Change some function signature

[Aya0wind]

Hi, I'm writing a C-FFI binding for this project, but i think some function signature is not reasonable enough.

Example

pub fn keygen(
    _pk: &KpAbePublicKey,
    _msk: &KpAbeMasterKey,
    _policy: &String,
    _language: PolicyLanguage,
) -> Result<KpAbeSecretKey, RabeError> 

the parameter _policy in this function is &String, but this function only need a immutable reference, i recommend use &str. Similarly, in this function:

pub fn encrypt(
    _gk: &Aw11GlobalKey,
    _pks: &Vec<Aw11PublicKey>,
    _policy: &String,
    _language: PolicyLanguage,
    _plaintext: &[u8],
) -> Result<Aw11Ciphertext, RabeError> 

the type of _pks should be &[Aw11PublicKey] instead of &Vec<Aw11PublicKey>

Reason

• I can construct a String from a *const c_char by let s = String::from_raw_parts(policy as *mut u8,len, len) during FFI calling.But, because this String not really own its memory, so we need a std::mem::forget(s) to make sure not free the memory passed by FFI calling.
• If use &str, i can construct a slice from pointer directly and no need to care about memory.
• Also, When i pass a array of pointer for &Vec<Aw11PublicKey>, i need to use Vec::from_raw_partsand not free the memory.
• Not only in FFI, if i want to pass a let policy = "xxxxx", i also need to construct a String and pass it to function. But if the parameter is &str, i can pass policy directly.
• And because String had impl trait Deref<str>, pass a &String to a &str is ok.
• Similarly, use &Vec<T> instead of &[T] has the same problem. Such as &Vec<String>, all of these are FFI unfriendly and may cause unnecessary overhead under certain circumstances.

[georgbramm]

Still interested ? we could do that with the next update

[georgbramm]

should be fixed now