github.com/klauspost/compress v1.20.0: gzip.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 github.com/klauspost/compress/gzip.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:
  - github.com/klauspost/compress/gzip.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:sha256:0968c6e63369c723221c0687a5b1f9cdcfeb0cb02f11de390b6c011249127e78","contract":["gzip.NewWriter compresses data stream and gzip.NewReader decompresses to restore exact original payload","gzip.NewWriterLevel compresses with specified compression levels including BestSpeed, BestCompression, and HuffmanOnly","gzip.NewWriter and gzip.NewReader correctly roundtrip empty input payload","gzip.NewReader returns error when reading invalid or corrupted gzip stream","gzip.NewWriter and gzip.NewReader support stream reuse via Reset","gzip.NewWriter preserves header metadata including Name, Comment, and ModTime during roundtrip"],"goal":"verify github.com/klauspost/compress/gzip.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":["github.com/klauspost/compress/gzip.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":["github.com/klauspost/compress/gzip.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"
	"log"

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

func main() {
	original := []byte("Hello, CodeSampleX with klauspost/compress gzip!")

	var buf bytes.Buffer
	writer := gzip.NewWriter(&buf)
	if _, err := writer.Write(original); err != nil {
		log.Fatalf("failed to write gzip data: %v", err)
	}
	if err := writer.Close(); err != nil {
		log.Fatalf("failed to close gzip writer: %v", err)
	}

	reader, err := gzip.NewReader(&buf)
	if err != nil {
		log.Fatalf("failed to create gzip reader: %v", err)
	}
	defer reader.Close()

	decompressed, err := io.ReadAll(reader)
	if err != nil {
		log.Fatalf("failed to read decompressed gzip data: %v", err)
	}

	fmt.Printf("Original:     %s\n", string(original))
	fmt.Printf("Decompressed: %s\n", string(decompressed))
}

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

package main

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

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

func main() {
	// 1. gzip.NewWriter compresses data stream and gzip.NewReader decompresses to restore exact original payload
	{
		original := []byte("CodeSampleX verification payload for github.com/klauspost/compress/gzip stream compression.")
		var buf bytes.Buffer
		zw := gzip.NewWriter(&buf)
		if _, err := zw.Write(original); err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewWriter Write failed: %v\n", err)
			os.Exit(1)
		}
		if err := zw.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewWriter Close failed: %v\n", err)
			os.Exit(1)
		}

		zr, err := gzip.NewReader(&buf)
		if err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewReader failed: %v\n", err)
			os.Exit(1)
		}
		decompressed, err := io.ReadAll(zr)
		if err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewReader ReadAll failed: %v\n", err)
			os.Exit(1)
		}
		if err := zr.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewReader Close failed: %v\n", err)
			os.Exit(1)
		}
		if !bytes.Equal(original, decompressed) {
			fmt.Fprintf(os.Stderr, "decompressed mismatch: got %q, want %q\n", string(decompressed), string(original))
			os.Exit(1)
		}
	}

	// 2. gzip.NewWriterLevel compresses with specified compression levels including BestSpeed, BestCompression, and HuffmanOnly
	{
		sampleData := bytes.Repeat([]byte("High repetition pattern for testing klauspost gzip compression levels. "), 40)
		for _, level := range []int{gzip.BestSpeed, gzip.DefaultCompression, gzip.BestCompression, gzip.HuffmanOnly} {
			var b bytes.Buffer
			zw, err := gzip.NewWriterLevel(&b, level)
			if err != nil {
				fmt.Fprintf(os.Stderr, "gzip.NewWriterLevel(%d) failed: %v\n", level, err)
				os.Exit(1)
			}
			if _, err := zw.Write(sampleData); err != nil {
				fmt.Fprintf(os.Stderr, "gzip write with level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			if err := zw.Close(); err != nil {
				fmt.Fprintf(os.Stderr, "gzip close with level %d failed: %v\n", level, err)
				os.Exit(1)
			}

			zr, err := gzip.NewReader(&b)
			if err != nil {
				fmt.Fprintf(os.Stderr, "gzip.NewReader for level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			decomp, err := io.ReadAll(zr)
			if err != nil {
				fmt.Fprintf(os.Stderr, "gzip read for level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			if err := zr.Close(); err != nil {
				fmt.Fprintf(os.Stderr, "gzip reader close for level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			if !bytes.Equal(sampleData, decomp) {
				fmt.Fprintf(os.Stderr, "level %d roundtrip mismatch\n", level)
				os.Exit(1)
			}
		}
	}

