Subversion Repositories javautils

                
                JavaMail 1.1
                ============

Following is a description of the new APIs that are being
introduced in JavaMail 1.1

Please send comments and feedback to javamail@sun.com

(1) MessageContext
==================

In some cases it is desirable for the object representing the content
of a BodyPart to know something about the "context" in which it is
operating, e.g., what other data is contained in the same Multipart
object, who sent the message containing the data, etc.  This allows
for more interesting content types that know more about the message
containing them and the mail system in general.

Some uses of multipart/related might require these capabilities.
For instance, the handler for a text/html body part contained in a
multipart/related object might need to know about the containing
object in order to find the related image data needed to display the
HTML document.

There is one particular case in the current implementation where
this need arises.  (This is a bug in the current release.)  When
constructing a MimeMessage object for a nested message contained
in another message, the DataContentHandler needs the Session
object in order to construct the new MimeMessage object.

To solve these problems we introduce a new class, a new interface,
and a number of new methods.

The MessageContext class provides the basic information about the
"context" in which a content object is operating:

/**
 * The context in which a piece of Message content is contained.  A
 * <code>MessageContext</code> object is returned by the
 * <code>getMessageContext</code> method of the
 * <code>MessageAware</code> interface.  <code>MessageAware</code> is
 * typically implemented by <code>DataSources</code> to allow a
 * <code>DataContentHandler</code> to pass on information about the
 * context in which a data content object is operating.
 *
 * @see javax.mail.MessageAware
 * @see javax.activation.DataSource
 * @see javax.activation.DataContentHandler
 */
public class MessageContext {

    /**
     * Create a MessageContext object describing the context of the 
     * given Part.
     */
    public MessageContext(Part part)

    /**
     * Return the Part that contains the content.
     *
     * @return  the containing Part, or null if not known
     */
    public Part getPart()

    /**
     * Return the Message that contains the content.
     * Follows the parent chain up through containing Multipart
     * objects until it comes to a Message object, or null.
     *
     * @return  the containing Message, or null if not known
     */
    public Message getMessage()

    /**
     * Return the Session we're operating in.
     *
     * @return  the Session, or null if not known
     */
    public Session getSession()
}


A MessageContext object can be obtained by a DataContentHandler from a
DataSource that also implements the MessageAware interface:

/**
 * An interface optionally implemented by <code>DataSources</code> to
 * supply information to a <code>DataContentHandler</code> about the
 * message context in which the data content object is operating.
 *
 * @see javax.mail.MessageContext
 * @see javax.activation.DataSource
 * @see javax.activation.DataContentHandler
 */
public interface MessageAware {
    /**
     * Return the message context.
     */
    public MessageContext getMessageContext();
}


This new interface and class provides the basic information needed by
the DataContentHandler to use in constructing more "interesting" objects
representing a particular type of data.

To allow navigation up the chain of components contained in a Message,
we add the following methods.

First, on BodyPart we add:

    /**
     * The <code>Multipart</code> object containing this 
     * <code>BodyPart</code>, if known.
     */
    protected Multipart parent;

    /**
     * Return the containing <code>Multipart</code> object,
     * or <code>null</code> if not known.
     */
    public Multipart getParent()


On Multipart we add:

    /**
     * The <code>Part</code> containing this <code>Multipart</code>,
     * if known.
     */
    protected Part parent;

    /**
     * Return the <code>Part</code> that contains this
     * (cod<code>Multipart</c object, or <code>null</code> if not known.
     */
    public Part getParent()

    /**
     * Set the parent of this <code>Multipart</code> to be the specified
     * <code>Part</code>.  Normally called by the <code>Message</code>
     * or <code>BodyPart</code> <code>setContent(Multipart)</code>
     * method. <p>
     *
     * <code>parent</code> may be <code>null</code> if the
     * <code>Multipart</code> is being removed from its containing
     * <code>Part</code>.
     */
    public void setParent(Part parent)


To enable this new functionality we change the implementations of
MimeBodyPart, MimeMessage, and MimeMultipart to maintain the "parent"
links where possible.  We also change MimePartDataSource to implement
the MessageAware interface.

===================================================================

(2) MessageID
=============
The MimeMessage class requires a getMessageID() method.

The client can now fetch it as a header, but since this is a "standard"
RFC822 header, we want to provide an easier access method. 

An added benefit is that protocols like IMAP, which provide this info
as part of the ENVELOPE structure, can implement this method much more
efficiently.

