Hi Craig,
This functionallity is indeed missing and I would really enjoy to have this in
PoDoFo! I hope you can use the current filter streams interface internally.
regards,
Dom
Am 23.10.2008 09:25 schrieb Craig Ringer:
> Hi
>
> Before I start work on this, I just want to check to make sure I'm not
> missing anything obvious. There isn't currently any interface exposed to
> permit users to progressively read a filtered PDF stream or do random
> I/O in an unfiltered stream, is there?
>
> I'd like to provide a PdfInputStream-like interface for PdfStream, so
> that users can read huge streams in small segments. For streams that
> don't have any filters applied (be they file or memory based) it could
> also do random I/O.
>
> This is different from GetFilteredCopy(PdfOutputStream*), in that
> there's no need for the caller to implement a custom PdfOutputStream to
> do whatever work they need to do, and for file streams it doesn't have
> to allocate a temporary copy of the whole stream in RAM in order to
> filter it. It'd also be an easier interface to use for most work,
> especially where you might not even want to decode all the stream.
>
> The main use I have for this is in PoDoFoBrowser, where we really
> shouldn't have to allocate a whole stream in memory and possibly
> allocate another decompressed copy of it if it's flate filtered or
> similar. The same principle will apply to other programs processing big
> PDF streams (say, huge images) though.
>
> I'd like to preserve the existing interfaces in PdfStream, but rewrite
> GetCopy and GetFilteredCopy to use the underlying progressive reading
> interfaces. PdfStream would no longer make any assumption that a stream
> has an "internal buffer" that may be accessed; instead, it'll request
> data from the stream in small chunks and feed those to the output or to
> any required filter. The chunk size can be big enough that the (minimal)
> overhead of the function calls etc for the progressive reading should be
> basically undetectable, and concrete stream implementations can override
> the methods if they have a simpler way to do it anyway.
>
> Once I've got the PdfStream interface adjustments done it should be
> possible to do something like extract and write a 100MB image from a PDF
> without using more than a few hundred kb of RAM.
>
> Sound good? If so, the next thing I'll want to do is write a variant on
> PdfFileStream that uses an external temp file instead of a view into the
> original PDF, so it's possible to edit a stream without having to load
> the whole thing into RAM at once. Again, I'm sure you can see uses
> outside the obvious ones in PoDoFoBrowser.
>
> --
> Craig Ringer
>
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