I would be satisfied when a returned 404 error code will be handled within a reasonable (configurable) time delay. As for redirection, there I would not mind if it is not included.
Restrictions like that are not a problem for me, because this is for building a pdf that accesses many internet located files. The check on existence is therefore especially meant for spotting missing or misnamed files.

Hans van der Meer

> On 16 May 2018, at 12:41, Henri Menke <henrimenke@gmail.com> wrote:
> 
> On 05/16/2018 09:31 PM, Hans van der Meer wrote:
>> I tried to determine the existence of a file on the internet. See the
>> following macro call:
>> 
>>         % Test if file exists.
>>         \edef\theurl{\linkprotocol://\urlbase\xmlatt{#1}{link}\thesuffix}
>>         \doiffileelse
>>         {\theurl}
>>         {\verbose{HVDM-PEV-TEST}{file exists: \theurl}}
>>         {\verbose{HVDM-PEV-TEST}{file does not exist: \theurl}}
>> 
>> It seems that \doiffileelse always results in true except for local
>> files where nonexistence is correctly handled.
>> 
>> For example the following url definitely does not exist but nevertheless
>> \doiffileelse reports its existence:
>> HVDM-PEV-TEST   > file exists:
>> http://hansvandermeer.myqnapcloud.com/archive/denhaag/hga-dtb-1869-6040.pdf
>> 
>> Is it possible that the \doiffile macros are extended for files on the
>> internet or a correponding set \doifurl is developed?
> 
> I'm not speaking for the devs here, but I don't think that this is going
> to be included.  It would require that all webpages send proper 404
> codes and timeout after reasonable delay.  Also how would you handle
> redirects?  Should the ConTeXt run be stalled because checking for a
> files existence on the web is caught in a redirect loop?
> 
>> 
>> Hans van der Meer
>> 
>> 
>> 
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