decode-from-uri – inverse for fn:encode-for-uri#1 recreates original uri from an encoded string.

decode-from-uri.xq

declare namespace functx = "http://www.functx.com";

(: copied from functx :)
declare function functx:replace-multi
  ( $arg as xs:string? ,
    $changeFrom as xs:string* ,
    $changeTo as xs:string* ) as xs:string? {

   if (count($changeFrom) > 0)
   then functx:replace-multi(
          replace($arg, $changeFrom[1], ($changeTo[1],'')[1]),
          tail($changeFrom),
          tail($changeTo)
        )
   else $arg
 } ;


(:~
 : decode-from-uri
 : the inverse to fn:encode-for-uri#1
 : 
 : @param  $input string
 : @return 
 :)
declare function local:decode-from-uri(
  $input as xs:string
) as xs:string? {
  (: converts string to character sequence :)
  let $chars :=
    function (
      $arg as xs:string
    ) as xs:string* {
      for $ch in string-to-codepoints($arg)
      return codepoints-to-string($ch)
    }
  (: all characters to be encoded in URL -- percent is last :)
  let $str :=  ("'
" || ' ";,/?:@&=+$[](){}%') ! $chars(.)
  (: encoded characters :)
  let $str-enc-seq := $str ! fn:encode-for-uri(.)
  (: chars in regexp with special meanings :)
  let $regexp-escapes := '.\?*|^$[]' ! $chars(.) (: +{}() :)
  let $str-esc := $str ! (
    if (. = $regexp-escapes)
    then '\\' || .
    else .
  )
  return
    functx:replace-multi($input, $str-enc-seq, $str-esc)
};

fn:encode-for-uri("http://basex.org/")
! (., local:decode-from-uri(.))

(:
outputs:

http%3A%2F%2Fbasex.org%2F
http://basex.org/

:)