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I am getting "<ip address> was resolved to null" message while using SendArpRequest class from Pcap4j library. How to implement it properly?

I am trying to get MAC address of the device in a local network by using its IP address. To implement this in java I found a library name Pcap4j. I am using its class SendArpRequest to generate ARP request and receive a reply, but it always says "IP-Address was resolved to null".
Here is the java code:
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.pcap4j.core.BpfProgram.BpfCompileMode;
import org.pcap4j.core.NotOpenException;
import org.pcap4j.core.PacketListener;
import org.pcap4j.core.PcapHandle;
import org.pcap4j.core.PcapNativeException;
import org.pcap4j.core.PcapNetworkInterface;
import org.pcap4j.core.PcapNetworkInterface.PromiscuousMode;
import org.pcap4j.core.Pcaps;
import org.pcap4j.packet.ArpPacket;
import org.pcap4j.packet.EthernetPacket;
import org.pcap4j.packet.Packet;
import org.pcap4j.packet.namednumber.ArpHardwareType;
import org.pcap4j.packet.namednumber.ArpOperation;
import org.pcap4j.packet.namednumber.EtherType;
import org.pcap4j.util.ByteArrays;
import org.pcap4j.util.MacAddress;
import org.pcap4j.util.NifSelector;
#SuppressWarnings("javadoc")
public class SendArpRequest {
private static final String COUNT_KEY = SendArpRequest.class.getName() + ".count";
private static final int COUNT = Integer.getInteger(COUNT_KEY, 1);
private static final String READ_TIMEOUT_KEY = SendArpRequest.class.getName() + ".readTimeout";
private static final int READ_TIMEOUT = Integer.getInteger(READ_TIMEOUT_KEY, 10); // [ms]
private static final String SNAPLEN_KEY = SendArpRequest.class.getName() + ".snaplen";
private static final int SNAPLEN =Integer.getInteger(SNAPLEN_KEY, 65536); // [bytes]
private static final MacAddress SRC_MAC_ADDR =MacAddress.getByName("00:db:df:8b:b1:a9");
private static MacAddress resolvedAddr;
private SendArpRequest() {}
public static void main(String[] args) throws PcapNativeException, NotOpenException {
String strSrcIpAddress = "192.168.0.11"; // for InetAddress.getByName()
//String strDstIpAddress = args[0]; // for InetAddress.getByName()
String strDstIpAddress = "192.168.0.3"; // for InetAddress.getByName()
System.out.println(COUNT_KEY + ": " + COUNT);
System.out.println(READ_TIMEOUT_KEY + ": " + READ_TIMEOUT);
System.out.println(SNAPLEN_KEY + ": " + SNAPLEN);
System.out.println("\n");
PcapNetworkInterface nif;
try {
nif = new NifSelector().selectNetworkInterface();
} catch (IOException e){
e.printStackTrace();
return;
}
if (nif == null) {
return;
}
System.out.println(nif.getName() + "(" + nif.getDescription() + ")");
PcapHandle handle = nif.openLive(SNAPLEN, PromiscuousMode.PROMISCUOUS, READ_TIMEOUT);
PcapHandle sendHandle = nif.openLive(SNAPLEN, PromiscuousMode.PROMISCUOUS, READ_TIMEOUT);
ExecutorService pool = Executors.newSingleThreadExecutor();
try {
handle.setFilter(
"arp and src host "
+ strDstIpAddress
+ " and dst host "
+ strSrcIpAddress
+ " and ether dst "
+ Pcaps.toBpfString(SRC_MAC_ADDR),
BpfCompileMode.OPTIMIZE);
PacketListener listener =
new PacketListener() {
public void gotPacket(Packet packet) {
if (packet.contains(ArpPacket.class)) {
ArpPacket arp = packet.get(ArpPacket.class);
if (arp.getHeader().getOperation().equals(ArpOperation.REPLY)) {
SendArpRequest.resolvedAddr = arp.getHeader().getSrcHardwareAddr();
}
}
System.out.println(packet);
}
};
Task t = new Task(handle, listener);
pool.execute(t);
ArpPacket.Builder arpBuilder = new ArpPacket.Builder();
try {
arpBuilder
.hardwareType(ArpHardwareType.ETHERNET)
.protocolType(EtherType.IPV4)