 /**
  * Returns the value of the "Message-ID" header field. Returns
  * null if this field is unavailable or its value is absent. <p>
  *
  * The default implementation provided here uses the
  * <code>getHeader()</code> method to return the value of the
  * "Message-ID" field.
  *
  * @return     Message-ID
  * @exception  MessagingException, if the retrieval of this field
  *             causes any exception.
  * @see        javax.mail.search.MessageIDTerm
  */
  public String getMessageID() throws MessagingException;

===================================================================

(3) UIDFolder
=============

The following methods in the UIDFolder interface have certain problems.

We are proposing changes that will fix these problems. These are
binary incompatible changes, but we think these changes are necessary for
this interface to work in a useful manner. We are also not aware of
anyone that has shipped a Store Provider that implements this interface,
so we are hoping that the effect of this change is minimal (non-existent).

(1) Message getMessageByUID(long uid)

Description:
        Get the Message corresponding to the given UID. If no such
message exists, the java.util.NoSuchElementException is thrown.

Problem:
        A disconnected client can have a stash of UIDs from a
previous session. Some of these UIDs may have been expunged from the
server, but the disconnected client does not know this. It is quite
reasonable (and expected) for a disconnected client to use this
method when reconnecting - to check whether a UID is valid or not at
the server.
        Since failure is an expected result here, using a
RunTimeException to indicate it, seems wrong and counter-intuitive for
the client.

Solution:
        Our solution is to allow this method to return null to indicate
that the requested UID is not valid anymore. Thus, this method will no
longer throw the java.util.NoSuchElementException.

(2)  Message[] getMessagesByUID(long start, long end)

Description:
        Get the Messages corresponding to the given UID range. If any
UID is invalid, the java.util.NoSuchElementException is thrown.

Problem:
        Similar, but worse than (1). We think that disconnected clients
(or clients that prefer to use UIDs) may issue 
        getMessagesByUID(1, LASTUID) 
to get all the Messages at the server, especially when the client does
not know the exact UIDs for this folder. In this case, we certainly
do not want this method to fail if some id in the given range is 
not a valid UID; rather we want it to return all available Messages from
the server.

Solution:
        Our solution is to remove the NoSuchElementException exception
and allow this method to return Message objects in the given range.

(3) Message[] getMessagesByUID(long[] uids)

Description:
        Get the Messages corresponding to the given UID range. If any
UID is invalid, the java.util.NoSuchElementException is thrown.

Problem:
        Identical to (1).
        A disconnected client can have a stash of UIDs from a
previous session. Some of these UIDs may have been expunged from the
server, but the disconnected client does not know this. It is quite
reasonable (and expected) for a disconnected client to use this
method when reconnecting - to check whether a set of UIDs are valid
or not at the server.
        Since failure can be an expected result, using a
RunTimeException to indicate it, seems wrong and counter-intuitive for
the client.

Solution:
        Our solution is to allow this method to return null entries
to indicate that a requested UID is not valid anymore. Thus, the
message array returned by this method can have null entries for the
invalid UIDs; and this method will no longer throw the 
java.util.NoSuchElementException.
        Note that the size of the returned Message array is the same
as the size of the request array of UIDs, and that each entry in the
Message array corresponds to the same index entry in the UID array.
===================================================================

(4) InternetAddress
===================

The InternetAddress class needs the following protected field to
properly support encoding of the "personal name".

        protected String encodedPersonal; // the encoded personal name

No other API changes are associated with this. 

This is a binary compatible change to JavaMail 1.0. However, there is
a potential problem for any existing InternetAddress subclasses, which
can cause them to break. This typically will affect only providers,
not clients.

Details:
-------

The InternetAddress implementation will use this field to store the
encoded personal name. 

        The getPersonal() method will return the protected
'personal' field; if this field is null, it will check the 'encodedPersonal'
field and decode its value and return it.
        The toString() method will use the protected 'encodedPersonal'
field to create the RFC2047 compliant address string. If this field is
null, it will check the 'personal' field, encode that if necessary and
use it.

This implies that, if an InternetAddress subclass changes either 
the 'personal' or 'encodedPersonal' fields,  it should set the other
to null to force its recomputation. Unfortunately, this also implies
that existing subclasses of InternetAddress that directly set the
'personal' field can break in certain situations.
        We feel that the risk of this happening is minimal, since we
don't expect that our users have subclassed InternetAddress. Also, this
is necessary to properly support encoded personal names, so we feel that
this has to be done.
================================================================

(5) MimeCharset
================

A utility method to convert java charsets into MIME charsets is
needed.

The JDK supports a variety of charsets. The JDK has names for these
charsets, unfortunately they dont always match to their MIME or IANA
equivalents. 

It is necessary in some cases, (especially for providers) to map the
JDK charset names into their MIME or IANA equivalents. This method does
that.

