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/scmp.rs

@@ -0,0 +1,15 @@
+//! 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
+
+pub mod error;
+pub use error::ScmpDecodeError;
+
+pub mod messages;
+pub use messages::{ScmpMessage, ScmpType};
+
+pub mod raw;
+pub use raw::ScmpMessageRaw;

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

@@ -0,0 +1,24 @@
+//! 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
+    /// [`ScmpMessageRaw::PROTOCOL_NUMBER`][super::ScmpMessageRaw::PROTOCOL_NUMBER].
+    #[error("next-header value of SCION header is not correct")]
+    WrongProtocolNumber(u8),
+}