Function ser_to_buf_asc_exact 

pub fn ser_to_buf_asc_exact<T>(buf: &mut [u8], value: &T) -> Result
where
    T: ?Sized + Serialize,

Serialize value into pre-allocated, exact size byte buffer

Buffer is expected to be of exact size to hold serialized data. You can use calc_size() to get exact size of required buffer before serialization.

In case of buffer underflow or buffer overflow, corresponding error is returned.

Example

#[derive(serde_derive::Serialize)]
struct Foo(u16, String);
let foo = Foo(1, "abc".to_string());

assert_eq!(calc_size_asc(&foo).unwrap(), 6);
let mut buf = [0_u8; 6];  // need buffer of exact size!
ser_to_buf_asc_exact(&mut buf, &foo).unwrap();
assert_eq!(&buf[2..5], b"abc");
assert_eq!(buf[5], 7); // last byte is string length (3) in varint encoding