The API:
-------

This is a new static method to the javax.mail.internet.MimeUtility class

        /**
         * Convert a java charset into its MIME charset name. <p>
         *
         * Note that a future version of JDK (post 1.2) might provide
         * this functionality, in which case, we might deprecate this
         * method then.
         *
         * @param   charset    the JDK charset
         * @return      the MIME/IANA equivalent. If a mapping
         *              is not possible, the passed in charset itself
         *              is returned.
         */                     
        public static String mimeCharset(String charset);

====================================================================

(6) getDefaultJavaCharset()
============================

This method returns the default charset for the platform's locale, as
a Java charset. This is a new static method to the MimeUtility class.

    /**
     * Get the default charset for this locale. <p>
     *
     * @return  the default charset of the platform's locale,
     *          as a Java charset. (NOT a MIME charset)
     */
    public static String getDefaultJavaCharset()

====================================================================

(7) Method to print out the nested Exceptions
=============================================

The MessagingException class currently allows nested exceptions. It
would be nice to have one single method to dump out all the 
nested exceptions' messages into System.out

Proposal
--------

Override the getMessage() method from the superclass (Throwable), to
append the messages from all nested Exceptions. This is similar to
java.rmi.RemoteException.

==================================================================

(8) New SearchTerms
====================

The current address related search terms - AddressTerm, FromTerm and
RecipientTerm are limited in that they operate on Address objects, not
Strings. These terms use the equals() method to compare the addresses -
which is not useful for the common case of substring comparisons.

Hence we introduce three new SearchTerms:

public AddressStringTerm extends StringTerm {
    /**
     * Constructor.
     * @param pattern   the address pattern to be compared
     */
    protected AddressStringTerm(String pattern);

    /**
     * Check whether the address pattern specified in the 
     * constructor is a substring of the string representation of 
     * the given Address object.
     *
     * @param   address the address to match against
     */
    protected boolean match(Address address);
}

public FromStringTerm extends AddressStringTerm {
    /**
     * Constructor.
     * @param   address the address to be compared.
     */
    public FromStringTerm(String string);

    /**
     * Check whether the address specified in the constructor is
     * a substring of the "From" attribute of this message.
     *
     * @param   msg the address comparison is applied to this Message
     */
     public boolean match(Message msg);
}

public RecipientStringTerm extends AddressStringTerm {

    /**
     * Constructor.
     *
     * @param type      the recipient type
     * @param address   the address to be compared.
     */
    public RecipientStringTerm(Message.RecipientType type, String address);

    /**
     * Return the type of recipient to match with.
     */
    public Message.RecipientType getRecipientType();

    /**
     * Check whether the address specified in the constructor is
     * a substring of the given Recipient attribute of this message.
     *
     * @param   msg the address comparison is applied to this Message
     */
     public boolean match(Message msg);
}

==================================================================

(9) InternetAddress.toString(Address[] addresses, int used)
===========================================================

As per RFC2047 (MIME), the length of a header field that contains
encoded-words is limited to 76 characters.

There are two methods in the InternetAddress class that generate
RFC822 style address strings:

 - The toString() method on InternetAddress, which generates
 the string for one InternetAddress object
 - The toString() static method, which generates a comma separated
 string for the given array of InternetAddress objects.

Both these methods currently do not honor the 76 character limit.
Actually, the former does to an extent, since the encodedWord
generator (i.e the MimeUtility.encodeWord() method) does break
encoded words into multiples, if they stretch beyond 76 characters.

Solution
--------

For the 1.1 release, we are planning to fix the the toString()
static method as follows:

Add a new static method 
        static String toString(Address[] address, int used)

This method takes an array of Address objects and an integer representing
the number of "used" character positions for the first line of this
field. The typical use of this method is when setting RFC822 headers,
like the "From" header. 'used' can be set to sizeof("From: ") in
this case.

When generating the string, this method starts a new line if the
addition of the next address.toString() causes the current line's 
line-length to go over 76.

Note that this algorithm does not work right if the length of a single
InternetAddress is itself more than 76 characters. Also, it does not
optimally break an address field, so that the maximum characters are
accommodated in a single line.

So, essentially, this is an initial attempt to solve this problem. We
will add more APIs in the next version to further refine this.
==================================================================

(10) Folder.getMode()
=====================

It is currently not possible to tell whether a folder is open READ_ONLY
or READ_WRITE without attempting to write it and catching the exception.

We propose to add a protected field to Folder to store the open mode and
a new method to Folder to return the open mode.  Because existing 
subclasses will not use this new field, we can't guarantee that the 
method will always return the correct value (although all Folder subclasses
in the JavaMail package will be updated to return the correct value).

