[Ur] Mandatory nginx conf: merge_slashes off

[Adam Chlipala]

Reviewing a PR just now, I'm reminded that the logic I half-recalled to 
avoid empty serializations is only for strings.  Would it be worth 
changing [unit] serialization to avoid empty serializations there, too?

On 1/25/19 8:21 AM, Simon Van Casteren wrote:
> It doesn't happen often of course, since you rarely use unit in a page 
> or RPC function. How I ran into it was actually via the now fixed bug
> https://github.com/urweb/urweb/issues/117, I made some ADT's that got 
> around that bug by declaring all constructors to have at least one 
> parameter, unit if nothing else. That came back to bite me now...
>
> A page with this signature:
>
> val page: unit -> string -> transaction page
>
> Would be affected by the issue I described. This obviously won't 
> happen much outside of you making a mistake (for example because first 
> the function took just a unit, then you added the string parameter), 
> but because it doesn't happen often and it's actually nginx making the 
> "mistake", I still thought it could help someone out in the future!
>
> Simon
>
> On Fri, 25 Jan 2019 at 13:57, Adam Chlipala <adamc at csail.mit.edu 
> <mailto:adamc at csail.mit.edu>> wrote:
>
>     Thanks for sharing that wisdom!  Somehow I remember making a
>     special effort to encode empty strings with underscores, precisely
>     to avoid this problem (though it was appearing in Apache, if I
>     recall correctly).  Can you point us to an example where it
>     arises, in a URL that an Ur/Web app generates itself?
>
>     On 1/25/19 5:13 AM, Simon Van Casteren wrote:
>>     Hi,
>>
>>     I just ran into an awful problem combining urweb with nginx. By
>>     default, nginx by default merges double slashes in urls, eg:
>>     http://www.bla.com//users becomes http//www.bla.com/users
>>     <http://www.bla.com/users>. This can be a problem for UrWeb
>>     applications since a double slash is actually how urweb encodes
>>     the unit or () value.
>>
>>     The solution is to use the option: "merge_slashes off".
>>
>>     It's not a bug in either application so I didnt want me make an
>>     issue for it, but this could be useful info for other people
>>     running Ur/Web programs behind nginx...
>>
>>     Simon
>
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