golang.org/x/text v0.31.0: encoding.HTMLEscapeUnsupported

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.HTMLEscapeUnsupported in pkg:golang/golang.org/x/text@v0.31.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/text@v0.31.0
Demonstrate these symbols/APIs:
  - golang.org/x/text/encoding.HTMLEscapeUnsupported

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:sha256:1d7f25f6f584e529ec645b35050bc6a2f0a939a3af0fd1daf1de244225d69424","contract":["encoding.HTMLEscapeUnsupported preserves characters within the underlying encoding repertoire","encoding.HTMLEscapeUnsupported replaces unsupported runes with decimal HTML numeric character references","encoding.HTMLEscapeUnsupported returns transform.ErrShortDst when destination buffer is insufficient","encoding.HTMLEscapeUnsupported replaces invalid UTF-8 byte sequences with escaped replacement character references"],"goal":"verify golang.org/x/text/encoding.HTMLEscapeUnsupported in pkg:golang/golang.org/x/text@v0.31.0","kind":"HOW","packages":["pkg:golang/golang.org/x/text@v0.31.0"],"schemaVersion":1,"symbols":["golang.org/x/text/encoding.HTMLEscapeUnsupported"]},"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@v0.31.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/text@v0.31.0","symbols":["golang.org/x/text/encoding.HTMLEscapeUnsupported"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.24.0

require golang.org/x/text v0.31.0

golang.org/x/text v0.31.0 h1:aC8ghyu4JhP8VojJ2lEHBnochRno1sgL6nEi9WGFGMM=
golang.org/x/text v0.31.0/go.mod h1:tKRAlv61yKIjGGHX/4tP1LTbc13YSec1pxVEWXzfoeM=

package main

import (
	"fmt"
	"os"

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

func main() {
	encoder := encoding.HTMLEscapeUnsupported(charmap.ISO8859_1.NewEncoder())

	input := "Hello World! Snowman: \u2603, Euro: \u20ac"
	encoded, err := encoder.String(input)
	if err != nil {
		fmt.Fprintf(os.Stderr, "encoding failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Input:   %s\n", input)
	fmt.Printf("Encoded: %s\n", encoded)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/text/encoding.HTMLEscapeUnsupported in pkg:golang/golang.org/x/text@v0.31.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/text@v0.31.0"
  ],
  "symbols": [
    "golang.org/x/text/encoding.HTMLEscapeUnsupported"
  ]
}

package main

import (
	"bytes"
	"errors"
	"fmt"
	"os"

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

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

func runTests() error {
	// Assertion 1: encoding.HTMLEscapeUnsupported preserves characters within the underlying encoding repertoire
	{
		enc := encoding.HTMLEscapeUnsupported(charmap.ISO8859_1.NewEncoder())
		supportedInputs := []string{
			"Hello, World!",
			"Numbers: 0123456789",
			"Punctuation: !@#$%^&*()-_=+[]{}|;:',.<>/?`~",
		}
		for _, in := range supportedInputs {
			out, err := enc.String(in)
			if err != nil {
				return fmt.Errorf("enc.String(%q) failed: %w", in, err)
			}
			if out != in {
				return fmt.Errorf("enc.String(%q) expected %q, got %q", in, in, out)
			}
		}
	}

	// Assertion 2: encoding.HTMLEscapeUnsupported replaces unsupported runes with decimal HTML numeric character references
	{
		enc := encoding.HTMLEscapeUnsupported(charmap.ISO8859_1.NewEncoder())
		testCases := []struct {
			input    string
			expected string
		}{
			{
				input:    "Snowman \u2603",
				expected: "Snowman &#9731;",
			},
			{
				input:    "Euro \u20ac",
				expected: "Euro &#8364;",
			},
			{
				input:    "CJK 世界",
				expected: "CJK &#19990;&#30028;",
			},
		}
		for _, tc := range testCases {
			out, err := enc.String(tc.input)
			if err != nil {
				return fmt.Errorf("enc.String(%q) failed: %w", tc.input, err)
			}
			if out != tc.expected {
				return fmt.Errorf("enc.String(%q) expected %q, got %q", tc.input, tc.expected, out)
			}
		}
	}

	// Assertion 3: encoding.HTMLEscapeUnsupported returns transform.ErrShortDst when destination buffer is insufficient
	{
		enc := encoding.HTMLEscapeUnsupported(charmap.ISO8859_1.NewEncoder())
		enc.Reset()
		dst := make([]byte, 2)
		src := []byte("A\u2603B")
		_, _, err := enc.Transform(dst, src, true)
		if !errors.Is(err, transform.ErrShortDst) {
			return fmt.Errorf("expected transform.ErrShortDst, got %v", err)
		}
	}

	// Assertion 4: encoding.HTMLEscapeUnsupported replaces invalid UTF-8 byte sequences with escaped replacement character references
	{
		enc := encoding.HTMLEscapeUnsupported(charmap.ISO8859_1.NewEncoder())
		enc.Reset()
		invalidInputs := []struct {
			input    []byte
			expected []byte
		}{
			{
				input:    []byte("bad \xff byte"),
				expected: []byte("bad &#65533; byte"),
			},
			{
				input:    []byte("\xfe\xff"),
				expected: []byte("&#65533;&#65533;"),
			},
		}
		for _, tc := range invalidInputs {
			out, err := enc.Bytes(tc.input)
			if err != nil {
				return fmt.Errorf("enc.Bytes(%q) failed: %w", tc.input, err)
			}
			if !bytes.Equal(out, tc.expected) {
				return fmt.Errorf("enc.Bytes(%q) expected %q, got %q", tc.input, string(tc.expected), string(out))
			}
		}
	}

	return nil
}