Sink CiphertextMessageType down to be FFI-only

Regular Rust code doesn't need CiphertextMessageType because it can
already match on CiphertextMessage. On the other hand, FFI code could
really use named constants for the various message types.

rust/bridge/ffi/cbindgen.toml

@@ -10,7 +10,7 @@ autogen_warning = "/* This file was automatically generated by cbindgen */"
 prefix_with_name = true
 
 [export]
-include = ["SignalErrorCode", "FfiDirection"]
+include = ["SignalErrorCode", "FfiDirection", "CiphertextMessageType"]
 prefix = "Signal"
 renaming_overrides_prefixing = true
 

rust/bridge/ffi/src/lib.rs

@@ -1284,14 +1284,31 @@ pub unsafe extern "C" fn signal_encrypt_message(
 
 ffi_fn_destroy!(signal_ciphertext_message_destroy destroys CiphertextMessage);
 
+#[derive(Debug, ToPrimitive)]
+#[repr(C)]
+pub enum CiphertextMessageType {
+    Whisper = 2,
+    PreKey = 3,
+    SenderKey = 4,
+    SenderKeyDistribution = 5,
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn signal_ciphertext_message_type(
     typ: *mut u8,
     msg: *const CiphertextMessage,
 ) -> *mut SignalFfiError {
     run_ffi_safe(|| {
         let msg = native_handle_cast::<CiphertextMessage>(msg)?;
-        *typ = msg.message_type().encoding();
+        let message_type = match msg {
+            CiphertextMessage::SignalMessage(_) => CiphertextMessageType::Whisper,
+            CiphertextMessage::PreKeySignalMessage(_) => CiphertextMessageType::PreKey,
+            CiphertextMessage::SenderKeyMessage(_) => CiphertextMessageType::SenderKey,
+            CiphertextMessage::SenderKeyDistributionMessage(_) => {
+                CiphertextMessageType::SenderKeyDistribution
+            }
+        };
+        *typ = num_traits::ToPrimitive::to_u8(&message_type).unwrap();
         Ok(())
     })
 }

rust/protocol/src/lib.rs

@@ -39,8 +39,8 @@ pub use {
     identity_key::{IdentityKey, IdentityKeyPair},
     kdf::HKDF,
     protocol::{
-        CiphertextMessage, CiphertextMessageType, PreKeySignalMessage,
-        SenderKeyDistributionMessage, SenderKeyMessage, SignalMessage,
+        CiphertextMessage, PreKeySignalMessage, SenderKeyDistributionMessage, SenderKeyMessage,
+        SignalMessage,
     },
     ratchet::{
         are_we_alice, initialize_alice_session, initialize_bob_session,

rust/protocol/src/protocol.rs

@@ -26,37 +26,7 @@ pub enum CiphertextMessage {
     SenderKeyDistributionMessage(SenderKeyDistributionMessage),
 }
 
-#[derive(Copy, Clone, Eq, PartialEq, Debug)]
-pub enum CiphertextMessageType {
-    Whisper,
-    PreKey,
-    SenderKey,
-    SenderKeyDistribution,
-}
-
-impl CiphertextMessageType {
-    pub fn encoding(&self) -> u8 {
-        match self {
-            CiphertextMessageType::Whisper => 2,
-            CiphertextMessageType::PreKey => 3,
-            CiphertextMessageType::SenderKey => 4,
-            CiphertextMessageType::SenderKeyDistribution => 5,
-        }
-    }
-}
-
 impl CiphertextMessage {
-    pub fn message_type(&self) -> CiphertextMessageType {
-        match self {
-            CiphertextMessage::SignalMessage(_) => CiphertextMessageType::Whisper,
-            CiphertextMessage::PreKeySignalMessage(_) => CiphertextMessageType::PreKey,
-            CiphertextMessage::SenderKeyMessage(_) => CiphertextMessageType::SenderKey,
-            CiphertextMessage::SenderKeyDistributionMessage(_) => {
-                CiphertextMessageType::SenderKeyDistribution
-            }
-        }
-    }
-
     pub fn serialize(&self) -> &[u8] {
         match self {
             CiphertextMessage::SignalMessage(x) => x.serialized(),