url-rewrite/url-rewrite.lisp

   1 ;;; -*- Mode: LISP; Syntax: COMMON-LISP; Package: CL-USER; Base: 10 -*-
   2
   3 ;;; Copyright (c) 2004-2010, Dr. Edmund Weitz. All rights reserved.
   4
   5 ;;; Redistribution and use in source and binary forms, with or without
   6 ;;; modification, are permitted provided that the following conditions
   7 ;;; are met:
   8
   9 ;;;   * Redistributions of source code must retain the above copyright
  10 ;;;     notice, this list of conditions and the following disclaimer.
  11
  12 ;;;   * Redistributions in binary form must reproduce the above
  13 ;;;     copyright notice, this list of conditions and the following
  14 ;;;     disclaimer in the documentation and/or other materials
  15 ;;;     provided with the distribution.
  16
  17 ;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
  18 ;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  19 ;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20 ;;; ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  21 ;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22 ;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  23 ;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  24 ;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  25 ;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  26 ;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  27 ;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28
  29 (in-package :url-rewrite)
  30
  31 (defun starts-with-scheme-p (string)
  32   "Checks whether the string STRING represents a URL which starts with
  33 a scheme, i.e. something like 'https://' or 'mailto:'."
  34   (loop with scheme-char-seen-p = nil
  35         for c across string
  36         when (or (char-not-greaterp #\a c #\z)
  37                  (digit-char-p c)
  38                  (member c '(#\+ #\- #\.) :test #'char=))
  39         do (setq scheme-char-seen-p t)
  40         else return (and scheme-char-seen-p
  41                          (char= c #\:))))
  42
  43 (defun url-encode (string)
  44   "URL-encode a string."
  45   (with-output-to-string (s)
  46     (loop for c across string
  47           do (cond ((or (char<= #\0 c #\9)
  48                         (char<= #\a c #\z)
  49                         (char<= #\A c #\Z)
  50                         (find c "$-_.!*'()," :test #'char=))
  51                      (write-char c s))
  52                    ((char= c #\Space)
  53                      (write-char #\+ s))
  54                    (t (format s "%~2,'0x" (char-code c)))))))
  55
  56 (defun add-get-param-to-url (url name value)
  57   "URL is assumed to be a http URL. The pair of NAME and VALUE will be
  58 added as a GET parameter to this URL. Assumes that there's no other
  59 parameter of the same name. Only checks if #\? is part of the string
  60 to decide how to attach the new parameter to the end of the string."
  61   ;; possible bug: doesn't check for #\? which is written as, say,
  62   ;; "&x3f;" - also, is there any other way a question mark could be a
  63   ;; legitimate part of a URL?
  64   (concatenate 'string
  65                url
  66                (if (find #\? url :test #'char=)
  67                  "&amp;"
  68                  "?")
  69                name
  70                "="
  71                (url-encode value)))
  72
  73 (defun rewrite-urls (rewrite-fn &optional (test-fn (complement #'starts-with-scheme-p)))
  74   "Reads an \(X)HTML document from *STANDARD-INPUT* and writes it back
  75 to *STANDARD-OUTPUT*. Any attribute value which is in one of the
  76 positions denoted by *URL-REWRITE-TAGS* is rewritten by REWRITE-FN if
  77 it passes the test denoted by the optional function TEST-FN which
  78 defaults to the complement of STARTS-WITH-SCHEME-P.
  79
  80 This function aims to yield correct results for correct \(X)HTML input
  81 and it also tries hard to never signal an error although it may warn
  82 if it encounters syntax errors. It will NOT detect any possible error
  83 nor is there any warranty that it will work correctly with faulty
  84 input."
  85   (loop
  86     ;; read (and write back) until we see a #\< which is a candidate
  87     ;; for a tag or a markup declaration
  88     (read-until "<")
  89     ;; get next char without reading it
  90     (let ((peek-char (peek-char*)))
  91       (cond ((null peek-char)
  92               ;; stop if EOF
  93               (return-from rewrite-urls))
  94             ((char= peek-char #\!)
