torrent-core 0.1.6

//! KRPC message encoding/decoding — BEP 5.
//!
//! Provides the [`KrpcMessage`] enum, builder helpers for queries
//! and responses, response parsers, and compact node I/O.

use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};

use crate::bencode::{self, Bencode, Bytes};
use crate::error::{Error, ErrorKind};

use super::Node;

/// Transaction ID type (2-byte random value).
pub type TransactionId = [u8; 2];

/// KRPC message types (BEP 5).
///
/// Each message is a bencoded dictionary with the following structure:
///
/// ```text
/// Query:  {"t": "<2-byte id>", "y": "q", "q": "<method>", "a": <args>}
/// Response: {"t": "<2-byte id>", "y": "r", "r": <result>}
/// Error:  {"t": "<2-byte id>", "y": "e", "e": [<code>, <msg>]}
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum KrpcMessage {
    Query {
        transaction_id: TransactionId,
        method: String,
        args: Bencode,
    },
    Response {
        transaction_id: TransactionId,
        result: Bencode,
    },
    Error {
        transaction_id: TransactionId,
        code: i64,
        message: String,
    },
}

impl KrpcMessage {
    /// Encode a KRPC message to bencoded bytes.
    pub fn to_bytes(&self) -> Vec<u8> {
        tracing::trace!("encoding KRPC message: {:?}", self);
        let dict = match self {
            KrpcMessage::Query {
                transaction_id,
                method,
                args,
            } => Bencode::Dict(vec![
                (
                    t_key(),
                    Bencode::Bytes(Bytes::copy_from_slice(transaction_id)),
                ),
                (y_key(), Bencode::Bytes(Bytes::copy_from_slice(b"q"))),
                (
                    q_key(),
                    Bencode::Bytes(Bytes::copy_from_slice(method.as_bytes())),
                ),
                (a_key(), args.clone()),
            ]),
            KrpcMessage::Response {
                transaction_id,
                result,
            } => Bencode::Dict(vec![
                (
                    t_key(),
                    Bencode::Bytes(Bytes::copy_from_slice(transaction_id)),
                ),
                (y_key(), Bencode::Bytes(Bytes::copy_from_slice(b"r"))),
                (r_key(), result.clone()),
            ]),
            KrpcMessage::Error {
                transaction_id,
                code,
                message,
            } => Bencode::Dict(vec![
                (
                    t_key(),
                    Bencode::Bytes(Bytes::copy_from_slice(transaction_id)),
                ),
                (y_key(), Bencode::Bytes(Bytes::copy_from_slice(b"e"))),
                (
                    e_key(),
                    Bencode::List(vec![
                        Bencode::Integer(*code),
                        Bencode::Bytes(Bytes::copy_from_slice(message.as_bytes())),
                    ]),
                ),
            ]),
        };
        bencode::encode(&dict)
    }

    /// Decode a KRPC message from bencoded bytes.
    pub fn from_bytes(data: &[u8]) -> Result<Self, Error> {
        tracing::trace!("decoding KRPC message ({} bytes)", data.len());
        let (val, _rest) = bencode::decode(data)?;
        KrpcMessage::from_bencode(&val)
    }

    /// Decode a KRPC message from a bencoded value.
    pub fn from_bencode(val: &Bencode) -> Result<Self, Error> {
        let t = dict_get_bytes(val, b"t").ok_or(Error::new(ErrorKind::Protocol))?;
        let mut transaction_id = [0u8; 2];
        let len = std::cmp::min(t.len(), 2);
        transaction_id[..len].copy_from_slice(&t[..len]);

        let y = dict_get_bytes(val, b"y").ok_or(Error::new(ErrorKind::Protocol))?;
        let y_byte = if !y.is_empty() { y[0] } else { 0 };

