gecko-dev/xpcom/io/nsIStorageStream.idl

/* -*- Mode: C++; 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 "nsISupports.idl"
#include "nsrootidl.idl"

interface nsIMemory;
interface nsIInputStream;
interface nsIOutputStream;

/**
 * The nsIStorageStream interface maintains an internal data buffer that can be
 * filled using a single output stream.  One or more independent input streams
 * can be created to read the data from the buffer non-destructively.
 */

[scriptable, uuid(604ad9d0-753e-11d3-90ca-34278643278f)]
interface nsIStorageStream : nsISupports
{
    /**
     *
     * Initialize the stream, setting up the amount of space that will be
     * allocated for the stream's backing-store.
     *
     * @param segmentSize
     *        Size of each segment. Must be a power of two.
     * @param maxSize
     *        Maximum total size of this stream. length will always be less
     *        than or equal to this value. Passing UINT32_MAX is safe.
     * @param segmentAllocator
     *        Which allocator to use for the segments. May be null, in which
     *        case a default allocator will be used.
     */
    void init(in uint32_t segmentSize, in uint32_t maxSize, in nsIMemory segmentAllocator);

    /**
     * Get a reference to the one and only output stream for this instance.
     * The zero-based startPosition argument is used is used to set the initial
     * write cursor position.  The startPosition cannot be set larger than the
     * current buffer length.  Calling this method has the side-effect of
     * truncating the internal buffer to startPosition bytes.
     */
    nsIOutputStream getOutputStream(in int32_t startPosition);

    /**
     * Create a new input stream to read data (written by the singleton output
     * stream) from the internal buffer.  Multiple, independent input streams
     * can be created.
     */
    nsIInputStream newInputStream(in int32_t startPosition);

    /** 
     * The length attribute indicates the total number of bytes stored in the
     * nsIStorageStream internal buffer, regardless of any consumption by input
     * streams.  Assigning to the length field can be used to truncate the
     * buffer data, but can not be used when either the instance's output
     * stream is in use.
     *
     * @See #writeInProgress */
    attribute uint32_t length;

    /**
     * True, when output stream has not yet been Close'ed
     */
    readonly attribute boolean writeInProgress;
};

%{C++
// Factory method
nsresult
NS_NewStorageStream(uint32_t segmentSize, uint32_t maxSize, nsIStorageStream **result);
%}