github.com/jackc/chunkreader/v2 v2.0.1: chunkreader.New

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 chunkreader.New in pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1
Demonstrate these symbols/APIs:
  - chunkreader.New
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.

{"case":{"caseId":"case:sha256:8352ef6353c33fe30f28b37884a81c95a6066d3b1fff13cbdd09b3203b74105b","contract":["chunkreader.New initializes a ChunkReader wrapping an io.Reader","ChunkReader.Next returns consecutive byte slices of requested lengths from stream","ChunkReader.Next returns io.ErrUnexpectedEOF or io.EOF when stream has fewer bytes than requested","ChunkReader.Next dynamically expands internal buffer when requested chunk exceeds default buffer"],"goal":"verify chunkreader.New in pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1","kind":"HOW","packages":["pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1"],"schemaVersion":1,"symbols":["chunkreader.New"]},"contractCommand":["go","test","./..."],"environment":{"arch":"amd64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","moduleSystem":"go","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/jackc/chunkreader/v2@v2.0.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1","symbols":["chunkreader.New"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/jackc/chunkreader/v2 v2.0.1

github.com/jackc/chunkreader/v2 v2.0.1 h1:i+RDz65UE+mmpjTfyz0MoVTnzeYxroil2G82ki7MGG8=
github.com/jackc/chunkreader/v2 v2.0.1/go.mod h1:odVSm741yZoC3dpHEUXIqA9tQRhFrgOHwnPIn9lDKlk=

package main

import (
	"bytes"
	"fmt"

	"github.com/jackc/chunkreader/v2"
)

func main() {
	data := []byte("Hello, ChunkReader!")
	cr := chunkreader.New(bytes.NewReader(data))

	chunk, err := cr.Next(5)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Read chunk: %s\n", string(chunk))
}

{
  "schemaVersion": 1,
  "goal": "verify chunkreader.New in pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1"
  ],
  "symbols": [
    "chunkreader.New"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package test

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

	"github.com/jackc/chunkreader/v2"
)

func TestChunkReaderNew(t *testing.T) {
	// 1. chunkreader.New initializes a ChunkReader wrapping an io.Reader
	payload := []byte("first chunk; second chunk; third chunk")
	r := bytes.NewReader(payload)
	cr := chunkreader.New(r)
	if cr == nil {
		t.Fatalf("expected non-nil ChunkReader")
	}

	// 2. ChunkReader.Next returns consecutive byte slices of requested lengths from stream
	c1, err := cr.Next(11)
	if err != nil {
		t.Fatalf("unexpected error reading chunk 1: %v", err)
	}
	if !bytes.Equal(c1, []byte("first chunk")) {
		t.Fatalf("expected 'first chunk', got %q", string(c1))
	}

	c2, err := cr.Next(2)
	if err != nil {
		t.Fatalf("unexpected error reading separator: %v", err)
	}
	if !bytes.Equal(c2, []byte("; ")) {
		t.Fatalf("expected '; ', got %q", string(c2))
	}

	c3, err := cr.Next(12)
	if err != nil {
		t.Fatalf("unexpected error reading chunk 2: %v", err)
	}
	if !bytes.Equal(c3, []byte("second chunk")) {
		t.Fatalf("expected 'second chunk', got %q", string(c3))
	}

	// 3. ChunkReader.Next returns io.ErrUnexpectedEOF or io.EOF when stream has fewer bytes than requested
	shortReader := bytes.NewReader([]byte("short"))
	crShort := chunkreader.New(shortReader)
	chunk, err := crShort.Next(100)
	if err == nil {
		t.Fatalf("expected error when requesting 100 bytes from 5-byte reader, got nil error and chunk %v", chunk)
	}
	if chunk != nil {
		t.Fatalf("expected nil chunk on error, got %v", chunk)
	}
	if !errors.Is(err, io.ErrUnexpectedEOF) && !errors.Is(err, io.EOF) {
		t.Fatalf("expected io.ErrUnexpectedEOF or io.EOF, got %v", err)
	}

	// 4. ChunkReader.Next dynamically expands internal buffer when requested chunk exceeds default buffer
	largeData := make([]byte, 16384)
	for i := range largeData {
		largeData[i] = byte('A' + (i % 26))
	}
	largeReader := bytes.NewReader(largeData)
	crLarge := chunkreader.New(largeReader)
	largeChunk, err := crLarge.Next(10000)
	if err != nil {
		t.Fatalf("failed reading large chunk: %v", err)
	}
	if !bytes.Equal(largeChunk, largeData[:10000]) {
		t.Fatalf("large chunk content mismatch")
	}
}