Re: The security of deflate-compressed streams with uncompressed-length field

On Sun, Feb 5, 2017 at 11:10 AM, Cosmin Truta <[email protected]> wrote:
> On 5 February 2017 at 12:34, John Bowler
> <[email protected]> wrote:
>> [I]it is not
>> possible to write a streaming conversion of compressed PNG data unless
>> the output PNG chunk size can be calculated before the output chunk
>> header has to be written.
>
> I'm not "missing" anything. It _is_ possible to do it,

Eh?  PNG chunk header:

[length]
[chunk-type]

How, in a streaming implementation, do you write this *without*
knowing the value of "length".  (I know how to do it in a
non-streaming implementation; I worded the above sentence very
carefully.)

> and it has been
> done, by the means of dynamically-allocated arrays. It only looks
> complicated from a C programmer perspective,

I think you do not understand the meaning of the word "streaming" as
used traditionally in PNG discussions.  Streaming means *NOT*
buffering.  Buffering the whole chunk is not streaming, regardless of
how you obscure the buffering.

John Bowler

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