xpcom/io/nsIAsyncOutputStream.idl

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #include "nsIOutputStream.idl"
   6
   7 interface nsIOutputStreamCallback;
   8 interface nsIEventTarget;
   9
  10 /**
  11  * If an output stream is non-blocking, it may return NS_BASE_STREAM_WOULD_BLOCK
  12  * when written to.  The caller must then wait for the stream to become
  13  * writable.  If the stream implements nsIAsyncOutputStream, then the caller can
  14  * use this interface to request an asynchronous notification when the stream
  15  * becomes writable or closed (via the AsyncWait method).
  16  *
  17  * While this interface is almost exclusively used with non-blocking streams, it
  18  * is not necessary that nsIOutputStream::isNonBlocking return true.  Nor is it
  19  * necessary that a non-blocking nsIOutputStream implementation also implement
  20  * nsIAsyncOutputStream.
  21  */
  22 [scriptable, uuid(beb632d3-d77a-4e90-9134-f9ece69e8200)]
  23 interface nsIAsyncOutputStream : nsIOutputStream
  24 {
  25     /**
  26      * This method closes the stream and sets its internal status.  If the
  27      * stream is already closed, then this method is ignored.  Once the stream
  28      * is closed, the stream's status cannot be changed.  Any successful status
  29      * code passed to this method is treated as NS_BASE_STREAM_CLOSED, which
  30      * is equivalent to nsIInputStream::close.
  31      *
  32      * NOTE: this method exists in part to support pipes, which have both an
  33      * input end and an output end.  If the output end of a pipe is closed, then
  34      * reads from the input end of the pipe will fail.  The error code returned
  35      * when an attempt is made to read from a "closed" pipe corresponds to the
  36      * status code passed in when the output end of the pipe is closed, which
  37      * greatly simplifies working with pipes in some cases.
  38      *
  39      * @param aStatus
  40      *        The error that will be reported if this stream is accessed after
  41      *        it has been closed.
  42      */
  43     void closeWithStatus(in nsresult reason);
  44
  45     /**
  46      * Asynchronously wait for the stream to be writable or closed.  The
  47      * notification is one-shot, meaning that each asyncWait call will result
  48      * in exactly one notification callback.  After the OnOutputStreamReady event
  49      * is dispatched, the stream releases its reference to the
  50      * nsIOutputStreamCallback object.  It is safe to call asyncWait again from the
  51      * notification handler.
  52      *
  53      * This method may be called at any time (even if write has not been called).
  54      * In other words, this method may be called when the stream already has
  55      * room for more data.  It may also be called when the stream is closed.  If
  56      * the stream is already writable or closed when AsyncWait is called, then the
  57      * OnOutputStreamReady event will be dispatched immediately.  Otherwise, the
  58      * event will be dispatched when the stream becomes writable or closed.
  59      *
  60      * @param aCallback
  61      *        This object is notified when the stream becomes ready.  This
  62      *        parameter may be null to clear an existing callback.
  63      * @param aFlags
  64      *        This parameter specifies optional flags passed in to configure
  65      *        the behavior of this method.  Pass zero to specify no flags.
  66      * @param aRequestedCount
  67      *        Wait until at least this many bytes can be written.  This is only
  68      *        a suggestion to the underlying stream; it may be ignored.  The
  69      *        caller may pass zero to indicate no preference.
  70      * @param aEventTarget
  71      *        Specify NULL to receive notification on ANY thread (possibly even
  72      *        recursively on the calling thread -- i.e., synchronously), or
  73      *        specify that the notification be delivered to a specific event
  74      *        target.
  75      */
  76     void asyncWait(in nsIOutputStreamCallback aCallback,
  77                    in unsigned long aFlags,
  78                    in unsigned long aRequestedCount,
  79                    in nsIEventTarget aEventTarget);
  80
  81     /**
  82      * If passed to asyncWait, this flag overrides the default behavior,
  83      * causing the OnOutputStreamReady notification to be suppressed until the
  84      * stream becomes closed (either as a result of closeWithStatus/close being
  85      * called on the stream or possibly due to some error in the underlying
  86      * stream).
  87      */
  88     const unsigned long WAIT_CLOSURE_ONLY = (1<<0);
  89 };
  90
  91 /**
  92  * This is a companion interface for nsIAsyncOutputStream::asyncWait.
  93  */
  94 [scriptable, uuid(40dbcdff-9053-42c5-a57c-3ec910d0f148)]
  95 interface nsIOutputStreamCallback : nsISupports
  96 {
  97     /**
  98      * Called to indicate that the stream is either writable or closed.
  99      *
 100      * @param aStream
 101      *        The stream whose asyncWait method was called.
 102      */
 103     void onOutputStreamReady(in nsIAsyncOutputStream aStream);
 104 };