Asynchronous Socket Echo Server¶
The sockets/echo-async sample application for Zephyr implements an
asynchronous IPv4/IPv6 TCP echo server using a BSD Sockets compatible API
with non-blocking sockets and a
poll() call. This is an extension of
the Socket Echo Server sample. It’s a more involved application,
supporting both IPv4 and IPv6 with concurrent connections, limiting
maximum number of simultaneous connections, and basic error handling.
The source code for this sample application can be found at:
Building and Running¶
Build the Zephyr version of the sockets/echo_async application like this:
# On Linux/macOS cd $ZEPHYR_BASE/samples/net/sockets/echo_async mkdir build && cd build # On Windows cd %ZEPHYR_BASE%\samples\net\sockets\echo_async mkdir build & cd build cmake -GNinja -DBOARD=<board_to_use> .. ninja
board_to_use defaults to
qemu_x86. In this case, you can run the
application in QEMU using
make run. If you used another BOARD, you
will need to consult its documentation for application deployment
instructions. You can read about Zephyr support for specific boards in
the documentation at Supported Boards.
After the sample starts, it expects connections at 192.0.2.1 (IPv4), or 2001:db8::1 (IPv6), port 4242. The easiest way to connect is:
$ telnet 192.0.2.1 4242 # use this for IPv4 $ telnet 2001:db8::1 4242 # or this for IPv6
After a connection is made, the application will echo back any line sent to
it. Unlike the above-mentioned Socket Echo Server, this application
supports multiple concurrent client connections. You can open
another terminal window and run the same telnet command as above.
The sample supports up to three connected clients, but this can be adjusted
NUM_FDS defined in the source code.
Running application on POSIX Host¶
The same application source code can be built for a POSIX system, e.g. Linux. (Note: if you look at the source, you will see that the code is the same except the header files are different for Zephyr vs POSIX, and there’s an additional option to set for Linux to make a socket IPv6-only).
To build for a host POSIX OS:
$ make -f Makefile.posix
$ telnet 127.0.0.1 4242 # use this for IPv4 $ telnet ::1 4242 # or this for IPv6
As can be seen, the behavior of the application is the same as the Zephyr version.