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Provide decodeToSequence to read multiple objects from stream lazily (#…
…1691) Hide JsonIterator and provide DecodeSequenceMode Fixes #1662 Co-authored-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>
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99
formats/json/jvmMain/src/kotlinx/serialization/json/internal/JsonIterator.kt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,99 @@ | ||
| /* | ||
| * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license. | ||
| */ | ||
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| @file:Suppress("FunctionName") | ||
| @file:OptIn(ExperimentalSerializationApi::class) | ||
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| package kotlinx.serialization.json.internal | ||
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| import kotlinx.serialization.DeserializationStrategy | ||
| import kotlinx.serialization.ExperimentalSerializationApi | ||
| import kotlinx.serialization.json.* | ||
|
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| 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.") | ||
| } | ||
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| 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 | ||
| } | ||
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| private fun AbstractJsonLexer.tryConsumeStartArray(): Boolean { | ||
| if (peekNextToken() == TC_BEGIN_LIST) { | ||
| consumeNextToken(TC_BEGIN_LIST) | ||
| return true | ||
| } | ||
| return false | ||
| } | ||
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| 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) | ||
| .decodeSerializableValue(deserializer) | ||
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| override fun hasNext(): Boolean = lexer.isNotEof() | ||
| } | ||
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| private class JsonIteratorArrayWrapped<T>( | ||
| private val json: Json, | ||
| private val lexer: ReaderJsonLexer, | ||
| private val deserializer: DeserializationStrategy<T> | ||
| ) : Iterator<T> { | ||
| private var first = true | ||
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| override fun next(): T { | ||
| if (first) { | ||
| first = false | ||
| } else { | ||
| lexer.consumeNextToken(COMMA) | ||
| } | ||
| val input = StreamingJsonDecoder(json, WriteMode.OBJ, lexer, deserializer.descriptor) | ||
| return input.decodeSerializableValue(deserializer) | ||
| } | ||
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| /** | ||
| * Note: if array separator (comma) is missing, hasNext() returns true, but next() throws an exception. | ||
| */ | ||
| override fun hasNext(): Boolean { | ||
| if (lexer.peekNextToken() == TC_END_LIST) { | ||
| 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()) lexer.fail(TC_END_LIST) | ||
| return true | ||
| } | ||
| } |
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