1.. zephyr:code-sample:: async-sockets-echo-select
2   :name: Asynchronous echo server using select()
3   :relevant-api: bsd_sockets
4
5   Implement an asynchronous IPv4/IPv6 TCP echo server using BSD sockets and select()
6
7Overview
8********
9
10The sockets/echo_async_select sample application for Zephyr implements an
11asynchronous IPv4/IPv6 TCP echo server using a BSD Sockets compatible API
12with non-blocking sockets and a ``select()`` call. This is a variant of
13the :zephyr:code-sample:`async-sockets-echo` sample.
14
15The source code for this sample application can be found at:
16:zephyr_file:`samples/net/sockets/echo_async_select`.
17
18Requirements
19************
20
21- :ref:`networking_with_host`
22- or, a board with hardware networking (including 6LoWPAN)
23
24Building and Running
25********************
26
27Build the Zephyr version of the sockets/echo_async application like this:
28
29.. zephyr-app-commands::
30   :zephyr-app: samples/net/sockets/echo_async_select
31   :board: <board_to_use>
32   :goals: build
33   :compact:
34
35After the sample starts, it expects connections at 192.0.2.1 (IPv4), or
362001:db8::1 (IPv6), port 4242. The easiest way to connect is:
37
38.. code-block:: console
39
40    $ telnet 192.0.2.1 4242     # use this for IPv4
41    $ telnet 2001:db8::1 4242   # or this for IPv6
42
43After a connection is made, the application will echo back any line sent to
44it. Unlike the :zephyr:code-sample:`sockets-echo` sample, this application
45supports multiple concurrent client connections. You can open
46another terminal window and run the same telnet command as above.
47The sample supports up to three connected clients, but this can be adjusted
48by changing ``NUM_FDS`` defined in the source code.
49
50Running application on POSIX Host
51=================================
52
53The same application source code can be built for a POSIX system, e.g.
54Linux. (Note: if you look at the source, you will see that the code is
55the same except the header files are different for Zephyr vs POSIX, and
56there's an additional option to set for Linux to make a socket IPv6-only).
57
58To build:
59
60.. code-block:: console
61
62    $ make -f Makefile.host
63
64To run:
65
66.. code-block:: console
67
68    $ ./socket_echo
69
70To test:
71
72.. code-block:: console
73
74    $ telnet 127.0.0.1 4242   # use this for IPv4
75    $ telnet ::1 4242         # or this for IPv6
76
77As can be seen, the behavior of the application is the same as the Zephyr
78version.
79