github.com/cespare/xxhash/v2 v2.1.1: xxhash.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 xxhash.New in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/cespare/xxhash/v2@v2.1.1
Demonstrate these symbols/APIs:
  - xxhash.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:sha256:0c99174fea4ae7bae779115a015c632c16408a45c755be98fb3d670f171c2265","contract":["xxhash.New creates a hash.Hash64 instance that computes 64-bit xxHash checksum via Write and Sum64","Digest.WriteString produces identical hash output to Write without extra byte allocation","Digest.Reset restores initial state allowing reuse for independent checksum calculations","Digest.Sum appends 8-byte big-endian representation of Sum64 to provided byte slice","Digest.MarshalBinary and UnmarshalBinary preserve and restore internal accumulator state across writes"],"goal":"verify xxhash.New in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1","kind":"HOW","packages":["pkg:golang/github.com/cespare/xxhash/v2@v2.1.1"],"schemaVersion":1,"symbols":["xxhash.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/cespare/xxhash/v2@v2.1.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/cespare/xxhash/v2@v2.1.1","symbols":["xxhash.New"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/cespare/xxhash/v2 v2.1.1

github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=
github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=

package main

import (
	"fmt"
	"io"
	"strings"

	"github.com/cespare/xxhash/v2"
)

// StreamHasher demonstrates streaming hash computation using xxhash.New.
type StreamHasher struct {
	hasher *xxhash.Digest
}

// NewStreamHasher creates a new StreamHasher instance.
func NewStreamHasher() *StreamHasher {
	return &StreamHasher{
		hasher: xxhash.New(),
	}
}

// HashReader computes the 64-bit xxHash checksum of an io.Reader stream.
func (s *StreamHasher) HashReader(r io.Reader) (uint64, error) {
	s.hasher.Reset()
	if _, err := io.Copy(s.hasher, r); err != nil {
		return 0, err
	}
	return s.hasher.Sum64(), nil
}

// HashString computes the 64-bit xxHash checksum using WriteString.
func (s *StreamHasher) HashString(str string) (uint64, error) {
	s.hasher.Reset()
	if _, err := s.hasher.WriteString(str); err != nil {
		return 0, err
	}
	return s.hasher.Sum64(), nil
}

func main() {
	hasher := NewStreamHasher()

	// Compute hash from streaming reader
	reader := strings.NewReader("sample payload data for xxhash")
	checksum1, err := hasher.HashReader(reader)
	if err != nil {
		fmt.Printf("Error: %v\n", err)
		return
	}
	fmt.Printf("Stream checksum: %016x\n", checksum1)

	// Compute hash using WriteString
	checksum2, err := hasher.HashString("sample payload data for xxhash")
	if err != nil {
		fmt.Printf("Error: %v\n", err)
		return
	}
	fmt.Printf("String checksum: %016x\n", checksum2)
}

{
  "schemaVersion": 1,
  "goal": "verify xxhash.New in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/cespare/xxhash/v2@v2.1.1"
  ],
  "symbols": [
    "xxhash.New"
  ]
}

package main

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"os"

	"github.com/cespare/xxhash/v2"
)

func main() {
	// Contract 1: xxhash.New creates a hash.Hash64 instance that computes 64-bit xxHash checksum via Write and Sum64
	{
		h := xxhash.New()
		if h.Size() != 8 {
			fmt.Fprintf(os.Stderr, "FAIL: expected size 8, got %d\n", h.Size())
			os.Exit(1)
		}
		if h.BlockSize() != 32 {
			fmt.Fprintf(os.Stderr, "FAIL: expected block size 32, got %d\n", h.BlockSize())
			os.Exit(1)
		}

		data := []byte("hello xxhash streaming computation")
		n, err := h.Write(data)
		if err != nil || n != len(data) {
			fmt.Fprintf(os.Stderr, "FAIL: Write returned err=%v, n=%d, expected len=%d\n", err, n, len(data))
			os.Exit(1)
		}

		expected := xxhash.Sum64(data)
		got := h.Sum64()
		if got != expected {
			fmt.Fprintf(os.Stderr, "FAIL: Sum64() = %x, expected %x\n", got, expected)
			os.Exit(1)
		}
	}

