Openthread CLI UDP communication from main.c (NRF52840) - udp

Question

We are working with NRF52840 dongles and want to be able to have them relay data over an OpenThread mesh network through UDP automatically. We have found within the OpenThread API a solid Udp.h library with all the Udp functions we need to create code that runs on the dongles from the main.c.
Below is our code that should broadcast the message: "Hallo" to all nodes that have an open socket on port 1994.
We have read that the ipv6 address ff03::1 is reserved for multicast UDP broadcasting and it works perfectly when manually performed with the CLI udp commands.
CLI: Udp open, udp send ff03::1 1994 Hallo
With all the nodes that have udp open, udp bind :: 1994, receiving the Hallo message from the sending node.
We are trying to recreate this in the main.c of our nodes so that we can provide the nodes with some intelligence of their own.
This piece of code is run once when the push button on the dongle is pressed.
The code compiles perfectly and we have tested the functions that have a return with the RGB led (green OK, red not) to confirm that there weren't any errors produced (sadly not all functions return a no_error value)
void udpSend(){
const char *buf = "Hallo";
otMessageInfo messageInfo;
otInstance *myInstance;
myInstance = thread_ot_instance_get();
otUdpSocket mySocket;
memset(&messageInfo, 0, sizeof(messageInfo));
// messageInfo.mPeerAddr = otIp6GetUnicastAddresses(myInstance)->mNext->mNext->mAddress;
otIp6AddressFromString("ff03::1", &messageInfo.mPeerAddr);
messageInfo.mPeerPort = 1994;
messageInfo.mInterfaceId = OT_NETIF_INTERFACE_ID_THREAD;
otUdpOpen(myInstance, &mySocket, NULL, NULL);
otMessage *test_Message = otUdpNewMessage(myInstance, NULL);
otMessageSetLength(test_Message, sizeof(buf));
if (otMessageAppend(test_Message, &buf, sizeof(buf)) == OT_ERROR_NONE){
nrf_gpio_pin_write(LED2_G, 0);
}
else{
nrf_gpio_pin_write(LED2_R, 0);
}
otUdpSend(&mySocket, test_Message, &messageInfo);
otCliUartOutputFormat("Done.\0");
otUdpClose(&mySocket);
}
Now, we aren't exactly experts, so we are not sure why this isn't working as we had a lot of trouble figuring out how everything is called/initialised.
We hope to create a way to send and receive data through UDP through the code, so that they can operate autonomously.
We would really appreciate it if someone could assist us with our project!
Thanks!
Jonathan

Answer 1

There are a few errors in your code:
Remove the call to otMessageSetLength(). The message length is automatically increased as part of otMessageAppend().
The call to otMessageAppend() should be: otMessageAppend(test_message, buf, (uint16_t)strlen(buf)).
Removed the & before buf.
Replaced sizeof() with strlen().
Couple other things you should consider:
After calling otUdpNewMessage(), if any following call returns an error, make sure to call otMessageFree() on the message buffer.
Custody is only given to OpenThread after a successful call to otUdpSend().
Do not call udpSend() from interrupt context.
OpenThread library was designed to assume a single thread of execution.
Hope that helps.