ProgressiveStringDecoder

Summary: Changelog: [Internal]

Differential Revision: D55981019

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

@@ -0,0 +1,75 @@
+/*
+ * 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
+    var decodeData: ByteArray = data
+    remainder?.let { remainder ->
+      decodeData = ByteArray(remainder.size + length)
+      System.arraycopy(remainder, 0, decodeData, 0, remainder.size)
+      System.arraycopy(data, 0, decodeData, remainder.size, length)
+      bufferLength += remainder.size
+    }
+    var decodeBuffer = ByteBuffer.wrap(decodeData, 0, bufferLength)
+    var result: CharBuffer? = null
+    var remainderLength = 0
+    while (result == null && (remainderLength < 4)) {
+      try {
+        result = decoder.decode(decodeBuffer)
+      } catch (e: CharacterCodingException) {
+        remainderLength++
+        decodeBuffer = ByteBuffer.wrap(decodeData, 0, bufferLength - remainderLength)
+      }
+    }
+    val hasRemainder = result != null && (remainderLength > 0)
+    if (hasRemainder) {
+      val newRemainder = ByteArray(remainderLength)
+      System.arraycopy(decodeData, bufferLength - remainderLength, newRemainder, 0, remainderLength)
+      remainder = newRemainder
+    } else {
+      remainder = 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 = ""