        match y_byte {
            b'q' => {
                let method = dict_get_bytes(val, b"q")
                    .and_then(|b| String::from_utf8(b.to_vec()).ok())
                    .ok_or(Error::new(ErrorKind::Protocol))?;
                let args = dict_get(val, b"a")
                    .cloned()
                    .unwrap_or(Bencode::Dict(vec![]));
                Ok(KrpcMessage::Query {
                    transaction_id,
                    method,
                    args,
                })
            }
            b'r' => {
                let result = dict_get(val, b"r")
                    .cloned()
                    .unwrap_or(Bencode::Dict(vec![]));
                Ok(KrpcMessage::Response {
                    transaction_id,
                    result,
                })
            }
            b'e' => {
                let err_val = dict_get(val, b"e").ok_or(Error::new(ErrorKind::Protocol))?;
                match err_val {
                    Bencode::List(items) if items.len() >= 2 => {
                        let code = match &items[0] {
                            Bencode::Integer(c) => *c,
                            _ => return Err(Error::new(ErrorKind::Protocol)),
                        };
                        let message = match &items[1] {
                            Bencode::Bytes(b) => String::from_utf8(b.to_vec()).unwrap_or_default(),
                            _ => return Err(Error::new(ErrorKind::Protocol)),
                        };
                        Ok(KrpcMessage::Error {
                            transaction_id,
                            code,
                            message,
                        })
                    }
                    _ => Err(Error::new(ErrorKind::Protocol)),
                }
            }
            _ => Err(Error::new(ErrorKind::Protocol)),
        }
    }
}

// ── Build helpers ────────────────────────────────────────────────────

/// Build a ping query (BEP 5).
///
/// Creates a KRPC `ping` query message with the given transaction ID
/// and node ID. The result is bencoded bytes ready to send over UDP.
pub fn build_ping(tid: TransactionId, node_id: &[u8; 20]) -> Vec<u8> {
    KrpcMessage::Query {
        transaction_id: tid,
        method: "ping".into(),
        args: Bencode::Dict(vec![(
            id_key(),
            Bencode::Bytes(Bytes::copy_from_slice(node_id)),
        )]),
    }
    .to_bytes()
}

/// Build a find_node query (BEP 5 / BEP 32).
///
/// Creates a KRPC `find_node` query for discovering nodes close to
/// a target ID. When `want` is `Some`, includes a `want` parameter
/// to request specific address families (`"n4"`, `"n6"`).
pub fn build_find_node(
    tid: TransactionId, node_id: &[u8; 20], target: &[u8; 20], want: Option<&[&str]>,
) -> Vec<u8> {
    let mut entries = vec![
        (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
        (target_key(), Bencode::Bytes(Bytes::copy_from_slice(target))),
    ];
    if let Some(w) = want {
        let want_list: Vec<Bencode> = w
            .iter()
            .map(|s| Bencode::Bytes(Bytes::copy_from_slice(s.as_bytes())))
            .collect();
        entries.push((Bytes::from("want"), Bencode::List(want_list)));
    }
    KrpcMessage::Query {
        transaction_id: tid,
        method: "find_node".into(),
        args: Bencode::Dict(entries),
    }
    .to_bytes()
}

/// Build a get_peers query (BEP 5 / BEP 32).
///
/// Creates a KRPC `get_peers` query to discover peers sharing a torrent
/// identified by `info_hash`. When `want` is `Some`, includes a `want`
/// parameter to request specific address families (`"n4"`, `"n6"`).
pub fn build_get_peers(
    tid: TransactionId, node_id: &[u8; 20], info_hash: &[u8; 20], want: Option<&[&str]>,
) -> Vec<u8> {
    let mut entries = vec![
        (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
        (
            info_hash_key(),
            Bencode::Bytes(Bytes::copy_from_slice(info_hash)),
        ),
    ];
    if let Some(w) = want {
        let want_list: Vec<Bencode> = w
            .iter()
            .map(|s| Bencode::Bytes(Bytes::copy_from_slice(s.as_bytes())))
            .collect();
        entries.push((Bytes::from("want"), Bencode::List(want_list)));
    }
    KrpcMessage::Query {
        transaction_id: tid,
        method: "get_peers".into(),
        args: Bencode::Dict(entries),
    }
    .to_bytes()
}

