ferrix/crates/server/src/error.rs

//! Error types of the server crate.

use std::io;
use std::net::SocketAddr;

use bgp_packet::errors::{BgpError, CeaseSubcode, DecodeError, FsmSubcode, OpenMsgSubcode};
use bgp_packet::message::NotificationMessage;
use bgp_primitives::parser::EncodeError;
use bgp_rib::RibStopped;
use thiserror::Error;

use crate::family::FamilySet;
use crate::fsm::State;

/// Why a session ended abnormally.
#[derive(Debug, Error)]
pub enum SessionError {
    #[error("connection failed: {0}")]
    Io(#[from] io::Error),
    #[error("received a message that could not be decoded: {0}")]
    Decode(#[from] DecodeError),
    #[error("could not encode a message: {0}")]
    Encode(#[from] EncodeError),
    /// The peer sent nothing for as long as the pre-negotiation hold time.
    #[error("timed out waiting for a message in the {0} state")]
    Timeout(State),
    #[error("hold timer expired")]
    HoldTimerExpired,
    #[error("received {received} in the {state} state")]
    UnexpectedMessage {
        state: State,
        received: &'static str,
    },
    /// The peer ended the session. Nothing is sent in return.
    #[error("peer sent NOTIFICATION: {0}")]
    NotifiedByPeer(BgpError),
    #[error("refused the peer's OPEN: {0}")]
    OpenRefused(BgpError),
    #[error("peer announced AS{actual} but AS{expected} was configured")]
    WrongPeerAs { expected: u32, actual: u32 },
    #[error("closed by connection collision resolution")]
    Collision,
    /// The peer offers none of the address families configured for it, so
    /// the session could carry nothing.
    /// The table the session's routes go into is gone. The server is on
    /// its way down; the peer is told so.
    #[error(transparent)]
    RibStopped(#[from] RibStopped),
    #[error("no address family in common: we offer {ours}, the peer offers {theirs}")]
    NoCommonAddressFamily { ours: FamilySet, theirs: FamilySet },
}

impl SessionError {
    /// The NOTIFICATION that tells the peer about this error (RFC 4271 §6),
    /// or `None` when there is nothing to say or no way to say it.
    pub fn notification(&self) -> Option<NotificationMessage> {
        let error = match self {
            Self::Io(_) | Self::Encode(_) | Self::NotifiedByPeer(_) => return None,
            Self::Decode(e) => {
                return Some(NotificationMessage {
                    error: e.notification.clone(),
                    data: e.data.clone(),
                });
            }
            Self::Timeout(_) | Self::HoldTimerExpired => BgpError::HoldTimer,
            Self::UnexpectedMessage { state, .. } => BgpError::FsmError(match state {
                State::OpenSent => FsmSubcode::UnexpectedOpenSent,
                State::OpenConfirm => FsmSubcode::UnexpectedOpenConfirm,
                // A closed machine handles no messages; Established is the
                // only other state one can arrive in.
                State::Established | State::Closed => FsmSubcode::UnexpectedEstablished,
            }),
            Self::OpenRefused(error) => error.clone(),
            Self::WrongPeerAs { .. } => BgpError::OpenMsg(OpenMsgSubcode::BadPeerAs),
            Self::Collision => BgpError::Cease(CeaseSubcode::ConnCollisionResolution),
            Self::RibStopped(_) => BgpError::Cease(CeaseSubcode::AdminShutdown),
            // RFC 5492 §5: the Data lists the capabilities we need and the
            // peer did not offer.
            Self::NoCommonAddressFamily { ours, .. } => {
                return Some(NotificationMessage {
                    error: BgpError::OpenMsg(OpenMsgSubcode::UnsupportedCapability),
                    data: ours.capabilities_wire(),
                });
            }
        };
        Some(NotificationMessage {
            error,
            data: vec![],
        })
    }
}

