[jira] Resolved: (DIRMINA-368) IoFilter.messageSent should have access to WriteRequest instead of the written message.

["Trustin Lee (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DIRMINA-368?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Trustin Lee resolved DIRMINA-368.
---------------------------------

    Resolution: Fixed

The change has been checked in.  DIRMINA-92 will be the first issue that utilizes this change.

> IoFilter.messageSent should have access to WriteRequest instead of the written message.
> ---------------------------------------------------------------------------------------
>
>                 Key: DIRMINA-368
>                 URL: https://issues.apache.org/jira/browse/DIRMINA-368
>             Project: MINA
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Trustin Lee
>         Assigned To: Trustin Lee
>             Fix For: 2.0.0-M1
>
>
> IoFilter.filterWrite() accepts WriteRequest as its parameter to allow an IoFilter implementation to alter the WriteRequest or create a new WriteRequest.  This is particularly useful when the filter transforms a received message.  Good examples of this scenario are ProtocolCodecFilter and SSLFilter.
> Because these examples are wrapping an outgoing message with an internal type, the filter implementor was able to get the original message by unwrapping in IoFilter.messageSent() like the following:
>     public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest req) {
>         nextFilter.filterWrite(session, new WriteRequest(new TransformedMessage(req.getMessage())));
>     }
>     public void messageSent(NextFilter nextFilter, IoSession session, Object message) {
>         if (message instanceof TransformedMessage) {
>             nextFilter.messageSent(session, ((TransformedMessage) message).getOriginalMessage());
>             return;
>         }
>         ......
>     }
> But, what if the transformation is not wrapping but unwrapping?  We can't perform the reverse-transformation like we did in the example above, because we don't know what the original message was in IoFilter.messageSent().
>     public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest req) {
>         nextFilter.filterWrite(session, new WriteRequest(
>                 ((OuterMessage) req.getMessage()).getInnerMessage()));  // Unwrap on write.
>     }
>     public void messageSent(NextFilter nextFilter, IoSession session, Object message) {
>         if (message instanceof InnerMessage) {
>             // TODO Transform the message back to OuterMessage.  But how?
>         }
>         ......
>     }
> To fix this problem, there should be at least one common type that any IoFilter implementation can understand, and that type has to be the parameter of IoFilter.messageSent().  A good candidate is WriteRequest, which is already exposed in the IoFilter interface.  With this change applied, the IoFilter implementation will look like the following:
>     public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest req) {
>         // Wrap on write.
>         nextFilter.filterWrite(session, new TransformedWriteRequest(request));
>     }
>     public void messageSent(NextFilter nextFilter, IoSession session, WriteRequest request) {
>         if (request instanceof TransformedWriteRequest) {
>             // Unwrap on messageSent.
>             nextFilter.messageSent(session, ((TransformedWriteRequest) request).getWriteRequest());
>             return;
>         }
>         ......
>     }
>     private static class TransformedWriteRequest extends WriteRequestWrapper {
>         private TransformedWriteRequest(WriteRequest req) {
>             super(req);
>         }
>         public Object getMessage() {
>             // Wrapping with TransformedWriteRequest is actually unwrapping the message.
>             // and unwrapping this write request is actually wrapping the message back.
>             return ((OuterMessage) super.getMessage()).getInnerMessage();
>         }
>     }

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