Monday, July 28, 2008

Home Made GPS Location Beamer

Mobility seems to be the new buzz. All the new smart phones coming out have some sort of location awareness built-in either through cell triangulation or through GPS.

There are a bunch of companies working on location based social networks. Loopt [] is one of them, the most well know i.e. There are a bunch more Plazes [], Zkout [] .... All of them are doing similar and exciting stuff.

To create a location based social recommendation engine is a very hard problem to solve but to post your GPS coordinates on the web very easy!!!!

With the help of YUI [], Moto Q9c, C#, and AppEngine [] / Fire Eagle [] I have put up this page where anyone can track my whereabouts [Only works on Firefox :=)].

This was a fun exercise. Will add more stuff (friend locator, location based services ... ) to it slowly ..... very slowly :)

Monday, March 31, 2008

Print hex stream byte array & ASCII representation (Java)

I have found it useful to print the raw hex stream & it's ASCII representation of the network traffic to help debug some protocol issues.

Here is a Java function to take a hex byte array and print it out to the STDOUT_FILENO

public static void prettyPrintHex(byte[] data) {

    int i = 0, j = 0;   // loop counters

    int line_addr = 0;  // memmory address printed on the left

    String line_to_print = "";

    if (data.length == 0) {




    StringBuilder _sbbuffer = new StringBuilder();


    //Loop through every input byte

    String _hexline = "";

    String _asciiline = "";

    for (i = 0, line_addr = 0; i < data.length; i++, line_addr++) {

        //Print the line numbers at the beginning of the line

        if ((i % 16) == 0) {

            if (i != 0) {



                _sbbuffer.append(_asciiline + "\n");


            _asciiline = "";

            _hexline = String.format("%#06x ", line_addr);



        _hexline = _hexline.concat(String.format("%#04x ", data[i]));

        if (data[i] > 31 && data[i] < 127) {

            _asciiline = _asciiline.concat(String.valueOf((char) data[i]));

        } else {

            _asciiline = _asciiline.concat(".");



    // Handle the ascii for the final line, which may not be completely filled.

    if (i % 16 > 0) {

        for (j = 0; j < 16 - (i % 16); j++) {

            _hexline = _hexline.concat("     ");








Saturday, March 15, 2008

VM On USB: Carry your OS on USB!

Ever wanted to carry your desktop environment with you?

An easy way would be to put your desktop environment(s) on a mass storage device along with the VMPlayer MSI and have a small executable that would take care of install/uninstall of VMWare Player and launching your VM(s).

Here is a small tool in C# for doing this. Here is how it looks:

These images above show the following sequence:

1. Installs VMWare Player.
2. Launches VM(s)
3. Uninstalls VmWare Player.

The code follows the same sequence as well.

The directory structure on the USB would look like:

Here are some files associated with it:

|---- autorun.inf
|---- config.icon
|---- VMOnUSB.exe
|---- LICENSE.txt
|---- vmplayer-installer
     |----VMware Player.msi
|---- images
     |---- DamnSmallLinux3.4
          |---- DamnSmallLinux3.4.png
          |---- dsl.vmx

Source can be downloaded from []

VM(s) can be downloaded from []

Saturday, February 9, 2008

JVM for Windows Mobile

JVM can be installed on a Windows Mobile device using WebSphere Everyplace Micro Environment

All you need from there is the CLDC 1.1/MIDP 2.0 for Windows Mobile 5.0 Smartphone Edition/ARM executable. Install it on your computer.

Then go to the installation directory and extract the only zip file there. In the extracted directory you will find docs/install.pdf. Just follow the simple steps showing you how to deploy J9 onto your phone.

Now you can install Gmail on your windows mobile device (yes that was my only goal :=))

To create a shortcut on your Start Menu create a .lnk file with the following contents in one line:

38#"\J9\MIDP20\bin\j9midp20.exe" -classpath "\J9\MIDP20\apps\gmail\gmail-g.jar" "-Xbootclasspath:\J9\MIDP20\lib\jclMidp20\jclMidp20.jxe" javax.microedition.lcdui.AppManager "\J9\MIDP20\apps\gmail\gmail.jad"


Friday, November 30, 2007

Setting up OpenMoko

OpenMoko [] is a Linux based open software development platform.

I got my OpenMoko device yesterday and tried installing it. It is a neat little device lets see where it goes after Google announced its Open Handset Alliance; Android []

So the first thing you want to do when you get your device is update the kernel and the rootfs on the phone.

You will need to put the phone on uboot menu by pressing the AUX button along with the POWER button when not connected to a computer.

1st thing that I did after that was to reset the timeout on the boot menu. Otherwise the phone will shutdown after 30 seconds when idle in uboot mode. Here is how you do it:

Install the uucp package.
cu -l /dev/ttyACM0
GTA01Bv4 # setenv boot_menu_timeout 65000
GTA01Bv4 # saveenv

Download the latest OpenMoko image from their site @

Download dfu-util from:

I installed the August 2007 image using the following commands.

