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resolve mdns hostnames if regular dns resolve fails

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This commit is contained in:
Anton Keks 2014-08-31 18:59:33 +03:00
parent a04d2db742
commit 6773d5d2ef
1 changed files with 20 additions and 5 deletions
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25
src/net/azib/ipscan/fetchers/HostnameFetcher.java
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@ -5,7 +5,9 @@
package net.azib.ipscan.fetchers;
import net.azib.ipscan.core.ScanningSubject;
import net.azib.ipscan.util.MDNSResolver;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
@ -21,7 +23,6 @@ import static java.util.logging.Level.WARNING;
* @author Anton Keks
*/
public class HostnameFetcher extends AbstractFetcher {
private static Object inetAddressImpl;
private static Method getHostByAddr;
@ -44,19 +45,33 @@ public class HostnameFetcher extends AbstractFetcher {
return ID;
}
public Object scan(ScanningSubject subject) {
private String resolveWithRegularDNS(InetAddress ip) {
try {
// faster way to do lookup - getCanonicalHostName() actually does both reverse and forward lookups inside
return getHostByAddr.invoke(inetAddressImpl, subject.getAddress().getAddress());
return (String)getHostByAddr.invoke(inetAddressImpl, ip.getAddress());
}
catch (Exception e) {
if (e instanceof InvocationTargetException && e.getCause() instanceof UnknownHostException)
return null;
// return the returned hostname only if it is not the same as the IP address (this is how the above method works)
String hostname = subject.getAddress().getCanonicalHostName();
return subject.getAddress().getHostAddress().equals(hostname) ? null : hostname;
String hostname = ip.getCanonicalHostName();
return ip.getHostAddress().equals(hostname) ? null : hostname;
}
}
private String resolveWithMulticastDNS(InetAddress ip) {
try {
return new MDNSResolver().resolve(ip);
}
catch (IOException e) {
return null;
}
}
public Object scan(ScanningSubject subject) {
String name = resolveWithRegularDNS(subject.getAddress());
if (name == null) name = resolveWithMulticastDNS(subject.getAddress());
return name;
}
}