Introduces author_hasKey and author_hasSessionKeys rpc endpoints (#4720)

* Introduces `author_hasKey` and `author_hasSessionKeys` rpc endpoints

Both endpoints can be used to check if a key is present in the keystore.

- `hasKey` works on with an individual public key and key type. It
checks if a private key for the given combination exists in the
keystore.
- `hasSessionKeys` works with the full encoded session key blob stored
on-chain in `nextKeys`. This requires that the given blob can be decoded
by the runtime. It will return `true`, iff all public keys of the
session key exist in the storage.

Fixes: https://github.com/paritytech/substrate/issues/4696

* Update client/rpc-api/src/author/error.rs

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

* Indentation

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

substrate/primitives/runtime/src/testing.rs

@@ -115,6 +115,10 @@ impl sp_application_crypto::RuntimeAppPublic for UintAuthorityId {
 
 		u64::from_le_bytes(msg_signature) == *signature
 	}
+
+	fn to_raw_vec(&self) -> Vec<u8> {
+		AsRef::<[u8]>::as_ref(self).to_vec()
+	}
 }
 
 impl OpaqueKeys for UintAuthorityId {

substrate/primitives/runtime/src/traits.rs

@@ -1106,12 +1106,14 @@ macro_rules! count {
 #[macro_export]
 macro_rules! impl_opaque_keys {
 	(
+		$( #[ $attr:meta ] )*
 		pub struct $name:ident {
 			$(
 				pub $field:ident: $type:ty,
 			)*
 		}
 	) => {
+		$( #[ $attr ] )*
 		#[derive(
 			Default, Clone, PartialEq, Eq,
 			$crate::codec::Encode,
@@ -1143,6 +1145,37 @@ macro_rules! impl_opaque_keys {
 				};
 				$crate::codec::Encode::encode(&keys)
 			}
+
+			/// Converts `Self` into a `Vec` of `(raw public key, KeyTypeId)`.
+			pub fn into_raw_public_keys(
+				self,
+			) -> $crate::sp_std::vec::Vec<($crate::sp_std::vec::Vec<u8>, $crate::KeyTypeId)> {
+				let mut keys = Vec::new();
+				$(
+					keys.push((
+						$crate::RuntimeAppPublic::to_raw_vec(&self.$field),
+						<
+							<
+								$type as $crate::BoundToRuntimeAppPublic
+							>::Public as $crate::RuntimeAppPublic
+						>::ID,
+					));
+				)*
+
+				keys
+			}
+
+			/// Decode `Self` from the given `encoded` slice and convert `Self` into the raw public
+			/// keys (see [`Self::into_raw_public_keys`]).
+			///
+			/// Returns `None` when the decoding failed, otherwise `Some(_)`.
+			pub fn decode_into_raw_public_keys(
+				encoded: &[u8],
+			) -> Option<$crate::sp_std::vec::Vec<($crate::sp_std::vec::Vec<u8>, $crate::KeyTypeId)>> {
+				<Self as $crate::codec::Decode>::decode(&mut &encoded[..])
+					.ok()
+					.map(|s| s.into_raw_public_keys())
+			}
 		}
 
 		impl $crate::traits::OpaqueKeys for $name {