ObjectStreamClass.java

/* ObjectStreamClass.java -- Class used to write class information
   about serialized objects.
   Copyright (C) 1998, 1999, 2000, 2001  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.io;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.security.DigestOutputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.Security;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Hashtable;
import java.util.Vector;
import gnu.java.io.NullOutputStream;
import gnu.java.lang.reflect.TypeSignature;
import gnu.java.security.provider.Gnu;


public class ObjectStreamClass implements Serializable
{
  /**
     Returns the <code>ObjectStreamClass</code> for <code>cl</code>.
     If <code>cl</code> is null, or is not <code>Serializable</code>,
     null is returned.  <code>ObjectStreamClass</code>'s are memorized;
     later calls to this method with the same class will return the
     same <code>ObjectStreamClass</code> object and no recalculation
     will be done.

     @see java.io.Serializable
  */
  public static ObjectStreamClass lookup (Class cl)
  {
    if (cl == null)
      return null;
    if (! (Serializable.class).isAssignableFrom (cl))
      return null;

    ObjectStreamClass osc = (ObjectStreamClass)classLookupTable.get (cl);

    if (osc != null)
      return osc;
    else
    {
      osc = new ObjectStreamClass (cl);
      classLookupTable.put (cl, osc);
      return osc;
    }
  }


  /**
     Returns the name of the class that this
     <code>ObjectStreamClass</code> represents.
  */
  public String getName ()
  {
    return name;
  }


  /**
     Returns the class that this <code>ObjectStreamClass</code>
     represents.  Null could be returned if this
     <code>ObjectStreamClass</code> was read from an
     <code>ObjectInputStream</code> and the class it represents cannot
     be found or loaded.

     @see java.io.ObjectInputStream
  */
  public Class forClass ()
  {
    return clazz;
  }


  /**
     Returns the serial version stream-unique identifier for the class
     represented by this <code>ObjectStreamClass</code>.  This SUID is
     either defined by the class as <code>static final long
     serialVersionUID</code> or is calculated as specified in
     Javasoft's "Object Serialization Specification" XXX: add reference
  */
  public long getSerialVersionUID ()
  {
    return uid;
  }


  // Returns the serializable (non-static and non-transient) Fields
  // of the class represented by this ObjectStreamClass.  The Fields
  // are sorted by name.
  // XXX doc
  public ObjectStreamField[] getFields ()
  {
    ObjectStreamField[] copy = new ObjectStreamField[ fields.length ];
    System.arraycopy (fields, 0, copy, 0, fields.length);
    return copy;
  }


  // XXX doc
  // Can't do binary search since fields is sorted by name and
  // primitiveness.
  public ObjectStreamField getField (String name)
  {
    for (int i=0; i < fields.length; i++)
      if (fields[i].getName ().equals (name))
	return fields[i];
    return null;
  }


  /**
     Returns a textual representation of this
     <code>ObjectStreamClass</code> object including the name of the
     class it represents as well as that class's serial version
     stream-unique identifier.

     @see getSerialVersionUID ()
     @see getName ()
  */
  public String toString ()
  {
    return "java.io.ObjectStreamClass< " + name + ", " + uid + " >";
  }


  // Returns true iff the class that this ObjectStreamClass represents
  // has the following method:
  //
  // private void writeObject (ObjectOutputStream)
  //
  // This method is used by the class to override default
  // serialization behavior.
  boolean hasWriteMethod ()
  {
    return (flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0;
  }


  // Returns true iff the class that this ObjectStreamClass represents
  // implements Serializable but does *not* implement Externalizable.
  boolean isSerializable ()
  {
    return (flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0;
  }


  // Returns true iff the class that this ObjectStreamClass represents
  // implements Externalizable.
  boolean isExternalizable ()
  {
    return (flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0;
  }


  // Returns the <code>ObjectStreamClass</code> that represents the
  // class that is the superclass of the class this
  // <code>ObjectStreamClass</code> represents.  If the superclass is
  // not Serializable, null is returned.
  ObjectStreamClass getSuper ()
  {
    return superClass;
  }


  // returns an array of ObjectStreamClasses that represent the super
  // classes of CLAZZ and CLAZZ itself in order from most super to
  // CLAZZ.  ObjectStreamClass[0] is the highest superclass of CLAZZ
  // that is serializable.
  static ObjectStreamClass[] getObjectStreamClasses (Class clazz)
  {
    ObjectStreamClass osc = ObjectStreamClass.lookup (clazz);

