github.com/klauspost/compress v1.20.0: snappy.NewWriter

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 snappy.NewWriter in pkg:golang/github.com/klauspost/compress@v1.20.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/klauspost/compress@v1.20.0
Demonstrate these symbols/APIs:
  - snappy.NewWriter

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:sha256:70a636d0e648acb736f7d38ad504f87242fb0c58045f0c22306ee5269c32c93b","contract":["snappy.NewWriter returns a non-nil *snappy.Writer wrapping the target io.Writer","snappy.Writer compresses data written through Write method into Snappy framing stream","snappy.Writer.Close flushes and finalizes the compressed stream","snappy.Writer.Reset redirects subsequent compressed writes to a new io.Writer","decompression with snappy.NewReader recovers the exact original bytes written by snappy.NewWriter"],"goal":"verify snappy.NewWriter in pkg:golang/github.com/klauspost/compress@v1.20.0","kind":"HOW","packages":["pkg:golang/github.com/klauspost/compress@v1.20.0"],"schemaVersion":1,"symbols":["snappy.NewWriter"]},"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/klauspost/compress@v1.20.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/klauspost/compress@v1.20.0","symbols":["snappy.NewWriter"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/klauspost/compress v1.20.0

github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=

package main

import (
	"bytes"
	"fmt"
	"io"

	"github.com/klauspost/compress/snappy"
)

func main() {
	var buf bytes.Buffer
	w := snappy.NewWriter(&buf)

	data := []byte("Streaming compression with klauspost/compress snappy.NewWriter")
	if _, err := w.Write(data); err != nil {
		panic(err)
	}

	if err := w.Close(); err != nil {
		panic(err)
	}

	compressedLen := buf.Len()
	r := snappy.NewReader(&buf)
	decompressed, err := io.ReadAll(r)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Compressed %d bytes down to %d bytes\n", len(data), compressedLen)
	fmt.Printf("Decompressed string: %s\n", string(decompressed))
}

{
  "schemaVersion": 1,
  "goal": "verify snappy.NewWriter in pkg:golang/github.com/klauspost/compress@v1.20.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/klauspost/compress@v1.20.0"
  ],
  "symbols": [
    "snappy.NewWriter"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"io"
	"os"

	"github.com/klauspost/compress/snappy"
)

func main() {
	// 1. snappy.NewWriter returns a non-nil *snappy.Writer wrapping the target io.Writer
	var buf bytes.Buffer
	w := snappy.NewWriter(&buf)
	if w == nil {
		fmt.Fprintln(os.Stderr, "FAIL: snappy.NewWriter returned nil")
		os.Exit(1)
	}

	// 2. snappy.Writer compresses data written through Write method into Snappy framing stream
	input1 := []byte("CodeSampleX contract verification: snappy.Writer streaming compression.")
	n, err := w.Write(input1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: w.Write failed: %v\n", err)
		os.Exit(1)
	}
	if n != len(input1) {
		fmt.Fprintf(os.Stderr, "FAIL: w.Write short write: got %d want %d\n", n, len(input1))
		os.Exit(1)
	}

	// 3. snappy.Writer.Close flushes and finalizes the compressed stream
	if err := w.Close(); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: w.Close failed: %v\n", err)
		os.Exit(1)
	}
	compressed1 := buf.Bytes()
	if len(compressed1) == 0 {
		fmt.Fprintln(os.Stderr, "FAIL: compressed stream is empty after Close")
		os.Exit(1)
	}
	snappyMagic := []byte("\xff\x06\x00\x00sNaPpY")
	if !bytes.HasPrefix(compressed1, snappyMagic) {
		fmt.Fprintf(os.Stderr, "FAIL: compressed stream missing Snappy magic header\n")
		os.Exit(1)
	}

	// 4. snappy.Writer.Reset redirects subsequent compressed writes to a new io.Writer
	var buf2 bytes.Buffer
	w.Reset(&buf2)
	input2 := []byte("Second stream payload following snappy.Writer.Reset call.")
	n2, err := w.Write(input2)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: w.Write after Reset failed: %v\n", err)
		os.Exit(1)
	}
	if n2 != len(input2) {
		fmt.Fprintf(os.Stderr, "FAIL: w.Write after Reset short write: got %d want %d\n", n2, len(input2))
		os.Exit(1)
	}
	if err := w.Close(); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: w.Close after Reset failed: %v\n", err)
		os.Exit(1)
	}
	compressed2 := buf2.Bytes()
	if !bytes.HasPrefix(compressed2, snappyMagic) {
		fmt.Fprintf(os.Stderr, "FAIL: second stream missing Snappy magic header\n")
		os.Exit(1)
	}

	// 5. decompression with snappy.NewReader recovers the exact original bytes written by snappy.NewWriter
	r1 := snappy.NewReader(bytes.NewReader(compressed1))
	decomp1, err := io.ReadAll(r1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ReadAll on stream 1 failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(decomp1, input1) {
		fmt.Fprintf(os.Stderr, "FAIL: stream 1 mismatch: got %q want %q\n", decomp1, input1)
		os.Exit(1)
	}

	r2 := snappy.NewReader(bytes.NewReader(compressed2))
	decomp2, err := io.ReadAll(r2)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ReadAll on stream 2 failed: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(decomp2, input2) {
		fmt.Fprintf(os.Stderr, "FAIL: stream 2 mismatch: got %q want %q\n", decomp2, input2)
		os.Exit(1)
	}

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