Allow params field to be omitted in requests for methods that don't require them (#17)

* Allow `params` field to be omitted in requests for methods with empty parameters

* Add ping request to roundtrip test

* Generalize decoding of non-required parameters

Tests/MCPTests/PromptTests.swift

@@ -142,6 +142,36 @@ struct PromptTests {
         let emptyParams = ListPrompts.Parameters()
         #expect(emptyParams.cursor == nil)
     }
+    
+    @Test("ListPrompts request decoding with omitted params")
+    func testListPromptsRequestDecodingWithOmittedParams() throws {
+        // Test decoding when params field is omitted
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"prompts/list"}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListPrompts>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListPrompts.name)
+    }
+    
+    @Test("ListPrompts request decoding with null params")
+    func testListPromptsRequestDecodingWithNullParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"prompts/list","params":null}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListPrompts>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListPrompts.name)
+    }
 
     @Test("ListPrompts result validation")
     func testListPromptsResult() throws {

Tests/MCPTests/RequestTests.swift

@@ -76,4 +76,49 @@ struct RequestTests {
         #expect(decoded.id == "test-id")
         #expect(decoded.method == EmptyMethod.name)
     }
+
+    @Test("NotRequired parameters request decoding - with params")
+    func testNotRequiredParametersRequestDecodingWithParams() throws {
+        // Test decoding when params field is present
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"ping","params":{}}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<Ping>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == Ping.name)
+    }
+
+    @Test("NotRequired parameters request decoding - without params")
+    func testNotRequiredParametersRequestDecodingWithoutParams() throws {
+        // Test decoding when params field is missing
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"ping"}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<Ping>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == Ping.name)
+    }
+
+    @Test("NotRequired parameters request decoding - with null params")
+    func testNotRequiredParametersRequestDecodingWithNullParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"ping","params":null}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<Ping>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == Ping.name)
+    }
 }

Tests/MCPTests/ResourceTests.swift

@@ -86,6 +86,36 @@ struct ResourceTests {
         let emptyParams = ListResources.Parameters()
         #expect(emptyParams.cursor == nil)
     }
+    
+    @Test("ListResources request decoding with omitted params")
+    func testListResourcesRequestDecodingWithOmittedParams() throws {
+        // Test decoding when params field is omitted
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"resources/list"}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListResources>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListResources.name)
+    }
+    
+    @Test("ListResources request decoding with null params")
+    func testListResourcesRequestDecodingWithNullParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"resources/list","params":null}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListResources>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListResources.name)
+    }
 
     @Test("ListResources result validation")
     func testListResourcesResult() throws {

Tests/MCPTests/RoundtripTests.swift

@@ -118,6 +118,26 @@ struct RoundtripTests {
             group.cancelAll()
         }
 
+        // Test ping
+        let pingTask = Task {
+            try await client.ping()
+            // Ping doesn't return anything, so just getting here without throwing is success
+            #expect(true)  // Test passed if we reach this point
+        }
+
+        try await withThrowingTaskGroup(of: Void.self) { group in
+            group.addTask {
+                try await Task.sleep(for: .seconds(1))
+                pingTask.cancel()
+                throw CancellationError()
+            }
+            group.addTask {
+                try await pingTask.value
+            }
+            try await group.next()
+            group.cancelAll()
+        }
+
         let listToolsTask = Task {
             let result = try await client.listTools()
             #expect(result.count == 1)

Tests/MCPTests/ToolTests.swift

@@ -111,6 +111,36 @@ struct ToolTests {
         let emptyParams = ListTools.Parameters()
         #expect(emptyParams.cursor == nil)
     }
+    
+    @Test("ListTools request decoding with omitted params")
+    func testListToolsRequestDecodingWithOmittedParams() throws {
+        // Test decoding when params field is omitted
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"tools/list"}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListTools>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListTools.name)
+    }
+    
+    @Test("ListTools request decoding with null params")
+    func testListToolsRequestDecodingWithNullParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":"test-id","method":"tools/list","params":null}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<ListTools>.self, from: data)
+
+        #expect(decoded.id == "test-id")
+        #expect(decoded.method == ListTools.name)
+    }
 
     @Test("ListTools result validation")
     func testListToolsResult() throws {