gecko-dev/xpcom/io/nsIInputStreamLength.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 "nsISupports.idl"

interface nsIEventTarget;
interface nsIInputStreamLengthCallback;

/**
 * Note: Instead of using these interfaces directly, consider to use
 * InputStreamLengthHelper class.
 */

[uuid(452d059f-9a9c-4434-8839-e10d1405647c)]
interface nsIInputStreamLength : nsISupports
{
  /**
   * Returns the total length of the stream if known. Otherwise it returns -1.
   * This is different than calling available() which returns the number of
   * bytes ready to be read from the stream.
   * -1 is a valid value for a stream that doesn't know its length. For
   * instance, a pipe stream could return such value.
   *
   * It could throw NS_BASE_STREAM_WOULD_BLOCK if the inputStream is
   * non-blocking. If this happens, you should use
   * nsIAsyncInputStreamLength::asyncLengthWait().
   *
   * If the stream has already been read (read()/readSegments()/close()/seek()
   * methods has been called), length() returns NS_ERROR_NOT_AVAILABLE.
   *
   * This is not an attribute because a stream can change its length. For
   * instance, if the stream is a file inputStream and the underlying OS file
   * changes, its length will change as well.
   */
  long long length();
};

[uuid(b63f9ecf-4668-44a3-93bd-72dbc65a6125)]
interface nsIAsyncInputStreamLength : nsISupports
{
  /**
   * If the stream is non-blocking, nsIInputStreamLength::length() can return
   * NS_BASE_STREAM_WOULD_BLOCK. The caller must then wait for the stream to
   * know its length.
   *
   * If the stream implements nsIAsyncInputStreamLength, then the caller can
   * use this interface to request an asynchronous notification when the
   * stream's length becomes known (via the AsyncLengthWait method).
   * If the length is already known, the aCallback will be still called
   * asynchronously.
   *
   * If the stream has already been read (read()/readSegments()/close()/seek()
   * methods has been called), length() returns NS_ERROR_NOT_AVAILABLE.
   *
   * @param aCallback
   *        This object is notified when the length becomes known. This
   *        parameter may be null to clear an existing callback.
   * @param aEventTarget
   *        Specify that the notification must be delivered to a specific event
   *        target.
   */
  void asyncLengthWait(in nsIInputStreamLengthCallback aCallback,
                      in nsIEventTarget aEventTarget);
};

/**
 * This is a companion interface for
 * nsIAsyncInputStreamLength::asyncLengthWait.
 */
[function, uuid(9c0c13b9-1b33-445d-8adb-a8a7866a6c06)]
interface nsIInputStreamLengthCallback : nsISupports
{
  /**
   * Called to inform what the total length of the stream is.
   *
   * @param aStream
   *        The stream whose asyncLengthWait method was called.
   * @param aLength
   *        The stream's length. It can be -1 if the stream doesn't know its
   *        length. For instance, this can happen for a pipe inputStream.
   */
  void onInputStreamLengthReady(in nsIAsyncInputStreamLength aStream,
                                in long long aLength);
};