JsonStringBuilder.appendStringSlowPath gives ArrayIndexOutOfBoundsException

[rnentjes]

Describe the bug

String serialization is broken if there are to many characters to escape in the string

In the JsonStringBuilder.appendStringSlowPath there seems to be a call missing to ensureTotalCapacity in the else block:

                when (val marker = ESCAPE_MARKERS[ch]) {
                    0.toByte() -> {
                        array[sz++] = ch.toChar()
                    }
                    1.toByte() -> {
                        val escapedString = ESCAPE_STRINGS[ch]!!
                        ensureTotalCapacity(sz + escapedString.length)
                        escapedString.toCharArray(array, sz, 0, escapedString.length)
                        sz += escapedString.length
                    }
                    else -> {
                        // I THINK THERE SHOULD BE A CALL TO ensureTotalCapacity HERE
                        array[sz] = '\\'
                        array[sz + 1] = marker.toChar()
                        sz += 2
                    }
                }

To Reproduce
Attach a code snippet or test data if possible.

@Serializable
class Test(val msg: String)

fun serializeTest() {
  val test = Test("""
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
    \n\n\n\n\n\n\n\n\n\n
  """.trimIndent())
  val result = JsonConfig.json.encodeToString(test)
  println(result)
}

This is the resulting stack trace:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 180 out of bounds for length 180
	at kotlinx.serialization.json.internal.JsonStringBuilder.appendStringSlowPath(JsonStringBuilder.kt:99)
	at kotlinx.serialization.json.internal.JsonStringBuilder.appendQuoted(JsonStringBuilder.kt:61)
	at kotlinx.serialization.json.internal.Composer.printQuoted(Composers.kt:42)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeString(StreamingJsonEncoder.kt:203)
	at kotlinx.serialization.encoding.AbstractEncoder.encodeStringElement(AbstractEncoder.kt:65)
	<serialize call here>

Expected behavior

The string should be serialized and no exception should be thrown.

Environment

• Kotlin version: 1.5.0
• Library version: 1.2.0
• Kotlin platforms: JVM
• Gradle version: 7.0
• IDE version (if bug is related to the IDE): na (but 2021.1)
• Other relevant context: Linux

[rnentjes]

PR #1465 fixes this problem.

[JBeet]

duplicate of #1441