/// Why the server could not start.
#[derive(Debug, Error)]
pub enum ServerError {
    #[error("failed to bind listener on {addr}: {source}")]
    Bind {
        addr: SocketAddr,
        #[source]
        source: io::Error,
    },
    #[error("listener failed: {0}")]
    Io(#[from] io::Error),
    /// A RIB's actor died. The server cannot work without its tables.
    #[error(transparent)]
    RibStopped(#[from] RibStopped),
    /// A task the server depends on ended, which none of them do unless
    /// they panic.
    #[error("the {task} task stopped unexpectedly: {reason}")]
    TaskStopped { task: &'static str, reason: String },
}

/// Why a configuration was rejected.
#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum ConfigError {
    #[error("invalid router_id {0:?}: must be a dotted-quad IPv4 address")]
    RouterId(String),
    #[error("local_asn must be non-zero")]
    LocalAsn,
    #[error("invalid IP address {0:?}")]
    Address(String),
    #[error("port {0} is out of range")]
    Port(u32),
    #[error("http_endpoint.port is required")]
    HttpPort,
    #[error("peer {peer:?}: {problem}")]
    Peer { peer: String, problem: PeerProblem },
    #[error("originate {prefix:?}: {problem}")]
    Originate {
        prefix: String,
        problem: OriginateProblem,
    },
}

/// What is wrong with one `peers` entry.
#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum PeerProblem {
    #[error("endpoint is missing")]
    MissingEndpoint,
    #[error("endpoint is invalid: {0}")]
    Endpoint(Box<ConfigError>),
    #[error("remote_asn must be non-zero")]
    RemoteAsn,
    #[error("hold_time_seconds must be 0 or at least 3")]
    HoldTime,
    #[error("local_address {0:?} is not an IP address")]
    LocalAddress(String),
    #[error("local_address and endpoint are different address families")]
    AddressFamilyMismatch,
    #[error("address_families has a value that is not an address family")]
    AddressFamily,
}

/// What is wrong with one `originate` entry.
#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum OriginateProblem {
    #[error("{0}")]
    Prefix(#[from] bgp_primitives::ip_prefix::PrefixError),
    #[error("origin {0:?} must be IGP, EGP or INCOMPLETE")]
    Origin(String),
    #[error("as_path_prepend must be at most {max}")]
    Prepend { max: u32 },
    #[error("{0}")]
    Community(#[from] bgp_packet::community::CommunityError),
    #[error("listed more than once")]
    Duplicate,
}

#[cfg(test)]
mod tests {
    use bgp_packet::errors::MsgHeaderSubcode;

    use super::*;

    #[test]
    fn each_session_error_names_the_notification_rfc_4271_assigns_it() {
        let notification = |e: SessionError| e.notification().map(|n| (n.error, n.data));

        assert_eq!(
            notification(SessionError::Decode(DecodeError {
                notification: BgpError::MsgHeader(MsgHeaderSubcode::BadMessageLength),
                data: vec![0x13, 0x88],
                detail: "too long".into(),
            })),
            Some((
                BgpError::MsgHeader(MsgHeaderSubcode::BadMessageLength),
                vec![0x13, 0x88]
            ))
        );
        assert_eq!(
            notification(SessionError::Timeout(State::OpenSent)),
            Some((BgpError::HoldTimer, vec![]))
        );
        assert_eq!(
            notification(SessionError::UnexpectedMessage {
                state: State::OpenConfirm,
                received: "update"
            }),
            Some((
                BgpError::FsmError(FsmSubcode::UnexpectedOpenConfirm),
                vec![]
            ))
        );
        assert_eq!(
            notification(SessionError::WrongPeerAs {
                expected: 1,
                actual: 2
            }),
            Some((BgpError::OpenMsg(OpenMsgSubcode::BadPeerAs), vec![]))
        );
        // A broken connection cannot carry a NOTIFICATION.
        assert_eq!(
            notification(SessionError::Io(io::ErrorKind::BrokenPipe.into())),
            None
        );
    }
}