html/escape.go

package html

import (
	"bytes"
	"code.squareroundforest.org/arpio/textedit"
	"io"
)

const unicodeNBSP = 0xa0

func escapeEdit(nonbreakSpaces bool) func(rune, []rune) ([]rune, []rune) {
	return func(r rune, state []rune) ([]rune, []rune) {
		var rr []rune
		switch r {
		case ' ':
			if !nonbreakSpaces {
				return []rune{r}, nil
			}

			if len(state) == 0 {
				return nil, []rune{' '}
			}

			return []rune(" "), []rune(" ")
		case '<':
			rr = []rune("&lt;")
		case '>':
			rr = []rune("&gt;")
		case '&':
			rr = []rune("&amp;")
		case unicodeNBSP:
			rr = []rune("&nbsp;")
		default:
			rr = []rune{r}
		}

		return append(state, rr...), nil
	}
}

func escapeReleaseState(state []rune) []rune {
	return state
}

func newEscapeWriter(out io.Writer, nonbreakSpaces bool) *textedit.Writer {
	return textedit.New(
		out,
		textedit.Func(
			escapeEdit(nonbreakSpaces),
			escapeReleaseState,
		),
	)
}

func escape(s string, nonbreakSpaces bool) string {
	var b bytes.Buffer
	w := newEscapeWriter(&b, nonbreakSpaces)
	w.Write([]byte(s))
	w.Flush()
	return b.String()
}

func escapeAttribute(value string) string {
	var b bytes.Buffer
	w := textedit.New(
		&b,
		textedit.Replace(
			"&", "&amp;",
			"\"", "&quot;",
		),
	)

	w.Write([]byte(value))
	w.Flush()
	return b.String()
}