github.com/rogpeppe/fastuuid v1.2.0: ValidHex128

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.ValidHex128 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.ValidHex128

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:e2f61b298af690bf8578b3529f1a14bb6b5e9a42474bf21f2b10f130881e2732","contract":["fastuuid.ValidHex128 accepts formatted 36-character UUID strings from fastuuid.Hex128","fastuuid.ValidHex128 rejects UUID strings whose length is not 36 characters","fastuuid.ValidHex128 rejects UUID strings missing hyphens at positions 8, 13, 18, or 23","fastuuid.ValidHex128 rejects strings containing uppercase hex or non-hex characters"],"goal":"verify github.com/rogpeppe/fastuuid.ValidHex128 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.ValidHex128"]},"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.ValidHex128"],"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 := fastuuid.MustNewGenerator()
	id := fastuuid.Hex128(gen.Next())

	if !fastuuid.ValidHex128(id) {
		log.Fatalf("expected valid UUID: %s", id)
	}

	invalidId := "F81D4FAE-7DEC-41D0-8765-00A0C91E6BF6" // Uppercase is disallowed
	if fastuuid.ValidHex128(invalidId) {
		log.Fatalf("expected uppercase UUID to be invalid: %s", invalidId)
	}

	fmt.Printf("UUID %s is valid: %v\n", id, fastuuid.ValidHex128(id))
	fmt.Printf("Uppercase UUID %s is valid: %v\n", invalidId, fastuuid.ValidHex128(invalidId))
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/rogpeppe/fastuuid.ValidHex128 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.ValidHex128"
  ]
}

package main

import (
	"fmt"
	"os"

	"github.com/rogpeppe/fastuuid"
)

func main() {
	// Assertion 1: fastuuid.ValidHex128 accepts formatted 36-character UUID strings from fastuuid.Hex128
	{
		gen := fastuuid.MustNewGenerator()
		for i := 0; i < 100; i++ {
			id := fastuuid.Hex128(gen.Next())
			if len(id) != 36 {
				fmt.Fprintf(os.Stderr, "assertion 1 failed: expected length 36, got %d\n", len(id))
				os.Exit(1)
			}
			if !fastuuid.ValidHex128(id) {
				fmt.Fprintf(os.Stderr, "assertion 1 failed: ValidHex128 returned false for %s\n", id)
				os.Exit(1)
			}
		}

		knownValid := "f81d4fae-7dec-41d0-8765-00a0c91e6bf6"
		if !fastuuid.ValidHex128(knownValid) {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: ValidHex128 returned false for known valid %s\n", knownValid)
			os.Exit(1)
		}
	}

	// Assertion 2: fastuuid.ValidHex128 rejects UUID strings whose length is not 36 characters
	{
		valid := "f81d4fae-7dec-41d0-8765-00a0c91e6bf6"
		invalidLengths := []string{
			"",
			valid[:35],
			valid + "a",
			"short",
			"f81d4fae-7dec-41d0-8765-00a0c91e6bf6-extra",
		}
		for _, s := range invalidLengths {
			if fastuuid.ValidHex128(s) {
				fmt.Fprintf(os.Stderr, "assertion 2 failed: ValidHex128 returned true for invalid length %q\n", s)
				os.Exit(1)
			}
		}
	}

	// Assertion 3: fastuuid.ValidHex128 rejects UUID strings missing hyphens at positions 8, 13, 18, or 23
	{
		valid := []byte("f81d4fae-7dec-41d0-8765-00a0c91e6bf6")
		hyphenPositions := []int{8, 13, 18, 23}
		for _, pos := range hyphenPositions {
			corrupted := make([]byte, len(valid))
			copy(corrupted, valid)
			corrupted[pos] = '0'
			if fastuuid.ValidHex128(string(corrupted)) {
				fmt.Fprintf(os.Stderr, "assertion 3 failed: accepted missing hyphen at position %d: %s\n", pos, corrupted)
				os.Exit(1)
			}
		}

		noHyphens := "f81d4fae7dec41d0876500a0c91e6bf60000"
		if fastuuid.ValidHex128(noHyphens) {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: accepted UUID with no hyphens: %s\n", noHyphens)
			os.Exit(1)
		}
	}

	// Assertion 4: fastuuid.ValidHex128 rejects strings containing uppercase hex or non-hex characters
	{
		upperCases := []string{
			"F81D4FAE-7DEC-41D0-8765-00A0C91E6BF6",
			"f81d4fae-7dec-41d0-8765-00a0c91e6bfA",
			"A81d4fae-7dec-41d0-8765-00a0c91e6bf6",
		}
		for _, s := range upperCases {
			if fastuuid.ValidHex128(s) {
				fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted uppercase string %s\n", s)
				os.Exit(1)
			}
		}

		nonHexCases := []string{
			"g81d4fae-7dec-41d0-8765-00a0c91e6bf6",
			"f81d4fae-7dec-41d0-8765-00a0c91e6bfz",
			"f81d4fae-7dec-41d0-8765-00a0c91e6bf!",
			"f81d4fae-7dec-41d0-8765-00a0c91e6bf ",
		}
		for _, s := range nonHexCases {
			if fastuuid.ValidHex128(s) {
				fmt.Fprintf(os.Stderr, "assertion 4 failed: accepted non-hex string %s\n", s)
				os.Exit(1)
			}
		}
	}

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