core/: Add Keypair::to_protobuf_encoding (#2142)

Co-authored-by: Max Inden <[email protected]>

core/CHANGELOG.md

@@ -1,5 +1,7 @@
 # 0.30.0 [unreleased]
 
+- Add `Keypair::to_protobuf_encoding` (see [PR 2142]).
+
 - Change `PublicKey::into_protobuf_encoding` to `PublicKey::to_protobuf_encoding` (see [PR 2145]).
 
 - Change `PublicKey::into_peer_id` to `PublicKey::to_peer_id` (see [PR 2145]).
@@ -9,6 +11,7 @@
 - Add `From<&PublicKey> for PeerId` (see [PR 2145]).
 
 [PR 2145]: https://github.com/libp2p/rust-libp2p/pull/2145
+[PR 2142]: https://github.com/libp2p/rust-libp2p/pull/2142
 
 # 0.29.0 [2021-07-12]
 

core/src/identity.rs

@@ -116,6 +116,33 @@ impl Keypair {
         }
     }
 
+    /// Encode a private key as protobuf structure.
+    pub fn to_protobuf_encoding(&self) -> Result<Vec<u8>, DecodingError> {
+        use prost::Message;
+
+        let pk = match self {
+            Self::Ed25519(data) => keys_proto::PrivateKey {
+                r#type: keys_proto::KeyType::Ed25519.into(),
+                data: data.encode().into(),
+            },
+            #[cfg(not(target_arch = "wasm32"))]
+            Self::Rsa(_) => {
+                return Err(DecodingError::new(
+                    "Encoding RSA key into Protobuf is unsupported",
+                ))
+            }
+            #[cfg(feature = "secp256k1")]
+            Self::Secp256k1(_) => {
+                return Err(DecodingError::new(
+                    "Encoding Secp256k1 key into Protobuf is unsupported",
+                ))
+            }
+        };
+
+        Ok(pk.encode_to_vec())
+    }
+
+
     /// Decode a private key from a protobuf structure and parse it as a [`Keypair`].
     pub fn from_protobuf_encoding(bytes: &[u8]) -> Result<Keypair, DecodingError> {
         use prost::Message;
@@ -255,6 +282,19 @@ mod tests {
     use super::*;
     use std::str::FromStr;
 
+    #[test]
+    fn keypair_protobuf_roundtrip() {
+        let expected_keypair = Keypair::generate_ed25519();
+        let expected_peer_id = expected_keypair.public().to_peer_id();
+
+        let encoded = expected_keypair.to_protobuf_encoding().unwrap();
+
+        let keypair = Keypair::from_protobuf_encoding(&encoded).unwrap();
+        let peer_id = keypair.public().to_peer_id();
+
+        assert_eq!(expected_peer_id, peer_id);
+    }
+
     #[test]
     fn keypair_from_protobuf_encoding() {
         // E.g. retrieved from an IPFS config file.