github.com/klauspost/compress v1.19.1: zlib.ErrHeader

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/zlib.ErrHeader in pkg:golang/github.com/klauspost/compress@v1.19.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/klauspost/compress@v1.19.1
Demonstrate these symbols/APIs:
  - github.com/klauspost/compress/zlib.ErrHeader

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:c572c35da2f5ce928a927ee03be6d3044aa3b6b1a75ff8bc5a587ada29038c3c","contract":["ErrHeader is the sentinel error variable exported by zlib with message \"zlib: invalid header\"","NewReader returns ErrHeader when decompressing a byte stream with an invalid zlib header","NewReader returns ErrHeader when decompressing a stream with corrupted header flag check bits","NewReaderDict returns ErrHeader when decompressing a stream with an invalid zlib header","Resetter.Reset returns ErrHeader when resetting an existing reader with an invalid zlib header stream","NewReader succeeds and does not return ErrHeader when reading a valid zlib compressed stream"],"goal":"verify github.com/klauspost/compress/zlib.ErrHeader in pkg:golang/github.com/klauspost/compress@v1.19.1","kind":"HOW","packages":["pkg:golang/github.com/klauspost/compress@v1.19.1"],"schemaVersion":1,"symbols":["github.com/klauspost/compress/zlib.ErrHeader"]},"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@v1.19.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/klauspost/compress@v1.19.1","symbols":["github.com/klauspost/compress/zlib.ErrHeader"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/klauspost/compress v1.19.1

github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=

package main

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

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

func main() {
	payload := []byte("Demonstrating ErrHeader handling with klauspost/compress")

	// 1. Produce a valid compressed stream
	var validBuf bytes.Buffer
	writer := zlib.NewWriter(&validBuf)
	if _, err := writer.Write(payload); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write: %v\n", err)
		os.Exit(1)
	}
	if err := writer.Close(); err != nil {
		fmt.Fprintf(os.Stderr, "failed to close writer: %v\n", err)
		os.Exit(1)
	}

	// 2. Read the valid stream successfully
	reader, err := zlib.NewReader(bytes.NewReader(validBuf.Bytes()))
	if err != nil {
		fmt.Fprintf(os.Stderr, "unexpected reader error: %v\n", err)
		os.Exit(1)
	}
	defer reader.Close()

	decompressed, err := io.ReadAll(reader)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read decompressed data: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Successfully decompressed %d bytes: %s\n", len(decompressed), string(decompressed))

	// 3. Attempt to initialize reader with invalid header bytes
	invalidData := []byte{0x00, 0x00, 0x00, 0x00}
	_, err = zlib.NewReader(bytes.NewReader(invalidData))
	if errors.Is(err, zlib.ErrHeader) {
		fmt.Printf("Successfully caught expected ErrHeader: %v\n", err)
	} else {
		fmt.Fprintf(os.Stderr, "expected zlib.ErrHeader, got: %v\n", err)
		os.Exit(1)
	}

	// 4. Attempt to initialize reader with corrupted header checksum (FLG check bits)
	corruptedHeader := []byte{0x78, 0x9d, 0x00, 0x00}
	_, err = zlib.NewReader(bytes.NewReader(corruptedHeader))
	if errors.Is(err, zlib.ErrHeader) {
		fmt.Printf("Successfully caught expected ErrHeader for corrupted header: %v\n", err)
	} else {
		fmt.Fprintf(os.Stderr, "expected zlib.ErrHeader, got: %v\n", err)
		os.Exit(1)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/klauspost/compress/zlib.ErrHeader in pkg:golang/github.com/klauspost/compress@v1.19.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/klauspost/compress@v1.19.1"
  ],
  "symbols": [
    "github.com/klauspost/compress/zlib.ErrHeader"
  ]
}

package main

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

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

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

func runContractTests() error {
	// 1. ErrHeader is the sentinel error variable exported by zlib with message "zlib: invalid header"
	{
		if zlib.ErrHeader == nil {
			return fmt.Errorf("expected zlib.ErrHeader to be non-nil")
		}
		if zlib.ErrHeader.Error() != "zlib: invalid header" {
			return fmt.Errorf("expected error string 'zlib: invalid header', got %q", zlib.ErrHeader.Error())
		}
	}

