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/*
* $Id: CallFilter.java,v 1.1 2003-02-01 02:10:18 cbj Exp $
* Copyright (C) 1999-2001 David Brownell
*
* This file is part of GNU JAXP, a library.
*
* GNU JAXP 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 of the License, or
* (at your option) any later version.
*
* GNU JAXP 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 this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* As a special exception, if you link this library with other files to
* produce an executable, this library does not by itself cause the
* resulting executable to be covered by the GNU General Public License.
* This exception does not however invalidate any other reasons why the
* executable file might be covered by the GNU General Public License.
*/
package gnu.xml.pipeline;
import java.io.*;
import java.net.*;
import org.xml.sax.*;
import org.xml.sax.ext.*;
import org.xml.sax.helpers.XMLReaderFactory;
import gnu.xml.util.Resolver;
import gnu.xml.util.XMLWriter;
// $Id: CallFilter.java,v 1.1 2003-02-01 02:10:18 cbj Exp $
/**
* Input is sent as an XML request to given URI, and the output of this
* filter is the parsed response to that request.
* A connection is opened to the remote URI when the startDocument call is
* issued through this filter, and the request is finished when the
* endDocument call is issued. Events should be written quickly enough to
* prevent the remote HTTP server from aborting the connection due to
* inactivity; you may want to buffer text in an earlier pipeline stage.
* If your application requires validity checking of such
* outputs, have the output pipeline include a validation stage.
*
* <p>In effect, this makes a remote procedure call to the URI, with the
* request and response document syntax as chosen by the application.
* <em>Note that all the input events must be seen, and sent to the URI,
* before the first output event can be seen. </em> Clients are delayed
* at least by waiting for the server to respond, constraining concurrency.
* Services can thus be used to synchronize concurrent activities, and
* even to prioritize service among different clients.
*
* <p> You are advised to avoid restricting yourself to an "RPC" model
* for distributed computation. With a World Wide Web, network latencies
* and failures (e.g. non-availability)
* are significant; adopting a "procedure" model, rather than a workflow
* model where bulk requests are sent and worked on asynchronously, is not
* generally an optimal system-wide architecture. When the messages may
* need authentication, such as with an OpenPGP signature, or when server
* loads don't argue in favor of immediate responses, non-RPC models can
* be advantageous. (So-called "peer to peer" computing models are one
* additional type of model, though too often that term is applied to
* systems that still have a centralized control structure.)
*
* <p> <em>Be strict in what you send, liberal in what you accept,</em> as
* the Internet tradition goes. Strictly conformant data should never cause
* problems to its receiver; make your request pipeline be very strict, and
* don't compromise on that. Make your response pipeline strict as well,
* but be ready to tolerate specific mild, temporary, and well-documented
* variations from specific communications peers.
*
* @see XmlServlet
*
* @author David Brownell
* @version $Date: 2003-02-01 02:10:18 $
*/
final public class CallFilter implements EventConsumer
{
private Requestor req;
private EventConsumer next;
private URL target;
private URLConnection conn;
private ErrorHandler errHandler;
/**
* Initializes a call filter so that its inputs are sent to the
* specified URI, and its outputs are sent to the next consumer
* provided.
*
* @exception IOException if the URI isn't accepted as a URL
*/
// constructor used by PipelineFactory
public CallFilter (String uri, EventConsumer next)
throws IOException
{
this.next = next;
req = new Requestor ();
setCallTarget (uri);
}
/**
* Assigns the URI of the call target to be used.
* Does not affect calls currently being made.
*/
final public void setCallTarget (String uri)
throws IOException
{
target = new URL (uri);
}
/**
* Assigns the error handler to be used to present most fatal
* errors.
*/
public void setErrorHandler (ErrorHandler handler)
{
req.setErrorHandler (handler);
}
/**
* Returns the call target's URI.
*/
final public String getCallTarget ()
{
return target.toString ();
}
/** Returns the content handler currently in use. */
final public org.xml.sax.ContentHandler getContentHandler ()
{
return req;
}
/** Returns the DTD handler currently in use. */
final public DTDHandler getDTDHandler ()
{
return req;
}
/**
* Returns the declaration or lexical handler currently in
* use, or throws an exception for other properties.
*/
final public Object getProperty (String id)
throws SAXNotRecognizedException
{
if (EventFilter.DECL_HANDLER.equals (id))
return req;
if (EventFilter.LEXICAL_HANDLER.equals (id))
return req;
throw new SAXNotRecognizedException (id);
}
// JDK 1.1 seems to need it to be done this way, sigh
ErrorHandler getErrorHandler () { return errHandler; }
//
// Takes input and echoes to server as POST input.
// Then sends the POST reply to the next pipeline element.
//
final class Requestor extends XMLWriter
{
Requestor ()
{
super ((Writer)null);
}
public synchronized void startDocument () throws SAXException
{
// Connect to remote object and set up to send it XML text
try {
if (conn != null)
throw new IllegalStateException ("call is being made");
conn = target.openConnection ();
conn.setDoOutput (true);
conn.setRequestProperty ("Content-Type",
"application/xml;charset=UTF-8");
setWriter (new OutputStreamWriter (
conn.getOutputStream (),
"UTF8"), "UTF-8");
} catch (IOException e) {
fatal ("can't write (POST) to URI: " + target, e);
}
// NOW base class can safely write that text!
super.startDocument ();
}
public void endDocument () throws SAXException
{
//
// Finish writing the request (for HTTP, a POST);
// this closes the output stream.
//
super.endDocument ();
//
// Receive the response.
// Produce events for the next stage.
//
InputSource source;
XMLReader producer;
String encoding;
try {
source = new InputSource (conn.getInputStream ());
// FIXME if status is anything but success, report it!! It'd be good to
// save the request data just in case we need to deal with a forward.
encoding = Resolver.getEncoding (conn.getContentType ());
if (encoding != null)
source.setEncoding (encoding);
producer = XMLReaderFactory.createXMLReader ();
producer.setErrorHandler (getErrorHandler ());
EventFilter.bind (producer, next);
producer.parse (source);
conn = null;
} catch (IOException e) {
fatal ("I/O Exception reading response, " + e.getMessage (), e);
}
}
}
}
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