+
+(defun decode-uri-query-string (s)
+ "Decode a URI query string field"
+ (declare (simple-string s)
+ (optimize (speed 3) (safety 0) (space 0)))
+ (do* ((old-len (length s))
+ (new-len (- old-len (* 2 (the fixnum (count-string-char s #\%)))))
+ (new (make-string new-len))
+ (p-old 0)
+ (p-new 0 (1+ p-new)))
+ ((= p-new new-len) new)
+ (declare (simple-string new)
+ (fixnum p-old p-new old-len new-len))
+ (let ((c (schar s p-old)))
+ (when (char= c #\+)
+ (setq c #\space))
+ (case c
+ (#\%
+ (unless (>= old-len (+ p-old 3))
+ (error "#\% not followed by enough characters"))
+ (setf (schar new p-new)
+ (code-char
+ (parse-integer (subseq s (1+ p-old) (+ p-old 3))
+ :radix 16)))
+ (incf p-old 3))
+ (t
+ (setf (schar new p-new) c)
+ (incf p-old))))))