  95               ;; we've seen "<!" so this might be a markup declaration
  96               ;; - first write #\! back
  97               (write-char (read-char))
  98               ;; peek at next char
  99               (let ((peek-char (peek-char*)))
 100                 (cond ((null peek-char)
 101                         ;; stop if EOF
 102                         (return-from rewrite-urls))
 103                       ((eql peek-char #\>)
 104                         ;; "<!>" is nothing special, just write the
 105                         ;; char and go back to the start of the loop
 106                         (write-char (read-char)))
 107                       ((letterp peek-char)
 108                         ;; a letter, so this should be something like
 109                         ;; <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2
 110                         ;; Final//EN"> - we just check for names and
 111                         ;; delimited strings separated by whitespace
 112                         ;; until we see the next #\>
 113                         (read-name)
 114                         (skip-whitespace)
 115                         (block parameter-loop
 116                           (loop
 117                             (let ((peek-char (peek-char*)))
 118                               (cond ((null peek-char)
 119                                       ;; stop if EOF
 120                                       (warn "EOF in markup declaration")
 121                                       (return-from rewrite-urls))
 122                                     ((char= peek-char #\>)
 123                                       ;; a #\> ends the markup
 124                                       ;; declaration - write it back
 125                                       ;; and exit the loop
 126                                       (write-char (read-char))
 127                                       (return-from parameter-loop))
 128                                     ((or (letterp peek-char)
 129                                          (find peek-char '(#\' #\") :test #'char=))
 130                                       ;; a delimiter or a letter, so
 131                                       ;; we expect a delimited string
 132                                       (read-delimited-string)
 133                                       (skip-whitespace))
 134                                     ((comment-start-p)
 135                                       ;; a comment - skip it and write it back
 136                                       (skip-comment))
 137                                     (t
 138                                       ;; something else - this is an error
 139                                       ;; so we warn and exit the loop
 140                                       (warn "Unexpected character ~S in markup declaration"
 141                                             peek-char)
 142                                       (return-from parameter-loop)))))))
 143                       ((comment-start-p)
 144                         ;; we've seen "<!--" so this starts a comment declaration
 145                         ;; - we'll read comments which are possibly separated
 146                         ;; by whitespace
 147                         (block comment-loop
 148                           (loop
 149                             (skip-comment)
 150                             (skip-whitespace)
 151                             (let ((peek-char (peek-char*)))
 152                               (cond ((null peek-char)
 153                                       ;; stop if EOF
 154                                       (warn "EOF in comment declaration")
 155                                       (return-from rewrite-urls))
 156                                     ((char= peek-char #\>)
 157                                       ;; a #\> ends the comment
 158                                       ;; declaration - write it back
 159                                       ;; and exit the loop
 160                                       (write-char (read-char))
 161                                       (return-from comment-loop))
 162                                     ;; a comment - do nothing
 163                                     ((comment-start-p))
 164                                     (t
 165                                       ;; something else - this is an error
 166                                       ;; so we warn and exit the loop
 167                                       (warn "Unexpected character ~S in comment declaration"
 168                                             peek-char)
 169                                       (return-from comment-loop)))))))
 170                       (t
 171                         ;; neither markup declaration nor comment declaration,
 172                         ;; so this was just "<!"
 173                         (write-char (read-char))))))
 174             ((char= peek-char #\/)
 175               (write-char (read-char))
 176               (let ((peek-char (peek-char*)))
 177                 (cond ((null peek-char)
 178                         ;; stop if EOF
 179                         (warn "EOF in end-tag")
 180                         (return-from rewrite-urls))
 181                       ((letterp peek-char)
 182                         ;; a letter, so this is supposed to start a name -
 183                         ;; read it and skip whitespace following it
 184                         (let ((name (read-name :skip nil)))
 185                           (skip-whitespace)
 186                           (let ((peek-char (peek-char*)))
 187                             (cond ((null peek-char)
 188                                     ;; stop if EOF
 189                                     (warn "EOF after </~A" name)
 190                                     (return-from rewrite-urls))
 191                                   ((char/= (peek-char*) #\>)
 192                                     ;; we expect to see #\> here - if not
 193                                     ;; we warn but do nothing else
 194                                     (warn "Expected #\> after </~A" name))
 195                                   (t
 196                                     ;; end of end tag, just consume the #\>
 197                                     (write-char (read-char)))))))
 198                       (t
