[cairo] Implementing cairo_read_func_t/cairo_write_func_t properly

[Bernhard Fischer]

On Monday 04 January 2016 10:24:36 Bill Spitzak wrote:
> On Sun, Jan 3, 2016 at 11:50 PM, Bernhard Fischer <bf at abenteuerland.at>
> 
> wrote:
> > On Sunday 03 January 2016 14:29:57 Behdad Esfahbod wrote:
> > > On 16-01-02 09:34 PM, Bill Spitzak wrote:
> > > > On 01/02/2016 01:27 PM, Bernhard Fischer wrote:
> > > >> On Saturday 02 January 2016 13:01:39 Bill Spitzak wrote:
> > > >>> I think the api has to be changed to return number of bytes read,
> > 
> > and a
> > 
> > > >>> negative number for eof.
> > > >> 
> > > >> The return value should be the number of bytes read and on eof it is
> > > >> something between 0 and length. If it is called again at/after eof it
> > > >> returns 0 again. A negative value (-1) is only returned in case of
> > 
> > error
> > 
> > > >> (but not EOF). This is exactly like read(3) behaves.
> > > > 
> > > > Yes you are correct, I made a typo, I meant to say "error" where I
> > 
> > wrote
> > 
> > > > "eof". I fully agree with your description.
> > > 
> > > Given that we cannot change the signature now, I suggest we hack it up
> > > to
> > > interpret negative numbers returned from the callback to be interpreted
> > 
> > as a
> > 
> > > short read; the absolute value of the returned negative number is the
> > > number of bytes read.
> > > 
> > > Cairo itself won't need to be updated, but clients should be encouraged
> > 
> > to
> > 
> > > implement the new behaviour.
> > > 
> > > b
> > 
> > I agree, that is a backwards compatible solution.
> 
> I think you need to make negative number mean "it was this short". Ie if a
> request to read 10 bytes only reads 8, it returns -2.


That's exactly what Behdad said.