com.google.gwt.safehtml.shared.UriUtils Maven / Gradle / Ivy
/*
* Copyright 2010 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.gwt.safehtml.shared;
/**
* Utility class containing static methods for validating and sanitizing URIs.
*/
public final class UriUtils {
/**
* Extracts the scheme of a URI.
*
* @param uri the URI to extract the scheme from
* @return the URI's scheme, or {@code null} if the URI does not have one
*/
public static String extractScheme(String uri) {
int colonPos = uri.indexOf(':');
if (colonPos < 0) {
return null;
}
String scheme = uri.substring(0, colonPos);
if (scheme.indexOf('/') >= 0 || scheme.indexOf('#') >= 0) {
/*
* The URI's prefix up to the first ':' contains other URI special
* chars, and won't be interpreted as a scheme.
*
* TODO(xtof): Consider basing this on URL#isValidProtocol or similar;
* however I'm worried that being too strict here will effectively
* allow dangerous schemes accepted in loosely parsing browsers.
*/
return null;
}
return scheme;
}
/**
* Determines if a {@link String} is safe to use as the value of a URI-valued
* HTML attribute such as {@code src} or {@code href}.
*
*
* In this context, a URI is safe if it can be established that using it as
* the value of a URI-valued HTML attribute such as {@code src} or {@code
* href} cannot result in script execution. Specifically, this method deems a
* URI safe if it either does not have a scheme, or its scheme is one of
* {@code http, https, ftp, mailto}.
*
* @param uri the URI to validate
* @return {@code true} if {@code uri} is safe in the above sense; {@code
* false} otherwise
*/
public static boolean isSafeUri(String uri) {
String scheme = extractScheme(uri);
if (scheme == null) {
return true;
}
/*
* Special care is be taken with case-insensitive 'i' in the Turkish locale.
* i -> to upper in Turkish locale -> İ
* I -> to lower in Turkish locale -> ı
* For this reason there are two checks for mailto: "mailto" and "MAILTO"
* For details, see: http://www.i18nguy.com/unicode/turkish-i18n.html
*/
String schemeLc = scheme.toLowerCase();
return ("http".equals(schemeLc)
|| "https".equals(schemeLc)
|| "ftp".equals(schemeLc)
|| "mailto".equals(schemeLc)
|| "MAILTO".equals(scheme.toUpperCase()));
}
/**
* Sanitizes a URI.
*
*
* This method returns the URI provided if it is safe to use as the the value
* of a URI-valued HTML attribute according to {@link #isSafeUri}, or the URI
* "{@code #}" otherwise.
*
* @param uri the URI to sanitize
* @return a sanitized String
*/
public static String sanitizeUri(String uri) {
if (isSafeUri(uri)) {
return uri;
} else {
return "#";
}
}
// prevent instantiation
private UriUtils() {
}
}