ProgressiveStringDecoder (facebook#44027)

Summary:
Pull Request resolved: facebook#44027

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D55981019

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/network/ProgressiveStringDecoder.kt

@@ -0,0 +1,82 @@
+/*
+ * 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