    ObjectStreamClass[] ret_val;

    if (osc == null)
      return new ObjectStreamClass[0];
    else
    {
      Vector oscs = new Vector ();

      while (osc != null)
      {
	oscs.addElement (osc);
	osc = osc.getSuper ();
      }

      int count = oscs.size ();
      ObjectStreamClass[] sorted_oscs = new ObjectStreamClass[ count ];

      for (int i = count - 1; i >= 0; i--)
	sorted_oscs[ count - i - 1 ] = (ObjectStreamClass)oscs.elementAt (i);

      return sorted_oscs;
    }
  }


  // Returns an integer that consists of bit-flags that indicate
  // properties of the class represented by this ObjectStreamClass.
  // The bit-flags that could be present are those defined in
  // ObjectStreamConstants that begin with `SC_'
  int getFlags ()
  {
    return flags;
  }


  ObjectStreamClass (String name, long uid, byte flags,
		     ObjectStreamField[] fields)
  {
    this.name = name;
    this.uid = uid;
    this.flags = flags;
    this.fields = fields;
  }

  void setClass (Class cl) throws InvalidClassException
  {
    this.clazz = cl;
    long class_uid = getClassUID (cl);
    if (uid == 0)
      {
       uid = class_uid;
       return;
      }
    
    // Check that the actual UID of the resolved class matches the UID from 
    // the stream.    
    if (uid != class_uid)
      {
       String msg = cl + 
	 ": Local class not compatible: stream serialVersionUID="
	 + uid + ", local serialVersionUID=" + class_uid;
       throw new InvalidClassException (msg);
      }
  }

  void setSuperclass (ObjectStreamClass osc)
  {
    superClass = osc;
  }


  void calculateOffsets ()
  {
    int i;
    ObjectStreamField field;
    primFieldSize = 0;
    int fcount = fields.length;
    for (i = 0; i < fcount; ++ i)
    {
      field = fields[i];

      if (! field.isPrimitive ())
	break;

      field.setOffset (primFieldSize);
      switch (field.getTypeCode ())
      {
	case 'B':
	case 'Z':
	  ++ primFieldSize;
	  break;
	case 'C':
	case 'S':
	  primFieldSize += 2;
	  break;
	case 'I':
	case 'F':
	  primFieldSize += 4;
	  break;
	case 'D':
	case 'J':
	  primFieldSize += 8;
	  break;
      }
    }

    for (objectFieldCount = 0; i < fcount; ++ i)
      fields[i].setOffset (objectFieldCount++);
  }


  private ObjectStreamClass (Class cl)
  {
    uid = 0;
    flags = 0;

    clazz = cl;
    name = cl.getName ();
    setFlags (cl);
    setFields (cl);
    uid = getClassUID (cl);
    superClass = lookup (cl.getSuperclass ());
  }


  // Sets bits in flags according to features of CL.
  private void setFlags (Class cl)
  {
    if ((java.io.Externalizable.class).isAssignableFrom (cl))
      flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;
    else if ((java.io.Serializable.class).isAssignableFrom (cl))
      // only set this bit if CL is NOT Externalizable
      flags |= ObjectStreamConstants.SC_SERIALIZABLE;

    try
    {
      Method writeMethod = cl.getDeclaredMethod ("writeObject",
						 writeMethodArgTypes);
      int modifiers = writeMethod.getModifiers ();

      if (writeMethod.getReturnType () == Void.TYPE
	  && Modifier.isPrivate (modifiers)
	  && !Modifier.isStatic (modifiers))
	flags |= ObjectStreamConstants.SC_WRITE_METHOD;
    }
    catch (NoSuchMethodException oh_well)
    {}
  }


