Protobuf Java 混淆后逆向特征点查找

如下代码中的字符串可以定位 CodedOutputStream 类。

public static class OutOfSpaceException extends IOException {
  private static final long serialVersionUID = -6947486886997889499L;

  OutOfSpaceException() {
    super("CodedOutputStream was writing to a flat byte array and ran " +
          "out of space.");
  }
}

CodedInputStream 的定位如下，依然根据字符串。然后可以从其 readString 的方法交叉引用查找生成的类，或者hook此方法也能看到实际相关生成类。

// Here we should refill the buffer as many bytes as possible.
int bytesRead =
    read(
        input,
        buffer,
        bufferSize,
        Math.min(
            //  the size of allocated but unused bytes in the buffer
            buffer.length - bufferSize,
            //  do not exceed the total bytes limit
            sizeLimit - totalBytesRetired - bufferSize));
if (bytesRead == 0 || bytesRead < -1 || bytesRead > buffer.length) {
  throw new IllegalStateException(
      input.getClass()
          + "#read(byte[]) returned invalid result: "
          + bytesRead
          + "\nThe InputStream implementation is buggy.");
}

if (bytesRead == 0 || bytesRead < -1 || bytesRead > this.buffer.length) {
    throw new IllegalStateException("InputStream#read(byte[]) returned invalid result: " + bytesRead + "\nThe InputStream implementation is buggy.");
}

如下代码中的字符串 "byte array" 定位 toByteArray 方法

@Override
public byte[] toByteArray() {
  try {
    final byte[] result = new byte[getSerializedSize()];
    final CodedOutputStream output = CodedOutputStream.newInstance(result);
    writeTo(output);
    output.checkNoSpaceLeft();
    return result;
  } catch (IOException e) {
    throw new RuntimeException(getSerializingExceptionMessage("byte array"), e);
  }
}