/// Build an announce_peer query (BEP 5).
///
/// Creates a KRPC `announce_peer` query that tells a DHT node we are
/// downloading the torrent identified by `info_hash` on the given `port`.
/// Requires a `token` obtained from a previous `get_peers` response.
pub fn build_announce_peer(
    tid: TransactionId, node_id: &[u8; 20], info_hash: &[u8; 20], port: u16, token: &[u8],
) -> Vec<u8> {
    KrpcMessage::Query {
        transaction_id: tid,
        method: "announce_peer".into(),
        args: Bencode::Dict(vec![
            (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
            (
                info_hash_key(),
                Bencode::Bytes(Bytes::copy_from_slice(info_hash)),
            ),
            (Bytes::from("port"), Bencode::Integer(port as i64)),
            (token_key(), Bencode::Bytes(Bytes::copy_from_slice(token))),
        ]),
    }
    .to_bytes()
}

// ── Response parsing helpers ─────────────────────────────────────────

/// Parse a ping response.
///
/// Expects a response dict containing `{"id": <20-byte node ID>}`.
///
/// # Errors
///
/// Returns an error if the message is not a response or is missing the `id` field.
pub fn parse_ping_response(msg: &KrpcMessage) -> Result<[u8; 20], Error> {
    match msg {
        KrpcMessage::Response { result, .. } => {
            let node_id = dict_get_bytes(result, b"id").ok_or(Error::new(ErrorKind::Protocol))?;
            let mut id = [0u8; 20];
            let len = std::cmp::min(node_id.len(), 20);
            id[..len].copy_from_slice(&node_id[..len]);
            Ok(id)
        }
        _ => Err(Error::new(ErrorKind::Protocol)),
    }
}

/// Result of a get_peers DHT query (BEP 5).
///
/// Two outcomes are possible:
/// - [`Values`](GetPeersResult::Values): the node returned peer addresses
///   and a token for later `announce_peer` calls
/// - [`Nodes`](GetPeersResult::Nodes): the node returned closer DHT nodes
///   for continued recursive lookup
#[derive(Debug, Clone)]
pub enum GetPeersResult {
    /// Token + list of SocketAddr.
    Values {
        token: Vec<u8>,
        peers: Vec<SocketAddr>,
    },
    /// Closer nodes in compact format.
    Nodes(Vec<Node>),
}

/// Parse a get_peers response (BEP 5).
///
/// Handles both possible responses:
/// - `values` key present → returns [`GetPeersResult::Values`] with token and peers
/// - `nodes` key present → returns [`GetPeersResult::Nodes`] with closer nodes
///
/// # Errors
///
/// Returns an error if the message is not a response or contains neither
/// `values` nor `nodes`.
pub fn parse_get_peers_response(msg: &KrpcMessage) -> Result<GetPeersResult, Error> {
    match msg {
        KrpcMessage::Response { result, .. } => {
            let token = dict_get_bytes(result, b"token")
                .map(|b| b.to_vec())
                .ok_or(Error::new(ErrorKind::Protocol))?;

            // Check for "values" field (list of compact peers)
            if let Some(Bencode::List(values)) = dict_get(result, b"values") {
                let mut peers = Vec::new();
                for v in values {
                    if let Bencode::Bytes(b) = v {
                        if b.len() == 6 {
                            let ip = Ipv4Addr::new(b[0], b[1], b[2], b[3]);
                            let port = u16::from_be_bytes([b[4], b[5]]);
                            peers.push(SocketAddr::new(IpAddr::V4(ip), port));
                        } else if b.len() == 18 {
                            let mut ip_bytes = [0u8; 16];
                            ip_bytes.copy_from_slice(&b[..16]);
                            let ip = Ipv6Addr::from(ip_bytes);
                            let port = u16::from_be_bytes([b[16], b[17]]);
                            peers.push(SocketAddr::new(IpAddr::V6(ip), port));
                        }
                    }
                }
                return Ok(GetPeersResult::Values { token, peers });
            }

            if let Some(nodes_bytes) = dict_get_bytes(result, b"nodes") {
                let nodes = parse_compact_nodes4(nodes_bytes);
                if !nodes.is_empty() {
                    return Ok(GetPeersResult::Nodes(nodes));
                }
            }

            if let Some(nodes6_bytes) = dict_get_bytes(result, b"nodes6") {
                let nodes = parse_compact_nodes6(nodes6_bytes);
                if !nodes.is_empty() {
                    return Ok(GetPeersResult::Nodes(nodes));
                }
            }

