// Define request handler for /hello
static int handle_hello_request(unicoap_message_t* message, 
    const unicoap_aux_t* aux, unicoap_request_context_t* ctx, void* arg) {
    // The aux parameter provides access to auxiliary information, such as local and remote endpoints,
    // transport-specific data and internal properties such as the message token.

    // Retrieve remote (client) endpoint and log string description of protocol number.
    printf("/hello/world resource invoked over %s\n", unicoap_string_from_proto(aux->remote->proto));

    // Craft response using convenience initializer. Vectored payloads are supported, too.
    unicoap_response_init_string(message, UNICOAP_STATUS_CONTENT, "Hello, World!");

    // Send response.
    return unicoap_send_response(message, ctx);
}

// Statically define resource, but dynamic registrations are also possible.
UNICOAP_RESOURCE(helloworld) {
    // When you specify a path, you now need to specify each component separately.
    // The UNICOAP_PATH macro checks if you passed garbage at compile time.
    .path = UNICOAP_PATH("hello", "world"), // /hello/world,
    
    // Instruct unicoap to send confirmable messages when communicating over UDP or DTLS.
    // This flag abstracts the transport-specific message type.
    .flags = UNICOAP_RESOURCE_FLAG_RELIABLE,
    
    // Specify what methods to allow. In unicoap, there are no duplicate defines for method flags.
    .methods = UNICOAP_METHODS(UNICOAP_METHOD_GET, UNICOAP_METHOD_PUT),
    
    // Optionally, you can also restrict the resource to a set of transports.
    .protocols = UNICOAP_PROTOCOLS(UNICOAP_PROTO_DTLS, UNICOAP_PROTO_UDP),
    
    .handler = handle_hello_request,
    .handler_arg = NULL
};