 199                         ;; not a letter, so this is an error -
 200                         ;; we warn and ignore this
 201                         (warn "Unexpected character ~S after </"
 202                               peek-char)))))
 203             ((letterp peek-char)
 204               ;; a letter so we expect a start tag, possibly followed by
 205               ;; attributes - first read name, check if it's mentioned
 206               ;; in *URL-REWRITE-TAGS*, and find the name of the
 207               ;; corresponding attribute
 208               (let* ((name (read-name :skip nil))
 209                      (rewrite-attribute (and name
 210                                              (cdr (assoc name *url-rewrite-tags*
 211                                                          :test #'string-equal))))
 212                      attribute-found-p)
 213                 (flet ((maybe-write-attribute (&optional value
 214                                                          (rewrite-attribute
 215                                                           (and (not attribute-found-p)
 216                                                                (cdr (assoc name
 217                                                                            *url-rewrite-fill-tags*
 218                                                                            :test #'string-equal)))))
 219                          ;; write the name of the attribute
 220                          ;; REWRITE-ATTRIBUTE and its (rewritten)
 221                          ;; value VALUE to *STANDARD-OUTPUT* if DO-IT
 222                          ;; is true - the default value for DO-IT
 223                          ;; means to only write the attribute if it
 224                          ;; has to be added
 225                          (when rewrite-attribute
 226                            (unless attribute-found-p
 227                              (write-char #\Space))
 228                            (write-string rewrite-attribute)
 229                            (write-char #\=)
 230                            (let ((delimiter (if (find #\' value :test #'char=)
 231                                               #\" #\')))
 232                              (write-char delimiter)
 233                              (write-string (funcall rewrite-fn value))
 234                              (write-char delimiter)))))
 235                   (skip-whitespace)
 236                   (block attribute-loop
 237                     (loop
 238                       (let ((peek-char (peek-char*)))
 239                         (cond ((null peek-char)
 240                                 ;; stop if EOF
 241                                 (warn "EOF before ~A tag was closed" name)
 242                                 (return-from rewrite-urls))
 243                               ((eql peek-char #\>)
 244                                 ;; end of tag - exit attribute loop
 245                                 (maybe-write-attribute)
 246                                 (write-char (read-char))
 247                                 (return-from attribute-loop))
 248                               ((eql peek-char #\/)
 249                                 ;; we've seen #\/, so this might be the XHTML way
 250                                 ;; to end a stand-alone tag
 251                                 (write-char (read-char))
 252                                 (cond ((eql (peek-char*) #\>)
 253                                         ;; yes, it is - exit this loop
 254                                         (maybe-write-attribute)
 255                                         (write-char (read-char)))
 256                                       (t
 257                                         ;; no, it's not - so this is an error
 258                                         (warn "Unexpected #\/ in ~A tag" name)))
 259                                 ;; exit attribute loop in any case
 260                                 (return-from attribute-loop))
 261                               ((letterp peek-char)
 262                                 ;; a letter - this should start an attribute
 263                                 (multiple-value-bind (name value string)
 264                                     ;; no need to cons up return values if we're
 265                                     ;; not going to rewrite anyway
 266                                     (read-attribute :skip (null rewrite-attribute)
 267                                                     :write-through (null rewrite-attribute))
 268                                   (cond ((and rewrite-attribute
 269                                               (string-equal name rewrite-attribute))
 270                                           ;; remember that we've seen the
 271                                           ;; attribute in question
 272                                           (setq attribute-found-p t)
 273                                           ;; if this an attribute which should be
 274                                           ;; rewritten do it and write the whole
 275                                           ;; stuff to *STANDARD-OUT* explicitly
 276                                           (cond ((funcall test-fn value)
 277                                                   (maybe-write-attribute value name))
 278                                                 (t
 279                                                   ;; otherwise write it back
 280                                                   (write-string string))))
 281                                         (rewrite-attribute
 282                                           ;; we didn't rewrite this attribute but we
 283                                           ;; have to write it back to *STANDARD-OUTPUT*
 284                                           ;; because READ-ATTRIBUTE didn't do it
 285                                           (write-string string))))
 286                                 (skip-whitespace))
 287                               (t
 288                                 ;; an error - exit the attribute loop
 289                                 (warn "Unexpected character ~A after <~A" peek-char name)
 290                                 (return-from attribute-loop)))))))))
 291             (t
 292               ;; anything else means this is just #\<, no markup
 293               (write-char (read-char)))))))