            Err(Error::new(ErrorKind::Protocol))
        }
        _ => Err(Error::new(ErrorKind::Protocol)),
    }
}

/// Parse compact IPv4 node info (BEP 5).
///
/// Each node is 26 bytes: 20-byte node ID + 4-byte IPv4 address + 2-byte port.
/// Incomplete trailing bytes are silently ignored.
pub fn parse_compact_nodes4(data: &[u8]) -> Vec<Node> {
    data.chunks_exact(26)
        .map(|chunk| {
            let mut id = [0u8; 20];
            id.copy_from_slice(&chunk[..20]);
            let ip = Ipv4Addr::new(chunk[20], chunk[21], chunk[22], chunk[23]);
            let port = u16::from_be_bytes([chunk[24], chunk[25]]);
            Node {
                id,
                addr: SocketAddr::new(IpAddr::V4(ip), port),
            }
        })
        .collect()
}

/// Backward-compatible alias for [`parse_compact_nodes4`].
#[deprecated(since = "0.1.6", note = "use `parse_compact_nodes4` instead")]
pub fn parse_compact_nodes(data: &[u8]) -> Vec<Node> {
    parse_compact_nodes4(data)
}

/// Encode IPv4 nodes into compact format (BEP 5).
///
/// Each node is 26 bytes: 20-byte node ID + 4-byte IPv4 address + 2-byte port.
/// IPv6 nodes are silently skipped.
pub fn encode_compact_nodes4(nodes: &[Node]) -> Vec<u8> {
    let mut data = Vec::with_capacity(nodes.len() * 26);
    for node in nodes {
        let ip = match node.addr.ip() {
            IpAddr::V4(v4) => v4.octets(),
            _ => continue,
        };
        data.extend_from_slice(&node.id);
        data.extend_from_slice(&ip);
        data.extend_from_slice(&node.addr.port().to_be_bytes());
    }
    data
}

/// Backward-compatible alias for [`encode_compact_nodes4`].
#[deprecated(since = "0.1.6", note = "use `encode_compact_nodes4` instead")]
pub fn encode_compact_nodes(nodes: &[Node]) -> Vec<u8> {
    encode_compact_nodes4(nodes)
}

/// Parse compact IPv6 node info (BEP 32).
///
/// Each node is 38 bytes: 20-byte node ID + 16-byte IPv6 address + 2-byte port.
/// Incomplete trailing bytes are silently ignored.
pub fn parse_compact_nodes6(data: &[u8]) -> Vec<Node> {
    data.chunks_exact(38)
        .map(|chunk| {
            let mut id = [0u8; 20];
            id.copy_from_slice(&chunk[..20]);
            let mut ip_bytes = [0u8; 16];
            ip_bytes.copy_from_slice(&chunk[20..36]);
            let ip = Ipv6Addr::from(ip_bytes);
            let port = u16::from_be_bytes([chunk[36], chunk[37]]);
            Node {
                id,
                addr: SocketAddr::new(IpAddr::V6(ip), port),
            }
        })
        .collect()
}

/// Encode IPv6 nodes into compact format (BEP 32).
///
/// Each node is 38 bytes: 20-byte node ID + 16-byte IPv6 address + 2-byte port.
/// IPv4 nodes are silently skipped.
pub fn encode_compact_nodes6(nodes: &[Node]) -> Vec<u8> {
    let mut data = Vec::with_capacity(nodes.len() * 38);
    for node in nodes {
        let ip = match node.addr.ip() {
            IpAddr::V6(v6) => v6.octets(),
            _ => continue,
        };
        data.extend_from_slice(&node.id);
        data.extend_from_slice(&ip);
        data.extend_from_slice(&node.addr.port().to_be_bytes());
    }
    data
}

// ── Response builders ─────────────────────────────────────────────────

/// Build a `ping` response (BEP 5).
pub fn build_ping_response(tid: TransactionId, node_id: &[u8; 20]) -> Vec<u8> {
    KrpcMessage::Response {
        transaction_id: tid,
        result: Bencode::Dict(vec![(
            id_key(),
            Bencode::Bytes(Bytes::copy_from_slice(node_id)),
        )]),
    }
    .to_bytes()
}

