You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: handshake_response.rs
    path of file: ./repos/sqlx/sqlx-mysql/src/protocol/connect
    
    the code of the file until where you have to start completion: use crate::io::MySqlBufMutExt;
use crate::io::{BufMutExt, Encode};
use crate::protocol::auth::AuthPlugin;
use crate::protocol::connect::ssl_request::SslRequest;
use crate::protocol::Capabilities;

// https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::HandshakeResponse
// https://mariadb.com/kb/en/connection/#client-handshake-response

#[derive(Debug)]
pub struct HandshakeResponse<'a> {
    pub database: Option<&'a str>,

    /// Max size of a command packet that the client wants to send to the server
    p
    
    fn encode_with(&self, buf: &mut Vec<u8>, mut capabilities: Capabilities) {
        if self.auth_plugin.is_none() {
            // ensure PLUGIN_AUTH is set *only* if we have a defined plugin
            capabilities.remove(Capabilities::PLUGIN_AUTH);
        }

        // NOTE: Half of this packet is identical to the SSL Request packet
        SslRequest {
            max_packet_size: self.max_packet_size,
            collation: self.collation,
        }
        .encode_with(buf, capabilities);

        buf.put_str_nul(self.username);

        if capabilities.contains(Capabilities::PLUGIN_AUTH_LENENC_DATA) {
            buf.put_bytes_lenenc(self.auth_response.unwrap_or_default());
        } else if capabilities.contains(Capabilities::SECURE_CONNECTION) {
            let response = self.auth_response.unwrap_or_default();

            buf.push(response.len() as u8);
            buf.extend(response);
        } else {
            buf.push(0);
        }

        if capabilities.contains(Capabilities::CONNECT_WITH_DB) {
            if let Some(database) = &self.database {
                buf.put_str_nul(database);
            } else {
                buf.push(0);
            }
        }

        if capabilities.contains(Capabilities::PLUGIN_AUTH) {
            if let Some(plugin) = &self.auth_plugin {
                buf.put_str_nul(plugin.name());
            } else {
                buf.push(0);
            }
        }
    }