[cairo] Implementing cairo_read_func_t/cairo_write_func_t properly

[Bernhard Fischer]

On Friday 01 January 2016 12:14:03 Behdad Esfahbod wrote:
> On 16-01-01 09:32 AM, Bernhard Fischer wrote:
> > On Thursday 31 December 2015 09:54:39 Lawrence D'Oliveiro wrote:
> >> > On Wed, 30 Dec 2015 15:27:13 +0100, Bernhard Fischer wrote:
> >>> > > when I would return STATUS_READ_ERROR, then the calling function
> >>> > > cannot detect how many bytes then actually have been read except in
> >>> > > the case that I read 1 byte after the other.
> >> > 
> >> > Does it matter? In any case, the file is clearly corrupted and the
> >> > image decoding has failed.
> >> > 
> >> > At least, that is my conclusion...
> > 
> > Yes, it matters!
> > cairo_..._stream() are stream reading functions. This is that it does not
> > know in advance how many bytes are available in the file.
> > 
> > The read_func_t is called with a buffer of a programmer-chosen length
> > (from
> > within cairo_..._stream()), e.g. 10k. But if the file has just 9k,
> > obviously only 9k are read. Unfortunately, the programmer has no way to
> > find that out.
> I agree this could be designed better...



I know that this is now getting deep into fundamental design issues.

I'd suggest a new prototype for that purpose. See the following file line 
numbers 17 - 32. I experimentally implemented it into my jpeg stream reader 
function (optionally chosen by cpp macro):

https://github.com/rahra/cairo_jpg/blob/master/src/cairo_jpg.h


Bernhard