Function encode_string 

pub fn encode_string<B: BufMut>(buf: &mut B, string: &str) -> Result<()>

Encodes a UTF-8 string with a 2-byte length prefix (compatibility function)

This function provides compatibility with the old string module API. Prefer using MqttString::create(string)?.to_be_bytes() for new code.

Errors

Returns an error if:

• The string contains null characters
• The string length exceeds maximum string length