Asynchronous Socket Echo Server Using select()¶
The sockets/echo_async_select sample application for Zephyr implements an
asynchronous IPv4/IPv6 TCP echo server using a BSD Sockets compatible API
with non-blocking sockets and a
select() call. This is a variant of
the Asynchronous Socket Echo Server sample.
The source code for this sample application can be found at: samples/net/sockets/echo_async_select.
- Networking with the host system
- or, a board with hardware networking (including 6LoWPAN)
Building and Running¶
Build the Zephyr version of the sockets/echo_async application like this:
west build -b <board_to_use> samples/net/sockets/echo_async_select
Using CMake and ninja:
cmake -B build -GNinja -DBOARD=<board_to_use> samples/net/sockets/echo_async_select ninja -C build
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 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.