github.com/jackc/chunkreader/v2 v2.0.1: chunkreader.ChunkReader.Next

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.ChunkReader.Next 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.ChunkReader.Next

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:sha256:11454345430aeeb6c47942978ba09c2813b7de5ce2cd8aeae614e46f58f76f31","contract":["Next(n) returns a slice of exactly n bytes from the reader when n bytes are available","Next returns io.EOF and nil buffer when attempting to read at EOF","Next returns io.ErrUnexpectedEOF and nil buffer when fewer than n bytes remain before EOF","Next(0) returns an empty slice and nil error","Next successfully reads across multiple internal chunk buffer boundaries"],"goal":"verify chunkreader.ChunkReader.Next 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.ChunkReader.Next"]},"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@v2.0.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/chunkreader/v2@v2.0.1","symbols":["chunkreader.ChunkReader.Next"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

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

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 (
	"fmt"
	"strings"

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

func main() {
	reader := strings.NewReader("Hello, ChunkReader!")
	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 chunkreader.ChunkReader.Next 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.ChunkReader.Next"
  ]
}

package main

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

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

func main() {
	// Test 1: Sequential reads of exact sizes
	{
		data := "Hello, World! 1234567890"
		r := chunkreader.New(strings.NewReader(data))

		chunk1, err := r.Next(5)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on chunk1: %v", err))
		}
		if string(chunk1) != "Hello" {
			panic(fmt.Sprintf("expected 'Hello', got '%s'", string(chunk1)))
		}

		chunk2, err := r.Next(2)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on chunk2: %v", err))
		}
		if string(chunk2) != ", " {
			panic(fmt.Sprintf("expected ', ', got '%s'", string(chunk2)))
		}

		chunk3, err := r.Next(6)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on chunk3: %v", err))
		}
		if string(chunk3) != "World!" {
			panic(fmt.Sprintf("expected 'World!', got '%s'", string(chunk3)))
		}

		chunk4, err := r.Next(11)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on chunk4: %v", err))
		}
		if string(chunk4) != " 1234567890" {
			panic(fmt.Sprintf("expected ' 1234567890', got '%s'", string(chunk4)))
		}

		// Reading at EOF returns io.EOF
		chunkEOF, err := r.Next(1)
		if !errors.Is(err, io.EOF) {
			panic(fmt.Sprintf("expected io.EOF, got %v", err))
		}
		if chunkEOF != nil {
			panic("expected nil buffer on EOF error")
		}
	}

	// Test 2: Partial read before EOF returns io.ErrUnexpectedEOF
	{
		r := chunkreader.New(strings.NewReader("abc"))
		chunk, err := r.Next(5)
		if !errors.Is(err, io.ErrUnexpectedEOF) {
			panic(fmt.Sprintf("expected io.ErrUnexpectedEOF when requesting 5 bytes from 3 byte stream, got %v", err))
		}
		if chunk != nil {
			panic("expected nil buffer on ErrUnexpectedEOF")
		}
	}

	// Test 3: Zero byte request returns empty slice and nil error
	{
		r := chunkreader.New(strings.NewReader("test"))
		chunk, err := r.Next(0)
		if err != nil {
			panic(fmt.Sprintf("unexpected error on Next(0): %v", err))
		}
		if len(chunk) != 0 {
			panic(fmt.Sprintf("expected 0 length chunk, got %d", len(chunk)))
		}
	}

	// Test 4: Large buffer crossing multiple internal chunks
	{
		largeData := bytes.Repeat([]byte("0123456789abcdef"), 1000) // 16000 bytes
		r := chunkreader.New(bytes.NewReader(largeData))

		var readData []byte
		for len(readData) < len(largeData) {
			toRead := 128
			if len(largeData)-len(readData) < toRead {
				toRead = len(largeData) - len(readData)
			}
			chunk, err := r.Next(toRead)
			if err != nil {
				panic(fmt.Sprintf("unexpected error during large read: %v", err))
			}
			readData = append(readData, chunk...)
		}

		if !bytes.Equal(readData, largeData) {
			panic("read data does not match original data")
		}

		// Verify EOF
		_, err := r.Next(1)
		if !errors.Is(err, io.EOF) {
			panic(fmt.Sprintf("expected EOF after full read, got: %v", err))
		}
	}

	fmt.Println("All chunkreader.ChunkReader.Next contract assertions passed.")
}