/* -*- 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 "nsIThreadRetargetableStreamListener.idl"

interface nsIChannel;
interface nsIInputStream;

/**
 * nsIStreamConverter provides an interface to implement when you have code
 * that converts data from one type to another.
 *
 * Suppose you had code that converted plain text into HTML. You could implement
 * this interface to allow everyone else to use your conversion logic using a
 * standard api.
 * <p>
 * <b>STREAM CONVERTER USERS</b>
 *
 * There are currently two ways to use a stream converter:
 * <ol>
 * <li> <b>SYNCHRONOUS</b> Stream to Stream
 *    You can supply the service with a stream of type X
 *    and it will convert it to your desired output type and return
 *    a converted (blocking) stream to you.</li>
 *
 * <li> <b>ASYNCHRONOUS</b> nsIStreamListener to nsIStreamListener
 *    You can supply data directly to the converter by calling it's
 *    nsIStreamListener::OnDataAvailable() method. It will then
 *    convert that data from type X to your desired output type and
 *    return converted data to you via the nsIStreamListener you passed
 *    in by calling its OnDataAvailable() method.</li>
 * </ol>
 * <p>
 *
 * <b>STREAM CONVERTER SUPPLIERS</b>
 *
 * Registering a stream converter:
 * Stream converter registration is a two step process. First of all the stream
 * converter implementation must register itself with the component manager using
 * a contractid in the format below. Second, the stream converter must add the contractid
 * to the registry.
 *
 * Stream converter contractid format (the stream converter root key is defined in this
 * file):
 *
 * <pre>@mozilla.org/streamconv;1?from=FROM_MIME_TYPE&to=TO_MIME_TYPE</pre>
 *
 * @author Jud Valeski
 * @see nsIStreamConverterService
 */

[scriptable, uuid(0b6e2c69-5cf5-48b0-9dfd-c95950e2cc7b)]
interface nsIStreamConverter : nsIThreadRetargetableStreamListener {

    /**
     * <b>SYNCRONOUS 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 aCtxt         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 converter 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 aCtxt);

    /**
     * <b>ASYNCRONOUS VERSION</b>
     * Converts data arriving via the converter's nsIStreamListener::OnDataAvailable()
     * method from one type to another, pushing the converted data out to the caller
     * via aListener::OnDataAvailable().
     *
     * 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 who receives the converted data.
     * @param aCtxt         Either an opaque context, or a converter specific context
     *                      (implementation specific).
     */
    void asyncConvertData(in string aFromType,
                          in string aToType,
                          in nsIStreamListener aListener,
                          in nsISupports aCtxt);

    /**
     * This is called after the request has installed the stream converter as its listener
     * giving the stream converter the option to request retargetting of onDataAvailable.
     */
    void maybeRetarget(in nsIRequest request);

    /**
     * Returns the content type that the stream listener passed to asyncConvertData will
     * see on the channel if the conversion is being done from aFromType to * /*.
     *
     * @param aFromType     The type of the content prior to conversion.
     * @param aChannel      The channel that we'd like to convert. May be null.
     *
     * @throws if the converter does not support conversion to * /* or if it doesn't know
     *         the type in advance.
     */
    ACString getConvertedType(in ACString aFromType, in nsIChannel aChannel);
};

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