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    * Licensed to the Apache Software Foundation (ASF) under one   *
    * or more contributor license agreements.  See the NOTICE file *
    * distributed with this work for additional information        *
    * regarding copyright ownership.  The ASF licenses this file   *
    * to you 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                 *
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   * 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 org.apache.james.jspf.terms;
  
  import org.apache.james.jspf.core.DNSService;
  import org.apache.james.jspf.core.SPF1Constants;
  import org.apache.james.jspf.core.SPF1Data;
  import org.apache.james.jspf.exceptions.PermErrorException;
  import org.apache.james.jspf.exceptions.TempErrorException;
  import org.apache.james.jspf.macro.MacroExpand;
  import org.apache.james.jspf.util.SPFTermsRegexps;
  import org.apache.james.jspf.wiring.DNSServiceEnabled;
  import org.apache.james.jspf.wiring.MacroExpandEnabled;
  
  import java.util.List;
  
  /***
   * This class represent the exp modifier
   * 
   */
  public class ExpModifier extends GenericModifier implements DNSServiceEnabled, MacroExpandEnabled {
  
      /***
       * ABNF: explanation = "exp" "=" domain-spec
       * 
       * NOTE: the last +"?" has been added to support RFC4408 ERRATA for the EXP modifier.
       * An "exp=" should not result in a perm error but should be ignored.
       * Errata: http://www.openspf.org/RFC_4408/Errata#empty-exp
       */
      public static final String REGEX = "[eE][xX][pP]" + "//="
              + SPFTermsRegexps.DOMAIN_SPEC_REGEX+"?";
  
      private DNSService dnsService;
      
      private MacroExpand macroExpand;
  
      /***
       * Generate the explanation and set it in SPF1Data so it can be accessed
       * easy later if needed
       * 
       * @param spfData
       *            The SPF1Data which should used
       * @throws PermErrorException 
       */
      protected void checkSPFLogged(SPF1Data spfData) throws PermErrorException {
          String exp = null;
          String host = getHost();
          
          // RFC4408 Errata: http://www.openspf.org/RFC_4408/Errata#empty-exp
          if (host == null) {
              return;
          }
  
          // If we should ignore the explanation we don't have to run this class
          if (spfData.ignoreExplanation() == true)
              return;
          
          // If the currentResult is not fail we have no need to run all these
          // methods!
          if (spfData.getCurrentResult()== null || !spfData.getCurrentResult().equals(SPF1Constants.FAIL))
              return;
  
          host = macroExpand.expand(host, spfData, MacroExpand.DOMAIN);
  
          try {
              try {
                  exp = getTxtType(dnsService, host);
              } catch (TempErrorException e) {
                  // Nothing todo here.. just return null
                  return;
              }
  
              if ((exp != null) && (!exp.equals(""))) {
                  String expandedExplanation = macroExpand.expand(exp, spfData, MacroExpand.EXPLANATION);
                  spfData.setExplanation(expandedExplanation);
              } 
          } catch (PermErrorException e) {
              // TODO add logging here!
              // Only catch the error and return null
              return;
          }
         return;
     }
 
 
     /***
      * Get TXT records as a string
      * 
      * @param dns The DNSService to query
      * @param strServer
      *            The hostname for which we want to retrieve the TXT-Record
      * @return String which reflect the TXT-Record
      * @throws PermErrorException
      *             if more then one TXT-Record for explanation was found
      * @throws TempErrorException
      *             if the lookup result was "TRY_AGAIN"
      */
     public String getTxtType(DNSService dns, String strServer) throws TempErrorException, PermErrorException {
         try {
             List records = dns.getRecords(strServer, DNSService.TXT);
         
             if (records == null) {
                 return null;
             }
     
             // See SPF-Spec 6.2
             //
             // If domain-spec is empty, or there are any DNS processing errors (any RCODE other than 0), 
             // or if no records are returned, or if more than one record is returned, or if there are syntax 
             // errors in the explanation string, then proceed as if no exp modifier was given.   
             if (records.size() > 1) {
                 log.debug("More then one TXT-Record found for explanation");
                 throw new PermErrorException("More then one TXT-Record for explanation");
             } else {
                 return (String) records.get(0);
             }
         } catch (DNSService.TimeoutException e) {
             throw new TempErrorException("Timeout querying dns server");
         }
     }
     
     /***
      * @see java.lang.Object#toString()
      */
     public String toString() {
        return "exp="+getHost();
     }
 
     /***
      * @see org.apache.james.jspf.wiring.DNSServiceEnabled#enableDNSService(org.apache.james.jspf.core.DNSService)
      */
     public void enableDNSService(DNSService service) {
         this.dnsService = service;
     }
 
 
     /***
      * @see org.apache.james.jspf.wiring.MacroExpandEnabled#enableMacroExpand(org.apache.james.jspf.macro.MacroExpand)
      */
     public void enableMacroExpand(MacroExpand macroExpand) {
         this.macroExpand = macroExpand;
     }
 
 }