Using netcat to pipe unix socket to tcp socket

Question

I am trying to expose a unix socket as a tcp socket using this command:

nc -lkv 44444 | nc -Uv /var/run/docker.sock

When I try to access localhost:44444/containers/json from a browser, it doesn't load anything but keeps the connection open (the loading thingy keeps spinning), but the console (because of the -v flag) shows proper http response.

Any ideas on how to get this working?

PS: I know I can use socat, or just tell docker to also listen on a tcp socket, but I am using the project atomic vm image, and it won't let me modify anything except /home.

your browser is expecting a proper http response, which is a header block followed by body content. until your stuff outputs at least one blank line, the browser will never see "body" content and just sit there waiting. — Marc B
– Marc B, Commented Aug 21, 2014 at 18:17
Pipes only go one way... the netcat on the left isn't going to get the output from the netcat on the right. The netcat on the left is reading from your original stdin (terminal?) — user2404501
– user2404501, Commented Aug 21, 2014 at 18:29

pqnet · Accepted Answer · 2014-08-21 19:12:15Z

16

You are only redirecting incoming data, not outgoing data. try with:

mkfifo myfifo
nc -lkv 44444 <myfifo | nc -Uv /var/run/docker.sock >myfifo

See http://en.wikipedia.org/wiki/Netcat#Proxying

Edit: in a script you would want to generate the name for the fifo at random, and remove it after opening it:

FIFONAME=`mktemp -u`
mkfifo $FIFONAME
nc -lkv 44444 < $FIFONAME | nc -Uv /var/run/docker.sock > $FIFONAME &
rm $FIFONAME
fg

edited Aug 21, 2014 at 19:12

answered Aug 21, 2014 at 18:32

pqnet

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3 Comments

crashandburn Over a year ago

Thanks! That works great. Also, I am stupid X-D. Just to add something small to your answer, I ran 2 commands: rm -f /tmp/myfifo; mkfifo /tmp/myfifo && nc -lkv 44444 </tmp/myfifo | nc -Uv /var/run/docker.sock >/tmp/myfifo .

pqnet Over a year ago

If you are scripting this, use mktemp -u to generate a name which is guaranteed to be a non-existant file

dormi330 Over a year ago

nice, i use this to open my docker remote port 2375

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