samples: net: sockets: Add READMEs for echo/echo_async samples

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>

samples/net/sockets/echo/README.rst

@@ -0,0 +1,78 @@
+.. _sockets-echo-sample:
+
+Socket Echo Server
+##################
+
+Overview
+********
+
+The sockets/echo sample application for Zephyr implements an IPv4 TCP echo
+server using a BSD Sockets like API. The purpose of this sample is to show
+how it's possible to develop a sockets application portable to both POSIX
+and Zephyr. As such, it is kept minimal and supports only IPv4 and TCP.
+
+The source code for this sample application can be found at:
+:file:`samples/net/sockets/echo`.
+
+Requirements
+************
+
+- :ref:`networking_with_qemu`
+- or, a board with hardware networking
+
+Building and Running
+********************
+
+Build the Zephyr version of the sockets/echo application like this:
+
+.. code-block:: console
+
+    $ cd $ZEPHYR_BASE/samples/net/sockets/echo
+    $ make pristine
+    $ make BOARD=<board_to_use>
+
+``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 :ref:`boards`.
+
+After the sample starts, it expects connections at 192.0.2.1, port 4242.
+The easiest way to connect is:
+
+.. code-block:: console
+
+    $ telnet 192.0.2.1 4242
+
+After a connection is made, the application will echo back any line sent
+to it. The application implements a single-threaded server using blocking
+sockets, and thus can serve only one client connection at time. After the
+current client disconnects, the next connection can proceed.
+
+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 code is the
+same except the header files are different for Zephyr vs POSIX.)
+
+To build for a host POSIX OS:
+
+.. code-block:: console
+
+    $ make -f Makefile.posix
+
+To run:
+
+.. code-block:: console
+
+    $ ./socket_echo
+
+To test:
+
+.. code-block:: console
+
+    $ telnet 127.0.0.1 4242
+
+As can be seen, the behavior of the application is the same as the Zephyr
+version.

samples/net/sockets/echo_async/README.rst

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+.. _async-sockets-echo-sample:
+
+Asynchronous Socket Echo Server
+###############################
+
+Overview
+********
+
+The sockets/echo-async sample application for Zephyr implements an
+asyncronous IPv4 TCP echo server using a BSD Sockets like API with
+non-blocking sockets and a ``poll()`` call. This is an extension of
+the :ref:`sockets-echo-sample` sample. The purpose of this sample is
+still to show how it's possible to develop a sockets application portable
+to both POSIX and Zephyr. As such, it is kept minimal and supports only
+IPv4 and TCP.
+
+The source code for this sample application can be found at:
+:file:`samples/net/sockets/echo_async`.
+
+Requirements
+************
+
+- :ref:`networking_with_qemu`
+- or, a board with hardware networking
+
+Building and Running
+********************
+
+Build the Zephyr version of the sockets/echo_async application like this:
+
+.. code-block:: console
+
+    $ cd $ZEPHYR_BASE/samples/net/sockets/echo_async
+    $ make pristine
+    $ make BOARD=<board_to_use>
+
+``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 :ref:`boards`.
+
+After the sample starts, it expects connections at 192.0.2.1, port 4242.
+The easiest way to connect is:
+
+.. code-block:: console
+
+    $ telnet 192.0.2.1 4242
+
+After a connection is made, the application will echo back any line sent to
+it. Unlike the above-mentioned :ref:`sockets-echo-sample`, 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
+by changing ``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 code is
+the same except the header files are different for Zephyr vs POSIX.)
+
+To build for a host POSIX OS:
+
+.. code-block:: console
+
+    $ make -f Makefile.posix
+
+To run:
+
+.. code-block:: console
+
+    $ ./socket_echo
+
+To test:
+
+.. code-block:: console
+
+    $ telnet 127.0.0.1 4242
+
+As can be seen, the behavior of the application is the same as the Zephyr
+version.