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:

Using west:

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

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=<board to use> -DCONF_FILE=<config file to use> samples/net/sockets/echo_client
ninja -C build

Example building for the nRF52840_pca10056 with OpenThread support:

Using west:

west build -t run

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=nrf52840_pca10056 -DCONF_FILE="prj.conf overlay-ot.conf" samples/net/sockets/echo_client
ninja -C build run

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:

Using west:

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

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=qemu_x86 -DCONF_FILE="prj.conf overlay-tls.conf" samples/net/sockets/echo_client
ninja -C build

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.

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:

Using west:

west build -t run

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=qemu_x86 -DCONF_FILE="prj.conf overlay-linux.conf" samples/net/sockets/echo_client
ninja -C build run

Note that echo-server must be running in the Linux host terminal window before you start the echo-client application in QEMU.

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.