Data commit

Task/URL-decoding/Common-Lisp/url-decoding.lisp

@@ -0,0 +1,23 @@
+(defun decode (string &key start)
+  (assert (char= (char string start) #\%))
+  (if (>= (length string) (+ start 3))
+      (multiple-value-bind (code pos)
+          (parse-integer string :start (1+ start) :end (+ start 3) :radix 16 :junk-allowed t)
+        (if (= pos (+ start 3))
+            (values (code-char code) pos)
+            (values #\% (1+ start))))
+      (values #\% (1+ start))))
+
+(defun url-decode (url)
+  (loop with start = 0
+        for pos = (position #\% url :start start)
+        collect (subseq url start pos) into chunks
+        when pos
+          collect (multiple-value-bind (decoded next) (decode url :start pos)
+                    (setf start next)
+                    (string decoded))
+            into chunks
+        while pos
+        finally (return (apply #'concatenate 'string chunks))))
+
+(url-decode "http%3A%2F%2Ffoo%20bar%2F")