github.com/songgao/water v0.0.0-20200317203138-2b4b6d7c09d8: Config, New

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/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8
Demonstrate these symbols/APIs:
  - water.Config
  - water.New

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:sha256:935377e6ee95aeca05f9af3cd9420ee73bd6e219d14d3e230071c738f03a5dc5","contract":["water.New returns an error for invalid device types","water.Config initializes TUN and TAP device configurations with optional platform parameters","water.New creates a TUN interface or returns a system permission error on unprivileged environments","water.New creates a TAP interface or returns a system permission error on unprivileged environments"],"goal":"verify pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8","kind":"HOW","packages":["pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8"],"schemaVersion":1,"symbols":["water.Config","water.New"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8"],"schemaVersion":1,"subject":"pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8","symbols":["water.Config","water.New"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/songgao/water v0.0.0-20200317203138-2b4b6d7c09d8

require golang.org/x/sys v0.47.0 // indirect

github.com/songgao/water v0.0.0-20200317203138-2b4b6d7c09d8 h1:TG/diQgUe0pntT/2D9tmUCz4VNwm9MfrtPr0SU2qSX8=
github.com/songgao/water v0.0.0-20200317203138-2b4b6d7c09d8/go.mod h1:P5HUIBuIWKbyjl083/loAegFkfbFNx5i2qEP4CNbm7E=
golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=

package main

import (
	"errors"
	"fmt"
	"os"

	"github.com/songgao/water"
)

func main() {
	cfg := water.Config{
		DeviceType: water.TUN,
		PlatformSpecificParams: water.PlatformSpecificParams{
			Name: "testun%d",
		},
	}
	ifce, err := water.New(cfg)
	if err != nil {
		fmt.Printf("water.New returned error: %v\n", err)
		var pathErr *os.PathError
		if errors.As(err, &pathErr) {
			fmt.Printf("PathError: op=%s path=%s err=%v\n", pathErr.Op, pathErr.Path, pathErr.Err)
		}
	} else {
		defer ifce.Close()
		fmt.Printf("water.New succeeded: name=%s isTUN=%v isTAP=%v\n", ifce.Name(), ifce.IsTUN(), ifce.IsTAP())
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/songgao/water@v0.0.0-20200317203138-2b4b6d7c09d8"
  ],
  "symbols": [
    "water.Config",
    "water.New"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/songgao/water"
)

func main() {
	if err := runContract(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract verification failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All github.com/songgao/water contract assertions passed.")
}

func runContract() error {
	// Assertion 1: water.New returns an error for invalid device types
	invalidConfig := water.Config{
		DeviceType: water.DeviceType(99),
	}
	if _, err := water.New(invalidConfig); err == nil {
		return fmt.Errorf("expected error when creating device with invalid DeviceType, got nil")
	} else if !strings.Contains(err.Error(), "unknown device type") {
		return fmt.Errorf("expected 'unknown device type' error message, got: %v", err)
	}

	// Assertion 2: water.Config initializes TUN and TAP device configurations with optional platform parameters
	tunCfg := water.Config{
		DeviceType: water.TUN,
		PlatformSpecificParams: water.PlatformSpecificParams{
			Name:       "custom-tun0",
			Persist:    false,
			MultiQueue: false,
		},
	}
	if tunCfg.DeviceType != water.TUN || tunCfg.Name != "custom-tun0" {
		return fmt.Errorf("unexpected tun configuration values: %+v", tunCfg)
	}

	tapCfg := water.Config{
		DeviceType: water.TAP,
		PlatformSpecificParams: water.PlatformSpecificParams{
			Name:       "custom-tap0",
			Persist:    false,
			MultiQueue: false,
		},
	}
	if tapCfg.DeviceType != water.TAP || tapCfg.Name != "custom-tap0" {
		return fmt.Errorf("unexpected tap configuration values: %+v", tapCfg)
	}

	// Assertion 3: water.New creates a TUN interface or returns a system permission error on unprivileged environments
	ifceTUN, errTUN := water.New(water.Config{DeviceType: water.TUN})
	if errTUN == nil {
		defer ifceTUN.Close()
		if !ifceTUN.IsTUN() {
			return fmt.Errorf("expected ifce.IsTUN() to be true")
		}
		if ifceTUN.IsTAP() {
			return fmt.Errorf("expected ifce.IsTAP() to be false for TUN device")
		}
		if len(ifceTUN.Name()) == 0 {
			return fmt.Errorf("expected non-empty interface name")
		}
	} else {
		// Verify the error is a valid system/device error (permission denied, operation not permitted, device not found, etc.)
		errStr := errTUN.Error()
		if !isAcceptableSystemError(errStr) {
			return fmt.Errorf("unexpected error from water.New(TUN): %w", errTUN)
		}
	}

	// Assertion 4: water.New creates a TAP interface or returns a system permission error on unprivileged environments
	ifceTAP, errTAP := water.New(water.Config{DeviceType: water.TAP})
	if errTAP == nil {
		defer ifceTAP.Close()
		if !ifceTAP.IsTAP() {
			return fmt.Errorf("expected ifce.IsTAP() to be true")
		}
		if ifceTAP.IsTUN() {
			return fmt.Errorf("expected ifce.IsTUN() to be false for TAP device")
		}
		if len(ifceTAP.Name()) == 0 {
			return fmt.Errorf("expected non-empty interface name")
		}
	} else {
		// Verify the error is a valid system/device error
		errStr := errTAP.Error()
		if !isAcceptableSystemError(errStr) {
			return fmt.Errorf("unexpected error from water.New(TAP): %w", errTAP)
		}
	}

	return nil
}

func isAcceptableSystemError(msg string) bool {
	lower := strings.ToLower(msg)
	return strings.Contains(lower, "operation not permitted") ||
		strings.Contains(lower, "permission denied") ||
		strings.Contains(lower, "no such file or directory") ||
		strings.Contains(lower, "no such device") ||
		strings.Contains(lower, "device or resource busy") ||
		strings.Contains(lower, "ioctl")
}