xpcom/io/nsIStreamBufferAccess.idl

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #include "nsISupports.idl"
   7
   8 /**
   9  * An interface for access to a buffering stream implementation's underlying
  10  * memory buffer.
  11  *
  12  * Stream implementations that QueryInterface to nsIStreamBufferAccess must
  13  * ensure that all buffers are aligned on the most restrictive type size for
  14  * the current architecture (e.g., sizeof(double) for RISCy CPUs).  malloc(3)
  15  * satisfies this requirement.
  16  */
  17 [scriptable, builtinclass, uuid(ac923b72-ac87-4892-ac7a-ca385d429435)]
  18 interface nsIStreamBufferAccess : nsISupports
  19 {
  20     /**
  21      * Get access to a contiguous, aligned run of bytes in the stream's buffer.
  22      * Exactly one successful getBuffer call must occur before a putBuffer call
  23      * taking the non-null pointer returned by the successful getBuffer.
  24      *
  25      * The run of bytes are the next bytes (modulo alignment padding) to read
  26      * for an input stream, and the next bytes (modulo alignment padding) to
  27      * store before (eventually) writing buffered data to an output stream.
  28      * There can be space beyond this run of bytes in the buffer for further
  29      * accesses before the fill or flush point is reached.
  30      *
  31      * @param aLength
  32      *    Count of contiguous bytes requested at the address A that satisfies
  33      *    (A & aAlignMask) == 0 in the buffer, starting from the current stream
  34      *    position, mapped to a buffer address B.  The stream implementation
  35      *    must pad from B to A by skipping bytes (if input stream) or storing
  36      *    zero bytes (if output stream).
  37      *
  38      * @param aAlignMask
  39      *    Bit-mask computed by subtracting 1 from the power-of-two alignment
  40      *    modulus (e.g., 3 or sizeof(uint32_t)-1 for uint32_t alignment).
  41      *
  42      * @return
  43      *    The aligned pointer to aLength bytes in the buffer, or null if the
  44      *    buffer has no room for aLength bytes starting at the next address A
  45      *    after the current position that satisfies (A & aAlignMask) == 0.
  46      */
  47     [notxpcom,noscript] charPtr getBuffer(in uint32_t aLength, in uint32_t aAlignMask);
  48
  49     /**
  50      * Relinquish access to the stream's buffer, filling if at end of an input
  51      * buffer, flushing if completing an output buffer.  After a getBuffer call
  52      * that returns non-null, putBuffer must be called.
  53      *
  54      * @param aBuffer
  55      *    A non-null pointer returned by getBuffer on the same stream buffer
  56      *    access object.
  57      *
  58      * @param aLength
  59      *    The same count of contiguous bytes passed to the getBuffer call that
  60      *    returned aBuffer.
  61      */
  62     [notxpcom,noscript] void putBuffer(in charPtr aBuffer, in uint32_t aLength);
  63
  64     /**
  65      * Disable and enable buffering on the stream implementing this interface.
  66      * DisableBuffering flushes an output stream's buffer, and invalidates an
  67      * input stream's buffer.
  68      */
  69     void disableBuffering();
  70     void enableBuffering();
  71
  72     /**
  73      * The underlying, unbuffered input or output stream.
  74      */
  75     readonly attribute nsISupports unbufferedStream;
  76 };
  77
  78 %{C++
  79
  80 /**
  81  * These macros get and put a buffer given either an sba parameter that may
  82  * point to an object implementing nsIStreamBufferAccess, nsIObjectInputStream,
  83  * or nsIObjectOutputStream.
  84  */
  85 #define NS_GET_BUFFER(sba,n,a)  ((sba)->GetBuffer(n, a))
  86 #define NS_PUT_BUFFER(sba,p,n)  ((sba)->PutBuffer(p, n))
  87
  88 %}