github.com/google/uuid v1.6.0: configure network interface for version 1 UUID generation with github.com/google/uuid SetNodeInterface and NodeInterface

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: configure network interface for version 1 UUID generation with github.com/google/uuid SetNodeInterface and NodeInterface
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/google/uuid@v1.6.0
Demonstrate these symbols/APIs:
  - github.com/google/uuid.NodeInterface
  - github.com/google/uuid.SetNodeInterface
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@11.8.0
  - runtime: node@24.13.1

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:sha256:5d7f0453fb2bd7db1f6225e79174fef8547a59f18cebb54ab20ba3154437c657","contract":["uuid.SetNodeInterface with empty string resets to default interface selection and returns true","uuid.SetNodeInterface returns false for non-existent network interface names","uuid.NodeInterface returns user when node ID is set via SetNodeID","uuid.SetNodeInterface configures node ID from named network interface hardware address","uuid.NewUUID generates valid Version 1 UUID containing configured interface or node ID"],"goal":"configure network interface for version 1 UUID generation with github.com/google/uuid SetNodeInterface and NodeInterface","kind":"HOW","packages":["pkg:golang/github.com/google/uuid@v1.6.0"],"schemaVersion":1,"symbols":["github.com/google/uuid.NodeInterface","github.com/google/uuid.SetNodeInterface"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","ecosystem":"golang","os":"windows","osVersionBucket":"11","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/google/uuid@v1.6.0"],"schemaVersion":1,"symbols":["github.com/google/uuid.NodeInterface","github.com/google/uuid.SetNodeInterface"],"verifierAdapter":"golang@1"}

module sample

go 1.22.0

require github.com/google/uuid v1.6.0

github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=

package sample

import (
	"fmt"

	"github.com/google/uuid"
)

// SelectNodeInterface configures the network interface to use for UUIDv1 node ID generation.
func SelectNodeInterface(name string) bool {
	return uuid.SetNodeInterface(name)
}

// CurrentNodeInterface returns the name of the currently configured interface.
func CurrentNodeInterface() string {
	return uuid.NodeInterface()
}

// GenerateV1UUID generates a Version 1 time-based UUID with the configured interface node ID.
func GenerateV1UUID() (uuid.UUID, error) {
	id, err := uuid.NewUUID()
	if err != nil {
		return uuid.Nil, fmt.Errorf("failed to generate UUIDv1: %w", err)
	}
	return id, nil
}

{
  "schemaVersion": 1,
  "goal": "configure network interface for version 1 UUID generation with github.com/google/uuid SetNodeInterface and NodeInterface",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/google/uuid@v1.6.0"
  ],
  "symbols": [
    "github.com/google/uuid.NodeInterface",
    "github.com/google/uuid.SetNodeInterface"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@11.8.0",
    "runtime": "node@24.13.1"
  }
}

package main

import (
	"bytes"
	"fmt"
	"net"
	"os"

	"github.com/google/uuid"
)

func main() {
	// 1. SetNodeInterface with empty string resets/selects default interface and returns true
	if !uuid.SetNodeInterface("") {
		fmt.Fprintf(os.Stderr, "expected SetNodeInterface empty string to return true\n")
		os.Exit(1)
	}

	// 2. SetNodeInterface returns false for non-existent network interface names
	nonExistentName := "csx_dummy_nonexistent_interface_xyz"
	if uuid.SetNodeInterface(nonExistentName) {
		fmt.Fprintf(os.Stderr, "expected SetNodeInterface to return false for non-existent interface\n")
		os.Exit(1)
	}

	// 3. SetNodeID sets custom node ID and causes NodeInterface() to return 'user'
	customNodeID := []byte{0x02, 0x00, 0x5e, 0x00, 0x53, 0x01}
	if !uuid.SetNodeID(customNodeID) {
		fmt.Fprintf(os.Stderr, "SetNodeID failed for 6-byte node ID\n")
		os.Exit(1)
	}
	if iface := uuid.NodeInterface(); iface != "user" {
		fmt.Fprintf(os.Stderr, "expected NodeInterface() to be user after SetNodeID, got %q\n", iface)
		os.Exit(1)
	}
	if !bytes.Equal(uuid.NodeID(), customNodeID) {
		fmt.Fprintf(os.Stderr, "NodeID() mismatch: got %v, want %v\n", uuid.NodeID(), customNodeID)
		os.Exit(1)
	}

	// 4. Version 1 UUID generated with custom NodeID contains the specified node bytes
	id1, err := uuid.NewUUID()
	if err != nil {
		fmt.Fprintf(os.Stderr, "NewUUID failed: %v\n", err)
		os.Exit(1)
	}
	if id1.Version() != 1 {
		fmt.Fprintf(os.Stderr, "expected version 1 UUID, got %d\n", id1.Version())
		os.Exit(1)
	}
	if id1.Variant() != uuid.RFC4122 {
		fmt.Fprintf(os.Stderr, "expected RFC4122 variant, got %v\n", id1.Variant())
		os.Exit(1)
	}
	if !bytes.Equal(id1.NodeID(), customNodeID) {
		fmt.Fprintf(os.Stderr, "UUID.NodeID() mismatch: got %v, want %v\n", id1.NodeID(), customNodeID)
		os.Exit(1)
	}

	// 5. Test with real interface if available on system
	interfaces, err := net.Interfaces()
	if err == nil {
		for _, iface := range interfaces {
			if len(iface.HardwareAddr) >= 6 {
				if uuid.SetNodeInterface(iface.Name) {
					if current := uuid.NodeInterface(); current != iface.Name {
						fmt.Fprintf(os.Stderr, "NodeInterface() expected %q, got %q\n", iface.Name, current)
						os.Exit(1)
					}
					node := uuid.NodeID()
					if !bytes.Equal(node, iface.HardwareAddr[:6]) {
						fmt.Fprintf(os.Stderr, "NodeID() expected MAC prefix %v, got %v\n", iface.HardwareAddr[:6], node)
						os.Exit(1)
					}
					break
				}
			}
		}
	}

	// 6. Reset with empty string again and verify UUIDv1 generation succeeds
	if !uuid.SetNodeInterface("") {
		fmt.Fprintf(os.Stderr, "expected SetNodeInterface empty string reset to succeed\n")
		os.Exit(1)
	}
	id2, err := uuid.NewUUID()
	if err != nil {
		fmt.Fprintf(os.Stderr, "NewUUID failed after reset: %v\n", err)
		os.Exit(1)
	}
	if id2.Version() != 1 {
		fmt.Fprintf(os.Stderr, "expected version 1 UUID after reset, got %d\n", id2.Version())
		os.Exit(1)
	}

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