Check for the existence of a file: URL that uses URLEncoding in Tcl 8.5.9

What is the simplest way to check for the existence of a file specified by a file: URL that uses URLEncoding in Tcl 8.5.9?

::http::geturl says it doesn't support file URLs.

file exists requires URLDecoding. There doesn't seem to be a builtin proc for URLDecoding. Have I missed it?

Are there any other builtin ways to do this? Do newer versions of Tcl provide more support for this?

If no builtin way, is there a recommended library for this? Either for directly handling file: URLs, or for URLDecoding?

In my projects, I tend to use a combination of a URI/URL processor (uri::split) plus a URL decoder (urlDecode) for postprocessing:

Step 1: URL processing

% package req uri
1.2.7
% set parsedURL [::uri::split file:///path/to/a%20file]
path /path/to/a%20file scheme file

Step 2: URL (percent-) decoding

Source the following:

proc urlDecode {str} {
    set specialMap {"[" "%5B" "]" "%5D"}
    set seqRE {%([0-9a-fA-F]{2})}
    set replacement {[format "%c" [scan "\1" "%2x"]]}
    set modStr [regsub -all $seqRE [string map $specialMap $str] $replacement]
    return [encoding convertfrom utf-8 [subst -nobackslash -novariable $modStr]]
}

Then:

% set fp [urlDecode [dict get $parsedURL path]]
/path/to/a file
% file exists $fp
% 0

Depending on the portability and robustness aimed at, you might want to use file normalize & friends.