Name: avC70361 Date: 05/13/99



  The java.math.BigInteger objects serialization is wrong under jdk1.3. In a case when BigInteger object
represents 0 has been serialized, it can't be deserialized then because the "java.io.StreamCorruptedException:
BigInteger: signum-magnitude mismatch" is thrown during deserialization. That is because BigInteger.
writeObject() method use toByteArray() method to intialize serializable field 'magnitude', but this method
returns not zero-length array for BigInteger representing 0. The 'magnitude' field should be zero-length array
for zero BigInteger in order to be correcty read by readObject() of jdk 1.3 and earlier versions.
  Here is a test demonstrating the bug.
----------------BigIntegerTest.java--------------------
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.math.BigInteger;

public class BigIntegerTest {
  public static void main(String[] args) {
    try {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      ObjectOutputStream oos = new ObjectOutputStream(baos);

      oos.writeObject(new BigInteger("0"));
      oos.flush();

      ObjectInputStream ois = new ObjectInputStream(
        new ByteArrayInputStream(baos.toByteArray())
      );

      ois.readObject();

      System.out.println("Passed.");
    } catch(Exception e) {
      System.out.println("Failed. Unexpected exception : " + e);
    }
  }
}
----------------The test output---------------------
> java BigIntegerTest
Failed. Unexpected exception : java.io.StreamCorruptedException: BigInteger: signum-magnitude mismatch

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