remove unnecessary mutable borrows in API

Thanks, @aep.
Fixes #32

Cargo.toml

@@ -4,7 +4,7 @@ description = "A pure-rust implementation of the Noise Protocol Framework"
 homepage = "https://snow.rs"
 documentation = "https://snow.rs/doc/snow"
 repository = "https://github.com/mcginty/snow"
-version = "0.4.0-alpha1"
+version = "0.4.0-alpha2"
 authors = ["Jake McGinty <[email protected]>", "trevp"]
 license = "Unlicense"
 categories = ["cryptography"]

src/session.rs

@@ -109,10 +109,10 @@ impl Session {
     ///
     /// Will result in `SnowError::StateProblem` if not in stateless transport mode.
     #[must_use]
-    pub fn write_message_with_nonce(&mut self, nonce: u64, payload: &[u8], output: &mut [u8]) -> Result<usize, SnowError> {
+    pub fn write_message_with_nonce(&self, nonce: u64, payload: &[u8], output: &mut [u8]) -> Result<usize, SnowError> {
         match *self {
-            Session::StatelessTransport(ref mut state) => state.write_transport_message(nonce, payload, output),
-            _                                          => bail!(StateProblem::StatelessTransportMode),
+            Session::StatelessTransport(ref state) => state.write_transport_message(nonce, payload, output),
+            _                                      => bail!(StateProblem::StatelessTransportMode),
         }
     }
 
@@ -149,10 +149,10 @@ impl Session {
     ///
     /// Will result in `SnowError::StateProblem` if not in stateless transport mode.
     #[must_use]
-    pub fn read_message_with_nonce(&mut self, nonce: u64, input: &[u8], payload: &mut [u8]) -> Result<usize, SnowError> {
+    pub fn read_message_with_nonce(&self, nonce: u64, input: &[u8], payload: &mut [u8]) -> Result<usize, SnowError> {
         match *self {
-            Session::StatelessTransport(ref mut state) => state.read_transport_message(nonce, input, payload),
-            _                                          => bail!(StateProblem::StatelessTransportMode),
+            Session::StatelessTransport(ref state) => state.read_transport_message(nonce, input, payload),
+            _                                      => bail!(StateProblem::StatelessTransportMode),
         }
     }
 
@@ -339,4 +339,4 @@ impl TryFrom<HandshakeState> for StatelessTransportState {
     fn try_from(old: HandshakeState) -> Result<Self, Self::Error> {
         StatelessTransportState::new(old)
     }
-}
+}

src/stateless_transportstate.rs

@@ -42,7 +42,7 @@ impl StatelessTransportState {
         self.rs.as_option_ref().map(|rs| &rs[..self.dh_len])
     }
 
-    pub fn write_transport_message(&mut self,
+    pub fn write_transport_message(&self,
                                    nonce: u64,
                                    payload: &[u8],
                                    message: &mut [u8]) -> Result<usize, SnowError> {
@@ -52,7 +52,7 @@ impl StatelessTransportState {
             bail!(SnowError::Input);
         }
 
-        let cipher = if self.initiator { &mut self.cipherstates.0 } else { &mut self.cipherstates.1 };
+        let cipher = if self.initiator { &self.cipherstates.0 } else { &self.cipherstates.1 };
         Ok(cipher.encrypt(nonce, payload, message))
     }