next())
		if !fastuuid.ValidHex128(validStr) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: ValidHex128 rejected %s\n", validStr)
			os.Exit(1)
		}

		if fastuuid.ValidHex128("") {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted empty string\n")
			os.Exit(1)
		}

		// Uppercase hex must be rejected
		upper := "F81D4FAE-7DEC-41D0-8765-00A0C91E6BF6"
		if fastuuid.ValidHex128(upper) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted uppercase string %s\n", upper)
			os.Exit(1)
		}

		// Length mismatch (35 or 37 chars)
		if fastuuid.ValidHex128(validStr[:35]) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted 35-char string\n")
			os.Exit(1)
		}
		if fastuuid.ValidHex128(validStr + "0") {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted 37-char string\n")
			os.Exit(1)
		}

		// Invalid characters
		invalidChars := "g81d4fae-7dec-41d0-8765-00a0c91e6bf6"
		if fastuuid.ValidHex128(invalidChars) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted invalid chars %s\n", invalidChars)
			os.Exit(1)
		}
	}

	fmt.Println("All contract assertions passed.")
}