golang.org/x/text v0.42.0: encoding.Encoding

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 golang.org/x/text/encoding.Encoding in pkg:golang/golang.org/x/text@v0.42.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/text@v0.42.0
Demonstrate these symbols/APIs:
  - golang.org/x/text/encoding.Encoding

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:b55c7a15eaef74453e7dd33aeccf80cb07987d9e779c1794d979861ec3807149","contract":["encoding.Encoding interface specifies NewDecoder to convert bytes to UTF-8 and NewEncoder to convert bytes from UTF-8","encoding.Nop implements encoding.Encoding and performs identity decoding and encoding of strings and byte slices","encoding.Replacement implements encoding.Encoding where NewDecoder yields a single replacement rune and NewEncoder replaces invalid UTF-8 sequences","custom types can implement encoding.Encoding by providing compliant Decoder and Encoder transformers"],"goal":"verify golang.org/x/text/encoding.Encoding in pkg:golang/golang.org/x/text@v0.42.0","kind":"HOW","packages":["pkg:golang/golang.org/x/text@v0.42.0"],"schemaVersion":1,"symbols":["golang.org/x/text/encoding.Encoding"]},"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/golang.org/x/text@v0.42.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/text@v0.42.0","symbols":["golang.org/x/text/encoding.Encoding"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/text v0.42.0

golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=

package main

import (
	"bytes"
	"fmt"
	"os"

	"golang.org/x/text/encoding"
)

func processWithEncoding(enc encoding.Encoding, input []byte) ([]byte, error) {
	dec := enc.NewDecoder()
	return dec.Bytes(input)
}

func main() {
	var enc encoding.Encoding = encoding.Nop
	input := []byte("Hello, Encoding interface!")

	output, err := processWithEncoding(enc, input)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error decoding: %v\n", err)
		os.Exit(1)
	}

	if !bytes.Equal(input, output) {
		fmt.Fprintf(os.Stderr, "Mismatch: expected %q, got %q\n", input, output)
		os.Exit(1)
	}

	fmt.Printf("Successfully verified encoding.Encoding: %s\n", string(output))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/text/encoding.Encoding in pkg:golang/golang.org/x/text@v0.42.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/text@v0.42.0"
  ],
  "symbols": [
    "golang.org/x/text/encoding.Encoding"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"golang.org/x/text/encoding"
)

type customEncoding struct{}

func (c customEncoding) NewDecoder() *encoding.Decoder {
	return encoding.Nop.NewDecoder()
}

func (c customEncoding) NewEncoder() *encoding.Encoder {
	return encoding.Nop.NewEncoder()
}

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract assertions passed.")
}

func runContractTests() error {
	// 1. encoding.Encoding interface specifies NewDecoder to convert bytes to UTF-8 and NewEncoder to convert bytes from UTF-8
	var enc encoding.Encoding = encoding.Nop
	dec := enc.NewDecoder()
	encr := enc.NewEncoder()
	if dec == nil || encr == nil {
		return fmt.Errorf("expected non-nil Decoder and Encoder from Encoding")
	}

	// 2. encoding.Nop implements encoding.Encoding and performs identity decoding and encoding of strings and byte slices
	testStr := "sample text encoding verification"
	decStr, err := encoding.Nop.NewDecoder().String(testStr)
	if err != nil || decStr != testStr {
		return fmt.Errorf("Nop Decoder.String failed: %v, got %q", err, decStr)
	}
	encStr, err := encoding.Nop.NewEncoder().String(testStr)
	if err != nil || encStr != testStr {
		return fmt.Errorf("Nop Encoder.String failed: %v, got %q", err, encStr)
	}

	testBytes := []byte("sample-bytes-\x00\xff")
	decBytes, err := encoding.Nop.NewDecoder().Bytes(testBytes)
	if err != nil || !bytes.Equal(decBytes, testBytes) {
		return fmt.Errorf("Nop Decoder.Bytes failed: %v", err)
	}
	encBytes, err := encoding.Nop.NewEncoder().Bytes(testBytes)
	if err != nil || !bytes.Equal(encBytes, testBytes) {
		return fmt.Errorf("Nop Encoder.Bytes failed: %v", err)
	}

	// 3. encoding.Replacement implements encoding.Encoding where NewDecoder yields a single replacement rune and NewEncoder replaces invalid UTF-8 sequences
	var replEnc encoding.Encoding = encoding.Replacement
	decOutput, err := replEnc.NewDecoder().Bytes([]byte("any payload"))
	if err != nil {
		return fmt.Errorf("Replacement.NewDecoder failed: %v", err)
	}
	if string(decOutput) != "\ufffd" {
		return fmt.Errorf("expected single replacement rune from Replacement decoder, got %q", string(decOutput))
	}

	encOutput, err := replEnc.NewEncoder().Bytes([]byte("valid \x80 invalid"))
	if err != nil {
		return fmt.Errorf("Replacement.NewEncoder failed: %v", err)
	}
	expectedEnc := "valid \ufffd invalid"
	if string(encOutput) != expectedEnc {
		return fmt.Errorf("expected %q from Replacement encoder, got %q", expectedEnc, string(encOutput))
	}

	// 4. custom types can implement encoding.Encoding by providing compliant Decoder and Encoder transformers
	var _ encoding.Encoding = customEncoding{}
	var customEnc encoding.Encoding = customEncoding{}
	if customEnc.NewDecoder() == nil || customEnc.NewEncoder() == nil {
		return fmt.Errorf("custom Encoding implementation returned nil transformer")
	}

	return nil
}