support timeout in Download

[ThomasBreuer]

The idea is to specify the maximum number of seconds to wait for a download, via the optional component maxTime in the optional second argument of Download.
The default value is given by the new user preference DownloadMaxTime of the utils package, and the default for that is zero, meaning that there is no timeout.

The methods stored in Download_Methods either use a given nonzero maxTime value or signal failure (the latter holds for the method from the IO package, which does not support timeouts).

(Up to now, I have not managed to test in which situations this timeout really helps. This is why this pull request is marked as draft.)

[codecov]

Codecov Report

❌ Patch coverage is 87.87879% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.40%. Comparing base (82b58c6) to head (086d7de).
⚠️ Report is 11 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/download.gi	84.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
+ Coverage   77.96%   83.40%   +5.43%     
==========================================
  Files          29       29              
  Lines        1829     1693     -136     
==========================================
- Hits         1426     1412      -14     
+ Misses        403      281     -122     

Files with missing lines	Coverage Δ
lib/download.gd	100.00% <100.00%> (ø)
lib/download.gi	82.71% <84.00%> (+0.83%)	⬆️

... and 3 files with indirect coverage changes

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[cdwensley]

Is this still "work in progress", or should I be doing something about it?

[ThomasBreuer]

@cdwensley

Is this still "work in progress", or should I be doing something about it?

I have to try again to reproduce the error situation, in order to see whether the timeout helps as expected.
At the moment, you need not do anything.

[fingolfin]

@ThomasBreuer have you considered using https://httpbun.com/delay/5 (replace "5" with any other amount of seconds) for tests, to emulate a server which accepts a connection but then is slow to respond?

It would be really good to get this merged and released so we can start using it, given that RWTH servers had another outage recently

[ThomasBreuer]

@fingolfin Thanks for the hint about https://httpbun.com.

The timeouts work as expected, except that old versions of wget ignore timeouts:

• With wget 1.20.3, the process waits until the delay time is over and then returns success.
• With wget 1.21.3, the process gives up after the prescribed time.

I am going to exclude wget when a timeout option is set, in the same way as IO's SingleHTTPRequest (which does not support timeouts) is excluded.

[fingolfin]

Looks good to me.

[fingolfin]

@cdwensley would be nice to have this in a release soon (perhaps even in time for the final GAP 4.15.0 release?). See also my PR #84 which makes it easier to produce releases.