.hardwareAddrLength((byte) MacAddress.SIZE_IN_BYTES)
.protocolAddrLength((byte) ByteArrays.INET4_ADDRESS_SIZE_IN_BYTES)
.operation(ArpOperation.REQUEST)
.srcHardwareAddr(SRC_MAC_ADDR)
.srcProtocolAddr(InetAddress.getByName(strSrcIpAddress))
.dstHardwareAddr(MacAddress.ETHER_BROADCAST_ADDRESS)
.dstProtocolAddr(InetAddress.getByName(strDstIpAddress));
} catch (UnknownHostException e) {
throw new IllegalArgumentException(e);
}
EthernetPacket.Builder etherBuilder = new EthernetPacket.Builder();
etherBuilder
.dstAddr(MacAddress.ETHER_BROADCAST_ADDRESS)
.srcAddr(SRC_MAC_ADDR)
.type(EtherType.ARP)
.payloadBuilder(arpBuilder)
.paddingAtBuild(true);
for (int i = 0; i < COUNT; i++) {
Packet p = etherBuilder.build();
System.out.println(p);
sendHandle.sendPacket(p);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
break;
}
}
} finally {
if (handle != null && handle.isOpen()) {
handle.close();
}
if (sendHandle != null && sendHandle.isOpen()) {
sendHandle.close();
}
if (pool != null && !pool.isShutdown()) {
pool.shutdown();
}
System.out.println(strDstIpAddress + " was resolved to " + resolvedAddr);
}
}
private static class Task implements Runnable {
private PcapHandle handle;
private PacketListener listener;
public Task(PcapHandle handle, PacketListener listener) {
this.handle = handle;
this.listener = listener;
}
public void run() {
try {
handle.loop(COUNT, listener);
} catch (PcapNativeException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (NotOpenException e) {
e.printStackTrace();
}
}
}
}
And I got this output by using sourceIP = "192.168.0.11", sourceMAC = "00:db:df:8b:b1:a9" and destinationIP = "192.168.0.3".
com.arpscan.SendArpRequest.count: 1
com.arpscan.SendArpRequest.readTimeout: 10
com.arpscan.SendArpRequest.snaplen: 65536
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
6
6
7
2
2
0
0
0
0
0
NIF[0]: wlp1s0
: link layer address: 00:db:df:8b:b1:a9
: address: /192.168.0.11
: address: /fe80:0:0:0:c090:df9:7448:e0be
NIF[1]: any
: description: Pseudo-device that captures on all interfaces
NIF[2]: lo
: link layer address: 00:00:00:00:00:00
: address: /127.0.0.1
: address: /0:0:0:0:0:0:0:1
NIF[3]: virbr0
: link layer address: 52:54:00:72:e9:70
: address: /192.168.122.1
NIF[4]: enp0s31f6
: link layer address: 50:7b:9d:cc:71:d2
NIF[5]: bluetooth0
: description: Bluetooth adapter number 0
NIF[6]: nflog
: description: Linux netfilter log (NFLOG) interface
NIF[7]: nfqueue
: description: Linux netfilter queue (NFQUEUE) interface
NIF[8]: usbmon1
: description: USB bus number 1
NIF[9]: usbmon2
: description: USB bus number 2
Select a device number to capture packets, or enter 'q' to quit > 0
wlp1s0(null)
[Ethernet Header (14 bytes)]
Destination address: ff:ff:ff:ff:ff:ff
Source address: 00:db:df:8b:b1:a9
Type: 0x0806 (ARP)
[ARP Header (28 bytes)]
Hardware type: 1 (Ethernet (10Mb))
Protocol type: 0x0800 (IPv4)
Hardware address length: 6 [bytes]
Protocol address length: 4 [bytes]
Operation: 1 (REQUEST)
Source hardware address: 00:db:df:8b:b1:a9
Source protocol address: /192.168.0.11
Destination hardware address: ff:ff:ff:ff:ff:ff
Destination protocol address: /192.168.0.3
[Ethernet Pad (18 bytes)]
Hex stream: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[data (42 bytes)]
Hex stream: 00 db df 8b b1 a9 d0 04 01 62 61 38 08 06 00 01 08 00 06 04 00 02 d0 04 01 62 61 38 c0 a8 00 03 00 db df 8b b1 a9 c0 a8 00 0b
192.168.0.3 was resolved to null
Here I got null for destination MAC Address as you can see.
But when I run arp-scan command I got correct MAC address for the given IP Address. Here is screenshot of arp-scan result.
Please suggest me how I can implement it properly.

