Avoid void-params deserialize errors

src/server/message.rs

@@ -269,10 +269,18 @@ impl RawMessage {
             Id::Null => None,
         };
 
-        let params = R::Params::deserialize(&self.params).map_err(|e| {
-            debug!("error when parsing as request: {}", e);
-            jsonrpc::Error::invalid_params(format!("{}", e))
-        })?;
+        let params = R::Params::deserialize(&self.params)
+            .or_else(|e| {
+                // Avoid tedious type errors trying to deserialize `()`
+                if std::mem::size_of::<R::Params>() == 0 {
+                    R::Params::deserialize(&serde_json::Value::Null).map_err(|_| e)
+                } else {
+                    Err(e)
+                }
+            }).map_err(|e| {
+                debug!("error when parsing as request: {}", e);
+                jsonrpc::Error::invalid_params(format!("{}", e))
+            })?;
 
         match parsed_id {
             Some(id) => Ok(Request {

src/server/mod.rs

@@ -465,4 +465,18 @@ mod test {
 
         assert_eq!(get_root_path(&params), root_path);
     }
+
+    /// Some clients send empty object params for void params requests (see #1038)
+    #[test]
+    fn parse_shutdown_object_params() {
+        let raw = RawMessage::try_parse(
+            r#"{"jsonrpc": "2.0", "id": 2, "method": "shutdown", "params": {}}"#,
+        ).ok()
+        .and_then(|x| x)
+        .expect("raw parse failed");
+
+        let _request: Request<ShutdownRequest> = raw
+            .parse_as_request()
+            .expect("Boring validation is happening");
+    }
 }