github.com/quic-go/qpack v0.6.0: DecodeFunc, Decoder, Encoder

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 pkg:golang/github.com/quic-go/qpack@v0.6.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/quic-go/qpack@v0.6.0
Demonstrate these symbols/APIs:
  - qpack.DecodeFunc
  - qpack.Decoder
  - qpack.Encoder
  - qpack.HeaderField

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.

package sample_test

import (
	"bytes"
	"errors"
	"io"
	"reflect"
	"testing"

	"github.com/quic-go/qpack"
)

func TestQpackEncodingAndDecoding(t *testing.T) {
	// 1. HeaderField.IsPseudo accurately identifies HTTP/3 pseudo-headers starting with a colon
	pseudoStatus := qpack.HeaderField{Name: ":status", Value: "200"}
	pseudoPath := qpack.HeaderField{Name: ":path", Value: "/index.html"}
	regularContentType := qpack.HeaderField{Name: "content-type", Value: "application/json"}
	customHeader := qpack.HeaderField{Name: "x-custom-key", Value: "custom-value"}

	if !pseudoStatus.IsPseudo() {
		t.Fatalf("expected :status to be identified as pseudo-header")
	}
	if !pseudoPath.IsPseudo() {
		t.Fatalf("expected :path to be identified as pseudo-header")
	}
	if regularContentType.IsPseudo() {
		t.Fatalf("expected content-type not to be identified as pseudo-header")
	}
	if customHeader.IsPseudo() {
		t.Fatalf("expected x-custom-key not to be identified as pseudo-header")
	}

	// 2. qpack.NewEncoder creates an encoder writing QPACK-encoded headers to an underlying io.Writer
	var buf bytes.Buffer
	enc := qpack.NewEncoder(&buf)

	headers := []qpack.HeaderField{
		{Name: ":method", Value: "GET"},
		{Name: ":scheme", Value: "https"},
		{Name: ":path", Value: "/api/v1/resource"},
		{Name: ":authority", Value: "example.com"},
		{Name: "accept", Value: "application/json"},
		{Name: "user-agent", Value: "csx-test/1.0"},
	}

	// 3. Encoder.WriteField encodes pseudo-headers and custom header fields into QPACK wire format
	for _, hf := range headers {
		if err := enc.WriteField(hf); err != nil {
			t.Fatalf("failed to write field %v: %v", hf, err)
		}
	}

	// 4. Encoder.Close finalizes the current header block and resets the encoder for subsequent header blocks
	if err := enc.Close(); err != nil {
		t.Fatalf("failed to close encoder: %v", err)
	}

	encodedBytes := buf.Bytes()
	if len(encodedBytes) == 0 {
		t.Fatalf("expected non-empty encoded byte slice")
	}

	// 5. qpack.NewDecoder creates a decoder whose Decode method returns a DecodeFunc yielding header fields sequentially until io.EOF
	dec := qpack.NewDecoder()
	decodeNext := dec.Decode(encodedBytes)

	var decoded []qpack.HeaderField
	for {
		hf, err := decodeNext()
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			t.Fatalf("unexpected decode error: %v", err)
		}
		decoded = append(decoded, hf)
	}

	if !reflect.DeepEqual(decoded, headers) {
		t.Fatalf("decoded headers mismatch: got %v, want %v", decoded, headers)
	}

	// 6. DecodeFunc returns an error when decoding malformed or invalid QPACK data
	malformedBytes := []byte{0xff, 0xff, 0xff, 0xff}
	malformedDecode := dec.Decode(malformedBytes)
	_, err := malformedDecode()
	if err == nil || errors.Is(err, io.EOF) {
		t.Fatalf("expected DecodeFunc to return a decoding error on malformed data, got %v", err)
	}

	// 7. Reuse Encoder and Decoder for subsequent independent header blocks
	buf.Reset()
	secondHeaders := []qpack.HeaderField{
		{Name: ":status", Value: "200"},
		{Name: "content-type", Value: "text/plain; charset=utf-8"},
		{Name: "content-length", Value: "12"},
	}

	for _, hf := range secondHeaders {
		if err := enc.WriteField(hf); err != nil {
			t.Fatalf("failed to write second field %v: %v", hf, err)
		}
	}
	if err := enc.Close(); err != nil {
		t.Fatalf("failed to close encoder on second block: %v", err)
	}

	secondDecode := dec.Decode(buf.Bytes())
	var secondDecoded []qpack.HeaderField
	for {
		hf, err := secondDecode()
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			t.Fatalf("unexpected decode error on second block: %v", err)
		}
		secondDecoded = append(secondDecoded, hf)
	}

	if !reflect.DeepEqual(secondDecoded, secondHeaders) {
		t.Fatalf("second block mismatch: got %v, want %v", secondDecoded, secondHeaders)
	}
}

{"case":{"caseId":"case:sha256:934e28aaed7b53d4f4e5ea1023002fcd60a7d160c2fe8fa9d7279a365e91b227","contract":["HeaderField.IsPseudo accurately identifies HTTP/3 pseudo-headers starting with a colon","qpack.NewEncoder creates an encoder writing QPACK-encoded headers to an underlying io.Writer","Encoder.WriteField encodes pseudo-headers and custom header fields into QPACK wire format","Encoder.Close finalizes the current header block and resets the encoder for subsequent header blocks","qpack.NewDecoder creates a decoder whose Decode method returns a DecodeFunc yielding header fields sequentially until io.EOF","DecodeFunc returns an error when decoding malformed or invalid QPACK data"],"goal":"verify pkg:golang/github.com/quic-go/qpack@v0.6.0","kind":"HOW","packages":["pkg:golang/github.com/quic-go/qpack@v0.6.0"],"schemaVersion":1,"symbols":["qpack.DecodeFunc","qpack.Decoder","qpack.Encoder","qpack.HeaderField"]},"contractCommand":["go","test","-v","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/quic-go/qpack@v0.6.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/quic-go/qpack@v0.6.0","symbols":["qpack.DecodeFunc","qpack.Decoder","qpack.Encoder","qpack.HeaderField"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/quic-go/qpack v0.6.0

require golang.org/x/net v0.28.0 // indirect

github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/quic-go/qpack v0.6.0 h1:g7W+BMYynC1LbYLSqRt8PBg5Tgwxn214ZZR34VIOjz8=
github.com/quic-go/qpack v0.6.0/go.mod h1:lUpLKChi8njB4ty2bFLX2x4gzDqXwUpaO1DP9qMDZII=
github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
golang.org/x/net v0.28.0 h1:a9JDOJc5GMUJ0+UDqmLT86WiEy7iWyIhz8gz8E4e5hE=
golang.org/x/net v0.28.0/go.mod h1:yqtgsTWOOnlGLG9GFRrK3++bGOUEkNBoHZc8MEDWPNg=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/quic-go/qpack@v0.6.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/quic-go/qpack@v0.6.0"
  ],
  "symbols": [
    "qpack.DecodeFunc",
    "qpack.Decoder",
    "qpack.Encoder",
    "qpack.HeaderField"
  ]
}