  // Sets fields to be a sorted array of the serializable fields of
  // clazz.
  private void setFields (Class cl)
  {
    if (! isSerializable () || isExternalizable ())
    {
      fields = NO_FIELDS;
      return;
    }

    try
    {
      Field serialPersistentFields
	= cl.getDeclaredField ("serialPersistentFields");
      int modifiers = serialPersistentFields.getModifiers ();

      if (Modifier.isStatic (modifiers)
	  && Modifier.isFinal (modifiers)
	  && Modifier.isPrivate (modifiers))
      {
	fields = getSerialPersistentFields (cl);
	Arrays.sort (fields);
	calculateOffsets ();
	return;
      }
    }
    catch (NoSuchFieldException ignore)
    {}

    int num_good_fields = 0;
    Field[] all_fields = cl.getDeclaredFields ();

    int modifiers;
    // set non-serializable fields to null in all_fields
    for (int i=0; i < all_fields.length; i++)
    {
      modifiers = all_fields[i].getModifiers ();
      if (Modifier.isTransient (modifiers)
	  || Modifier.isStatic (modifiers))
	all_fields[i] = null;
      else
	num_good_fields++;
    }

    // make a copy of serializable (non-null) fields
    fields = new ObjectStreamField[ num_good_fields ];
    for (int from=0, to=0; from < all_fields.length; from++)
      if (all_fields[from] != null)
      {
	Field f = all_fields[from];
	fields[to] = new ObjectStreamField (f.getName (), f.getType ());
	to++;
      }

    Arrays.sort (fields);
    calculateOffsets ();
  }

  // Returns the serial version UID defined by class, or if that
  // isn't present, calculates value of serial version UID.
  private long getClassUID (Class cl)
  {
    try
    {
      Field suid = cl.getDeclaredField ("serialVersionUID");
      int modifiers = suid.getModifiers ();

      if (Modifier.isStatic (modifiers) && Modifier.isFinal (modifiers))
	return suid.getLong (null);	  
    }
    catch (NoSuchFieldException ignore)
    {
    }
    catch (IllegalAccessException ignore)
    {
    }

    // cl didn't define serialVersionUID, so we have to compute it
    try
    {
      MessageDigest md = null;
      DigestOutputStream digest_out = null;
      DataOutputStream data_out = null;

      try 
	{
	  md = MessageDigest.getInstance ("SHA");
	}
      catch (NoSuchAlgorithmException e)
	{
	  // If a provider already provides SHA, use it; otherwise, use this.
	  Gnu gnuProvider = new Gnu();
	  Security.addProvider(gnuProvider);
	  md = MessageDigest.getInstance ("SHA");
	}

      digest_out = new DigestOutputStream (nullOutputStream, md);
      data_out = new DataOutputStream (digest_out);
      data_out.writeUTF (cl.getName ());

      int modifiers = cl.getModifiers ();
      // just look at interesting bits
      modifiers = modifiers & (Modifier.ABSTRACT | Modifier.FINAL
  				| Modifier.INTERFACE | Modifier.PUBLIC);
      data_out.writeInt (modifiers);

      // Pretend that an array has no interfaces, because when array
      // serialization was defined (JDK 1.1), arrays didn't have it.
      if (! cl.isArray ())
	{
	  Class[] interfaces = cl.getInterfaces ();
	  Arrays.sort (interfaces, interfaceComparator);
	  for (int i=0; i < interfaces.length; i++)
	    data_out.writeUTF (interfaces[i].getName ());
	}

      Field field;
      Field[] fields = cl.getDeclaredFields ();
      Arrays.sort (fields, memberComparator);
      for (int i=0; i < fields.length; i++)
      {
	field = fields[i];
	modifiers = field.getModifiers ();
	if (Modifier.isPrivate (modifiers)
	    && (Modifier.isStatic (modifiers)
		 || Modifier.isTransient (modifiers)))
	  continue;

	data_out.writeUTF (field.getName ());
	data_out.writeInt (modifiers);
	data_out.writeUTF (TypeSignature.getEncodingOfClass (field.getType ()));
      }

      // write class initializer method if present
      boolean has_init;
      try
      {
	has_init = hasClassInitializer (cl);
      }
      catch (NoSuchMethodError e)
      {
	has_init = false;
      }

      if (has_init)
      {
	data_out.writeUTF ("<clinit>");
	data_out.writeInt (Modifier.STATIC);
	data_out.writeUTF ("()V");
      }

      Constructor constructor;
      Constructor[] constructors = cl.getDeclaredConstructors ();
      Arrays.sort (constructors, memberComparator);
      for (int i=0; i < constructors.length; i++)
      {
	constructor = constructors[i];
	modifiers = constructor.getModifiers ();
	if (Modifier.isPrivate (modifiers))
	  continue;

	data_out.writeUTF ("<init>");
	data_out.writeInt (modifiers);

