This is the documentation for the latest (main) development branch of Zephyr. If you are looking for the documentation of previous releases, use the drop-down menu on the left and select the desired version.

Socket Echo Client


The echo-client sample application for Zephyr implements a UDP/TCP client that will send IPv4 or IPv6 packets, wait for the data to be sent back, and then verify it matches the data that was sent.

The source code for this sample application can be found at: samples/net/sockets/echo_client.

Building and Running

There are multiple ways to use this application. One of the most common usage scenario is to run echo-client application inside QEMU. This is described in Networking with QEMU.

There are configuration files for different boards and setups in the echo-client directory:

  • prj.conf Generic config file, normally you should use this.

  • overlay-ot.conf This overlay config enables support for OpenThread.

  • overlay-802154.conf This overlay config enables support for native IEEE 802.15.4 connectivity. Note, that by default IEEE 802.15.4 L2 uses unacknowledged communication. To improve connection reliability, acknowledgments can be enabled with shell command: ieee802154 ack set.

  • overlay-bt.conf This overlay config enables support for Bluetooth IPSP connectivity.

  • overlay-qemu_802154.conf This overlay config enables support for two QEMU’s when simulating IEEE 802.15.4 network that are connected together.

  • overlay-tls.conf This overlay config enables support for TLS.

Build echo-client sample application like this:

west build -b <board to use> samples/net/sockets/echo_client -- -DCONF_FILE=<config file to use>

Example building for the nrf52840dk_nrf52840 with OpenThread support:

west build -b nrf52840dk_nrf52840 samples/net/sockets/echo_client -- -DCONF_FILE="prj.conf overlay-ot.conf"
west build -t run

Example building for the IEEE 802.15.4 RF2XX transceiver:

west build -b [atsamr21_xpro | sam4s_xplained | sam_v71_xult] samples/net/sockets/echo_client -- -DOVERLAY_CONFIG=overlay-802154.conf
west flash

In a terminal window you can check if communication is happen:

$ minicom -D /dev/ttyACM1

Enabling TLS support

Enable TLS support in the sample by building the project with the overlay-tls.conf overlay file enabled, for example, using these commands:

west build -b qemu_x86 samples/net/sockets/echo_client -- -DCONF_FILE="prj.conf overlay-tls.conf"

An alternative way is to specify -DOVERLAY_CONFIG=overlay-tls.conf when running west build or cmake.

The certificate and private key used by the sample can be found in the sample’s src directory. The default certificates used by Socket Echo Client and Socket Echo Server enable establishing a secure connection between the samples.

SOCKS5 proxy support

It is also possible to connect to the echo-server through a SOCKS5 proxy. To enable it, use -DOVERLAY_CONFIG=overlay-socks5.conf when running west build or cmake.

By default, to make the testing easier, the proxy is expected to run on the same host as the echo-server in Linux host.

To start a proxy server, for example a builtin SOCKS server support in ssh can be used (-D option). Use the following command to run it on your host with the default port:

For IPv4 proxy server:

For IPv6 proxy server:

Run both commands if you are testing IPv4 and IPv6.

To connect to a proxy server that is not running under the same IP as the echo-server or uses a different port number, modify the following values in echo_client/src/tcp.c.

#define SOCKS5_PROXY_PORT    1080

Running echo-server in Linux Host

There is one useful testing scenario that can be used with Linux host. Here echo-client is run in QEMU and echo-server is run in Linux host.

To use QEMU for testing, follow the Networking with QEMU guide.

In a terminal window:

$ sudo ./echo-server -i tap0

Run echo-client application in QEMU:

west build -b qemu_x86 samples/net/sockets/echo_client -- -DCONF_FILE="prj.conf overlay-linux.conf"
west build -t run

Note that echo-server must be running in the Linux host terminal window before you start the echo-client application in QEMU. Exit QEMU by pressing CTRL+A x.

You can verify TLS communication with a Linux host as well. See documentation for information on how to test TLS with Linux host samples.

See the Socket Echo Server documentation for an alternate way of running, with the echo-client on the Linux host and the echo-server in QEMU.