github.com/quic-go/qpack v0.5.1: 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 qpack.Encoder in pkg:golang/github.com/quic-go/qpack@v0.5.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/quic-go/qpack@v0.5.1
Demonstrate these symbols/APIs:
  - qpack.Encoder
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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"
	"reflect"
	"testing"

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

func TestQpackEncoder(t *testing.T) {
	// 1. HeaderField.IsPseudo accurately identifies 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 decodes encoded header blocks produced by Encoder to recover original HeaderField values
	dec := qpack.NewDecoder(func(hf qpack.HeaderField) {})
	fullDecoded, err := dec.DecodeFull(encodedBytes)
	if err != nil {
		t.Fatalf("failed to decode encoded header block: %v", err)
	}

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

	// 6. Reuse Encoder after Close 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)
	}

	secondDec := qpack.NewDecoder(func(hf qpack.HeaderField) {})
	secondDecoded, err := secondDec.DecodeFull(buf.Bytes())
	if err != nil {
		t.Fatalf("failed to decode second block: %v", err)
	}
	if !reflect.DeepEqual(secondDecoded, secondHeaders) {
		t.Fatalf("second block mismatch: got %v, want %v", secondDecoded, secondHeaders)
	}
}

{"case":{"caseId":"case:sha256:e18ab5ceeb61d8050900fab69db280b3b213fd2931c3f22989b4de3a20272e15","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 decodes encoded header blocks produced by Encoder to recover original HeaderField values"],"goal":"verify qpack.Encoder in pkg:golang/github.com/quic-go/qpack@v0.5.1","kind":"HOW","packages":["pkg:golang/github.com/quic-go/qpack@v0.5.1"],"schemaVersion":1,"symbols":["qpack.Encoder"]},"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@v0.5.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/quic-go/qpack@v0.5.1","symbols":["qpack.Encoder"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/quic-go/qpack v0.5.1

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 v0.5.1 h1:giqksBPnT/HDtZ6VhtFKgoLOWmlyo9Ei6u9PqzIMbhI=
github.com/quic-go/qpack v0.5.1/go.mod h1:+PC4XFrEskIVkcLzpEkbLqq1uCoxPhQuvK5rH1ZgaEg=
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 qpack.Encoder in pkg:golang/github.com/quic-go/qpack@v0.5.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/quic-go/qpack@v0.5.1"
  ],
  "symbols": [
    "qpack.Encoder"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}