content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.Wifi
   */
  
  package com.android.server.wifi;
  
  import com.android.internal.annotations.VisibleForTesting;
  
  import java.nio.BufferUnderflowException;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.nio.charset.Charset;
  
  /**
   * Utility class for reading generic data (e.g. various length integer, string) from ByteBuffer.
   */
  public class ByteBufferReader {
      @VisibleForTesting
      public static final int MINIMUM_INTEGER_SIZE = Byte.BYTES;
  
      @VisibleForTesting
      public static final int MAXIMUM_INTEGER_SIZE = Long.BYTES;
  
      /**
       * Read an integer value from a buffer.
       *
       * @param payload The buffer to read from
       * @param byteOrder Byte order of the buffer
       * @param size The number of bytes to read from the buffer
       * @return The integer value
       * @throws BufferUnderflowException
       * @throws IllegalArgumentException
       */
      public static long readInteger(ByteBuffer payload, ByteOrder byteOrder, int size) {
          if (size < MINIMUM_INTEGER_SIZE || size > MAXIMUM_INTEGER_SIZE) {
              throw new IllegalArgumentException("Invalid size " + size);
          }
  
          // Read the necessary bytes.
          byte[] octets = new byte[size];
          payload.get(octets);
  
          // Format the value based on byte order.
          long value = 0;
          if (byteOrder == ByteOrder.LITTLE_ENDIAN) {
              for (int n = octets.length - 1; n >= 0; n--) {
                  value = (value << Byte.SIZE) | (octets[n] & 0xFF);
              }
          } else {
              for (byte octet : octets) {
                  value = (value << Byte.SIZE) | (octet & 0xFF);
              }
          }
          return value;
      }
  
      /**
       * Read a string from a buffer. An empty String will be returned for a String with 0 length.
       *
       * @param payload The buffer to read from
       * @param length Number of bytes to read from the buffer
       * @param charset The character set of the string
       * @return {@link String}
       * @throws BufferUnderflowException
       * @throws NegativeArraySizeException
       */
      public static String readString(ByteBuffer payload, int length, Charset charset) {
          byte[] octets = new byte[length];
          payload.get(octets);
          return new String(octets, charset);
      }
  
      /**
       * Read a string from a buffer where the string value is preceded by the length of the string
       * (1 byte) in the buffer.
       *
       * @param payload The buffer to read from
       * @param charset The character set of the string
       * @return {@link String}
       * @throws BufferUnderflowException
       */
      public static String readStringWithByteLength(ByteBuffer payload, Charset charset) {
          int length = payload.get() & 0xFF;
          return readString(payload, length, charset);
      }
  }
  