You need to add a packet factory moudle (e.g. pcap4j-packetfactory-static.jar) to your class path so that Pcap4J can dessect the ARP response.
And, probably you'd better add volatile to private static MacAddress resolvedAddr;.

Why not serialize my protobuf?

my widgets.proto:
option java_package = "example";
option java_outer_classname = "WidgetsProtoc";
message Widget {
required string name = 1;
required int32 id = 2;
}
message WidgetList {
repeated Widget widget = 1;
}
my rest: (Path: /widgets)
#GET
#Produces("application/x-protobuf")
public WidgetsProtoc.WidgetList getAllWidgets() {
Widget widget1 =
Widget.newBuilder().setId(1).setName("testing").build();
Widget widget2 =
Widget.newBuilder().setId(100).setName("widget 2").build();
System.err.println("widgets1: " + widget1);
System.err.println("widgets2: " + widget2);
WidgetsProtoc.WidgetList list = WidgetsProtoc.WidgetList.newBuilder().addWidget(widget1).addWidget(widget2).build();
System.err.println("list: " + list.toByteArray());
return list;
}
And when i use postman i get this response:
(emptyline)
(emptyline)
testing
(emptyline)
widget 2d
This is normal? I think not really...in my messagebodywriter class i override writeto like this:
#Override
public void writeTo(WidgetsProtoc.WidgetList widgetList, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {
entityStream.write(widgetList.toByteArray());
}
I thought its good to send a byte array...but it is a little bit weird that not serialize nothing....or just my be the id...Thanks for the help :)

It already is in binary.
Have you noticed that you message consists of name and id but you get only name displayed?
That's what I get displayed when I just save the response as a "test" file from the browser's GET call:
$ cat test
testing
widget 2d%
You can see cat being barely able to display it, but there is more content into it.
Now if I open it in bless (hex editor in ubuntu) I can get more out of it
0A 0B 0A 07 74 65 73 74 69 6E 67 10 01 0A 0C 0A 08 77 69 64 67 65 74 20 32 10 64
In general I wouldn't trust Postman to display binary data. You need to know how to decode it, and apparently Postman doesn't.
And here's the final proof:
$ cat test | protoc --decode_raw
1 {
1: "testing"
2: 1
}
1 {
1: "widget 2"
2: 100
}

Is jol a little broken under Java9?

