*work around scsh bug (?) in definition of charset UNRESERVED

*new procs for encoding URIs:
-general proc ESCAPE taking an RegExp representing forbidden chars as argument
-specialized procs ESCAPE-SEGMENT, ESCAPE-QUERY
*new helper proc ASCII->ESCAPED
*use ESCAPE-SEGMENT and ESCAPE-URI in HTTP-URL->URI-STRING

scheme/lib/url.scm

@@ -50,7 +50,7 @@
 
 (define mark (rx ( "-_.!~*'()")))
 
-(define unreserved (rx (| ,alphanum ,mark)))
+(define unreserved (rx (~ (~ (| ,alphanum ,mark)))))
 
 (define reserved (rx ( ";/?:@&=+$,")))
 
@@ -238,18 +238,17 @@
 	(path-string 
 	 (fold-right
 	  (lambda (segment res)
-	    (string-append "/" (escape-uri segment) res))
+	    (string-append "/" (escape-segment segment) res))
 	  ""
 	  path))
 
 	(query (http-url-query http-url))
 	(query-string (if query
-			(string-append "?" (escape-uri query))
+			(string-append "?" (escape-query query))
 			"")))
 
     (string-append scheme-and-host-string port-string path-string query-string)))
 
-;;TODO: separate procedures for encoding path and query
 
 
 
@@ -262,7 +261,7 @@
 ;;; represents to a char.
 
 ;;; Caution:
-;;; a URI must be separated into its components (i.e. parsed by
+;;; a URI must be separated into its components (e.g. parsed by
 ;;; PARSE-URI) before the escaped characters within those components
 ;;; can be safely decoded. Don't use UNESCAPE on an unparsed URI.
 
@@ -297,3 +296,57 @@
 	    10))))
 
 
+;;; encode URIs:
+;;; replace characters which are reserved or excluded by their escaped representation.
+
+;;; Caution:  
+;;; Each component of a URI may have its own set of characters that are reserved,
+;;; -> differentiate between components.
+
+;;; Caution: 
+;;; don't encode an already encoded string; #\% chars would be escaped again.
+
+;;; not allowed within component 'segment' in 'abs_path'
+(define segment-reserved-and-excluded (rx (~ ,unreserved ,pchar-charset (";"))))
+
+;;; not allowed within component 'query' 
+(define query-reserved-and-excluded (rx (~ ,unreserved ,reserved )))
+
+;;; encode 'abs_path' portion of a URI:
+;;; use SPLIT-PATH to split abs_path into its segments,
+;;; then apply UNESCAPE-SEGMENT to the segments. 
+(define (escape-segment segment)
+  (escape segment segment-reserved-and-excluded))
+
+;;; encode 'query' portion of a URI
+(define (escape-query query)
+  (escape query query-reserved-and-excluded))
+
+(define (escape s regexp)
+  (regexp-fold 
+   regexp
+   (lambda (start-search match res)
+     (let* ((start-match (match:start match))
+	   (forbidden-char (string-ref s start-match)))
+       (string-append
+	res
+	(substring s start-search start-match)
+	(ascii->escaped (char->ascii forbidden-char)))))
+   ""
+   s
+   (lambda (start-search res)
+     (string-append res (substring s start-search (string-length s))))))
+
+(define (ascii->escaped dec-int)
+  (let* ((hex-int-high (bitwise-and (arithmetic-shift dec-int -4) #xF))
+	(hex-int-low (bitwise-and dec-int #xF)))
+    (string-append 
+     "%" (int->hexstring hex-int-high) (int->hexstring hex-int-low))))
+
+(define int->hexstring
+  (let ((table '#("0" "1" "2" "3" "4" "5" "6" "7" "8" "9"
+		  "A" "B" "C" "D" "E" "F")))
+    (lambda (i) (vector-ref table i))))
+
+   
+