	// 2. NewReader returns ErrHeader when decompressing a byte stream with an invalid zlib header
	{
		invalidData := []byte{0x00, 0x00, 0x00, 0x00}
		_, err := zlib.NewReader(bytes.NewReader(invalidData))
		if !errors.Is(err, zlib.ErrHeader) {
			return fmt.Errorf("assertion 2: expected ErrHeader from NewReader, got: %v", err)
		}
	}

	// 3. NewReader returns ErrHeader when decompressing a stream with corrupted header flag check bits
	{
		// Valid deflate header: 0x78 (CM=8, CINFO=7), 0x9c (FLEVEL=2, FDICT=0, FCHECK satisfies (0x78*256+0x9c)%31 == 0).
		// Corrupting FLG to 0x9d breaks the header check bits.
		corruptHeader := []byte{0x78, 0x9d, 0x00, 0x00}
		_, err := zlib.NewReader(bytes.NewReader(corruptHeader))
		if !errors.Is(err, zlib.ErrHeader) {
			return fmt.Errorf("assertion 3: expected ErrHeader for corrupted header flags, got: %v", err)
		}
	}

	// 4. NewReaderDict returns ErrHeader when decompressing a stream with an invalid zlib header
	{
		dict := []byte("test-contract-dictionary")
		invalidData := []byte{0x05, 0x05, 0x05, 0x05}
		_, err := zlib.NewReaderDict(bytes.NewReader(invalidData), dict)
		if !errors.Is(err, zlib.ErrHeader) {
			return fmt.Errorf("assertion 4: expected ErrHeader from NewReaderDict, got: %v", err)
		}
	}

	// 5. Resetter.Reset returns ErrHeader when resetting an existing reader with an invalid zlib header stream
	{
		payload := []byte("Valid payload for initial reader setup.")
		var validBuf bytes.Buffer
		zw := zlib.NewWriter(&validBuf)
		if _, err := zw.Write(payload); err != nil {
			return fmt.Errorf("assertion 5: writer.Write failed: %w", err)
		}
		if err := zw.Close(); err != nil {
			return fmt.Errorf("assertion 5: writer.Close failed: %w", err)
		}

		zr, err := zlib.NewReader(&validBuf)
		if err != nil {
			return fmt.Errorf("assertion 5: NewReader failed: %w", err)
		}
		defer zr.Close()

		resetter, ok := zr.(zlib.Resetter)
		if !ok {
			return fmt.Errorf("assertion 5: reader does not implement zlib.Resetter")
		}

		invalidHeaderStream := []byte{0x00, 0x11, 0x22, 0x33}
		err = resetter.Reset(bytes.NewReader(invalidHeaderStream), nil)
		if !errors.Is(err, zlib.ErrHeader) {
			return fmt.Errorf("assertion 5: expected ErrHeader from resetter.Reset with invalid header, got: %v", err)
		}
	}

	// 6. NewReader succeeds and does not return ErrHeader when reading a valid zlib compressed stream
	{
		payload := []byte("Valid zlib payload confirming normal operation succeeds.")
		var validBuf bytes.Buffer
		zw := zlib.NewWriter(&validBuf)
		if _, err := zw.Write(payload); err != nil {
			return fmt.Errorf("assertion 6: zw.Write failed: %w", err)
		}
		if err := zw.Close(); err != nil {
			return fmt.Errorf("assertion 6: zw.Close failed: %w", err)
		}

		zr, err := zlib.NewReader(&validBuf)
		if err != nil {
			return fmt.Errorf("assertion 6: expected nil error from NewReader, got: %v", err)
		}
		defer zr.Close()

		decompressed, err := io.ReadAll(zr)
		if err != nil {
			return fmt.Errorf("assertion 6: io.ReadAll failed: %w", err)
		}
		if !bytes.Equal(decompressed, payload) {
			return fmt.Errorf("assertion 6: decompressed data mismatch")
		}
	}

	return nil
}