1.. zephyr:code-sample:: async-sockets-echo
2   :name: Asynchronous echo server using poll()
3   :relevant-api: bsd_sockets
4
5   Implement an asynchronous IPv4/IPv6 TCP echo server using BSD sockets and poll()
6
7Overview
8********
9
10The sockets/echo-async sample application for Zephyr implements an
11asynchronous IPv4/IPv6 TCP echo server using a BSD Sockets compatible API
12with non-blocking sockets and a ``poll()`` call. This is an extension of
13the :zephyr:code-sample:`sockets-echo` sample. It's a more involved application,
14supporting both IPv4 and IPv6 with concurrent connections, limiting
15maximum number of simultaneous connections, and basic error handling.
16
17The source code for this sample application can be found at:
18:zephyr_file:`samples/net/sockets/echo_async`.
19
20Requirements
21************
22
23- :ref:`networking_with_host`
24- or, a board with hardware networking (including 6LoWPAN)
25
26Building and Running
27********************
28
29Build the Zephyr version of the sockets/echo_async application like this:
30
31.. zephyr-app-commands::
32   :zephyr-app: samples/net/sockets/echo_async
33   :board: <board_to_use>
34   :goals: build
35   :compact:
36
37After the sample starts, it expects connections at 192.0.2.1 (IPv4), or
382001:db8::1 (IPv6), port 4242. The easiest way to connect is:
39
40.. code-block:: console
41
42    $ telnet 192.0.2.1 4242     # use this for IPv4
43    $ telnet 2001:db8::1 4242   # or this for IPv6
44
45After a connection is made, the application will echo back any line sent to
46it. Unlike the above-mentioned :zephyr:code-sample:`sockets-echo` sample, this application
47supports multiple concurrent client connections. You can open
48another terminal window and run the same telnet command as above.
49The sample supports up to three connected clients, but this can be adjusted
50by changing ``NUM_FDS`` defined in the source code.
51
52Wi-Fi
53=====
54
55The IPv4 Wi-Fi support can be enabled in the sample with
56:ref:`Wi-Fi snippet <snippet-wifi-ipv4>`.
57
58Running application on POSIX Host
59=================================
60
61The same application source code can be built for a POSIX system, e.g.
62Linux. (Note: if you look at the source, you will see that the code is
63the same except the header files are different for Zephyr vs POSIX, and
64there's an additional option to set for Linux to make a socket IPv6-only).
65
66To build:
67
68.. code-block:: console
69
70    $ make -f Makefile.host
71
72To run:
73
74.. code-block:: console
75
76    $ ./socket_echo
77
78To test:
79
80.. code-block:: console
81
82    $ telnet 127.0.0.1 4242   # use this for IPv4
83    $ telnet ::1 4242         # or this for IPv6
84
85As can be seen, the behavior of the application is the same as the Zephyr
86version.
87