[Marble-devel] [OpenSeaMap-develop] technical question about http return code for empty tiles

[Anders Lund]

On Tirsdag den 13. december 2011, Bernhard R. Fischer wrote:
> On Monday 12 December 2011 08:50:41 Anders Lund wrote:
> > Hi,
> > 
> > It appears that map.openseamap.org returns 203 when a tile is not
> > available. Is there a reason that 204 (request ok, no content) is not
> > used?
> > 
> > Reason I ask is that marble keeps a cache, and I need to find out how to
> > make sure that seamark tiles that were emptied (ie a light was moved out
> > of it) are expired from the cache.
> > 
> > It appears to me that a 204 would be a reason for that, while 203 is
> > questionable.
> > 
> > Anders
> 
> Is it the map.openseamap.org server or any tile server?
> Openseamap runs an Apache thus the return code probably is generated by it
> and not any other software.
> Do you have an URL?
> 
> Bernhard

I think it happens when there is on content that no tile is returned, the 
answer is code 203.

I base this on the fact that marble appears to display old tiles when 
openseamap is edited, eg seamarks are moved from one tile to another, so that 
a seamark might be shown in both the old and the new position.

To experience this problem, you need to load the openseamap theme in a 
location where something is going to change this way, and then again after 
that change has been rendered, press F5 to update tiles. Not easy to achieve, 
but I could maybe arrange a demonstration if I can find an appropriate spot.

To avoid that, marble needs to discard the cached tile image in those cases.

If my assumption is correct, I think 204 - no content - would be a better 
return code than 203, but I am no expert in this field. Alternatively, marble 
should discard cached tiles when 203 is returned (or there may be a better 
fix).

-- 
Anders