	// the replacement of '/' with '.' was needed to make computed
	// SUID's agree with those computed by JDK
	data_out.writeUTF (
	  TypeSignature.getEncodingOfConstructor (constructor).replace ('/','.'));
      }

      Method method;
      Method[] methods = cl.getDeclaredMethods ();
      Arrays.sort (methods, memberComparator);
      for (int i=0; i < methods.length; i++)
      {
	method = methods[i];
	modifiers = method.getModifiers ();
	if (Modifier.isPrivate (modifiers))
	  continue;

	data_out.writeUTF (method.getName ());
	data_out.writeInt (modifiers);

	// the replacement of '/' with '.' was needed to make computed
	// SUID's agree with those computed by JDK
	data_out.writeUTF (
	  TypeSignature.getEncodingOfMethod (method).replace ('/', '.'));
      }

      data_out.close ();
      byte[] sha = md.digest ();
      long result = 0;
      int len = sha.length < 8 ? sha.length : 8;
      for (int i=0; i < len; i++)
	result += (long)(sha[i] & 0xFF) << (8 * i);

      return result;
    }
    catch (NoSuchAlgorithmException e)
    {
      throw new RuntimeException ("The SHA algorithm was not found to use in computing the Serial Version UID for class "
				  + cl.getName ());
    }
    catch (IOException ioe)
    {
      throw new RuntimeException (ioe.getMessage ());
    }
  }

  // Returns the value of CLAZZ's private static final field named
  // `serialPersistentFields'.
  private ObjectStreamField[] getSerialPersistentFields (Class clazz)
  {
    ObjectStreamField[] o = null;
    try
      {
	// Use getDeclaredField rather than getField for the same reason
	// as above in getDefinedSUID.
	Field f = clazz.getDeclaredField ("getSerialPersistentFields");
	o = (ObjectStreamField[])f.get (null);
      }
    catch (java.lang.NoSuchFieldException e)
      {
      }
    catch (java.lang.IllegalAccessException e)
      {
      }

    return o;
  }


  // Returns true if CLAZZ has a static class initializer
  // (a.k.a. <clinit>).
  //
  // A NoSuchMethodError is raised if CLAZZ has no such method.
  private static boolean hasClassInitializer (Class clazz)
    throws java.lang.NoSuchMethodError
  {
    Method m = null;

    try
      {
	Class classArgs[] = {};
	m = clazz.getDeclaredMethod ("<clinit>", classArgs);
      }
    catch (java.lang.NoSuchMethodException e)
      {
	throw new java.lang.NoSuchMethodError ();
      }

    return m != null;
  }

  public static final ObjectStreamField[] NO_FIELDS = {};

  private static Hashtable classLookupTable = new Hashtable ();
  private static final NullOutputStream nullOutputStream = new NullOutputStream ();
  private static final Comparator interfaceComparator = new InterfaceComparator ();
  private static final Comparator memberComparator = new MemberComparator ();
  private static final
    Class[] writeMethodArgTypes = { java.io.ObjectOutputStream.class };

  private ObjectStreamClass superClass;
  private Class clazz;
  private String name;
  private long uid;
  private byte flags;

  // this field is package protected so that ObjectInputStream and
  // ObjectOutputStream can access it directly
  ObjectStreamField[] fields;

  // these are accessed by ObjectIn/OutputStream
  int primFieldSize = -1;  // -1 if not yet calculated
  int objectFieldCount;

  // This is probably not necessary because this class is special cased already
  // but it will avoid showing up as a discrepancy when comparing SUIDs.
  private static final long serialVersionUID = -6120832682080437368L;
}


// interfaces are compared only by name
class InterfaceComparator implements Comparator
{
  public int compare (Object o1, Object o2)
  {
    return ((Class)o1).getName ().compareTo (((Class)o2).getName ());
  }
}


// Members (Methods and Constructors) are compared first by name,
// conflicts are resolved by comparing type signatures
class MemberComparator implements Comparator
{
  public int compare (Object o1, Object o2)
  {
    Member m1 = (Member)o1;
    Member m2 = (Member)o2;

    int comp = m1.getName ().compareTo (m2.getName ());

    if (comp == 0)
      return TypeSignature.getEncodingOfMember (m1).
	compareTo (TypeSignature.getEncodingOfMember (m2));
    else
      return comp;
  }
}