Throw JsonDecodingException on empty string literal at the end of the…

… input (#1011)

This PR fixes a bug where an unfinished string literal at the end of the input throws a StringIndexOutOfBoundsException instead of a JsonDecodingException.

Similar to #704, this should be a generic decoding exception instead.

runtime/commonMain/src/kotlinx/serialization/json/internal/JsonReader.kt

@@ -241,7 +241,11 @@ internal class JsonReader(private val source: String) {
  private fun nextString(source: String, startPosition: Int) {
  tokenPosition = startPosition
  length = 0 // in buffer
- var currentPosition = startPosition + 1
+ var currentPosition = startPosition + 1 // skip starting "
+ // except if the input ends
+ if (currentPosition >= source.length) {
+ fail("EOF", currentPosition)
+ }
  var lastPosition = currentPosition
  while (source[currentPosition] != STRING) {
  if (source[currentPosition] == STRING_ESC) {

runtime/commonTest/src/kotlinx/serialization/json/JsonParserTest.kt

@@ -76,4 +76,15 @@ class JsonParserTest : JsonTestBase() {
  val msg = e.message!!
  assertTrue(msg.contains("Expected end of the object"))
  }
+
+ @Test
+ fun testUnclosedStringLiteral() {
+ assertFailsWith<JsonDecodingException> {
+ parse("\"")
+ }
+
+ assertFailsWith<JsonDecodingException> {
+ parse("""{"id":"""")
+ }
+ }
 }