github.com/rogpeppe/fastuuid v1.2.0

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 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

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:e3d7df665107e1be5170a18a3d219daaec626e198d47ee5a77d2c5e3c162dcfa","contract":["fastuuid.NewGenerator returns an initialized Generator without error and fastuuid.MustNewGenerator creates an operational Generator","Generator.Next produces 24-byte UUIDs and returns distinct values across consecutive invocations","Generator.Hex128 formats sequential UUIDs into valid 36-character RFC-4122 V4 representations","fastuuid.Hex128 encodes a 24-byte UUID array into an RFC-4122 V4 string consistent with Generator.Next","fastuuid.ValidHex128 accepts valid lowercase UUID strings and rejects invalid lengths uppercase hex or malformed inputs"],"goal":"verify pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0","kind":"HOW","packages":["pkg:golang/github.com/rogpeppe/fastuuid@v1.2.0"],"schemaVersion":1},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","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","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 create generator: %v", err)
	}

	id := gen.Next()
	fmt.Printf("Generated 192-bit UUID: %x\n", id)

	hexID := gen.Hex128()
	fmt.Printf("Formatted RFC-4122 V4 UUID: %s\n", hexID)

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

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

package main

import (
	"fmt"
	"os"

	"github.com/rogpeppe/fastuuid"
)

func main() {
	// Assertion 1: fastuuid.NewGenerator returns an initialized Generator without error and fastuuid.MustNewGenerator creates an operational Generator
	{
		gen, err := fastuuid.NewGenerator()
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: NewGenerator returned error: %v\n", err)
			os.Exit(1)
		}
		if gen == nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: NewGenerator returned nil\n")
			os.Exit(1)
		}

		mustGen := fastuuid.MustNewGenerator()
		if mustGen == nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: MustNewGenerator returned nil\n")
			os.Exit(1)
		}
	}

	// Assertion 2: Generator.Next produces 24-byte UUIDs and returns distinct values across consecutive invocations
	{
		gen, err := fastuuid.NewGenerator()
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: NewGenerator returned error: %v\n", err)
			os.Exit(1)
		}

		id1 := gen.Next()
		id2 := gen.Next()

		if len(id1) != 24 || len(id2) != 24 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: UUID length is not 24 bytes\n")
			os.Exit(1)
		}

		if id1 == id2 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: consecutive Next() calls produced identical UUIDs\n")
			os.Exit(1)
		}

		seen := make(map[[24]byte]bool)
		for i := 0; i < 1000; i++ {
			id := gen.Next()
			if seen[id] {
				fmt.Fprintf(os.Stderr, "assertion 2 failed: duplicate UUID generated at iteration %d\n", i)
				os.Exit(1)
			}
			seen[id] = true
		}
	}

	// Assertion 3: Generator.Hex128 formats sequential UUIDs into valid 36-character RFC-4122 V4 representations
	{
		gen := fastuuid.MustNewGenerator()
		hex1 := gen.Hex128()
		hex2 := gen.Hex128()

		if len(hex1) != 36 || len(hex2) != 36 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: Hex128 returned invalid length: len=%d, %d\n", len(hex1), len(hex2))
			os.Exit(1)
		}

		if hex1 == hex2 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: consecutive Hex128() calls returned identical strings\n")
			os.Exit(1)
		}

		if !fastuuid.ValidHex128(hex1) || !fastuuid.ValidHex128(hex2) {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: Hex128 output failed ValidHex128 validation: %s, %s\n", hex1, hex2)
			os.Exit(1)
		}

		// RFC-4122 V4 structure: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where y is 8, 9, a, or b
		if hex1[8] != '-' || hex1[13] != '-' || hex1[18] != '-' || hex1[23] != '-' {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: delimiter positions invalid in %s\n", hex1)
			os.Exit(1)
		}
		if hex1[14] != '4' {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: version character is not '4' in %s\n", hex1)
			os.Exit(1)
		}
		variantChar := hex1[19]
		if variantChar != '8' && variantChar != '9' && variantChar != 'a' && variantChar != 'b' {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: variant character invalid (%c) in %s\n", variantChar, hex1)
			os.Exit(1)
		}
	}

	// Assertion 4: fastuuid.Hex128 encodes a 24-byte UUID array into an RFC-4122 V4 string consistent with Generator.Next
	{
		gen := fastuuid.MustNewGenerator()
		rawUUID := gen.Next()
		encoded := fastuuid.Hex128(rawUUID)

		if len(encoded) != 36 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: Hex128(uuid) length is not 36: %s\n", encoded)
			os.Exit(1)
		}

		if !fastuuid.ValidHex128(encoded) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: Hex128(uuid) failed ValidHex128: %s\n", encoded)
			os.Exit(1)
		}

		if encoded[8] != '-' || encoded[13] != '-' || encoded[18] != '-' || encoded[23] != '-' {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: Hex128(uuid) format invalid: %s\n", encoded)
			os.Exit(1)
		}
		if encoded[14] != '4' {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: Hex128(uuid) version character is not '4': %s\n", encoded)
			os.Exit(1)
		}
	}

	// Assertion 5: fastuuid.ValidHex128 accepts valid lowercase UUID strings and rejects invalid lengths uppercase hex or malformed inputs
	{
		gen := fastuuid.MustNewGenerator()
		validSample := gen.Hex128()
		if !fastuuid.ValidHex128(validSample) {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 returned false on valid sample %s\n", validSample)
			os.Exit(1)
		}

		// Known valid RFC-4122 v4 UUID
		knownValid := "f81d4fae-7dec-41d0-8765-00a0c91e6bf6"
		if !fastuuid.ValidHex128(knownValid) {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 returned false on known valid UUID %s\n", knownValid)
			os.Exit(1)
		}

		// Invalid: Uppercase hex (fastuuid explicitly disallows uppercase hex)
		upperCase := "F81D4FAE-7DEC-41D0-8765-00A0C91E6BF6"
		if fastuuid.ValidHex128(upperCase) {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted uppercase UUID %s\n", upperCase)
			os.Exit(1)
		}

		// Invalid: Empty string
		if fastuuid.ValidHex128("") {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted empty string\n")
			os.Exit(1)
		}

		// Invalid: Truncated length (35 chars)
		if fastuuid.ValidHex128("f81d4fae-7dec-41d0-8765-00a0c91e6bf") {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted truncated string\n")
			os.Exit(1)
		}

		// Invalid: Extended length (37 chars)
		if fastuuid.ValidHex128("f81d4fae-7dec-41d0-8765-00a0c91e6bf60") {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted 37-char string\n")
			os.Exit(1)
		}

		// Invalid: Non-hex characters
		if fastuuid.ValidHex128("g81d4fae-7dec-41d0-8765-00a0c91e6bf6") {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted non-hex string\n")
			os.Exit(1)
		}

		// Invalid: Incorrect hyphen positions
		if fastuuid.ValidHex128("f81d4fae7-dec-41d0-8765-00a0c91e6bf6") {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ValidHex128 accepted displaced hyphen string\n")
			os.Exit(1)
		}
	}

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