Skip to content

SOCAT

socat = SOcket CAT A general-purpose tool for connecting two data streams (network, serial, files, pipes, PTYs, etc.).

Demo

keyboard->udp
1
socat STDIO,raw,echo=0 UDP:127.0.0.1:7000
udp->screen
1
socat UDP4-LISTEN:7000,reuseaddr STDOUT

udp 2 serial

  • UDP-LISTEN = Connected UDP socket
  • UDP-RECVFROM = Unconnected UDP socket - raw UDP socket with source tracking

Connected UDP socket (UDP-LISTEN) - You call connect() on a UDP socket - Kernel remembers one peer You can: - send() (no address needed) - recv() (only from that peer) - Replies automatically go to that peer

Unconnected UDP socket (UDP-RECVFROM) - You call bind() only - You must: - recvfrom() (get source address) - sendto() (specify destination) - Can talk to many peers

Udp listener

Any UDP packet sent to host IP will be forwarded to the serial device. The sender’s address is remembered so responses can be sent back.

1
2
3
socat -d -d \
  UDP4-LISTEN:14550,reuseaddr \
  FILE:/dev/ttyUSB0,b115200,raw,echo=0
  • reuseaddr Allows rebinding to the same port Useful if:
  • the program crashed

  • you restart quickly

  • raw Disables all terminal processing:

  • No newline translation

  • No character filtering
  • No flow control

  • Binary-safe

  • echo=0 Disable echo, Prevents characters sent to the serial port from being echoed back

multiple clients

  • One serial port multiple udp clients

fork

fork open multiple process that write and read against the serial process

echo server

I use usb2uart and connect the TX with RX

1
socat -d -d   UDP4-RECVFROM:14550,fork   FILE:/dev/ttyUSB0,b115200,raw,echo=0
test
1
2
3
4
# using nc as client
# can open multiple nc client

nc -u 127.0.0.1 14550
  • UDP4-RECVFROM:14550
    • Create a UDP IPv4 socket
    • Bind to local port 14550
    • Receive datagrams from any remote host/port
    • Reply packets go back to the source of the last received datagram
  • fork For each new incoming peer, socat: fork()s a child process The child handles data forwarding The parent keeps listening For UDP, it works per sender address (IP:port), not per connection.

TCP 2 serial

Not working for multiple connection

1
2
3
socat -d -d \
  TCP4-LISTEN:14550,reuseaddr,fork \
  FILE:/dev/ttyUSB0,b115200,raw,echo=0