Add protocol version to message header (#140)

chitchat/src/message.rs

@@ -1,6 +1,6 @@
 use std::io::BufRead;
 
-use anyhow::Context;
+use anyhow::{bail, Context};
 
 use crate::delta::Delta;
 use crate::digest::Digest;
@@ -26,7 +26,26 @@ pub enum ChitchatMessage {
     BadCluster,
 }
 
-#[derive(Copy, Clone)]
+#[derive(Clone, Copy, Eq, PartialEq)]
+#[repr(u8)]
+enum ProtocolVersion {
+    V0 = 0,
+}
+
+impl ProtocolVersion {
+    pub fn from_code(code: u8) -> Option<Self> {
+        match code {
+            0 => Some(Self::V0),
+            _ => None,
+        }
+    }
+
+    pub fn to_code(self) -> u8 {
+        self as u8
+    }
+}
+
+#[derive(Clone, Copy)]
 #[repr(u8)]
 enum MessageType {
     Syn = 0,
@@ -45,13 +64,16 @@ impl MessageType {
             _ => None,
         }
     }
+
     pub fn to_code(self) -> u8 {
         self as u8
     }
 }
 
 impl Serializable for ChitchatMessage {
     fn serialize(&self, buf: &mut Vec<u8>) {
+        ProtocolVersion::V0.to_code().serialize(buf);
+
         match self {
             ChitchatMessage::Syn { cluster_id, digest } => {
                 buf.push(MessageType::Syn.to_code());
@@ -74,7 +96,7 @@ impl Serializable for ChitchatMessage {
     }
 
     fn serialized_len(&self) -> usize {
-        match self {
+        1 + match self {
             ChitchatMessage::Syn { cluster_id, digest } => {
                 1 + cluster_id.serialized_len() + digest.serialized_len()
             }
@@ -89,13 +111,28 @@ impl Serializable for ChitchatMessage {
 
 impl Deserializable for ChitchatMessage {
     fn deserialize(buf: &mut &[u8]) -> anyhow::Result<Self> {
-        let code = buf
+        let protocol_version = buf
+            .first()
+            .copied()
+            .and_then(ProtocolVersion::from_code)
+            .context("invalid protocol version")?;
+
+        if protocol_version != ProtocolVersion::V0 {
+            bail!(
+                "unsupported protocol version `{}`",
+                protocol_version.to_code()
+            )
+        }
+        buf.consume(1);
+
+        let message_type = buf
             .first()
             .copied()
             .and_then(MessageType::from_code)
             .context("invalid message type")?;
         buf.consume(1);
-        match code {
+
+        match message_type {
             MessageType::Syn => {
                 let digest = Digest::deserialize(buf)?;
                 let cluster_id = String::deserialize(buf)?;
@@ -127,7 +164,7 @@ mod tests {
                 cluster_id: "cluster-a".to_string(),
                 digest: Digest::default(),
             };
-            test_serdeser_aux(&syn, 14);
+            test_serdeser_aux(&syn, 15);
         }
         {
             let mut digest = Digest::default();
@@ -138,7 +175,7 @@ mod tests {
                 cluster_id: "cluster-a".to_string(),
                 digest,
             };
-            test_serdeser_aux(&syn, 65);
+            test_serdeser_aux(&syn, 66);
         }
     }
 
@@ -149,8 +186,8 @@ mod tests {
                 digest: Digest::default(),
                 delta: Delta::default(),
             };
-            // 1 (message tag) + 2 (digest len) + 1 (delta end op)
-            test_serdeser_aux(&syn_ack, 4);
+            // 1 (protocol version) + 1 (message tag) + 2 (digest len) + 1 (delta end op)
+            test_serdeser_aux(&syn_ack, 5);
         }
         {
             // 2 bytes.
@@ -173,8 +210,9 @@ mod tests {
             delta.set_serialized_len(60);
 
             let syn_ack = ChitchatMessage::SynAck { digest, delta };
-            // 1 bytes (syn ack message) + 45 bytes (digest) + 69 bytes (delta).
-            test_serdeser_aux(&syn_ack, 1 + 53 + 60);
+            // 1 byte (protocol version) + 1 byte (message tag) + 53 bytes (digest) + 60 bytes
+            // (delta).
+            test_serdeser_aux(&syn_ack, 1 + 1 + 53 + 60);
         }
     }
 
@@ -183,7 +221,7 @@ mod tests {
         {
             let delta = Delta::default();
             let ack = ChitchatMessage::Ack { delta };
-            test_serdeser_aux(&ack, 2);
+            test_serdeser_aux(&ack, 3);
         }
         {
             // 4 bytes.
@@ -195,12 +233,12 @@ mod tests {
             delta.add_kv(&node, "key", "value", 0, true);
             delta.set_serialized_len(60);
             let ack = ChitchatMessage::Ack { delta };
-            test_serdeser_aux(&ack, 1 + 60);
+            test_serdeser_aux(&ack, 1 + 1 + 60);
         }
     }
 
     #[test]
     fn test_bad_cluster() {
-        test_serdeser_aux(&ChitchatMessage::BadCluster, 1);
+        test_serdeser_aux(&ChitchatMessage::BadCluster, 2);
     }
 }