	// 3. gzip.NewWriter and gzip.NewReader correctly roundtrip empty input payload
	{
		var emptyBuf bytes.Buffer
		zwEmpty := gzip.NewWriter(&emptyBuf)
		if err := zwEmpty.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "gzip empty write close failed: %v\n", err)
			os.Exit(1)
		}
		zrEmpty, err := gzip.NewReader(&emptyBuf)
		if err != nil {
			fmt.Fprintf(os.Stderr, "gzip empty reader failed: %v\n", err)
			os.Exit(1)
		}
		emptyDecomp, err := io.ReadAll(zrEmpty)
		if err != nil {
			fmt.Fprintf(os.Stderr, "gzip empty read failed: %v\n", err)
			os.Exit(1)
		}
		if err := zrEmpty.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "gzip empty reader close failed: %v\n", err)
			os.Exit(1)
		}
		if len(emptyDecomp) != 0 {
			fmt.Fprintf(os.Stderr, "expected empty decompressed payload, got %d bytes\n", len(emptyDecomp))
			os.Exit(1)
		}
	}

	// 4. gzip.NewReader returns error when reading invalid or corrupted gzip stream
	{
		corrupted := []byte{0x1f, 0x8b, 0xff, 0xff, 0x00, 0x00}
		zrBad, err := gzip.NewReader(bytes.NewReader(corrupted))
		if err == nil {
			_, readErr := io.ReadAll(zrBad)
			_ = zrBad.Close()
			if readErr == nil {
				fmt.Fprintf(os.Stderr, "expected error reading corrupted gzip stream, got nil\n")
				os.Exit(1)
			}
		}
	}

	// 5. gzip.NewWriter and gzip.NewReader support stream reuse via Reset
	{
		var buf1 bytes.Buffer
		zwReuse := gzip.NewWriter(&buf1)
		p1 := []byte("first stream payload for reusable gzip writer")
		if _, err := zwReuse.Write(p1); err != nil {
			fmt.Fprintf(os.Stderr, "p1 write failed: %v\n", err)
			os.Exit(1)
		}
		if err := zwReuse.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "p1 close failed: %v\n", err)
			os.Exit(1)
		}

		var buf2 bytes.Buffer
		zwReuse.Reset(&buf2)
		p2 := []byte("second stream payload after gzip writer reset")
		if _, err := zwReuse.Write(p2); err != nil {
			fmt.Fprintf(os.Stderr, "p2 write failed: %v\n", err)
			os.Exit(1)
		}
		if err := zwReuse.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "p2 close failed: %v\n", err)
			os.Exit(1)
		}

		zrReuse, err := gzip.NewReader(&buf1)
		if err != nil {
			fmt.Fprintf(os.Stderr, "zrReuse init failed: %v\n", err)
			os.Exit(1)
		}
		res1, err := io.ReadAll(zrReuse)
		if err != nil || !bytes.Equal(res1, p1) {
			fmt.Fprintf(os.Stderr, "p1 mismatch: %v\n", err)
			os.Exit(1)
		}

		if err := zrReuse.Reset(&buf2); err != nil {
			fmt.Fprintf(os.Stderr, "zrReuse.Reset failed: %v\n", err)
			os.Exit(1)
		}
		res2, err := io.ReadAll(zrReuse)
		if err != nil || !bytes.Equal(res2, p2) {
			fmt.Fprintf(os.Stderr, "p2 mismatch: %v\n", err)
			os.Exit(1)
		}
		_ = zrReuse.Close()
	}

	// 6. gzip.NewWriter preserves header metadata including Name, Comment, and ModTime during roundtrip
	{
		var buf bytes.Buffer
		zw := gzip.NewWriter(&buf)
		zw.Name = "contract_artifact.txt"
		zw.Comment = "contract verification test"
		zw.ModTime = time.Unix(1700000000, 0)
		payload := []byte("sample payload with header metadata")
		if _, err := zw.Write(payload); err != nil {
			fmt.Fprintf(os.Stderr, "write failed: %v\n", err)
			os.Exit(1)
		}
		if err := zw.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "close failed: %v\n", err)
			os.Exit(1)
		}

		zr, err := gzip.NewReader(&buf)
		if err != nil {
			fmt.Fprintf(os.Stderr, "gzip.NewReader failed: %v\n", err)
			os.Exit(1)
		}
		decomp, err := io.ReadAll(zr)
		if err != nil {
			fmt.Fprintf(os.Stderr, "read failed: %v\n", err)
			os.Exit(1)
		}
		if zr.Name != "contract_artifact.txt" || zr.Comment != "contract verification test" || !zr.ModTime.Equal(time.Unix(1700000000, 0)) {
			fmt.Fprintf(os.Stderr, "header metadata mismatch: got Name=%q Comment=%q ModTime=%v\n", zr.Name, zr.Comment, zr.ModTime)
			os.Exit(1)
		}
		if !bytes.Equal(decomp, payload) {
			fmt.Fprintf(os.Stderr, "payload mismatch\n")
			os.Exit(1)
		}
		_ = zr.Close()
	}

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