nsIStreamBufferAccess in Firefox 2.0

 Disable and enable buffering on the stream implementing this interface.
 DisableBuffering flushes an output stream's buffer, and invalidates an
 input stream's buffer.

 Get access to a contiguous, aligned run of bytes in the stream's buffer.
 Exactly one successful getBuffer call must occur before a putBuffer call
 taking the non-null pointer returned by the successful getBuffer.

 The run of bytes are the next bytes (modulo alignment padding) to read
 for an input stream, and the next bytes (modulo alignment padding) to
 store before (eventually) writing buffered data to an output stream.
 There can be space beyond this run of bytes in the buffer for further
 accesses before the fill or flush point is reached.

 @param aLength
    Count of contiguous bytes requested at the address A that satisfies
    (A & aAlignMask) == 0 in the buffer, starting from the current stream
    position, mapped to a buffer address B.  The stream implementation
    must pad from B to A by skipping bytes (if input stream) or storing
    zero bytes (if output stream).

 @param aAlignMask
    Bit-mask computed by subtracting 1 from the power-of-two alignment
    modulus (e.g., 3 or sizeof(PRUint32)-1 for PRUint32 alignment).

 @return
    The aligned pointer to aLength bytes in the buffer, or null if the
    buffer has no room for aLength bytes starting at the next address A
    after the current position that satisfies (A & aAlignMask) == 0.

 Relinquish access to the stream's buffer, filling if at end of an input
 buffer, flushing if completing an output buffer.  After a getBuffer call
 that returns non-null, putBuffer must be called.

 @param aBuffer
    A non-null pointer returned by getBuffer on the same stream buffer
    access object.

 @param aLength
    The same count of contiguous bytes passed to the getBuffer call that
    returned aBuffer.