Thread: Re: [Jnetstream-users] Error in TCP decode
Brought to you by:
voytechs
Menu
▾
▴
jnetstream-users
|
From: Frédéric D. <fre...@dr...> - 2008-08-05 18:19:39
|
Actually I will fligh back in europe tomorrow and also have to visit my
chiro :-)
Actually the "readBitsOneAtATime()" I posted correct something but break
the TCP decoding (start offset is wrong). so I will look at it again (I
find the exercise quite interessting) and I could wait some days. No
problem, really. I will share my thoughts if I find something pertinent.
Regards,
Frederic
Mark Bednarczyk a écrit :
> I made changes in there recently. Its possible I screwed up.
>
> I hurt my back coming back from Europe yesterday and I can barely sit at the
> computer right now. Hopefully tomorrow I'll feel better after my visit to
> the chiropractor today and be able to take a look at the problem quickly. I
> do have some jUnit test cases checked in that test various BitBuffer
> conditions in the CommonUtils module.
>
> Cheers,
> mark...
>
>
>> -----Original Message-----
>> From: jne...@li...
>> [mailto:jne...@li...] On
>> Behalf Of Frédéric Dreier
>> Sent: Tuesday, August 05, 2008 1:10 PM
>> To: Jne...@li...
>> Subject: Re: [Jnetstream-users] Error in TCP decode
>>
>> Hi,
>>
>> I checkout the code from SVN and I thing there is something
>> odd in the "BitBuffer.readBitsOneAtATime()" method. Its
>> probably about the posBits which ich not always added to the offset.
>>
>> I temporary use the following implementation until a fix is
>> commited in SVN (This concats the buffer byte per byte
>> instead bit per bit)
>>
>> Regards,
>> Frédéric
>>
>> private static final int[] RIGHT_BIT_MASK = new int[32];
>> static {
>> // initialize mask used by readBitsOneAtATime()
>> for (int i = 1; i < RIGHT_BIT_MASK.length; i++) {
>> RIGHT_BIT_MASK[i] = (RIGHT_BIT_MASK[i - 1] << 1) | 1;
>> }
>> }
>>
>> private int readBitsOneAtATime(int length) {
>> // basic checks to avoid unnecessary computation
>> if (length == 0) {
>> return 0;
>> }
>> if (length > 32) {
>> throw new IndexOutOfBoundsException("0 >= range
>> <= 32bits");
>> }
>> // value is stored in long since length+posBits
>> // could be greater than 32.
>> long value = current;
>> int acc = 8 - posBits;
>> // concatenate buffer byte per byte
>> for (; acc < length; acc += 8) {
>> // fetch next byte
>> posBits = 8;
>> fetch();
>> // append new current byte
>> value = (value << 8) | (current & 0xFF);
>> }
>> // right-align the bits and mask high bits
>> value = (value >> (acc - length)) & RIGHT_BIT_MASK[length];
>> // update posBits value
>> posBits = (posBits + length) % 8;
>> // return
>> return (int) value;
>> }
>>
>>
>>
>>
>>
>>
>>
>>
>> Frédéric Dreier a écrit :
>>
>>> Hi,
>>>
>>> I have some trouble decoding IP and TCP headers. the header length
>>> and the offset are wrongly decoded in most of the packets.
>>>
>>> Did I do something wrong?
