github.com/jackc/chunkreader/v2 v2.0.0: chunkreader.ChunkReader.Next, chunkreader.New, chunkreader.NewConfig

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/jackc/chunkreader/v2@v2.0.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0
Demonstrate these symbols/APIs:
  - chunkreader.ChunkReader.Next
  - chunkreader.New
  - chunkreader.NewConfig

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:sha256:9b3e669f7933ff52c8af053efac9b292c10bb6ba990c50b17a81383666882516","contract":["chunkreader.New initializes a ChunkReader wrapping an io.Reader with default configuration","chunkreader.NewConfig initializes a ChunkReader with custom MinBufLen in Config","chunkreader.ChunkReader.Next returns consecutive byte slices of requested lengths from stream","chunkreader.ChunkReader.Next returns io.ErrUnexpectedEOF or io.EOF when stream has fewer bytes than requested","chunkreader.ChunkReader.Next expands internal buffer when requested chunk exceeds initial buffer length","chunkreader.ChunkReader.Next returns empty byte slice with nil error when requested length is 0"],"goal":"verify pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0","kind":"HOW","packages":["pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0"],"schemaVersion":1,"symbols":["chunkreader.ChunkReader.Next","chunkreader.New","chunkreader.NewConfig"]},"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/jackc/chunkreader/v2@v2.0.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0","symbols":["chunkreader.ChunkReader.Next","chunkreader.New","chunkreader.NewConfig"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/jackc/chunkreader/v2 v2.0.0 // indirect

github.com/jackc/chunkreader/v2 v2.0.0 h1:DUwgMQuuPnS0rhMXenUtZpqZqrR/30NWY+qQvTpSvEs=
github.com/jackc/chunkreader/v2 v2.0.0/go.mod h1:odVSm741yZoC3dpHEUXIqA9tQRhFrgOHwnPIn9lDKlk=

package main

import (
	"fmt"
	"strings"

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

func main() {
	reader := strings.NewReader("Hello, ChunkReader v2!")
	cr := chunkreader.New(reader)

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

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/chunkreader/v2@v2.0.0"
  ],
  "symbols": [
    "chunkreader.ChunkReader.Next",
    "chunkreader.New",
    "chunkreader.NewConfig"
  ]
}

package main

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"strings"

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

func main() {
	// 1. chunkreader.New initializes a ChunkReader wrapping an io.Reader with default configuration
	{
		r := strings.NewReader("sample data for testing")
		cr := chunkreader.New(r)
		if cr == nil {
			panic("expected non-nil ChunkReader from chunkreader.New")
		}
		chunk, err := cr.Next(6)
		if err != nil || string(chunk) != "sample" {
			panic(fmt.Sprintf("expected 'sample', got '%s', err: %v", string(chunk), err))
		}
	}

	// 2. chunkreader.NewConfig initializes a ChunkReader with custom MinBufLen in Config
	{
		r := strings.NewReader("custom config stream data")
		cfg := chunkreader.Config{MinBufLen: 16}
		cr, err := chunkreader.NewConfig(r, cfg)
		if err != nil {
			panic(fmt.Sprintf("unexpected error from NewConfig: %v", err))
		}
		if cr == nil {
			panic("expected non-nil ChunkReader from NewConfig")
		}
		chunk, err := cr.Next(6)
		if err != nil || string(chunk) != "custom" {
			panic(fmt.Sprintf("expected 'custom', got '%s', err: %v", string(chunk), err))
		}
	}

	// 3. chunkreader.ChunkReader.Next returns consecutive byte slices of requested lengths from stream
	{
		data := "first, second, third"
		cr := chunkreader.New(strings.NewReader(data))

		c1, err := cr.Next(5)
		if err != nil || string(c1) != "first" {
			panic(fmt.Sprintf("unexpected c1: %q, err: %v", string(c1), err))
		}

		c2, err := cr.Next(2)
		if err != nil || string(c2) != ", " {
			panic(fmt.Sprintf("unexpected c2: %q, err: %v", string(c2), err))
		}

		c3, err := cr.Next(6)
		if err != nil || string(c3) != "second" {
			panic(fmt.Sprintf("unexpected c3: %q, err: %v", string(c3), err))
		}

		c4, err := cr.Next(7)
		if err != nil || string(c4) != ", third" {
			panic(fmt.Sprintf("unexpected c4: %q, err: %v", string(c4), err))
		}

		// EOF behavior
		cEOF, err := cr.Next(1)
		if !errors.Is(err, io.EOF) {
			panic(fmt.Sprintf("expected io.EOF at end of stream, got %v", err))
		}
		if cEOF != nil {
			panic("expected nil buffer on EOF")
		}
	}

	// 4. chunkreader.ChunkReader.Next returns io.ErrUnexpectedEOF or io.EOF when stream has fewer bytes than requested
	{
		cr := chunkreader.New(strings.NewReader("short"))
		c, err := cr.Next(10)
		if !errors.Is(err, io.ErrUnexpectedEOF) {
			panic(fmt.Sprintf("expected io.ErrUnexpectedEOF, got %v", err))
		}
		if c != nil {
			panic("expected nil buffer on ErrUnexpectedEOF")
		}
	}

	// 5. chunkreader.ChunkReader.Next expands internal buffer when requested chunk exceeds initial buffer length
	{
		cfg := chunkreader.Config{MinBufLen: 16}
		largePayload := bytes.Repeat([]byte("A"), 128)
		cr, err := chunkreader.NewConfig(bytes.NewReader(largePayload), cfg)
		if err != nil {
			panic(fmt.Sprintf("unexpected error: %v", err))
		}
		chunk, err := cr.Next(128)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on large chunk read: %v", err))
		}
		if len(chunk) != 128 || !bytes.Equal(chunk, largePayload) {
			panic("large chunk payload mismatch")
		}
	}

	// 6. chunkreader.ChunkReader.Next returns empty byte slice with nil error when requested length is 0
	{
		cr := chunkreader.New(strings.NewReader("non-empty"))
		chunk, err := cr.Next(0)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on Next(0): %v", err))
		}
		if len(chunk) != 0 {
			panic(fmt.Sprintf("expected empty slice from Next(0), got len %d", len(chunk)))
		}
	}

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