/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsISupports.idl"

interface nsIInputStream;
interface nsIStreamListener;

%{C++
#define NS_ISTREAMCONVERTER_KEY         "@mozilla.org/streamconv;1"
%}

/**
 * The nsIStreamConverterService is a higher level stream converter factory
 * responsible for locating and creating stream converters
 * (nsIStreamConverter).
 *
 * This service retrieves an interface that can convert data from a particular
 * MIME type, to a particular MIME type. It is responsible for any intermediary
 * conversion required in order to get from X to Z, assuming direct conversion
 * is not possible.
 *
 * @author Jud Valeski
 * @see nsIStreamConverter
 */
[scriptable, uuid(f2b1ab53-f0bd-4adb-9365-e59b1701a258)]
interface nsIStreamConverterService : nsISupports {
    /**
     * Tests whether conversion between the two specified types is possible.
     * This is cheaper than calling convert()/asyncConvertData(); it is not
     * necessary to call this function before calling one of those, though.
     */
    boolean canConvert(in string aFromType, in string aToType);

    /**
     * <b>SYNCHRONOUS VERSION</b>
     * Converts a stream of one type, to a stream of another type.
     *
     * Use this method when you have a stream you want to convert.
     *
     * @param aFromStream   The stream representing the original/raw data.
     * @param aFromType     The MIME type of aFromStream.
     * @param aToType       The MIME type of the returned stream.
     * @param aContext      Either an opaque context, or a converter specific
     *                      context (implementation specific).
     * @return              The converted stream. NOTE: The returned stream
     *                      may not already be converted. An efficient stream
     *                      converter implementation will convert data on
     *                      demand rather than buffering the converted data
     *                      until it is used.
     */
    nsIInputStream convert(in nsIInputStream aFromStream,
                           in string aFromType,
                           in string aToType,
                           in nsISupports aContext);

    /**
     * <b>ASYNCHRONOUS VERSION</b>
     * Retrieves a nsIStreamListener that receives the original/raw data via its
     * nsIStreamListener::OnDataAvailable() callback, then converts and pushes 
     * the data to aListener.
     *
     * Use this method when you want to proxy (and convert) nsIStreamListener
     * callbacks asynchronously.
     *
     * @param aFromType     The MIME type of the original/raw data.
     * @param aToType       The MIME type of the converted data.
     * @param aListener     The listener that receives the converted data.
     * @param aCtxt         Either an opaque context, or a converter specific
     *                      context (implementation specific).
     * @return              A nsIStreamListener that receives data via its
     *                      OnDataAvailable() method.
     */
    nsIStreamListener asyncConvertData(in string aFromType, 
                                       in string aToType, 
                                       in nsIStreamListener aListener,
                                       in nsISupports aContext);
};