/// Build a `find_node` response (BEP 5 / BEP 32).
///
/// Includes both `nodes` (IPv4) and `nodes6` (IPv6) keys per BEP 32.
pub fn build_find_node_response(tid: TransactionId, node_id: &[u8; 20], nodes: &[Node]) -> Vec<u8> {
    let compact4 = encode_compact_nodes4(nodes);
    let compact6 = encode_compact_nodes6(nodes);
    let mut entries = vec![
        (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
        (Bytes::from("nodes"), Bencode::Bytes(Bytes::from(compact4))),
    ];
    if !compact6.is_empty() {
        entries.push((Bytes::from("nodes6"), Bencode::Bytes(Bytes::from(compact6))));
    }
    KrpcMessage::Response {
        transaction_id: tid,
        result: Bencode::Dict(entries),
    }
    .to_bytes()
}

/// Build a `get_peers` response with peer values (BEP 5).
pub fn build_get_peers_response_values(
    tid: TransactionId, node_id: &[u8; 20], token: &[u8], peers: &[SocketAddr],
) -> Vec<u8> {
    let peer_list: Vec<Bencode> = peers
        .iter()
        .map(|addr| {
            let mut data = Vec::new();
            match addr.ip() {
                IpAddr::V4(v4) => {
                    data.extend_from_slice(&v4.octets());
                }
                IpAddr::V6(v6) => {
                    data.extend_from_slice(&v6.octets());
                }
            }
            data.extend_from_slice(&addr.port().to_be_bytes());
            Bencode::Bytes(Bytes::from(data))
        })
        .collect();
    KrpcMessage::Response {
        transaction_id: tid,
        result: Bencode::Dict(vec![
            (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
            (
                Bytes::from("token"),
                Bencode::Bytes(Bytes::copy_from_slice(token)),
            ),
            (Bytes::from("values"), Bencode::List(peer_list)),
        ]),
    }
    .to_bytes()
}

/// Build a `get_peers` response with closer nodes (BEP 5 / BEP 32).
///
/// Includes both `nodes` (IPv4) and `nodes6` (IPv6) keys per BEP 32.
pub fn build_get_peers_response_nodes(
    tid: TransactionId, node_id: &[u8; 20], token: &[u8], nodes: &[Node],
) -> Vec<u8> {
    let compact4 = encode_compact_nodes4(nodes);
    let compact6 = encode_compact_nodes6(nodes);
    let mut entries = vec![
        (id_key(), Bencode::Bytes(Bytes::copy_from_slice(node_id))),
        (
            Bytes::from("token"),
            Bencode::Bytes(Bytes::copy_from_slice(token)),
        ),
        (Bytes::from("nodes"), Bencode::Bytes(Bytes::from(compact4))),
    ];
    if !compact6.is_empty() {
        entries.push((Bytes::from("nodes6"), Bencode::Bytes(Bytes::from(compact6))));
    }
    KrpcMessage::Response {
        transaction_id: tid,
        result: Bencode::Dict(entries),
    }
    .to_bytes()
}

/// Build a KRPC error response (BEP 5).
pub fn build_error_response(tid: TransactionId, code: i64, message: &str) -> Vec<u8> {
    KrpcMessage::Error {
        transaction_id: tid,
        code,
        message: message.into(),
    }
    .to_bytes()
}

// ── Helpers ──────────────────────────────────────────────────────────

fn t_key() -> Bytes {
    Bytes::from("t")
}
fn y_key() -> Bytes {
    Bytes::from("y")
}
fn q_key() -> Bytes {
    Bytes::from("q")
}
fn a_key() -> Bytes {
    Bytes::from("a")
}
fn r_key() -> Bytes {
    Bytes::from("r")
}
fn e_key() -> Bytes {
    Bytes::from("e")
}
fn id_key() -> Bytes {
    Bytes::from("id")
}
fn target_key() -> Bytes {
    Bytes::from("target")
}
fn info_hash_key() -> Bytes {
    Bytes::from("info_hash")
}
fn token_key() -> Bytes {
    Bytes::from("token")
}

fn dict_get<'a>(val: &'a Bencode, key: &[u8]) -> Option<&'a Bencode> {
    match val {
        Bencode::Dict(entries) => entries
            .iter()
            .find(|(k, _)| k.as_ref() == key)
            .map(|(_, v)| v),
        _ => None,
    }
}

