Function write_request 

pub fn write_request(
    method: &str,
    path: &str,
    headers: &[(&str, &str)],
    dst: &mut [u8],
) -> Result<usize, HttpError>

Write an HTTP/1.1 request into a byte buffer. Returns bytes written.

Returns HttpError::BufferTooSmall if dst is undersized. Use request_size to compute the exact size needed.