feat: add types and de/encoding for SCMP messages

crates/scion-proto/src/lib.rs

@@ -5,6 +5,7 @@ pub mod datagram;
 pub mod packet;
 pub mod path;
 pub mod reliable;
+pub mod scmp;
 pub(crate) mod utils;
 pub mod wire_encoding;
 

crates/scion-proto/src/packet/headers/address_header.rs

@@ -63,6 +63,14 @@ impl From<ByEndpoint<SocketAddr>> for AddressHeader {
         }
     }
 }
+impl From<ByEndpoint<ScionAddr>> for AddressHeader {
+    fn from(value: ByEndpoint<ScionAddr>) -> Self {
+        AddressHeader {
+            ia: value.map(ScionAddr::isd_asn),
+            host: value.map(|e| MaybeEncoded::Decoded(e.host())),
+        }
+    }
+}
 
 impl<T: Buf> WireDecodeWithContext<T> for AddressHeader {
     type Error = DecodeError;

crates/scion-proto/src/scmp.rs

@@ -0,0 +1,52 @@
+//! Types and conversion for the SCION Control Message Protocol.
+//!
+//! This implements the specification at the [SCION documentation page][scion-doc-scmp] but currently
+//! does not cover DRKey-based authentication.
+//!
+//! [scion-doc-scmp]: https://docs.scion.org/en/latest/protocols/scmp.html
+
+mod error;
+pub use error::ScmpDecodeError;
+
+mod messages;
+pub use messages::*;
+
+mod raw;
+pub use raw::ScmpMessageRaw;
+
+use crate::packet::AddressHeader;
+
+/// Trait implemented by all SCMP messages.
+pub trait ScmpMessageBase {
+    /// Returns the SCMP type of this message.
+    fn get_type(&self) -> ScmpType;
+
+    /// Returns the additional SCMP code of this message.
+    fn code(&self) -> u8 {
+        0
+    }
+}
+
+/// Trait implemented by all SCMP messages to handle checksums.
+pub trait ScmpMessageChecksum: ScmpMessageBase {
+    /// Returns the currently stored checksum of the message.
+    fn checksum(&self) -> u16;
+
+    /// Clears then sets the checksum to the value returned by [`Self::calculate_checksum()`].
+    fn set_checksum(&mut self, address_header: &AddressHeader);
+
+    /// Compute the checksum for this SCMP message using the provided address header.
+    fn calculate_checksum(&self, address_header: &AddressHeader) -> u16;
+
+    /// Returns true if the checksum successfully verifies, otherwise false.
+    fn verify_checksum(&self, address_header: &AddressHeader) -> bool {
+        self.calculate_checksum(address_header) == 0
+    }
+}
+
+/// SCION protocol number for SCMP.
+///
+/// See the [IETF SCION-dataplane RFC draft][rfc] for possible values.
+///
+///[rfc]: https://www.ietf.org/archive/id/draft-dekater-scion-dataplane-00.html#protnum
+pub const SCMP_PROTOCOL_NUMBER: u8 = 202;

crates/scion-proto/src/scmp/error.rs

@@ -0,0 +1,23 @@
+//! Errors encountered when handling SCMP messages.
+
+/// Error encountered when attempting to decode an SCMP message.
+#[derive(Debug, thiserror::Error)]
+pub enum ScmpDecodeError {
+    /// The data is shorter than the minimum length of the corresponding SCMP message.
+    #[error("message is empty or was truncated")]
+    MessageEmptyOrTruncated,
+    /// When attempting to decode a specific message type and the data contains a different message
+    /// type.
+    #[error("the type of the message does not match the type being decoded")]
+    MessageTypeMismatch,
+    /// Informational messages of unknown types need to be dropped.
+    #[error("unknown info message type {0}")]
+    UnknownInfoMessage(u8),
+    /// Depending on the type of SCMP message, only specific values of the `code` field are allowed.
+    #[error("invalid code for this message type")]
+    InvalidCode,
+    /// When decoding a SCION packet presumably containing an SCMP message but the next-header value
+    /// of the SCION header doesn't match [`SCMP_PROTOCOL_NUMBER`][super::SCMP_PROTOCOL_NUMBER].
+    #[error("next-header value of SCION header is not correct")]
+    WrongProtocolNumber(u8),
+}