/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim:set ts=4 sw=4 sts=4 cin: */
/* 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 nsIChannel;
interface nsIAsyncVerifyRedirectCallback;

/**
 * Implement this interface to receive control over various channel events.
 * Channels will try to get this interface from a channel's
 * notificationCallbacks or, if not available there, from the loadGroup's
 * notificationCallbacks.
 *
 * These methods are called before onStartRequest.
 */
[scriptable, uuid(a430d870-df77-4502-9570-d46a8de33154)]
interface nsIChannelEventSink : nsISupports
{
    /**
     * This is a temporary redirect. New requests for this resource should
     * continue to use the URI of the old channel.
     *
     * The new URI may be identical to the old one.
     */
    const unsigned long REDIRECT_TEMPORARY = 1 << 0;

    /**
     * This is a permanent redirect. New requests for this resource should use
     * the URI of the new channel (This might be an HTTP 301 reponse).
     * If this flag is not set, this is a temporary redirect.
     *
     * The new URI may be identical to the old one.
     */
    const unsigned long REDIRECT_PERMANENT = 1 << 1;

    /**
     * This is an internal redirect, i.e. it was not initiated by the remote
     * server, but is specific to the channel implementation.
     *
     * The new URI may be identical to the old one.
     */
    const unsigned long REDIRECT_INTERNAL = 1 << 2;

    /**
     * Called when a redirect occurs. This may happen due to an HTTP 3xx status
     * code. The purpose of this method is to notify the sink that a redirect
     * is about to happen, but also to give the sink the right to veto the
     * redirect by throwing or passing a failure-code in the callback.
     *
     * Note that vetoing the redirect simply means that |newChannel| will not
     * be opened. It is important to understand that |oldChannel| will continue
     * loading as if it received a HTTP 200, which includes notifying observers
     * and possibly display or process content attached to the HTTP response.
     * If the sink wants to prevent this loading it must explicitly deal with
     * it, e.g. by calling |oldChannel->Cancel()|
     *
     * There is a certain freedom in implementing this method:
     *
     * If the return-value indicates success, a callback on |callback| is
     * required. This callback can be done from within asyncOnChannelRedirect
     * (effectively making the call synchronous) or at some point later
     * (making the call asynchronous). Repeat: A callback must be done
     * if this method returns successfully.
     *
     * If the return value indicates error (method throws an exception)
     * the redirect is vetoed and no callback must be done. Repeat: No
     * callback must be done if this method throws!
     *
     * @see nsIAsyncVerifyRedirectCallback::onRedirectVerifyCallback()
     *
     * @param oldChannel
     *        The channel that's being redirected.
     * @param newChannel
     *        The new channel. This channel is not opened yet.
     * @param flags
     *        Flags indicating the type of redirect. A bitmask consisting
     *        of flags from above.
     *        One of REDIRECT_TEMPORARY and REDIRECT_PERMANENT will always be
     *        set.
     * @param callback
     *        Object to inform about the async result of this method
     *
     * @throw <any> Throwing an exception will cause the redirect to be
     *        cancelled
     */
    void asyncOnChannelRedirect(in nsIChannel oldChannel, 
                                in nsIChannel newChannel,
                                in unsigned long flags,
                                in nsIAsyncVerifyRedirectCallback callback);
};
