golang.org/x/sys v0.22.0: unix.Seek

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 golang.org/x/sys/unix.Seek in pkg:golang/golang.org/x/sys@v0.22.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.22.0
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.Seek

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:sha256:04fcba920163a52c2db5bfeb4ee2b98f4b8507c1a5690d5b12ed5279f670a94f","contract":["unix.Seek repositions the read/write file offset of an open file descriptor","unix.Seek with SEEK_SET sets the offset relative to the beginning of the file","unix.Seek with SEEK_CUR sets the offset relative to the current file offset","unix.Seek with SEEK_END sets the offset relative to the end of the file","unix.Seek returns unix.EBADF for an invalid file descriptor","unix.Seek returns unix.EINVAL for a negative resulting offset"],"goal":"verify golang.org/x/sys/unix.Seek in pkg:golang/golang.org/x/sys@v0.22.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.22.0"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.Seek"]},"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/golang.org/x/sys@v0.22.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.22.0","symbols":["golang.org/x/sys/unix.Seek"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require golang.org/x/sys v0.22.0

golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

package main

import (
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func main() {
	tmpFile, err := os.CreateTemp("", "seek_sample_*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp file: %v\n", err)
		os.Exit(1)
	}
	defer os.Remove(tmpFile.Name())
	defer tmpFile.Close()

	if _, err := tmpFile.Write([]byte("hello world")); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write temp file: %v\n", err)
		os.Exit(1)
	}

	fd := int(tmpFile.Fd())

	offset, err := unix.Seek(fd, 6, unix.SEEK_SET)
	if err != nil {
		fmt.Fprintf(os.Stderr, "unix.Seek failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("unix.Seek succeeded: new offset=%d\n", offset)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.Seek in pkg:golang/golang.org/x/sys@v0.22.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.22.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.Seek"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func main() {
	if err := runTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract assertions passed.")
}

func runTests() error {
	tmpFile, err := os.CreateTemp("", "contract_seek_*")
	if err != nil {
		return fmt.Errorf("failed to create temp file: %w", err)
	}
	defer os.Remove(tmpFile.Name())
	defer tmpFile.Close()

	if _, err := tmpFile.Write([]byte("abcdefghij")); err != nil {
		return fmt.Errorf("failed to write test data: %w", err)
	}

	fd := int(tmpFile.Fd())

	// 1. unix.Seek repositions the read/write file offset of an open file descriptor
	off, err := unix.Seek(fd, 0, unix.SEEK_SET)
	if err != nil {
		return fmt.Errorf("unix.Seek to 0 failed: %w", err)
	}
	if off != 0 {
		return fmt.Errorf("expected offset 0, got %d", off)
	}

	// 2. unix.Seek with SEEK_SET sets the offset relative to the beginning of the file
	off, err = unix.Seek(fd, 4, unix.SEEK_SET)
	if err != nil {
		return fmt.Errorf("unix.Seek SEEK_SET failed: %w", err)
	}
	if off != 4 {
		return fmt.Errorf("expected offset 4, got %d", off)
	}

	buf := make([]byte, 1)
	n, err := unix.Read(fd, buf)
	if err != nil || n != 1 || buf[0] != 'e' {
		return fmt.Errorf("expected 'e' at offset 4, got %q (n=%d, err=%v)", buf, n, err)
	}

	// 3. unix.Seek with SEEK_CUR sets the offset relative to the current file offset
	off, err = unix.Seek(fd, 2, unix.SEEK_CUR)
	if err != nil {
		return fmt.Errorf("unix.Seek SEEK_CUR failed: %w", err)
	}
	if off != 7 {
		return fmt.Errorf("expected offset 7, got %d", off)
	}

	n, err = unix.Read(fd, buf)
	if err != nil || n != 1 || buf[0] != 'h' {
		return fmt.Errorf("expected 'h' at offset 7, got %q (n=%d, err=%v)", buf, n, err)
	}

	// 4. unix.Seek with SEEK_END sets the offset relative to the end of the file
	off, err = unix.Seek(fd, -2, unix.SEEK_END)
	if err != nil {
		return fmt.Errorf("unix.Seek SEEK_END failed: %w", err)
	}
	if off != 8 {
		return fmt.Errorf("expected offset 8, got %d", off)
	}

	n, err = unix.Read(fd, buf)
	if err != nil || n != 1 || buf[0] != 'i' {
		return fmt.Errorf("expected 'i' at offset 8, got %q (n=%d, err=%v)", buf, n, err)
	}

	// 5. unix.Seek returns unix.EBADF for an invalid file descriptor
	_, err = unix.Seek(-1, 0, unix.SEEK_SET)
	if err == nil {
		return fmt.Errorf("expected error for fd=-1, got nil")
	}
	if !errors.Is(err, unix.EBADF) {
		return fmt.Errorf("expected unix.EBADF for fd=-1, got: %w", err)
	}

	// 6. unix.Seek returns unix.EINVAL for a negative resulting offset
	_, err = unix.Seek(fd, -1, unix.SEEK_SET)
	if err == nil {
		return fmt.Errorf("expected error for negative offset with SEEK_SET, got nil")
	}
	if !errors.Is(err, unix.EINVAL) {
		return fmt.Errorf("expected unix.EINVAL for negative offset, got: %w", err)
	}

	return nil
}