Fix DiscordBitSet deserialization from JSON number

Also throw NumberFormatException from DiscordBitSet factory function
for large negative numbers while I'm here.

Fixes #911

common/src/commonMain/kotlin/DiscordBitSet.kt

@@ -1,5 +1,6 @@
 package dev.kord.common
 
+import dev.kord.common.serialization.LongOrStringSerializer
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.descriptors.PrimitiveKind
@@ -16,7 +17,7 @@ private const val WIDTH = Long.SIZE_BITS
 public fun EmptyBitSet(): DiscordBitSet = DiscordBitSet()
 
 internal expect fun formatIntegerFromLittleEndianLongArray(data: LongArray): String
-internal expect fun parseIntegerToBigEndianByteArray(value: String): ByteArray
+internal expect fun parseNonNegativeIntegerToBigEndianByteArray(value: String): ByteArray
 
 @Serializable(with = DiscordBitSet.Serializer::class)
 public class DiscordBitSet(internal var data: LongArray) { // data is in little-endian order
@@ -116,7 +117,8 @@ public class DiscordBitSet(internal var data: LongArray) { // data is in little-
     internal object Serializer : KSerializer<DiscordBitSet> {
         override val descriptor = PrimitiveSerialDescriptor("dev.kord.common.DiscordBitSet", PrimitiveKind.STRING)
         override fun serialize(encoder: Encoder, value: DiscordBitSet) = encoder.encodeString(value.value)
-        override fun deserialize(decoder: Decoder) = DiscordBitSet(decoder.decodeString())
+        override fun deserialize(decoder: Decoder) =
+            DiscordBitSet(decoder.decodeSerializableValue(LongOrStringSerializer))
     }
 }
 
@@ -129,7 +131,7 @@ public fun DiscordBitSet(value: String): DiscordBitSet {
         return DiscordBitSet(longArrayOf(value.toULong().toLong()))
     }
 
-    val bytes = parseIntegerToBigEndianByteArray(value)
+    val bytes = parseNonNegativeIntegerToBigEndianByteArray(value)
 
     val longSize = (bytes.size / Long.SIZE_BYTES) + 1
     val destination = LongArray(longSize)

common/src/commonTest/kotlin/BitSetTests.kt

@@ -1,5 +1,9 @@
 package dev.kord.common
 
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.encodeToJsonElement
 import kotlin.js.JsName
 import kotlin.random.Random
 import kotlin.random.nextLong
@@ -126,4 +130,36 @@ class BitSetTests {
             assertTrue(bits.value.all { it in '0'..'9' })
         }
     }
+
+    @Test
+    fun negative_values_cant_be_parsed() {
+        assertFailsWith<NumberFormatException> { DiscordBitSet("-1") }
+        assertFailsWith<NumberFormatException> { DiscordBitSet("-99999999999999999999999999999999") }
+    }
+
+    private val numberStrings = listOf("0", "1", "1024", "6543654", "59946645771238946")
+
+    // https://github.com/kordlib/kord/issues/911
+    @Test
+    fun deserialization_works_with_json_strings_and_numbers() {
+        numberStrings.forEach { number ->
+            val string = "\"$number\""
+            val expected = DiscordBitSet(number)
+            assertEquals(expected, Json.decodeFromString(string))
+            assertEquals(expected, Json.decodeFromString(number))
+        }
+    }
+
+    @Test
+    fun serialization_works_and_produces_json_strings() {
+        numberStrings.forEach { number ->
+            val bitSet = DiscordBitSet(number)
+            val string = Json.encodeToString(bitSet)
+            val json = Json.encodeToJsonElement(bitSet)
+            assertEquals("\"$number\"", string)
+            assertIs<JsonPrimitive>(json)
+            assertTrue(json.isString)
+            assertEquals(number, json.content)
+        }
+    }
 }

common/src/jvmMain/kotlin/DiscordBitSetJvm.kt

@@ -10,4 +10,6 @@ internal actual fun formatIntegerFromLittleEndianLongArray(data: LongArray): Str
     return BigInteger(/* signum = */ 1, /* magnitude = */ buffer.array()).toString()
 }
 
-internal actual fun parseIntegerToBigEndianByteArray(value: String): ByteArray = BigInteger(value).toByteArray()
+internal actual fun parseNonNegativeIntegerToBigEndianByteArray(value: String): ByteArray = BigInteger(value)
+    .also { if (it.signum() < 0) throw NumberFormatException("Invalid DiscordBitSet format: '$value'") }
+    .toByteArray()

common/src/nonJvmMain/kotlin/DiscordBitSet.kt

@@ -11,5 +11,7 @@ internal actual fun formatIntegerFromLittleEndianLongArray(data: LongArray) =
         BigInteger.fromByteArray(readBytes(), Sign.POSITIVE).toString()
     }
 
-internal actual fun parseIntegerToBigEndianByteArray(value: String): ByteArray =
-    BigInteger.parseString(value).toByteArray()
+internal actual fun parseNonNegativeIntegerToBigEndianByteArray(value: String): ByteArray = BigInteger
+    .parseString(value)
+    .also { if (it.isNegative) throw NumberFormatException("Invalid DiscordBitSet format: '$value'") }
+    .toByteArray()