How to prevent a program from crashing when the "OSError: Too many open files" error occurs?

[cblake]

You're welcome. The next step from here would be either to reduce further (e.g. 
ditch the http stuff and just do a TCP server or maybe even just pipes with a 
program which is its own client&server) or else try from the other side doing 
the smallest program that might cause the issue, maybe not with `async`, though 
I expect you probably need async. Or you could just file a github issue from my 
last example. Personally, I think you tripped on a pretty bad bug here which 
deserves some attention. One of Nim's main selling points is to be "safer" than 
this.