>>>
>>> Regards,
>>> Frederic Dreier
>>>
>>>
>>>
>>> Console output ------------------------------- PACKET DUMP::
>>> 00 12 3F 19 FC 3F 00 07
>>> 84 BC A0 C0 08 00 45 00
>>> 00 28 9D 7A 40 00 2B 06
>>> 25 94 D0 50 98 03 81 AD
>>> A2 C0 00 50 D7 59 29 F4
>>> BC EF 33 C8 F3 C5 50 11
>>> Vers : 4
>>> Hlen : 4 <----- should be 5
>>> TOS : 0
>>> Lgt : 40
>>> ident: 40314
>>> flags: 2
>>> offs : 1 <---- should be 0
>>> TTL : 43
>>> Prot : 6
>>> Src : 208.80.152.3
>>> Dst : 129.173.162.192
>>> Console output -------------------------------
>>>
>>>
>>>
>>> Code snipet ------------------------------
>>> Ip4 ipHd = packet.getHeader(Ip4.class);
>>> Tcp tcpHd = packet.getHeader(Tcp.class);
>>> System.out.println("PACKET DUMP::");
>>> for (int i = 0; i < 6; i++) {
>>> for (int k = i * 8; k < ((i
>>>
>> + 1) * 8);
>>
>>> k++) {
>>> System.out.printf("%02X ",
>>> packet.getBuffer().getBackingBuffer().get(k) & 0xFF);
>>> }
>>> System.out.println();
>>> }
>>> System.out.printf("Vers : %d\n",
>>>
>> ipHd.ver());
>>
>>> System.out.printf("Hlen : %d\n",
>>>
>> ipHd.hlen());
>>
>>> System.out.printf("TOS : %d\n",
>>>
>> ipHd.tos());
>>
>>> System.out.printf("Lgt : %d\n",
>>>
>> ipHd.length());
>>
>>> System.out.printf("ident: %d\n",
>>> ipHd.id()&0xFFFF);
>>> System.out.printf("flags: %d\n",
>>>
>> ipHd.flags());
>>
>>> System.out.printf("offs : %d\n",
>>>
>> ipHd.offset());
>>
>>> System.out.printf("TTL : %d\n",
>>>
>> ipHd.ttl());
>>
>>> System.out.printf("Prot : %d\n",
>>> ipHd.protocol());
>>> System.out.printf("Src : %s\n",
>>>
>> ipHd.source());
>>
>>> System.out.printf("Dst : %s\n",
>>> ipHd.destination());
>>> --------------------------------------------
>>>
>>>
>>>
>> --------------------------------------------------------------
>> -----------
>>
>>> This SF.Net email is sponsored by the Moblin Your Move
>>>
>> Developer's challenge
>>
>>> Build the coolest Linux based applications with Moblin SDK
>>>
>> & win great prizes
>>
>>> Grand prize is a trip for two to an Open Source event
>>>
>> anywhere in the world
>>
>>> http://moblin-contest.org/redirect.php?banner_id=100&url=/
>>> _______________________________________________
>>> Jnetstream-users mailing list
>>> Jne...@li...
>>> https://lists.sourceforge.net/lists/listinfo/jnetstream-users
>>>
>>>
>> --------------------------------------------------------------
>> -----------
>> This SF.Net email is sponsored by the Moblin Your Move
>> Developer's challenge
>> Build the coolest Linux based applications with Moblin SDK &
>> win great prizes
>> Grand prize is a trip for two to an Open Source event
>> anywhere in the world
>> http://moblin-contest.org/redirect.php?banner_id=100&url=/
>> _______________________________________________
>> Jnetstream-users mailing list
>> Jne...@li...
>> https://lists.sourceforge.net/lists/listinfo/jnetstream-users
>>
>
>
>
|
|
From: Frédéric D. <fre...@dr...> - 2008-08-06 14:31:30
|
Good morning Mark,
I will be unreachable until next monday so I already send you what I found.
- my implementation of readBitsOneAtATime(). Perhaps it is not so good
but it just does the trick until the original one will be fixed.
- something in FastScanner didn't work after I changed
readBitsOneAtATime(). 32 kept to be added to the ip header length.
Regards,
Frédéric
Fast Scanner ---------------------------------
/**
*
*/
public final boolean scanIp4() {
addToCache(IP4);
r1 = readUByte(Ip4.StaticField.PROTOCOL);
if (DEBUG) {
logger.debug(String.format("Ip4 p=%d, r1=%d\n", offset, r1));
}
//offset += bits.getBits(offset + 4, 4) * 4 * 8 + 32; <<== why +32 ?