Using java-9 build 9-ea+149 and jol 0.6.
Running this simple code:
ArrayList<Integer> list = new ArrayList<>();
list.add(12);
System.out.println(ClassLayout.parseInstance(list).toPrintable());
Output:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) 0e 8d 00 f8 (00001110 10001101 00000000 11111000) (-134181618)
12 4 int AbstractList.modCount (access denied)
16 4 int ArrayList.size (access denied)
20 4 Object[] ArrayList.elementData (access denied)
This access denied part comes from FieldData.java in the method:
public String safeValue(Object object) {
if (refField != null) {
try {
return ObjectUtils.safeToString(refField.get(object));
} catch (IllegalAccessException iae) {
// exception, try again
}
try {
refField.setAccessible(true);
return ObjectUtils.safeToString(refField.get(object));
} catch (Exception e) {
return "(access denied)";
}
} else {
return "N/A";
}
}
And the actual exception is :
Unable to make field protected transient int java.util.AbstractList.modCount accessible: module java.base does not "opens java.util" to unnamed module #479d31f3.
I think that this has to do with Unsafe features being locked down. The question is how do I get this to run?
I've looked at properties like :
-XaddExports:java.base/sun.security.provider=ALL-UNNAMED
But can't really tell what it is supposed to look like.

The solutions was indeed to put the correct argument..
--add-opens java.base/java.util=ALL-UNNAMED
as suggested here

Promise timeouts and WS.get Timeout in PlayFramework 2.1 JAVA

I am trying to access to an URL using WS on Play Framework 2.1 using JAVA api.
Here is what I want:
Some where in the code, start a WS request using WS.get() (I set timeout 1000ms)
If WS.get times out or another exception happens, I don't want my Promise throw an exception (since my flow reqiures it that way) So I use Promise.recover() to wrap that promise with another. Which returns a null Reponse object in case of failures.
Some where else in code I want to "get" my Response. I wait for 5000ms but what I get is java.util.concurrent.TimeoutException: Futures timed out after [5000 milliseconds]
How? WS.get() timesout after 1000ms and since it throws an java.util.concurrent.TimeoutException: No response received after 1000 it is catched by my recover function. It returns a null response instead of an exception.
So promise is "completed" after 1000ms at most. Why it times out and throws an exception after 5000 ms?
Code:
Logger.info("Fetch started: " + new Date().toString());
Promise<WS.Response> p1 = WS.url("http://athena.ics.forth.gr:9090/RDF/VRP/Examples/tap.rdf").setTimeout(1000).get();
Promise<WS.Response> p2 = p1.recover(new Function<Throwable, WS.Response>() {
#Override
public Response apply(Throwable a) throws Throwable {
Logger.error("Promise thrown an exception so I will return null. " + new Date().toString() + " " + System.currentTimeMillis(), a);
return null;
}
});
try {
/* This should return null or valid response but shouldn't throw an exception */
Response r = p2.get(5000L);
Logger.info(r.toString());
} catch (Exception e) {
/* Sholdn't happen! */
Logger.error("Outer exception: " + " " + System.currentTimeMillis(), e);
}
Logger.error("Fetch finished: " + new Date().toString() + " " + System.currentTimeMillis());
Output I get:
[info] application - Fetch started: Tue Mar 19 10:04:42 EET 2013
[error] application - Outer exception: 1363680287626
java.util.concurrent.TimeoutException: Futures timed out after [5000 milliseconds]
at scala.concurrent.impl.Promise$DefaultPromise.ready(Promise.scala:96) ~[scala-library.jar:na]
at scala.concurrent.impl.Promise$DefaultPromise.ready(Promise.scala:58) ~[scala-library.jar:na]
at scala.concurrent.Await$$anonfun$ready$1.apply(package.scala:86) ~[scala-library.jar:na]
at scala.concurrent.Await$$anonfun$ready$1.apply(package.scala:86) ~[scala-library.jar:na]
at akka.dispatch.MonitorableThreadFactory$AkkaForkJoinWorkerThread$$anon$3.block(ThreadPoolBuilder.scala:173) ~[akka-actor_2.10.jar:na]
at scala.concurrent.forkjoin.ForkJoinPool.managedBlock(ForkJoinPool.java:2803) [scala-library.jar:na]
[error] application - Fetch finished: Tue Mar 19 10:04:47 EET 2013 1363680287627
[error] application - Promise thrown an exception so I will return null. Tue Mar 19 10:04:47 EET 2013 1363680287627
java.util.concurrent.TimeoutException: No response received after 1000
at com.ning.http.client.providers.netty.NettyAsyncHttpProvider$ReaperFuture.run(NettyAsyncHttpProvider.java:1809) ~[async-http-client.jar:na]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) ~[na:1.7.0_11]
at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) ~[na:1.7.0_11]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) ~[na:1.7.0_11]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) ~[na:1.7.0_11]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) ~[na:1.7.0_11]
Even I wait for promise2 and promise2 is "recover wrapped promise1" recover function runs AFTER exception is thrown.