    /**
     * The open mode (<code>Folder.READ_ONLY</code>,
     * <code>Folder.READ_WRITE</code>, or -1 if not known).
     */
    protected int mode = -1;

    /**
     * Return the open mode of this folder.  Returns
     * <code>Folder.READ_ONLY</code>, <code>Folder.READ_WRITE</code>,
     * or -1 if the open mode is not known (usually only because an older
     * <code>Folder</code> provider has not been updated to use this new
     * method).
     *
     * @exception       IllegalStateException if this folder is not opened
     * @return          the open mode of this folder
     */
    public int getMode() {
        if (!isOpen())
            throw new IllegalStateException("Folder not open");
        return mode;
    }

====================================================================

(11) Folder.getURLName()
========================

The URLName support in the JavaMail 1.0 API's is incomplete and
inadequately specified.  While you can get a Folder from a Session
given a URLName for the folder, you can't find out the URLName
for a given Folder object.  We propose adding the following method
to Folder:

    /**
     * Return a URLName representing this folder.  The returned URLName
     * does <em>not</em> include the password used to access the store.
     *
     * @return  the URLName representing this folder
     * @see     URLName
     */
    public URLName getURLName() throws MessagingException

Previously it was not specified whether the URLName returned from
the Store.getURLName method would include the password field or
not, but sometimes it did.  We propose to tighen the specification
and fix the implementation so that the password field is not returned:

    /**
     * Return a URLName representing this store.  The returned URLName
     * does <em>not</em> include the password field.  <p>
     *
     * Subclasses should only override this method if their
     * URLName does not follow the standard format.
     *
     * @return  the URLName representing this store
     * @see     URLName
     */
    public URLName getURLName()

Similarly for Transport.

Previously it was unspecified how the Store and Transport connect
methods interacted with the url field.  In some cases it would be
updated and in other cases it would not.  We propose to tighen the
specification as follows:

    /**
     * Connect to the specified address. This method provides a simple
     * authentication scheme that requires a username and password. <p>
     *
     * If the connection is successful, an "open" ConnectionEvent is
     * delivered to any ConnectionListeners on this Store. <p>
     *
     * It is an error to connect to an already connected Store. <p>
     *
     * The implementation in the Store class will collect defaults
     * for the host, user, and password from the session, prompting the
     * user if necessary, and will then call the protocolConnect method,
     * which the subclass must override.  The subclass should also
     * implement the <code>getURLName</code> method, or use the 
     * implementation in this class. <p>
     *
     * On a successful connection, the <code>setURLName</code> method is
     * called with a URLName that includes the information used to make
     * the connection, including the password. <p>
     *
     * If the password passed in is null and this is the first successful
     * connection to this store, the user name and the password
     * collected from the user will be saved as defaults for subsequent
     * connection attempts to this same store.  If the password passed
     * in is not null, it is not saved, on the assumption that the 
     * application is managing passwords explicitly.
     *
     * @param host      the host to connect to
     * @param user      the user name
     * @param password  this user's password
     * @exception AuthenticationFailedException for authentication failures
     * @exception MessagingException            for other failures
     * @exception IllegalStateException if the store is already connected
     * @see javax.mail.event.ConnectionEvent
     */
    public void connect(String host, String user, String password)
                        throws MessagingException

And add this method to Store and Transport:

    /**
     * Set the URLName representing this store.
     * Normally used to update the <code>url</code> field
     * after a store has successfully connected. <p>
     *
     * Subclasses should only override this method if their
     * URLName does not follow the standard format. <p>
     *
     * The implementation in the Store class simply sets the
     * <code>url</code> field.
     *
     * @see URLName
     */
    protected void setURLName(URLName url)

And finally, to simplify the implementation of Store and Transport,
and make the common design patterns between them more clear, we're
considering introducing a new Service class as a superclass of
Store and Transport, and moving all common methods (the various
connnect methods, URLName methods, and some listener methods) to
the superclass.  Note that this is a binary compatible change.

=====================================================================

12) New Service class
======================

To emphasize the commonality in behavior between the Store and
Transport classes, and to simplify maintenance of these classes, we
propose moving many of the common methods to a new superclass called
javax.mail.Service.  Store and Transport would then extend Service.
These existing methods currently have identical implementations in the
Store and Transport classes so moving them to a common superclass will
not change the behavior of either Store or Transport.

The Service class will contain all the methods and fields having to do
with connecting, connection listeners, and naming via URLNames.  The
Store class retains the methods for getting Folders and managing Store
and Folder listeners.  The Transport class retains the methods for
sending messages and managing Transport listeners.

Note that this is a binary compatible change both for existing users of
the Store and Transport classes, as well as for existing subclasses of
these classes.

======================================================================