Home | History | Annotate | Download | only in html 
      1 /*
      2  * Copyright (C) 2010 Google Inc.
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  * http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.google.clearsilver.jsilver.functions.html;
     18 
     19 import com.google.clearsilver.jsilver.functions.TextFilter;
     20 
     21 import java.io.IOException;
     22 import java.lang.Character.UnicodeBlock;
     23 
     24 /**
     25  * Validates that a given string is either something that looks like a relative URI, or looks like
     26  * an absolute URI using one of a set of allowed schemes (http, https, ftp, mailto). If the string
     27  * is valid according to these criteria, the string is escaped with an appropriate escaping
     28  * function. Otherwise, the string "#" is returned.
     29  *
     30  * Subclasses will apply the necessary escaping function to the string by overriding {@code
     31  * applyEscaping}.
     32  *
     33  * <p>
     34  * Note: this function does <em>not</em> validate that the URI is well-formed beyond the scheme part
     35  * (and if the URI appears to be relative, not even then). Note in particular that this function
     36  * considers strings of the form "www.google.com:80" to be invalid.
     37  */
     38 public abstract class BaseUrlValidateFunction implements TextFilter {
     39 
     40   @Override
     41   public void filter(String in, Appendable out) throws IOException {
     42     if (!isValidUri(in)) {
     43       out.append('#');
     44       return;
     45     }
     46     applyEscaping(in, out);
     47   }
     48 
     49   /**
     50    * Called by {@code filter} after verifying that the input is a valid URI. Should apply any
     51    * appropriate escaping to the input string.
     52    *
     53    * @throws IOException
     54    */
     55   protected abstract void applyEscaping(String in, Appendable out) throws IOException;
     56 
     57   /**
     58    * @return true if a given string either looks like a relative URI, or like an absolute URI with
     59    *         an allowed scheme.
     60    */
     61   protected boolean isValidUri(String in) {
     62     // Quick check for the allowed absolute URI schemes.
     63     String maybeScheme = toLowerCaseAsciiOnly(in.substring(0, Math.min(in.length(), 8)));
     64     if (maybeScheme.startsWith("http://") || maybeScheme.startsWith("https://")
     65         || maybeScheme.startsWith("ftp://") || maybeScheme.startsWith("mailto:")) {
     66       return true;
     67     }
     68 
     69     // If it's an absolute URI with a different scheme, it's invalid.
     70     // ClearSilver defines an absolute URI as one that contains a colon prior
     71     // to any slash.
     72     int slashPos = in.indexOf('/');
     73     if (slashPos != -1) {
     74       // only colons before this point are bad.
     75       return in.lastIndexOf(':', slashPos - 1) == -1;
     76     } else {
     77       // then any colon is bad.
     78       return in.indexOf(':') == -1;
     79     }
     80   }
     81 
     82   /**
     83    * Converts an ASCII string to lowercase. Non-ASCII characters are replaced with '?'.
     84    */
     85   private String toLowerCaseAsciiOnly(String string) {
     86     char[] ca = string.toCharArray();
     87     for (int i = 0; i < ca.length; i++) {
     88       char ch = ca[i];
     89       ca[i] =
     90           (Character.UnicodeBlock.of(ch) == UnicodeBlock.BASIC_LATIN)
     91               ? Character.toLowerCase(ch)
     92               : '?';
     93     }
     94     return new String(ca);
     95   }
     96 }
     97