Send empty response to clientPin instead of empty map

For the SetPin and ChangePin subcommands, the clientPin command does not
return any parameters.  Previously, we sent an empty map for these
cases.  With this patch, we sent an empty response instead.

Fixes: https://github.com/solokeys/ctap-types/issues/13

CHANGELOG.md

@@ -8,9 +8,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Rename `url` to `icon` in `PublicKeyCredentialRpEntity` and ignore its
   content ([#9][])
 - Truncate overlong `name` and `displayName` values for `PublicKeyCredentialEntity` instances ([#30][])
+- Send empty response to clientPin instead of empty map ([#13][])
 
 [#9]: https://github.com/solokeys/ctap-types/issues/9
 [#30]: https://github.com/solokeys/fido-authenticator/issues/30
+[#13]: https://github.com/solokeys/ctap-types/issues/13
 
 ## [0.1.2] - 2022-03-07
 

src/ctap2.rs

@@ -148,7 +148,13 @@ impl Response {
         let outcome = match self {
             GetInfo(response) => cbor_serialize(response, data),
             MakeCredential(response) => cbor_serialize(response, data),
-            ClientPin(response) => cbor_serialize(response, data),
+            ClientPin(response) => {
+                if response.is_empty() {
+                    Ok([].as_slice())
+                } else {
+                    cbor_serialize(response, data)
+                }
+            },
             GetAssertion(response) | GetNextAssertion(response) => cbor_serialize(response, data),
             CredentialManagement(response) => cbor_serialize(response, data),
             Reset | Selection | Vendor => Ok([].as_slice()),

src/ctap2/client_pin.rs

@@ -73,6 +73,12 @@ pub struct Response {
     pub retries: Option<u8>,
 }
 
+impl Response {
+    pub fn is_empty(&self) -> bool {
+        self.key_agreement.is_none() && self.pin_token.is_none() && self.retries.is_none()
+    }
+}
+
 #[cfg(test)]
 mod tests {