Printing Garbage Sometimes

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I'm using a sniffer. When I use printf to console, I get no garbage on the screen, When I prin to my logfile I get garbage sometimes, and it seems to be on sequence numbers that are at least 9 characters in length. This is what is printing to my text file.

CSS

Sequence Number:  617122025
   »$ÈˆéÛ¸^|Púð9—

The printf followed by the (log) text file...
printf("\n Sequence Number : %lu\n", ntohl(tcp_header->seq_number));
myfile << "\n Sequence Number: "<< ntohl(tcp_header->seq_number);

Posted 31-Oct-11 7:20am

Member 7766180

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Chuck O'Toole 31-Oct-11 13:35pm

Examine your output statements. Both print a string ("sequence number") an unsigned long integer (ntohl() is defined to return ulong) and a newline ("\n") and that's all. You show us output with two distinct lines, the output from the above sequence and some junk. Clearly, the statements you show are not producing the junk output, some other statements are. You are not showing all the relevant information so there's nothing anybody can do to help you.

Member 7766180 31-Oct-11 13:38pm

Right again Chuck. Here is the complete package...
printf("\n Sequence Number : %lu\n", ntohl(tcp_header->seq_number));
myfile << "\n Sequence Number: "<< ntohl(tcp_header->seq_number);
myfile << "\n ";

I just need the last line to be a spacer. Am I doing it wrong?

Member 7766180 31-Oct-11 13:44pm

This works...
myfile << "\n Sequence Number: "<< ntohl(tcp_header->seq_number)<< "\n";

Member 7766180 31-Oct-11 13:50pm

Chuck, Put this in a solution so that I may give you credit.

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Nish Nishant · Accepted Answer · 2011-10-31T07:26:00

Solution 1

Most likely cause is that the console will just replace non-regular characters with space (or null). But with the text file, it tries to render it as Unicode text. So your problem is not that it is not showing up on the console, but rather you may not be interpreting the data correctly. Or it may be a secure connection and thus the data will be mostly meaningless (and thus garbage like).

Posted 31-Oct-11 7:26am

Nish Nishant

Updated 31-Oct-11 7:28am

v2

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Member 7766180 31-Oct-11 13:34pm

Thank you. I am using ANSI. So how can I fix this? I am not on a secure connection.

Nish Nishant 31-Oct-11 13:38pm

It is possible that tcp_header->seq_number is returning an invalid value. And thus ntohl will return some random value too.

Member 7766180 31-Oct-11 13:41pm

See above I forgot to include a line. The problem is that it doesn't always print garbage. Just sometimes. I just need a space.

Nish Nishant 31-Oct-11 13:43pm

Yes but my point was that the u_long returned may be corresponding to some arbitrary Unicode character and thus the text file interprets it incorrectly as a character (when it is not).

Member 7766180 31-Oct-11 13:47pm

Thank you. I understand what you are saying. How long are sequence numbers? I'm getting anywhere from 6 to 9 digits.

Nish Nishant 31-Oct-11 13:48pm

Based on the TCP header from http://en.wikipedia.org/wiki/Transmission_Control_Protocol, 32 bits.

Member 7766180 31-Oct-11 13:50pm

Thnak you. I appreciate the input!

Nish Nishant 31-Oct-11 13:50pm

And since it's a u_long, that'd be 0xffffffff which is 4,294,967,295 (maximum value). So 6-9 digits seem okay to me.

Member 7766180 31-Oct-11 13:52pm

Thank you! I'm good to go. Have a nice day, Nishant.

Nish Nishant 31-Oct-11 13:53pm

You are welcome. Hopefully you got something out of this discussion. I was a little disappointed that I could not help you pinpoint your exact error. Oh well.

Nish Nishant 31-Oct-11 13:51pm

Try opening the log file in a different editor. It may just be a case of Notepad misinterpreting the text as Unicode.

Member 7766180 31-Oct-11 13:54pm

Apparently, The space was printing something at times. This seems to have fixed the problem. myfile << "\n Sequence Number: "<< ntohl(tcp_header->seq_number)<< "\n";

Nish Nishant 31-Oct-11 13:56pm

Interesting!

Chuck O'Toole 31-Oct-11 14:21pm

<< will convert the ulong (a number) into the printable form of the number so there's no chance that it will be taking the binary long integer and interpreting the characters as unicode. This path of investigation won't get anywhere.

Espen Harlinn 31-Oct-11 15:40pm

5'ed!

Nish Nishant 31-Oct-11 15:41pm

Thank you, Espen!

Chuck O'Toole · Accepted Answer · 2011-10-31T08:18:00

Examine your output statements. Both print a string ("sequence number") an unsigned long integer (ntohl() is defined to return ulong) and a newline ("\n") and that's all. You show us output with two distinct lines, the output from the above sequence and some junk. Clearly, the statements you show are not producing the junk output, some other statements are. You are not showing all the relevant information so there's nothing anybody can do to help you.

Now that you've added the "\n" to the myfile<< statement, you are just mimicing what's in the printf. However, that simple addition does not explain why you have garbage in the file. Adding "newline" just gives you, well, a new line. That extra output in the file comes from somewhere.

Printing Garbage Sometimes

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Printing Garbage Sometimes

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