To update the kernel:
./dfu-util -a kernel -R -D ./uImage-

To update the root filesystem:
./dfu-util -a rootfs -R -D ./OpenMoko-openmoko-devel-image-glibc-P1-August-Snapshot-20070819-fic-gta01.rootfs.jffs2

You are all set!

Play with Qtopia [] as well. the UI for qtopia is pretty cool.
On the Qtopia website you will see a download for NEO 1973 thats the one that you want. The commands are the same as above.

For some reason the phone is not able to recognize the SIM card that I am putting in there. Trying to figure this one out :-)

Sunday, November 25, 2007

Using Libpcap

Libpcap (pcap) is a high level OpenSource API for packet-capturing framework. I was surprised to find out how ridiculously easy it is to use :-)

libpcap can be downloaded at:

To do packet-sniffing using libpcap you need to:
  1. Setup an interface to listen on. You can listen on all the available interfaces if you like.
  2. Filtering network traffic.
  3. Doing the real sniffing.
The people at Berkley did a great job in making this API so easy to use.

Setting up an interface.
This is very easy. You have 2 options:
  • pcap_lookupdev

    char *dev, errbuf[PCAP_ERRBUF_SIZE];

    dev = pcap_lookupdev(errbuf);

    if (dev == NULL)


      fprintf(stderr, "Couldn't find default device: %s\n", errbuf);



    printf("Device: %s\n", dev);

  • pcap_findalldevs

    char *dev, errbuf[PCAP_ERRBUF_SIZE];

    int udev;

    pcap_if_t *alldevsp;

    if(pcap_findalldevs(&alldevsp, errbuf))


      fprintf(stderr, "Couldn't find devices: %s\n", errbuf);



    char *trav = alldevsp;

    printf("Available Device(s): \n");

    while(trav != NULL)


      printf("\t%d) %s\n\t\t%s\n",i++,trav->name,trav->description);

      trav = trav->next;


    printf("Capture on Device (1 - %d): ", (i-1));

    scanf ("%d",&udev);


    trav = alldevsp;

    while((udev-1) > 0)


      trav = trav->next;



    dev = trav->name;

    printf("Device: %s\n",dev);

    I am sure there are better ways of doing this. I thought this was the easiest to understand.

    Remember to free the memory:


One really cool thing about pcap is that it provides all the functions with a char ptr to a error string. errbuff should be of size PCAP_ERRBUF_SIZE.

After this you just need to open the device for sniffing.

int promiscuous= 1;

pcap_t *handle = pcap_open_live(dev, BUFSIZ, promiscuous, 1000, errbuf);

if (handle == NULL)


  fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);



Good practice to close the handle:


Filtering network traffic.
Yes you can get all the packets and then decide what packets you want to look at OR HAVE BPF DO IT FOR YOU!!!!

This is a two step process.
  1. Compile the filter.
  2. Set the filter.
Easily done :

char *FILTER = "tcp";

struct bpf_program filter_code;

bpf_u_int32 local_net, netmask;

/* Lookup the subnet and mask for the device */

if(pcap_lookupnet(dev, &local_net, &netmask, errbuf) == -1)


/* Compile the BPF filter expression */

if(pcap_compile(handle, &filter_code, FILTER, 1, netmask) == -1)


/* Apply the BPF filter */

if(pcap_setfilter(handle, &filter_code) == -1)


Starting sniffing is fairly easy. I am just interested in indefinitely looping (-1) for packets.

pcap_loop(handle, -1, packet_handler, NULL);

packet_handler is the callback function.

Now What
cast cast cast! Do as much casting as possible :)
Here is some snippet form the callback function:

void packet_handler(u_char *args, const struct pcap_pkthdr *pkthdr, const u_char *packet)


  printf("length of this packet (off wire): %d\n", pkthdr->len);

  struct ether_header *ethheader;

  struct iphdr *ipheader;

  struct tcphdr *tcpheader;

  struct in_addr source, dest;


  ethheader = (struct ether_header *)packet;

  ipheader = (struct iphdr *)(packet + sizeof(struct ether_header));

  tcpheader = (struct tcphdr *)(packet + sizeof(struct ether_header) + sizeof(struct iphdr));

  const char *payload = (u_char *)(packet + sizeof(struct ether_header) + sizeof(struct iphdr) + sizeof(struct tcphdr));


  source.s_addr = ipheader->saddr;

  dest.s_addr = ipheader->daddr;


  printf("From: %s:%i\t", inet_ntoa(source), ntohs(tcpheader->source));

  printf("To: %s:%i\n", inet_ntoa(dest), ntohs(tcpheader->dest));


Now you have the payload do whatever you want to do with it!