Function fit_string 

pub fn fit_string(
    at: usize,
    value: String,
    bound: usize,
    behaviour: TryConstruct,
) -> Result<Narrowed<String>, WireError>

A string that has been read whole, against the receiver’s bound.

The bound counts octets, which is what string<N> means to every peer that has to hold the value: char[N + 1] in the C mapping of all four DDS implementations, fixed_string<N> in Fast DDS’s. Counting Unicode scalar values instead would accept a five-character value of ten octets that no C peer can hold.

A wstring<N> bound counts UTF-16 code units instead and goes to fit_wstring, which is a second function and not an argument: the two bounds count different things, and one function taking “octets or units” would be a call site deciding which by getting an argument right.

Errors

WireError::Discarded under TryConstruct::Discard, and WireError::OutOfRange for a TryConstruct::Trim the front end should have refused — Table 11 makes TRIM on a type that cannot be trimmed “unspecified and may be treated as an error”, Cyclone refuses such a declaration by name, and reaching here means a model that did not come through the front end.