/// Extract a byte-string value from a bencode dictionary by key.
///
/// Returns `None` if the key is not present or the value is not bytes.
pub fn dict_get_bytes<'a>(val: &'a Bencode, key: &[u8]) -> Option<&'a [u8]> {
    match dict_get(val, key)? {
        Bencode::Bytes(b) => Some(b),
        _ => None,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn krpc_ping_roundtrip() {
        let tid = [0xAB, 0xCD];
        let node_id = [0x42u8; 20];
        let bytes = build_ping(tid, &node_id);

        let msg = KrpcMessage::from_bytes(&bytes).unwrap();
        match &msg {
            KrpcMessage::Query {
                transaction_id,
                method,
                ..
            } => {
                assert_eq!(*transaction_id, tid);
                assert_eq!(method, "ping");
            }
            _ => panic!("expected query"),
        }
    }

    #[test]
    fn krpc_find_node_roundtrip() {
        let tid = [0x12, 0x34];
        let node_id = [0x11u8; 20];
        let target = [0x22u8; 20];
        let bytes = build_find_node(tid, &node_id, &target, None);

        let msg = KrpcMessage::from_bytes(&bytes).unwrap();
        match &msg {
            KrpcMessage::Query { method, .. } => {
                assert_eq!(method, "find_node");
            }
            _ => panic!("expected query"),
        }
    }

    #[test]
    fn krpc_response_roundtrip() {
        let tid = [0xFF, 0xEE];
        let msg = KrpcMessage::Response {
            transaction_id: tid,
            result: Bencode::Dict(vec![(
                Bytes::from("id"),
                Bencode::Bytes(Bytes::copy_from_slice(&[0x55u8; 20])),
            )]),
        };
        let bytes = msg.to_bytes();
        let decoded = KrpcMessage::from_bytes(&bytes).unwrap();
        match decoded {
            KrpcMessage::Response {
                transaction_id,
                result,
            } => {
                assert_eq!(transaction_id, tid);
                let id = dict_get_bytes(&result, b"id").unwrap();
                assert_eq!(id, &[0x55u8; 20]);
            }
            _ => panic!("expected response"),
        }
    }

    #[test]
    fn krpc_error_roundtrip() {
        let msg = KrpcMessage::Error {
            transaction_id: [0x01, 0x02],
            code: 203,
            message: "Server Error".into(),
        };
        let bytes = msg.to_bytes();
        let decoded = KrpcMessage::from_bytes(&bytes).unwrap();
        match decoded {
            KrpcMessage::Error { code, message, .. } => {
                assert_eq!(code, 203);
                assert_eq!(message, "Server Error");
            }
            _ => panic!("expected error"),
        }
    }

    #[test]
    fn test_parse_compact_nodes() {
        let mut data = Vec::new();
        // Node 1: id + 127.0.0.1:6881
        data.extend_from_slice(&[0x01u8; 20]);
        data.extend_from_slice(&[127, 0, 0, 1]);
        data.extend_from_slice(&6881u16.to_be_bytes());
        // Node 2: id + 192.168.1.1:51413
        data.extend_from_slice(&[0x02u8; 20]);
        data.extend_from_slice(&[192, 168, 1, 1]);
        data.extend_from_slice(&51413u16.to_be_bytes());

        let nodes = parse_compact_nodes4(&data);
        assert_eq!(nodes.len(), 2);
        assert_eq!(nodes[0].id, [0x01u8; 20]);
        assert_eq!(nodes[0].addr.to_string(), "127.0.0.1:6881");
        assert_eq!(nodes[1].addr.to_string(), "192.168.1.1:51413");
    }

    #[test]
    fn parse_ping_response_valid() {
        let msg = KrpcMessage::Response {
            transaction_id: [0xAB, 0xCD],
            result: Bencode::Dict(vec![(
                Bytes::from("id"),
                Bencode::Bytes(Bytes::copy_from_slice(&[0x42u8; 20])),
            )]),
        };
        let id = parse_ping_response(&msg).unwrap();
        assert_eq!(id, [0x42u8; 20]);
    }

