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ProgressiveStringDecoder (#44027)
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Summary:
Pull Request resolved: #44027

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D55981019
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Thomas Nardone authored and facebook-github-bot committed Jun 11, 2024
1 parent a97e3d0 commit 3278220
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/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/

package com.facebook.react.modules.network

import com.facebook.common.logging.FLog
import com.facebook.react.common.ReactConstants
import java.nio.ByteBuffer
import java.nio.CharBuffer
import java.nio.charset.CharacterCodingException
import java.nio.charset.Charset
import java.nio.charset.CharsetDecoder

/**
* Class to decode encoded strings from byte array chunks. As in different encodings single
* character could take up to 4 characters byte array passed to decode could have parts of the
* characters which can't be correctly decoded.
*
* This class is designed in assumption that original byte stream is correctly formatted string in
* given encoding. Otherwise some parts of the data won't be decoded.
*/
internal class ProgressiveStringDecoder(charset: Charset) {

private val decoder: CharsetDecoder = charset.newDecoder()
private var remainder: ByteArray? = null

/**
* Parses data to String If there is a partial multi-byte symbol on the edge of the String it get
* saved to the reminder and added to the string on the decodeNext call.
*
* @param data
* @return
*/
fun decodeNext(data: ByteArray, length: Int): String {
var bufferLength = length
val currentRemainder = remainder
val decodeData: ByteArray =
if (currentRemainder != null) {
ByteArray(currentRemainder.size + length).also { newData ->
System.arraycopy(currentRemainder, 0, newData, 0, currentRemainder.size)
System.arraycopy(data, 0, newData, currentRemainder.size, length)
bufferLength += currentRemainder.size
}
} else {
data
}
var decodeBuffer = ByteBuffer.wrap(decodeData, 0, bufferLength)
var result: CharBuffer? = null
var remainderLength = 0
while (result == null && (remainderLength < MAX_BYTES)) {
try {
result = decoder.decode(decodeBuffer)
} catch (e: CharacterCodingException) {
remainderLength++
decodeBuffer = ByteBuffer.wrap(decodeData, 0, bufferLength - remainderLength)
}
}
val hasRemainder = result != null && (remainderLength > 0)
remainder =
if (hasRemainder) {
ByteArray(remainderLength).also { newRemainder ->
System.arraycopy(
decodeData, bufferLength - remainderLength, newRemainder, 0, remainderLength)
}
} else {
null
}
if (result == null) {
FLog.w(ReactConstants.TAG, "failed to decode string from byte array")
return EMPTY_STRING
} else {
return String(result.array(), 0, result.length)
}
}
}

private const val EMPTY_STRING = ""
private const val MAX_BYTES = 4

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