Implementing URL filtering.

* eval.c (eval_init): New intrinsic functions: url-encode, url-decode.

* filter.c (tourl_k, fromurl_k): New keyword variables.
(is_url_reserved, digit_value): New static functions.
(url_encode, url_decode): New functions.
(filter_init): Intialize new keyword variables and register
new :tourl and :fromurl filters.

* filter.h (tourl_k, fromurl_k, url_encode, url_decode): Declared.

* txr.1: Updated.

* txr.vim: Likewise.

1 files changed, 21 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index fbc61d4d..e5e63478 100644
--- a/txr.1
+++ b/txr.1
@@ -3638,6 +3638,25 @@ Convert the 26 lower case letters of the English alphabet to upper case.
 .IP :downcase
 Convert the 26 upper case letters of the English alphabet to lower case.
 
+.IP :fromurl
+Decode URL-encoded (a.k.a. percent-encoded) text. Character triplets consisting
+of the % character followed by a pair of hexadecimal digits (case insensitive)
+are are converted to bytes having the value represented by the hexadecimal
+digits (most significant nybble first). Sequences of one or more such bytes are
+treated as UTF-8 data  and decoded to characters.
+
+.IP :tourl
+Convert to URL encoding according to RFC 3986. The text is first converted
+to UTF-8 bytes. The bytes are then converted back to text as follows.
+Bytes in the range 0 to 32, and 127 to 255 (note: including the ASCII DEL), 
+bytes whose values correspond to ASCII characters which are listed by RFC 3986 
+as being in the "reserved set", and the byte value corresponding to the
+ASCII % character are encoded as a three-character sequence consisting
+of the % character followed by two hexadecimal digits derived from the
+byte value (most significant nybble first, upper case). All other bytes
+are converted directly to characters of the same value without any such
+encoding.
+
 Example: to escape HTML characters in all variable substitutions occuring in an
 output clause, specify :filter :to_html in the directive:
 
@@ -6754,6 +6773,8 @@ Certain object types have a custom equal function.
 
 .SS Function match-fun
 
+.SS Functions url-encode and url-decode
+
 .SH APPENDIX A: NOTES ON EXOTIC REGULAR EXPRESSIONS
 
 Users familiar with regular expressions may not be familiar with the complement