I have a linux machine which is listening for connections on port 4450. Where there is an incomming connection, this is supposed to send continuously over the socket the content of a file. Did you do this before ?
What I've done so far was to send once the content of the file like this:
x=$(filename); echo $x | nc -l 4450
On the client side I have an Android app, which connects to the server and then using a BufferedReader gets the data from the stream and processes it.
Any help would be highly appreciated.
Thanks
Use socat instead of netcat (nc). With socat you can do almost everything that can be done with netcat. But socat has a lot more features and is easier to use.
socat TCP-LISTEN:4450,fork OPEN:/tmp/filename,rdonly
You can also use the output of a command instead of some file contents:
socat TCP-LISTEN:4450,fork EXEC:/bin/date
Related
So right now I have a server that is pinging an api and writes to stdout. I pipe that to nc as such.
node server.js | nc -lk 9999
I then have a job that listens to that and outputs 5 second snapshots of the data.
My question is that when I try to do that in multiple sessions with multiple server.js programs eg. server1.js, server2.js which all hit different parts of the api and pipe them all to port 9999. Only the first program gets picked up by the snapshot job. How do I pipe multiple outputs to:
nc -lk 9999
such that they all get handled as if it's the output of one program?
If you execute multiple times that command, it simply won't work. You cannot listen with several instances of netcat on the same port. You should get a nc: Address already in use error.
What you can do is something like:
mkfifo queue
nc -lk 9999 < queue
node server.js | cat > queue
Btw I did a nice and fully working Netcat porting in Node.js: https://github.com/roccomuso/netcat
This easily address the issue you're encountering, because you can implement the whole logic in JS without using the native nc bin or pipe data on the stdin.
I have a command which out outputs certain data which i store in a ext file using a '>>' command.Now Instead of doing that I want to have a socket or a port on any server which will catch the output of the command.Basically i want to output all my script data to a socket or url which ever is possible.
Any help in this direction is most welcomed.
You can use socat to listening on a port 12345 and echo any data sent to it like this:
socat -u TCP-LISTEN:12345,keepalive,reuseaddr,fork STDOUT
If you want to capture it to a file as well (file.log), you can use the same command with tee:
socat -u TCP-LISTEN:12345,keepalive,reuseaddr,fork STDOUT | tee file.log
You can run your program to output to bash's TCP virtual device:
./prog > /dev/tcp/localhost/12345
If you don't want to use bash magic then you can also use socat to send the data:
./prog | socat - TCP-CONNECT:localhost:12345
The above example assume you are running your program and "logger" on the same system but you can replace "localhost" with the hostname or address of the system you wish to send to (where the socat is listening).
I am running embedded linux program, so that the kernel init script automatically start the program, and the stdin/stdout are going through the serial device, which is also the shell.
When I connect to target with telnet, I don't see the same stdin/stdout of the program.
Maybe I can redirect console stdin/stdout to telnet connection ?
What ways do I have to gain such capabilities using the telnet connection ?
Thanks,
Ran
I don't know if it is possible with telnet, but you can mock it through netcat. Just like below:
<STDOUT> | netcat -t www.example.com 80
I'm developing some gateway product connected to host PC via USB, with embedded linux inside.
My task is read to read logs UDP stream from device file and to forward it both to remote host and to save it to file in my file system (ramfs)
I do this using the following command:
socat -b1450 -u /dev/ueservice0 - | tee -a /tmp/ModemFW.log | socat -b1450 -u - UDP4-DATAGRAM:${IPADDR}:4566
The problem is that when there's heavy data traffic (FTP) stream running on the same USB interface approx. half of the stream doesn't reach the destination, though the ModemFW.log file contains all the logs.
The weird thing is that if I don't save the logs to file on ramfs everything works fine and the host receives all the stream even with the same heavy traffic:
socat -b1450 -u /dev/ueservice0 UDP4-DATAGRAM:${IPADDR}:4566
Does anybody know what is the problem that tee causes that half of the packets get lost? Is there another way to do it?
Any help will be very appreciated!
Assume a legacy Linux application listening on a UNIX domain socket /tmp/foo.
In addition to communicating with this legacy application over the UNIX domain socket mechanism I want to be able to connect to it via a TCP-connection on port say 1234.
What is the easiest way to bind to TCP port 1234 and then redirect all incoming connections to the UNIX domain socket /tmp/foo?
Turns out socat can be used to achieve this:
socat TCP-LISTEN:1234,reuseaddr,fork UNIX-CLIENT:/tmp/foo
And with a bit of added security:
socat TCP-LISTEN:1234,bind=127.0.0.1,reuseaddr,fork,su=nobody,range=127.0.0.0/8 UNIX-CLIENT:/tmp/foo
These examples have been tested and work as expected.
Easiest? Probably Netcat (aka nc):
nc -l 1234 | nc -U /tmp/foo
The first command listens on port 1234 for incoming connections, and pipes the resulting data to the second command. The second connects to the Unix domain socket /tmp/foo, and writes its input to that socket. Note that this will only accept a single connection, and exit as soon as that connection is dropped. If you want to keep listening for more connections, use the -k option:
nc -lk 1234 | nc -U /tmp/foo
You can test that this is working by setting up a listener for that socket in one terminal:
nc -lUk /tmp/foo
And writing to it in another:
nc localhost 1234
socat, as recommended by knorv, is more capable, but more complicated to use.
You should be able to bind to TCP 1234, get a socket fd for /tmp/foo and use the select call to 'listen' for data on both 1234, and /tmp/foo. Any data written to 1234, you rewrite to /tmp/foo and vice-versa.
You now act as a proxy and transfer data back and forth.
And here is a web-page which might help: http://osr507doc.sco.com/en/netguide/dusockC.io_multiplexing.html
In additons to #knorv's answer: with xinetd it can work like a daemon
# cat /etc/xined.d/mysrv
service mysrv
{
disable = no
type = UNLISTED
socket_type = stream
protocol = tcp
wait = no
server = /usr/bin/socat
server_args = STDIN UNIX-CLIENT:/tmp/mysocket.sock
bind = 127.0.0.1
port = 1234
}
Not tried it : but it looks like 'lighttpd' can do this for you:
http://redmine.lighttpd.net/wiki/lighttpd/Docs:ModProxyCore