Omit params field from requests instead of sending null value

core/src/types/params.rs

@@ -36,6 +36,11 @@ impl Params {
 			p => Err(Error::invalid_params_with_details("No parameters were expected", p)),
 		}
 	}
+
+	/// Check for None
+	pub fn is_none(&self) -> bool {
+		matches!(*self, Params::None)
+	}
 }
 
 impl From<Params> for Value {
@@ -110,4 +115,12 @@ mod tests {
 		let params: (u64,) = Params::Array(vec![Value::from(1)]).parse().unwrap();
 		assert_eq!(params, (1,));
 	}
+
+	#[test]
+	fn detect_none() {
+		let none = Params::None;
+		assert!(none.is_none());
+		let some = Params::Array(vec![]);
+		assert!(!some.is_none());
+	}
 }

core/src/types/request.rs

@@ -12,7 +12,7 @@ pub struct MethodCall {
 	pub method: String,
 	/// A Structured value that holds the parameter values to be used
 	/// during the invocation of the method. This member MAY be omitted.
-	#[serde(default = "default_params")]
+	#[serde(default = "default_params", skip_serializing_if = "Params::is_none")]
 	pub params: Params,
 	/// An identifier established by the Client that MUST contain a String,
 	/// Number, or NULL value if included. If it is not included it is assumed
@@ -105,6 +105,21 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn call_serialize_without_params() {
+		use serde_json;
+
+		let m = MethodCall {
+			jsonrpc: Some(Version::V2),
+			method: "status".to_owned(),
+			params: Params::None,
+			id: Id::Num(1),
+		};
+
+		let serialized = serde_json::to_string(&m).unwrap();
+		assert_eq!(serialized, r#"{"jsonrpc":"2.0","method":"status","id":1}"#);
+	}
+
 	#[test]
 	fn notification_serialize() {
 		use serde_json;

derive/tests/macros.rs

@@ -30,6 +30,10 @@ pub trait Rpc {
 	#[rpc(name = "raw", params = "raw")]
 	fn raw(&self, params: Params) -> Result<String>;
 
+	/// Squares a number, default value is 1.
+	#[rpc(name = "sqr")]
+	fn sqr(&self, a: Option<u64>) -> Result<u64>;
+
 	/// Handles a notification.
 	#[rpc(name = "notify")]
 	fn notify(&self, a: u64);
@@ -55,6 +59,11 @@ impl Rpc for RpcImpl {
 		Ok("OK".into())
 	}
 
+	fn sqr(&self, a: Option<u64>) -> Result<u64> {
+		let a = a.unwrap_or(1);
+		Ok(a * a)
+	}
+
 	fn notify(&self, a: u64) {
 		println!("Received `notify` with value: {}", a);
 	}
@@ -222,6 +231,47 @@ fn should_accept_any_raw_params() {
 	assert_eq!(expected, result4);
 }
 
+#[test]
+fn should_accept_optional_param() {
+	let mut io = IoHandler::new();
+	let rpc = RpcImpl::default();
+	io.extend_with(rpc.to_delegate());
+
+	// when
+	let req1 = r#"{"jsonrpc":"2.0","id":1,"method":"sqr","params":[2]}"#;
+	let req2 = r#"{"jsonrpc":"2.0","id":1,"method":"sqr"}"#;
+
+	let res1 = io.handle_request_sync(req1);
+	let res2 = io.handle_request_sync(req2);
+
+	// then
+	let result1: Response = serde_json::from_str(&res1.unwrap()).unwrap();
+	assert_eq!(
+		result1,
+		serde_json::from_str(
+			r#"{
+		"jsonrpc": "2.0",
+		"result": 4,
+		"id": 1
+	}"#
+		)
+		.unwrap()
+	);
+
+	let result2: Response = serde_json::from_str(&res2.unwrap()).unwrap();
+	assert_eq!(
+		result2,
+		serde_json::from_str(
+			r#"{
+		"jsonrpc": "2.0",
+		"result": 1,
+		"id": 1
+	}"#
+		)
+		.unwrap()
+	);
+}
+
 #[test]
 fn should_accept_only_notifications() {
 	let mut io = IoHandler::new();