1 files changed, 113 insertions, 0 deletions
diff --git a/runtime/commonMain/src/kotlinx/serialization/json/internal/StreamingJsonInput.kt b/runtime/commonMain/src/kotlinx/serialization/json/internal/StreamingJsonInput.kt
new file mode 100644
index 00000000..f4a9ae3d
--- /dev/null
+++ b/runtime/commonMain/src/kotlinx/serialization/json/internal/StreamingJsonInput.kt
@@ -0,0 +1,113 @@
+package kotlinx.serialization.json.internal
+
+import kotlinx.serialization.*
+import kotlinx.serialization.internal.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.modules.*
+
+/**
+ * [JsonInput] which reads given JSON from [JsonReader] field by field.
+ */
+internal class StreamingJsonInput internal constructor(
+    public override val json: Json,
+    private val mode: WriteMode,
+    private val reader: JsonReader
+) : JsonInput, ElementValueDecoder() {
+
+    public override val context: SerialModule = json.context
+    private var currentIndex = -1
+    private var entryIndex = 0
+    private val configuration = json.configuration
+    
+    public override fun decodeJson(): JsonElement = JsonParser(reader).read()
+
+    @Suppress("DEPRECATION")
+    override val updateMode: UpdateMode
+        get() = configuration.updateMode
+
+    override fun <T> decodeSerializableValue(deserializer: DeserializationStrategy<T>): T {
+        return decodeSerializableValuePolymorphic(deserializer)
+    }
+
+    override fun beginStructure(desc: SerialDescriptor, vararg typeParams: KSerializer<*>): CompositeDecoder {
+        val newMode = switchMode(desc, typeParams)
+        if (newMode.begin != INVALID) {
+            reader.requireTokenClass(newMode.beginTc) { "Expected '${newMode.begin}, kind: ${desc.kind}'" }
+            reader.nextToken()
+        }
+        return when (newMode) {
+            WriteMode.LIST, WriteMode.MAP, WriteMode.POLY_OBJ -> StreamingJsonInput(
+                json,
+                newMode,
+                reader
+            ) // need fresh cur index
+            else -> if (mode == newMode) this else
+                StreamingJsonInput(json, newMode, reader) // todo: reuse instance per mode
+        }
+    }
+
+    override fun endStructure(desc: SerialDescriptor) {
+        if (mode.end != INVALID) {
+            reader.requireTokenClass(mode.endTc) { "Expected '${mode.end}'" }
+            reader.nextToken()
+        }
+    }
+
+    override fun decodeNotNullMark(): Boolean {
+        return reader.tokenClass != TC_NULL
+    }
+
+    override fun decodeNull(): Nothing? {
+        reader.requireTokenClass(TC_NULL) { "Expected 'null' literal" }
+        reader.nextToken()
+        return null
+    }
+
+    override fun decodeElementIndex(desc: SerialDescriptor): Int {
+        while (true) {
+            if (reader.tokenClass == TC_COMMA) reader.nextToken()
+            when (mode) {
+                WriteMode.LIST -> {
+                    return if (!reader.canBeginValue) CompositeDecoder.READ_DONE else ++currentIndex
+                }
+                WriteMode.MAP -> {
+                    if (currentIndex % 2 == 0 && reader.tokenClass == TC_COLON) reader.nextToken()
+                    return if (!reader.canBeginValue) CompositeDecoder.READ_DONE else ++currentIndex
+                }
+                WriteMode.POLY_OBJ -> {
+                    return when (entryIndex++) {
+                        0 -> 0
+                        1 -> 1
+                        else -> {
+                            entryIndex = 0
+                            CompositeDecoder.READ_DONE
+                        }
+                    }
+                }
+                else -> {
+                    if (!reader.canBeginValue) return CompositeDecoder.READ_DONE
+                    val key = reader.takeString()
+                    reader.requireTokenClass(TC_COLON) { "Expected ':'" }
+                    reader.nextToken()
+                    val index = desc.getElementIndex(key)
+                    if (index != CompositeDecoder.UNKNOWN_NAME) {
+                        return index
+                    }
+                    if (configuration.strictMode) throw JsonUnknownKeyException(key)
+                    else reader.skipElement()
+                }
+            }
+        }
+    }
+
+    override fun decodeBoolean(): Boolean = reader.takeString().run { if (configuration.strictMode) toBooleanStrict() else toBoolean() }
+    override fun decodeByte(): Byte = reader.takeString().toByte()
+    override fun decodeShort(): Short = reader.takeString().toShort()
+    override fun decodeInt(): Int = reader.takeString().toInt()
+    override fun decodeLong(): Long = reader.takeString().toLong()
+    override fun decodeFloat(): Float = reader.takeString().toFloat()
+    override fun decodeDouble(): Double = reader.takeString().toDouble()
+    override fun decodeChar(): Char = reader.takeString().single()
+    override fun decodeString(): String = reader.takeString()
+    override fun decodeEnum(enumDescription: EnumDescriptor): Int = enumDescription.getElementIndexOrThrow(reader.takeString())
+}