See https://medium.com/@ly.lee/safer-simpler-embedded-rust-with-apache-mynewt-on-stm32-blue-pill-d8fcb41969ac?source=friends_link&sk=16a27a4b9910aadcfcb9881c02d84adc

run-unexpanded.rs

run({
    let encoder = COAP_CONTEXT.encoder("COAP_CONTEXT", "_map");
    cbor_encode_text_string(
        encoder,
        COAP_CONTEXT.key_to_cstr(key_with_opt_null),
        COAP_CONTEXT.cstr_len(key_with_opt_null));
    cbor_encode_int(encoder, value);
})