Adding gzip compression to a netcat proxy

haggismn · 03-02-2012, 08:21 PM

Hello all,
I am trying to add gzip compression to a netcat proxy connection. I have the connection working without compression with the following on both sides.

Code:

mkfifo /tmp/rev
while true ; do cat /tmp/rev | nc -l 8080 | nc localhost 80 > /tmp/rev ; done

The idea is that the data entering the connection will be gzipped, then passed onto httptunnel, which forwards it to the remote host. The remote host will then pass the result to the opposing nc/gzip -d , and forward it from there to a test application.

I have made an educated attempt at the following, but it doenst work;

Code:

while true ; do cat /tmp/rev | gzip | nc -l 8008 | nc localhost 80 | gzip -d > /tmp/rev ; done

I am aware that I can use an array of other protocols like ssh and ssl, however I need to have a gzipped tunnel to test out suricata's ability to decompress gzip on the fly.

Can anyone advise on how to alter the statement to implement compression on input and decompression on output? Or, if anyone understands what I am trying to do and believes it not to be possible, this advice would be welcome too so I do not keep wasting my time!

Thanks in advance for any help.

kbp · 03-03-2012, 02:21 AM

It looks like you're trying to do it all in one command pipeline, try doing it in 2 - 1 sending and 1 receiving. From memory, having the same file as a source and destination in the same command will truncate the file to zero bytes.

haggismn · 03-03-2012, 11:22 AM

Thanks for your response!
How would I go about putting this into 2 commands? I am trying this first without using gzip. Please bear with me as I am not well versed on how piping works.

I believe the following command shows the points that gzip should occur;

Code:

while true ; do cat /tmp/fifo | nc -l -p 8008 | gzip | nc localhost 80 | gzip -d > /tmp/fifo ; done

I get the following error, which indicates you may be right

Code:

gzip: stdin: unexpected end of file

Code:

while true ; do nc -l 8080 (| gzip )| nc localhost 80 ; done

This would send from from client to the server, wouldn't it?

This is the part I get stuck at. How can I read back data only in one command? The following is an educated guess, however I can't use it because port 8080 is already in use.

Code:

while true ; do nc localhost 80 (| gzip -d )> /tmp/rev | nc -l 8080 ; done

How can I adjust this to make it work?

Another possible problem I was thinking of might be that gzip will not know when to stop compressing, then at the end send everything in one big gz file. Optimally, I would like only one packet compressed, then sent on. Will this happen, or is there something I can add to make sure that compression only occurs for x bytes (eg the MTU size). Of course, I don't think I am limited to using gzip, if there is another program which can act in this way, I will use it instead.

Thanks again for any help.

Edit: I now have 2 separate commands working although I am not sure where to go next. It seems as though reading and writing are still occurring in both commands so it might not be useful;

Code:

cat fifo2 | nc -l 8080 > fifo1

Code:

cat fifo1 | nc localhost 80 > fifo2

Can gzip be added to these commands, or do I need to make different changes? The following does not seem to work.

Code:

cat fifo2 | nc -l 8080 | gzip > fifo1

Code:

cat fifo1 | nc localhost 80 | gzip -d fifo2

kbp · 03-04-2012, 04:31 AM

Netcat should be the end/start of each command:

Example:

Quote:

nc -l -p 2000 -q 0 | gzip -d | destcmd
srccmd | gzip | nc -q 0 otherhost 2000

Ref: http://www.debian-administration.org/articles/58