Intercept, monitor and manipulate a TCP connection.

mkfifo /tmp/fifo; cat /tmp/fifo | nc -l -p 1234 | tee -a to.log | nc machine port | tee -a from.log > /tmp/fifo
Forwards localhost:1234 to machine:port, running all data through your chain of piped commands. The above command logs inbound and outbound traffic to two files. Tip: replace tee with sed to manipulate the data in real time (use "sed -e 's/400 Bad Request/200 OK/'" to tweak a web server's responses ;-) Limitless possibilities.

By: prutser
2009-02-20 04:00:15

1 Alternatives + Submit Alt

What Others Think

Having the command like that only listens to one request. To keep listening, you should put it inside a loop. Like this: mkfifo /tmp/fifo ; while :; do cat /tmp/fifo | nc -l -p 80 | tee -a to.log | nc localhost 8000 | tee -a from.log > /tmp/fifo; done mkfifo /tmp/fifo ; while :; do cat /tmp/fifo | nc -l -p 80 | tee -a to.log | nc localhost 8000 | tee -a from.log > /tmp/fifo; done Also, it took me quite a while to find out what was done and how. For example if you want to debug your http-server running on port 8000, you would do the command as I did and then go to http://localhost instead of http://localhost:8000 as you would normally
Masse · 641 weeks and 4 days ago
should be nc -l 80 (without the -p)
5partan · 505 weeks and 6 days ago
@5partan: true for Linux, but on Mac you need to add -p IIRC.
prutser · 505 weeks and 6 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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