Simple dbunit table comparison fails

Why doesn't this work? I'm trying to test that an empty database is the same before doing nothing as after doing nothing. In other words, this is the simplest dbunit test with a database that I can think of. And it doesn't work. The test methods are practically lifted from http://www.dbunit.org/howto.html
The error message I'm getting for comparing empty database is:
java.lang.AssertionError: expected:
org.dbunit.dataset.xml.FlatXmlDataSet<AbstractDataSet[_orderedTableNameMap=null]>
but was:
org.dbunit.database.DatabaseDataSet<AbstractDataSet[_orderedTableNameMap=null]>
The error message I'm getting for comparing empty table is:
java.lang.AssertionError: expected:
<org.dbunit.dataset.DefaultTable[_metaData=tableName=test, columns=[], keys=[], _rowList.size()=0]>
but was:
<org.dbunit.database.CachedResultSetTable[_metaData=table=test, cols=[(id, DOUBLE, noNulls), (txt, VARCHAR, nullable)], pk=[(id, DOUBLE, noNulls)], _rowList.size()=0]>
(I've added newlines for readability)
I can edit in the full stack trace (or anything else) if it'll be useful. Or you can browse through the public git repo: https://bitbucket.org/djeikyb/simple_dbunit
Do I need to somehow convert my actual IDataSet to xml then back to IDataSet to properly compare? What am I doing/expecting wrong?
34 public class TestCase
35 {
36
37 private IDatabaseTester database_tester;
38
39 #Before
40 public void setUp() throws Exception
41 {
42 database_tester = new JdbcDatabaseTester("com.mysql.jdbc.Driver",
43 "jdbc:mysql://localhost/cal",
44 "cal",
45 "cal");
46
47 IDataSet data_set = new FlatXmlDataSetBuilder().build(
48 new FileInputStream("src/simple_dbunit/dataset.xml"));
49 database_tester.setDataSet(data_set);
50
51 database_tester.onSetup();
52 }
53
54 #Test
55 public void testDbNoChanges() throws Exception
56 {
57 // expected
58 IDataSet expected_data_set = new FlatXmlDataSetBuilder().build(
59 new FileInputStream("src/simple_dbunit/dataset.xml"));
60
61 // actual
62 IDatabaseConnection connection = database_tester.getConnection();
63 IDataSet actual_data_set = connection.createDataSet();
64
65 // test
66 assertEquals(expected_data_set, actual_data_set);
67 }
68
69 #Test
70 public void testTableNoChanges() throws Exception
71 {
72 // expected
73 IDataSet expected_data_set = new FlatXmlDataSetBuilder().build(
74 new FileInputStream("src/simple_dbunit/dataset.xml"));
75 ITable expected_table = expected_data_set.getTable("test");
76
77 // actual
78 IDatabaseConnection connection = database_tester.getConnection();
79 IDataSet actual_data_set = connection.createDataSet();
80 ITable actual_table = actual_data_set.getTable("test");
81
82 // test
83 assertEquals(expected_table, actual_table);
84 }
85
86 }

When you compare the IDataSet and other DBUnit components, you have to use the assert method that provided by DBUnit.
If you use assert methods provided by JUnit, it will only be compared via equals method in Object
That's why you get the error complaining about different object type.