    #[test]
    fn parse_ping_response_not_a_response() {
        let msg = KrpcMessage::Query {
            transaction_id: [0; 2],
            method: "ping".into(),
            args: Bencode::Dict(vec![]),
        };
        assert!(parse_ping_response(&msg).is_err());
    }

    #[test]
    fn parse_get_peers_values() {
        let msg = KrpcMessage::Response {
            transaction_id: [0; 2],
            result: Bencode::Dict(vec![
                (Bytes::from("token"), Bencode::Bytes(Bytes::from("tok"))),
                (
                    Bytes::from("values"),
                    Bencode::List(vec![
                        // compact peer: 6 bytes (127.0.0.1:6881)
                        Bencode::Bytes(Bytes::from(vec![127, 0, 0, 1, 0x1A, 0xE1])),
                    ]),
                ),
            ]),
        };
        match parse_get_peers_response(&msg).unwrap() {
            GetPeersResult::Values { token, peers } => {
                assert_eq!(token, b"tok");
                assert_eq!(peers.len(), 1);
            }
            _ => panic!("expected Values"),
        }
    }

    #[test]
    fn parse_get_peers_nodes() {
        let mut compact = Vec::new();
        compact.extend_from_slice(&[0x01u8; 20]); // node ID
        compact.extend_from_slice(&[10, 0, 0, 1]); // IP
        compact.extend_from_slice(&6881u16.to_be_bytes());

        let msg = KrpcMessage::Response {
            transaction_id: [0; 2],
            result: Bencode::Dict(vec![
                (Bytes::from("token"), Bencode::Bytes(Bytes::from("tok"))),
                (Bytes::from("nodes"), Bencode::Bytes(Bytes::from(compact))),
            ]),
        };
        match parse_get_peers_response(&msg).unwrap() {
            GetPeersResult::Nodes(nodes) => {
                assert_eq!(nodes.len(), 1);
                assert_eq!(nodes[0].addr.to_string(), "10.0.0.1:6881");
            }
            _ => panic!("expected Nodes"),
        }
    }

    #[test]
    fn parse_get_peers_neither_values_nor_nodes() {
        let msg = KrpcMessage::Response {
            transaction_id: [0; 2],
            result: Bencode::Dict(vec![]),
        };
        assert!(parse_get_peers_response(&msg).is_err());
    }

    #[test]
    fn parse_get_peers_non_response() {
        let msg = KrpcMessage::Query {
            transaction_id: [0; 2],
            method: "get_peers".into(),
            args: Bencode::Dict(vec![]),
        };
        assert!(parse_get_peers_response(&msg).is_err());
    }

    #[test]
    fn decode_truncated_krpc() {
        let data = b"d1:t2:ab1:y1:q"; // truncated dict
        assert!(KrpcMessage::from_bytes(data).is_err());
    }

    #[test]
    fn decode_unknown_y_type() {
        // y = 'x' is not valid
        let _ = KrpcMessage::Error {
            transaction_id: [0; 2],
            code: 0,
            message: String::new(),
        };
        // Instead build a valid message and test internal from_bencode directly
        let dict = Bencode::Dict(vec![
            (Bytes::from("t"), Bencode::Bytes(Bytes::from(vec![0, 0]))),
            (Bytes::from("y"), Bencode::Bytes(Bytes::from(&b"x"[..]))),
            (
                Bytes::from("e"),
                Bencode::List(vec![Bencode::Integer(0), Bencode::Bytes(Bytes::from(""))]),
            ),
        ]);
        assert!(KrpcMessage::from_bencode(&dict).is_err());
    }

    #[test]
    fn decode_missing_t_field() {
        let dict = Bencode::Dict(vec![
            (Bytes::from("y"), Bencode::Bytes(Bytes::from(&b"q"[..]))),
            (Bytes::from("q"), Bencode::Bytes(Bytes::from(&b"ping"[..]))),
            (Bytes::from("a"), Bencode::Dict(vec![])),
        ]);
        assert!(KrpcMessage::from_bencode(&dict).is_err());
    }

