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: disco.rs
    path of file: ./repos/iroh/iroh-net/src
    
    the code of the file until where you have to start completion: //! Contains the discovery message types.
//!
//! A discovery message is:
//!
//! Header:
//!
//! ```ignore
//! magic:            [u8; 6]  // ‚ÄúTSüí¨‚Äù (0x54 53 f0 9f 92 ac)
//! sender_disco_pub: [u8; 32] // nacl public key
//! nonce:            [u8; 24]
//! ````
//! The recipient then decrypts the bytes following (the nacl secretbox)
//! and then the inner payload structure is:
//!
//! ```ignore
//! message_type:    u8   // (the MessageType constants below)
//! message_version: u8   // (0 for now; but always ignore bytes at the end)
//! message_payload: &[u8]
//! ```

use std::{
    fmt::Display,
    net::{IpAddr, SocketAddr},
};

use anyhow::{anyhow, bail, ensure, Context, Result};
use url::Url;

use crate::{derp::DerpUrl, key, net::ip::to_canonical};

use super::{key::PublicKey, stun};

// TODO: custom magicn
/// The 6 byte header of all discovery messages.
pub const MAGIC: &str = "TSüí¨"; // 6 bytes: 0x54 53 f0 9f 92 ac
pub const MAGIC_LEN: usize = MAGIC.as_bytes().len();

/// Current Version.
const V0: u8 = 0;

pub(crate) const KEY_LEN: usize = 32;
const TX_LEN: usize = 12;

// Sizes for the inner message structure.

/// Header: Type | Version
const HEADER_LEN: usize = 2;

const PING_LEN: usize = TX_LEN + key::PUBLIC_KEY_LENGTH;
const EP_LENGTH: usize = 16 + 2; // 16 byte IP address + 2 byte port

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[repr(u8)]
pub enum MessageType {
    Ping = 0x01,
    Pong = 0x02,
    CallMeMaybe = 0x03,
}

impl TryFrom<u8> for MessageType {
    type Error = u8;

    fn try_from(value: u8) -> std::res
    
    fn test_to_from_bytes() {
        struct Test {
            name: &'static str,
            m: Message,
            want: &'static str,
        }
        let tests = [
            Test {
                name: "ping_with_nodekey_src",
                m: Message::Ping(Ping {
                    tx_id: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12].into(),
                    node_key: PublicKey::try_from(&[
                        190, 243, 65, 104, 37, 102, 175, 75, 243, 22, 69, 200, 167, 107, 24, 63, 216, 140, 120, 43, 4, 112, 16, 62, 117, 155, 45, 215, 72, 175, 40, 189][..]).unwrap(),
                }),
                want: "01 00 01 02 03 04 05 06 07 08 09 0a 0b 0c be f3 41 68 25 66 af 4b f3 16 45 c8 a7 6b 18 3f d8 8c 78 2b 04 70 10 3e 75 9b 2d d7 48 af 28 bd",
            },
            Test {
                name: "pong",
                m: Message::Pong(Pong{
                    tx_id: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12].into(),
                    src:  SendAddr::Udp("2.3.4.5:1234".parse().unwrap()),
                }),
                want: "02 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 00 00 00 00 00 00 00 00 00 00 00 ff ff 02 03 04 05 d2 04",
            },
            Test {
                name: "pongv6",
                m: Message::Pong(Pong {
                    tx_id: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12].into(),
                    src: SendAddr::Udp("[fed0::12]:6666".parse().unwrap()),
                }),
                want: "02 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 00 fe d0 00 00 00 00 00 00 00 00 00 00 00 00 00 12 0a 1a",
            },
            Test {
                name: "call_me_maybe",
                m: Message::CallMeMaybe(CallMeMaybe { my_numbers: Vec::new() }),
                want: "03 00",
            },
            Test {
                name: "call_me_maybe_endpoints",
                m: Message::CallMeMaybe(CallMeMaybe {
                    my_numbers: vec![
                        "1.2.3.4:567".parse().unwrap(),
                        "[2001::3456]:789".parse().unwrap(),
                    ],
                }),
                want: "03 00 00 00 00 00 00 00 00 00 00 00 ff ff 01 02 03 04 37 02 20 01 00 00 00 00 00 00 00 00 00 00 00 00 34 56 15 03",
            },
        ];
        for test in tests {
            println!("{}", test.name);

            let got = test.m.as_bytes();
            assert_eq!(
                got,
                hex::decode(test.want.replace(' ', "")).unwrap(),
                "wrong as_bytes"
            );

            let back = Message::from_bytes(&got).expect("failed to parse");
            assert_eq!(test.m, back, "wrong from_bytes");
        }
    }