Re: [Evolution-hackers] Loading really large E-mails on devices with not enough Vm

[Philip Van Hoof <spam pvanhoof be>]

On Sat, 2008-01-26 at 23:22 -0500, Jeffrey Stedfast wrote:
> Something like the attached patch might work, tho it is untested.

I had to change 

	else if (!CAMEL_IS_SEEKABLE_SUBSTREAM (stream))

into

	else if (!CAMEL_IS_SEEKABLE_STREAM (stream))

I don't know why you where testing for substream, as substream provides
no extra functionality that seems to be related here ...

> So my guess is that this will break the parser :(
> 
> It might break in the stream case as well, you'd have to follow the code
> paths a bit to know for sure. For instance, even if creating the
> seekable substream doesn't perform an underlying seek on the original
> stream, setting it in a data wrapper might call camel_stream_reset()
> which /might/ do an lseek() on the source fs stream.

The problem with the patch is that it makes each MIME part's data start
at the headers, in stead of at the actual content.

I tried determining the "start" right after the first call to
camel_mime_parser_step but that just resulted in start == end.


> Not an insurmountable problem to solve, but it does make things a little
> more difficult and possibly touchy.

> 
> 
> On Sat, 2008-01-26 at 22:48 -0500, Jeffrey Stedfast wrote:
> > On Sat, 2008-01-26 at 22:12 -0500, Jeffrey Stedfast wrote:
> > > On Sat, 2008-01-26 at 13:44 +0100, Philip Van Hoof wrote:
> > > > This is what happens if you try to open a truly large E-mail on a device
> > > > that has not as much memory available:
> > > > 
> > > > Is there something we can do about this? Can we change the MIME parsing
> > > > algorithm to be less memory demanding for example?
> > > > 
> > > > Note that GArray is not really very sparse with memory once you start
> > > > having a really large array. Perhaps we can in stead change this to a
> > > > normal pointer array of a fixed size (do we know the size before we
> > > > start parsing, so that we can allocate an exact size in stead, perhaps?)
> > > 
> > > eh, why would you change it to a GPtrArray? It doesn't hold pointers, it
> > > holds message part content.
> > > 
> > > Unfortunately we don't know the size ahead of time.
> > > 
> > > I suppose you could use a custom byte array allocator so that you can
> > > force it to grow by larger chunks or something, dunno.
> > >
> > >
> > > The way GMime handles this is by not loading content into RAM, but 
> > > that may be harder to do with Camel, especially in the mbox case.
> > 
> > er, I should probably explain this:
> > 
> > - writing the code should be relatively easy to do, but in the mbox
> > case, the mbox may end up getting expunged or rewritten for some other
> > reason which may cause problems, not sure how that would work.
> > 
> > I think in Maildir, as long as the fd remains open, the file won't
> > actually disappear after an unlink() until the fd gets closed, so that
> > might work out ok assuming you can spare the fd (which might be the
> > other problem with Evolution?).
> > 
> > Jeff
> > 
> > 
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-- 
Philip Van Hoof, freelance software developer
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gnome: pvanhoof at gnome dot org 
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