	// Contract 2: Digest.WriteString produces identical hash output to Write without extra byte allocation
	{
		str := "testing xxhash.WriteString equivalence"
		h1 := xxhash.New()
		n1, err1 := h1.WriteString(str)
		if err1 != nil || n1 != len(str) {
			fmt.Fprintf(os.Stderr, "FAIL: WriteString returned err=%v, n=%d\n", err1, n1)
			os.Exit(1)
		}

		h2 := xxhash.New()
		_, _ = h2.Write([]byte(str))

		if h1.Sum64() != h2.Sum64() {
			fmt.Fprintf(os.Stderr, "FAIL: WriteString hash %x != Write hash %x\n", h1.Sum64(), h2.Sum64())
			os.Exit(1)
		}

		if h1.Sum64() != xxhash.Sum64String(str) {
			fmt.Fprintf(os.Stderr, "FAIL: WriteString hash %x != Sum64String %x\n", h1.Sum64(), xxhash.Sum64String(str))
			os.Exit(1)
		}
	}

	// Contract 3: Digest.Reset restores initial state allowing reuse for independent checksum calculations
	{
		h := xxhash.New()
		_, _ = h.WriteString("initial payload before reset")
		_ = h.Sum64()

		h.Reset()

		fresh := xxhash.New()
		if h.Sum64() != fresh.Sum64() {
			fmt.Fprintf(os.Stderr, "FAIL: Reset hash %x != fresh hash %x\n", h.Sum64(), fresh.Sum64())
			os.Exit(1)
		}

		payload := "new independent stream payload"
		_, _ = h.WriteString(payload)
		_, _ = fresh.WriteString(payload)

		if h.Sum64() != fresh.Sum64() {
			fmt.Fprintf(os.Stderr, "FAIL: after Reset, computed hash %x != fresh hash %x\n", h.Sum64(), fresh.Sum64())
			os.Exit(1)
		}
	}

	// Contract 4: Digest.Sum appends 8-byte big-endian representation of Sum64 to provided byte slice
	{
		h := xxhash.New()
		_, _ = h.WriteString("checksum serialization test")
		sum64 := h.Sum64()

		prefix := []byte("prefix-data:")
		result := h.Sum(prefix)

		if len(result) != len(prefix)+8 {
			fmt.Fprintf(os.Stderr, "FAIL: expected length %d, got %d\n", len(prefix)+8, len(result))
			os.Exit(1)
		}

		if !bytes.Equal(result[:len(prefix)], prefix) {
			fmt.Fprintf(os.Stderr, "FAIL: prefix was modified in Sum output\n")
			os.Exit(1)
		}

		appended := binary.BigEndian.Uint64(result[len(prefix):])
		if appended != sum64 {
			fmt.Fprintf(os.Stderr, "FAIL: Sum appended %x, expected %x\n", appended, sum64)
			os.Exit(1)
		}
	}

	// Contract 5: Digest.MarshalBinary and UnmarshalBinary preserve and restore internal accumulator state across writes
	{
		part1 := []byte("first chunk of multipart payload, ")
		part2 := []byte("followed by second chunk.")

		h1 := xxhash.New()
		_, _ = h1.Write(part1)

		state, err := h1.MarshalBinary()
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: MarshalBinary returned err: %v\n", err)
			os.Exit(1)
		}

		h2 := xxhash.New()
		if err := h2.UnmarshalBinary(state); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: UnmarshalBinary returned err: %v\n", err)
			os.Exit(1)
		}

		_, _ = h1.Write(part2)
		_, _ = h2.Write(part2)

		if h1.Sum64() != h2.Sum64() {
			fmt.Fprintf(os.Stderr, "FAIL: restored digest hash %x != original digest hash %x\n", h2.Sum64(), h1.Sum64())
			os.Exit(1)
		}
	}

	fmt.Println("PASS: github.com/cespare/xxhash/v2 xxhash.New contract passed")
}