github.com/klauspost/compress v1.20.0: flate.NewReader

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/flate.NewReader 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/flate.NewReader

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:sha256:515a7242c11a43d6b28ee119fa76b76f7ed1685100cd192ff11ecc78a85a656f","contract":["flate.NewReader decompresses deflated stream to restore exact original payload","flate.NewReader decompresses data compressed at different compression levels including BestSpeed and BestCompression","flate.NewReader correctly decompresses empty deflated payload","flate.NewReader returns error when reading invalid or corrupted deflated data","flate.NewReader implements Resetter allowing reuse of reader across multiple streams","flate.NewReaderDict decompresses stream compressed with preset dictionary"],"goal":"verify github.com/klauspost/compress/flate.NewReader 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/flate.NewReader"]},"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/flate.NewReader"],"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/flate"
)

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

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

	reader := flate.NewReader(&buf)
	defer reader.Close()

	decompressed, err := io.ReadAll(reader)
	if err != nil {
		log.Fatalf("failed to read decompressed 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/flate.NewReader 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/flate.NewReader"
  ]
}

package main

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

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

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

		r := flate.NewReader(&buf)
		decompressed, err := io.ReadAll(r)
		if err != nil {
			fmt.Fprintf(os.Stderr, "flate.NewReader ReadAll failed: %v\n", err)
			os.Exit(1)
		}
		if err := r.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "flate reader 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. flate.NewReader decompresses data compressed at different compression levels including BestSpeed and BestCompression
	{
		sampleData := bytes.Repeat([]byte("Repeat pattern for flate compression levels. "), 50)
		levels := []int{flate.BestSpeed, flate.BestCompression, flate.HuffmanOnly}
		for _, level := range levels {
			var b bytes.Buffer
			w, err := flate.NewWriter(&b, level)
			if err != nil {
				fmt.Fprintf(os.Stderr, "flate.NewWriter(level %d) failed: %v\n", level, err)
				os.Exit(1)
			}
			if _, err := w.Write(sampleData); err != nil {
				fmt.Fprintf(os.Stderr, "flate write level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			if err := w.Close(); err != nil {
				fmt.Fprintf(os.Stderr, "flate close level %d failed: %v\n", level, err)
				os.Exit(1)
			}

			r := flate.NewReader(&b)
			decomp, err := io.ReadAll(r)
			if err != nil {
				fmt.Fprintf(os.Stderr, "flate read level %d failed: %v\n", level, err)
				os.Exit(1)
			}
			if err := r.Close(); err != nil {
				fmt.Fprintf(os.Stderr, "flate close reader 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. flate.NewReader correctly decompresses empty deflated payload
	{
		var emptyBuf bytes.Buffer
		w, err := flate.NewWriter(&emptyBuf, flate.DefaultCompression)
		if err != nil {
			fmt.Fprintf(os.Stderr, "flate empty writer creation failed: %v\n", err)
			os.Exit(1)
		}
		if err := w.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "flate empty writer close failed: %v\n", err)
			os.Exit(1)
		}

		r := flate.NewReader(&emptyBuf)
		decomp, err := io.ReadAll(r)
		if err != nil {
			fmt.Fprintf(os.Stderr, "flate empty reader read failed: %v\n", err)
			os.Exit(1)
		}
		if err := r.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "flate empty reader close failed: %v\n", err)
			os.Exit(1)
		}
		if len(decomp) != 0 {
			fmt.Fprintf(os.Stderr, "expected empty decompressed output, got %d bytes\n", len(decomp))
			os.Exit(1)
		}
	}

	// 4. flate.NewReader returns error when reading invalid or corrupted deflated data
	{
		corruptData := []byte{0x00, 0xff, 0xff, 0xff, 0xff, 0xff}
		r := flate.NewReader(bytes.NewReader(corruptData))
		_, err := io.ReadAll(r)
		if err == nil {
			fmt.Fprintf(os.Stderr, "expected error on corrupt flate stream, got nil\n")
			os.Exit(1)
		}
		_ = r.Close()
	}

	// 5. flate.NewReader implements Resetter allowing reuse of reader across multiple streams
	{
		payload1 := []byte("Stream 1 content for reset testing")
		payload2 := []byte("Stream 2 content for reset testing with different length")

		var buf1 bytes.Buffer
		w1, _ := flate.NewWriter(&buf1, flate.DefaultCompression)
		_, _ = w1.Write(payload1)
		_ = w1.Close()

		var buf2 bytes.Buffer
		w2, _ := flate.NewWriter(&buf2, flate.DefaultCompression)
		_, _ = w2.Write(payload2)
		_ = w2.Close()

		r := flate.NewReader(&buf1)
		out1, err := io.ReadAll(r)
		if err != nil || !bytes.Equal(payload1, out1) {
			fmt.Fprintf(os.Stderr, "stream 1 read failed: %v\n", err)
			os.Exit(1)
		}

		resetter, ok := r.(flate.Resetter)
		if !ok {
			fmt.Fprintf(os.Stderr, "expected flate reader to implement flate.Resetter\n")
			os.Exit(1)
		}

		if err := resetter.Reset(&buf2, nil); err != nil {
			fmt.Fprintf(os.Stderr, "resetter.Reset failed: %v\n", err)
			os.Exit(1)
		}

		out2, err := io.ReadAll(r)
		if err != nil || !bytes.Equal(payload2, out2) {
			fmt.Fprintf(os.Stderr, "stream 2 read after reset failed: %v\n", err)
			os.Exit(1)
		}
		_ = r.Close()
	}

	// 6. flate.NewReaderDict decompresses stream compressed with preset dictionary
	{
		dict := []byte("preset dictionary with common vocabulary terms")
		dictPayload := []byte("vocabulary terms common in sample dictionary compression")

		var bufDict bytes.Buffer
		wDict, err := flate.NewWriterDict(&bufDict, flate.DefaultCompression, dict)
		if err != nil {
			fmt.Fprintf(os.Stderr, "flate.NewWriterDict failed: %v\n", err)
			os.Exit(1)
		}
		if _, err := wDict.Write(dictPayload); err != nil {
			fmt.Fprintf(os.Stderr, "flate write dict failed: %v\n", err)
			os.Exit(1)
		}
		if err := wDict.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "flate close dict failed: %v\n", err)
			os.Exit(1)
		}

		rDict := flate.NewReaderDict(&bufDict, dict)
		decompDict, err := io.ReadAll(rDict)
		if err != nil {
			fmt.Fprintf(os.Stderr, "flate.NewReaderDict ReadAll failed: %v\n", err)
			os.Exit(1)
		}
		if err := rDict.Close(); err != nil {
			fmt.Fprintf(os.Stderr, "flate reader dict Close failed: %v\n", err)
			os.Exit(1)
		}
		if !bytes.Equal(dictPayload, decompDict) {
			fmt.Fprintf(os.Stderr, "dict decompression mismatch: got %q, want %q\n", string(decompDict), string(dictPayload))
			os.Exit(1)
		}
	}

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