1 files changed, 102 insertions, 0 deletions
diff --git a/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonIterator.kt b/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonIterator.kt
new file mode 100644
index 00000000..00f36b2b
--- /dev/null
+++ b/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonIterator.kt
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+@file:Suppress("FunctionName")
+@file:OptIn(ExperimentalSerializationApi::class)
+
+package kotlinx.serialization.json.internal
+
+import kotlinx.serialization.DeserializationStrategy
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.json.*
+
+internal fun <T> JsonIterator(
+    mode: DecodeSequenceMode,
+    json: Json,
+    lexer: ReaderJsonLexer,
+    deserializer: DeserializationStrategy<T>
+): Iterator<T> = when (lexer.determineFormat(mode)) {
+    DecodeSequenceMode.WHITESPACE_SEPARATED -> JsonIteratorWsSeparated(
+        json,
+        lexer,
+        deserializer
+    ) // Can be many WS-separated independent arrays
+    DecodeSequenceMode.ARRAY_WRAPPED -> JsonIteratorArrayWrapped(
+        json,
+        lexer,
+        deserializer
+    )
+    DecodeSequenceMode.AUTO_DETECT -> error("AbstractJsonLexer.determineFormat must be called beforehand.")
+}
+
+
+private fun AbstractJsonLexer.determineFormat(suggested: DecodeSequenceMode): DecodeSequenceMode = when (suggested) {
+    DecodeSequenceMode.WHITESPACE_SEPARATED ->
+        DecodeSequenceMode.WHITESPACE_SEPARATED // do not call consumeStartArray here so we don't confuse parser with stream of lists
+    DecodeSequenceMode.ARRAY_WRAPPED ->
+        if (tryConsumeStartArray()) DecodeSequenceMode.ARRAY_WRAPPED
+        else fail(TC_BEGIN_LIST)
+    DecodeSequenceMode.AUTO_DETECT ->
+        if (tryConsumeStartArray()) DecodeSequenceMode.ARRAY_WRAPPED
+        else DecodeSequenceMode.WHITESPACE_SEPARATED
+}
+
+private fun AbstractJsonLexer.tryConsumeStartArray(): Boolean {
+    if (peekNextToken() == TC_BEGIN_LIST) {
+        consumeNextToken(TC_BEGIN_LIST)
+        return true
+    }
+    return false
+}
+
+private class JsonIteratorWsSeparated<T>(
+    private val json: Json,
+    private val lexer: ReaderJsonLexer,
+    private val deserializer: DeserializationStrategy<T>
+) : Iterator<T> {
+    override fun next(): T =
+        StreamingJsonDecoder(json, WriteMode.OBJ, lexer, deserializer.descriptor, null)
+            .decodeSerializableValue(deserializer)
+
+    override fun hasNext(): Boolean = lexer.isNotEof()
+}
+
+private class JsonIteratorArrayWrapped<T>(
+    private val json: Json,
+    private val lexer: ReaderJsonLexer,
+    private val deserializer: DeserializationStrategy<T>
+) : Iterator<T> {
+    private var first = true
+    private var finished = false
+
+    override fun next(): T {
+        if (first) {
+            first = false
+        } else {
+            lexer.consumeNextToken(COMMA)
+        }
+        val input = StreamingJsonDecoder(json, WriteMode.OBJ, lexer, deserializer.descriptor, null)
+        return input.decodeSerializableValue(deserializer)
+    }
+
+    /**
+     * Note: if array separator (comma) is missing, hasNext() returns true, but next() throws an exception.
+     */
+    override fun hasNext(): Boolean {
+        if (finished) return false
+        if (lexer.peekNextToken() == TC_END_LIST) {
+            finished = true
+            lexer.consumeNextToken(TC_END_LIST)
+            if (lexer.isNotEof()) {
+                if (lexer.peekNextToken() == TC_BEGIN_LIST) lexer.fail("There is a start of the new array after the one parsed to sequence. " +
+                        "${DecodeSequenceMode.ARRAY_WRAPPED.name} mode doesn't merge consecutive arrays.\n" +
+                        "If you need to parse a stream of arrays, please use ${DecodeSequenceMode.WHITESPACE_SEPARATED.name} mode instead.")
+                lexer.expectEof()
+            }
+            return false
+        }
+        if (!lexer.isNotEof() && !finished) lexer.fail(TC_END_LIST)
+        return true
+    }
+}