    #[test]
    fn decode_error_missing_list() {
        let dict = Bencode::Dict(vec![
            (Bytes::from("t"), Bencode::Bytes(Bytes::from(vec![0, 0]))),
            (Bytes::from("y"), Bencode::Bytes(Bytes::from(&b"e"[..]))),
            (Bytes::from("e"), Bencode::Integer(203)), // not a list
        ]);
        assert!(KrpcMessage::from_bencode(&dict).is_err());
    }

    // ── BEP 32 IPv6 tests ──────────────────────────────────────

    #[test]
    fn parse_compact_nodes4_roundtrip() {
        let node = Node {
            id: [0x01u8; 20],
            addr: "127.0.0.1:6881".parse().unwrap(),
        };
        let encoded = encode_compact_nodes4(&[node.clone()]);
        assert_eq!(encoded.len(), 26);
        let decoded = parse_compact_nodes4(&encoded);
        assert_eq!(decoded.len(), 1);
        assert_eq!(decoded[0], node);
    }

    #[test]
    fn parse_compact_nodes6_roundtrip() {
        let node = Node {
            id: [0x02u8; 20],
            addr: "[::1]:6881".parse().unwrap(),
        };
        let encoded = encode_compact_nodes6(&[node.clone()]);
        assert_eq!(encoded.len(), 38);
        let decoded = parse_compact_nodes6(&encoded);
        assert_eq!(decoded.len(), 1);
        assert_eq!(decoded[0], node);
    }

    #[test]
    fn encode_compact_nodes4_skips_ipv6() {
        let v4 = Node {
            id: [0x01u8; 20],
            addr: "10.0.0.1:6881".parse().unwrap(),
        };
        let v6 = Node {
            id: [0x02u8; 20],
            addr: "[::1]:6881".parse().unwrap(),
        };
        let encoded = encode_compact_nodes4(&[v4, v6]);
        assert_eq!(encoded.len(), 26);
    }

    #[test]
    fn encode_compact_nodes6_skips_ipv4() {
        let v4 = Node {
            id: [0x01u8; 20],
            addr: "10.0.0.1:6881".parse().unwrap(),
        };
        let v6 = Node {
            id: [0x02u8; 20],
            addr: "[::1]:6881".parse().unwrap(),
        };
        let encoded = encode_compact_nodes6(&[v4, v6]);
        assert_eq!(encoded.len(), 38);
    }

    #[test]
    fn parse_get_peers_response_nodes6() {
        let mut compact6 = Vec::new();
        compact6.extend_from_slice(&[0x03u8; 20]);
        compact6.extend_from_slice(&[0u8; 16]);
        compact6[35] = 1;
        compact6.extend_from_slice(&6881u16.to_be_bytes());

        let msg = KrpcMessage::Response {
            transaction_id: [0; 2],
            result: Bencode::Dict(vec![
                (Bytes::from("token"), Bencode::Bytes(Bytes::from("tok"))),
                (Bytes::from("nodes6"), Bencode::Bytes(Bytes::from(compact6))),
            ]),
        };
        match parse_get_peers_response(&msg).unwrap() {
            GetPeersResult::Nodes(nodes) => {
                assert_eq!(nodes.len(), 1);
                assert_eq!(nodes[0].addr.to_string(), "[::1]:6881");
            }
            _ => panic!("expected Nodes"),
        }
    }

    #[test]
    fn parse_get_peers_values_ipv6() {
        let mut peer6 = Vec::new();
        peer6.extend_from_slice(&[0u8; 16]);
        peer6[15] = 1;
        peer6.extend_from_slice(&6881u16.to_be_bytes());

        let msg = KrpcMessage::Response {
            transaction_id: [0; 2],
            result: Bencode::Dict(vec![
                (Bytes::from("token"), Bencode::Bytes(Bytes::from("tok"))),
                (
                    Bytes::from("values"),
                    Bencode::List(vec![Bencode::Bytes(Bytes::from(peer6))]),
                ),
            ]),
        };
        match parse_get_peers_response(&msg).unwrap() {
            GetPeersResult::Values { peers, .. } => {
                assert_eq!(peers.len(), 1);
                assert_eq!(peers[0].to_string(), "[::1]:6881");
            }
            _ => panic!("expected Values"),
        }
    }
}