offset += bits.getBits(offset + 4, 4) * 32;
switch (r1) {
case 1:
return scanIcmp();
case 6:
return scanTcp();
case 17:
return scanUdp();
}
return true;
}
BitBuffer -------------------------------------
private static final int[] RIGHT_BIT_MASK = new int[33];
static {
// initialize mask used by readBitsOneAtATime()
for (int i = 1; i < RIGHT_BIT_MASK.length; i++) {
RIGHT_BIT_MASK[i] = (RIGHT_BIT_MASK[i - 1] << 1) | 1;
}
}
private int readBitsOneAtATime(int length) {
// basic checks to avoid unnecessary computation
if (length == 0) {
return 0;
}
if (length > 32) {
throw new IndexOutOfBoundsException("0 >= range <= 32bits");
}
// value is stored in long since length+posBits
// could be greater than 32.
long value = current;
int acc = 8 - posBits;
// concatenate buffer byte per byte
for (; acc < length; acc += 8) {
// fetch next byte
posBits = 8;
fetch();
// append new current byte
value = (value << 8) | (current & 0xFF);
}
// right-align the bits and mask high bits
value = (value >> (acc - length)) & RIGHT_BIT_MASK[length];
// update posBits value
posBits = (posBits + length) % 8;
// return
return (int) value;
}
|
|
From: Mark B. <voy...@ya...> - 2008-08-06 16:21:20
|
Thanks Frederic,
I'm still out of commission myself.
I will revist the BitBuffer as that is a core routine that has to be 100%
correct all the time under all circumstances.
Cheers,
mark...
----- Original Message -----
From: "Frédéric Dreier" <fre...@dr...>
Cc: <Jne...@li...>
Sent: Wednesday, August 06, 2008 4:31 PM
Subject: Re: [Jnetstream-users] Error in TCP decode
Good morning Mark,
I will be unreachable until next monday so I already send you what I found.
- my implementation of readBitsOneAtATime(). Perhaps it is not so good
but it just does the trick until the original one will be fixed.
- something in FastScanner didn't work after I changed
readBitsOneAtATime(). 32 kept to be added to the ip header length.
Regards,
Frédéric
Fast Scanner ---------------------------------
/**
*
*/
public final boolean scanIp4() {
addToCache(IP4);
r1 = readUByte(Ip4.StaticField.PROTOCOL);
if (DEBUG) {
logger.debug(String.format("Ip4 p=%d, r1=%d\n", offset, r1));
}
//offset += bits.getBits(offset + 4, 4) * 4 * 8 + 32; <<== why +32 ?
offset += bits.getBits(offset + 4, 4) * 32;
switch (r1) {
case 1:
return scanIcmp();
case 6:
return scanTcp();
case 17:
return scanUdp();
}
return true;
}
BitBuffer -------------------------------------
private static final int[] RIGHT_BIT_MASK = new int[33];
static {
// initialize mask used by readBitsOneAtATime()
for (int i = 1; i < RIGHT_BIT_MASK.length; i++) {
RIGHT_BIT_MASK[i] = (RIGHT_BIT_MASK[i - 1] << 1) | 1;
}
}
private int readBitsOneAtATime(int length) {
// basic checks to avoid unnecessary computation
if (length == 0) {
return 0;
}
if (length > 32) {
throw new IndexOutOfBoundsException("0 >= range <= 32bits");
}
// value is stored in long since length+posBits
// could be greater than 32.
long value = current;
int acc = 8 - posBits;
// concatenate buffer byte per byte
for (; acc < length; acc += 8) {
// fetch next byte
posBits = 8;
fetch();
// append new current byte
value = (value << 8) | (current & 0xFF);
}
// right-align the bits and mask high bits
value = (value >> (acc - length)) & RIGHT_BIT_MASK[length];
// update posBits value
posBits = (posBits + length) % 8;
// return
return (int) value;
}
-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great
prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
Jnetstream-users mailing list
Jne...@li...
https://lists.sourceforge.net/lists/listinfo/jnetstream-users
|
×
Want the latest updates on software, tech news, and AI?
Get latest updates about software, tech news, and AI from SourceForge directly in your inbox once a month.
Thanks for helping keep SourceForge clean.
X