gecko-dev/xpcom/io/nsIAsyncOutputStream.idl

/* 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 "nsIOutputStream.idl"

interface nsIOutputStreamCallback;
interface nsIEventTarget;

/**
 * If an output stream is non-blocking, it may return NS_BASE_STREAM_WOULD_BLOCK
 * when written to.  The caller must then wait for the stream to become
 * writable.  If the stream implements nsIAsyncOutputStream, then the caller can
 * use this interface to request an asynchronous notification when the stream
 * becomes writable or closed (via the AsyncWait method).
 *
 * While this interface is almost exclusively used with non-blocking streams, it
 * is not necessary that nsIOutputStream::isNonBlocking return true.  Nor is it
 * necessary that a non-blocking nsIOutputStream implementation also implement
 * nsIAsyncOutputStream.
 */
[scriptable, uuid(beb632d3-d77a-4e90-9134-f9ece69e8200)]
interface nsIAsyncOutputStream : nsIOutputStream
{
    /**
     * This method closes the stream and sets its internal status.  If the 
     * stream is already closed, then this method is ignored.  Once the stream
     * is closed, the stream's status cannot be changed.  Any successful status
     * code passed to this method is treated as NS_BASE_STREAM_CLOSED, which
     * is equivalent to nsIInputStream::close. 
     *
     * NOTE: this method exists in part to support pipes, which have both an 
     * input end and an output end.  If the output end of a pipe is closed, then
     * reads from the input end of the pipe will fail.  The error code returned 
     * when an attempt is made to read from a "closed" pipe corresponds to the
     * status code passed in when the output end of the pipe is closed, which
     * greatly simplifies working with pipes in some cases.
     *
     * @param aStatus
     *        The error that will be reported if this stream is accessed after
     *        it has been closed.
     */
    void closeWithStatus(in nsresult reason);

    /**
     * Asynchronously wait for the stream to be writable or closed.  The
     * notification is one-shot, meaning that each asyncWait call will result
     * in exactly one notification callback.  After the OnOutputStreamReady event
     * is dispatched, the stream releases its reference to the 
     * nsIOutputStreamCallback object.  It is safe to call asyncWait again from the
     * notification handler.
     *
     * This method may be called at any time (even if write has not been called).
     * In other words, this method may be called when the stream already has
     * room for more data.  It may also be called when the stream is closed.  If
     * the stream is already writable or closed when AsyncWait is called, then the
     * OnOutputStreamReady event will be dispatched immediately.  Otherwise, the
     * event will be dispatched when the stream becomes writable or closed.
     * 
     * @param aCallback
     *        This object is notified when the stream becomes ready.  This
     *        parameter may be null to clear an existing callback.
     * @param aFlags
     *        This parameter specifies optional flags passed in to configure
     *        the behavior of this method.  Pass zero to specify no flags.
     * @param aRequestedCount
     *        Wait until at least this many bytes can be written.  This is only
     *        a suggestion to the underlying stream; it may be ignored.  The
     *        caller may pass zero to indicate no preference.
     * @param aEventTarget
     *        Specify NULL to receive notification on ANY thread (possibly even
     *        recursively on the calling thread -- i.e., synchronously), or
     *        specify that the notification be delivered to a specific event
     *        target.
     */
    void asyncWait(in nsIOutputStreamCallback aCallback,
                   in unsigned long aFlags,
                   in unsigned long aRequestedCount,
                   in nsIEventTarget aEventTarget);

    /**
     * If passed to asyncWait, this flag overrides the default behavior,
     * causing the OnOutputStreamReady notification to be suppressed until the
     * stream becomes closed (either as a result of closeWithStatus/close being
     * called on the stream or possibly due to some error in the underlying
     * stream).
     */
    const unsigned long WAIT_CLOSURE_ONLY = (1<<0);
};

/**
 * This is a companion interface for nsIAsyncOutputStream::asyncWait.
 */
[scriptable, uuid(40dbcdff-9053-42c5-a57c-3ec910d0f148)]
interface nsIOutputStreamCallback : nsISupports
{
    /**
     * Called to indicate that the stream is either writable or closed.
     *
     * @param aStream
     *        The stream whose asyncWait method was called.
     */
    void onOutputStreamReady(in nsIAsyncOutputStream aStream);
};