fast XML DSL in 70 lines

xml.kt

package lib.xml

import org.apache.commons.text.StringEscapeUtils

fun StringBuilder.put(attrs: Array<out Pair<String, Any?>>) {
    for ((k, v) in attrs) {
        if (v == null) continue

        append(' ')
        append(k)
        append('=')
        append('"')
        append(StringEscapeUtils.escapeXml10(v.toString()))
        append('"')
    }
}

context(StringBuilder)
operator fun String.invoke(vararg attrs: Pair<String, Any?>) {
    val name = this

    append('<')
    append(name)
    put(attrs)
    append("/>")
    appendLine()
}

context(StringBuilder)
inline operator fun String.invoke(vararg attrs: Pair<String, Any?>, f: StringBuilder.() -> Unit) {
    val name = this

    append('<')
    append(name)
    put(attrs)
    append('>')
    f(this@StringBuilder)
    append("</")
    append(name)
    append('>')
    appendLine()
}

context(StringBuilder)
operator fun String?.unaryPlus() {
    if (isNullOrBlank()) return

    append(StringEscapeUtils.escapeXml10(this))
}

/** when you don't need to escape */
context(StringBuilder)
operator fun String?.unaryMinus() {
    if (isNullOrBlank()) return

    append(this)
}

inline fun rss2(chan: StringBuilder.() -> Unit): String =
    buildString {
        appendLine("""<?xml version="1.0" encoding="UTF-8"?>""")

        "rss"("xmlns:itunes" to "http://www.itunes.com/dtds/podcast-1.0.dtd", "version" to "2.0") {
            "channel" {
                chan()
            }
        }
    }