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kotlinlang

Unforunately -- its *extremely painful* to fully and correctly follow the HTTP specs wrt the  'URL' on the initial line of the request  ('quoted' as its not really a URL anymore).  In fact there is some ambiguity like you mention with the %2F -- its 'application dependent' in some parts of the URL whether or not to encode/decode/escape etc and at what point in the parsing,  let alone what gets reported to the application layer in the server when they ask for "Request Path"
Double trouble when put into a query param (or as well as a path component) --
A common design pattern for a passthrough or redirect of sorts being either    (NO escaping shown -- )
goal:  pass-through "<http://host2/path>" to "<http://host/>" unmolested

<http://host/redirect?http://host2/path>

--
a more 'RESTful' but uglier being

<http://host/http://host2/path>

Or -- god help me now -- pass through pre-url-encoded paths into the above