user/src/com/google/gwt/safehtml/shared/SafeUriHostedModeUtils.java

/*
 * Copyright 2011 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;

import com.google.gwt.core.client.GWT;
import com.google.gwt.thirdparty.guava.common.base.Preconditions;

import java.net.URI;
import java.net.URISyntaxException;

/**
 * SafeUri utilities whose implementation differs between Development and
 * Production Mode.
 *
 * <p>
 * This class has a super-source peer that provides the Production Mode
 * implementation.
 *
 * <p>
 * Do not use this class - it is used for implementation only, and its methods
 * may change in the future.
 */
public class SafeUriHostedModeUtils {

  /**
   * All valid Web Addresses, i.e. the href-ucschar production from RFC 3987bis.
   *
   * @see <a href="http://tools.ietf.org/html/rfc3986#section-2">RFC 3986</a>
   * @see <a href="http://tools.ietf.org/html/draft-ietf-iri-3987bis-05#section-7.2">RFC 3987bis Web Addresses</a>
   */
  static final String HREF_UCSCHAR = "("
    + "["
    + ":/?#\\[\\]@!$&'()*+,;=" // reserved
    + "a-zA-Z0-9\\-._~" // iunreserved
    + " <>\"{}|\\\\^`\u0000-\u001F\u001F-\uD7FF\uE000-\uFFFD" // href-ucschar
    + "]"
    + "|"
    + "[\uD800-\uDBFF][\uDC00-\uDFFF]" // surrogate pairs
    + ")*";

  /**
   * Name of system property that if set, enables checks in server-side code
   * (even if assertions are disabled).
   */
  public static final String FORCE_CHECK_VALID_URI = "com.google.gwt.safehtml.ForceCheckValidUri";

  private static boolean forceCheckValidUri;

  static {
    setForceCheckValidUriFromProperty();
  }

  /**
   * Checks if the provided URI is a valid Web Address (per RFC 3987bis).
   *
   * @param uri the URL to check
   */
  public static void maybeCheckValidUri(String uri) {
    if (GWT.isClient() || forceCheckValidUri) {
      Preconditions.checkArgument(isValidUri(uri), "String is not a valid URI: %s", uri);
    } else {
      assert isValidUri(uri) : "String is not a valid URI: " + uri;
    }
  }

  /**
   * Sets a global flag that controls whether or not
   * {@link #maybeCheckValidUri(String)} should perform its check in a
   * server-side environment.
   *
   * @param check if true, perform server-side checks.
   */
  public static void setForceCheckValidUri(boolean check) {
    forceCheckValidUri = check;
  }

  /**
   * Sets a global flag that controls whether or not
   * {@link #maybeCheckValidUri(String)} should perform its check in a
   * server-side environment from the value of the {@value
   * FORCE_CHECK_VALID_URI} property.
   */
  // The following annotation causes javadoc to crash on Mac OS X 10.5.8,
  // using java 1.5.0_24.
  //
  // See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6442982
  //
  // @VisibleForTesting
  public static void setForceCheckValidUriFromProperty() {
    forceCheckValidUri = System.getProperty(FORCE_CHECK_VALID_URI) != null;
  }

  private static boolean isValidUri(String uri) {
    // TODO(xtof): The regex appears to cause stack overflows in some cases.
    // Investigate and re-enable.
    // if (!uri.matches(HREF_UCSCHAR)) {
    //   return false;
    // }
    /*
     * pre-process to turn href-ucschars into ucschars, and encode to URI.
     *
     * This is done by encoding everything, and decoding back "%25" to "%".
     */
    uri = UriUtils.encode(uri).replace("%25", "%");
    try {
      new URI(uri);
      return true;
    } catch (URISyntaxException e) {
      return false;
    }
  }
}