Validate ToolCall Args against Schema

(cherry picked from commit eeb287117535dfb43785704171625323f01d5bda)

test/mcp/configuration_test.rb

@@ -61,5 +61,45 @@ module MCP
       merged = config3.merge(config1)
       assert_equal "2025-03-27", merged.protocol_version
     end
+
+    test "defaults validate_tool_call_arguments to true" do
+      config = Configuration.new
+      assert config.validate_tool_call_arguments
+    end
+
+    test "can set validate_tool_call_arguments to false" do
+      config = Configuration.new(validate_tool_call_arguments: false)
+      refute config.validate_tool_call_arguments
+    end
+
+    test "validate_tool_call_arguments? returns false when set" do
+      config = Configuration.new(validate_tool_call_arguments: false)
+      refute config.validate_tool_call_arguments?
+    end
+
+    test "validate_tool_call_arguments? returns true when not set" do
+      config = Configuration.new
+      assert config.validate_tool_call_arguments?
+    end
+
+    test "merge preserves validate_tool_call_arguments from other config" do
+      config1 = Configuration.new(validate_tool_call_arguments: false)
+      config2 = Configuration.new
+      merged = config1.merge(config2)
+      assert merged.validate_tool_call_arguments?
+    end
+
+    test "merge preserves validate_tool_call_arguments from self when other not set" do
+      config1 = Configuration.new(validate_tool_call_arguments: false)
+      config2 = Configuration.new
+      merged = config2.merge(config1)
+      refute merged.validate_tool_call_arguments
+    end
+
+    test "raises ArgumentError when validate_tool_call_arguments is not a boolean" do
+      assert_raises(ArgumentError) do
+        Configuration.new(validate_tool_call_arguments: "true")
+      end
+    end
   end
 end

test/mcp/server_test.rb

@@ -839,5 +839,123 @@ module MCP
 
       refute_includes server_without_resources.capabilities, :resources
     end
+
+    test "tools/call validates arguments against input schema when validate_tool_call_arguments is true" do
+      server = Server.new(
+        tools: [TestTool],
+        configuration: Configuration.new(validate_tool_call_arguments: true),
+      )
+
+      response = server.handle(
+        {
+          jsonrpc: "2.0",
+          id: 1,
+          method: "tools/call",
+          params: {
+            name: "test_tool",
+            arguments: { message: 123 },
+          },
+        },
+      )
+
+      assert_equal "2.0", response[:jsonrpc]
+      assert_equal 1, response[:id]
+      assert_equal(-32603, response[:error][:code])
+      assert_includes response[:error][:data], "Invalid arguments"
+    end
+
+    test "tools/call skips argument validation when validate_tool_call_arguments is false" do
+      server = Server.new(
+        tools: [TestTool],
+        configuration: Configuration.new(validate_tool_call_arguments: false),
+      )
+
+      response = server.handle(
+        {
+          jsonrpc: "2.0",
+          id: 1,
+          method: "tools/call",
+          params: {
+            name: "test_tool",
+            arguments: { message: 123 },
+          },
+        },
+      )
+
+      assert_equal "2.0", response[:jsonrpc]
+      assert_equal 1, response[:id]
+      assert response[:result], "Expected result key in response"
+      assert_equal "text", response[:result][:content][0][:type]
+      assert_equal "OK", response[:result][:content][0][:content]
+    end
+
+    test "tools/call validates arguments with complex types" do
+      server = Server.new(
+        tools: [ComplexTypesTool],
+        configuration: Configuration.new(validate_tool_call_arguments: true),
+      )
+
+      response = server.handle(
+        {
+          jsonrpc: "2.0",
+          id: 1,
+          method: "tools/call",
+          params: {
+            name: "complex_types_tool",
+            arguments: {
+              numbers: [1, 2, 3],
+              strings: ["a", "b", "c"],
+              objects: [{ name: "test" }],
+            },
+          },
+        },
+      )
+
+      assert_equal "2.0", response[:jsonrpc]
+      assert_equal 1, response[:id]
+      assert response[:result], "Expected result key in response"
+      assert_equal "text", response[:result][:content][0][:type]
+      assert_equal "OK", response[:result][:content][0][:content]
+    end
+
+    class TestTool < Tool
+      tool_name "test_tool"
+      description "a test tool for testing"
+      input_schema({ properties: { message: { type: "string" } }, required: ["message"] })
+
+      class << self
+        def call(message:, server_context: nil)
+          Tool::Response.new([{ type: "text", content: "OK" }])
+        end
+      end
+    end
+
+    class ComplexTypesTool < Tool
+      tool_name "complex_types_tool"
+      description "a test tool with complex types"
+      input_schema({
+        properties: {
+          numbers: { type: "array", items: { type: "number" } },
+          strings: { type: "array", items: { type: "string" } },
+          objects: {
+            type: "array",
+            items: {
+              type: "object",
+              properties: {
+                name: { type: "string" },
+              },
+              required: ["name"],
+            },
+          },
+        },
+        required: ["numbers", "strings", "objects"],
+      })
+
+      class << self
+        def call(numbers:, strings:, objects:, server_context: nil)
+          Tool::Response.new([{ type: "text", content: "OK" }])
+        end
+      end
+    end
   end
 end

test/mcp/tool/input_schema_test.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "test_helper"
+require "mcp/tool/input_schema"
 
 module MCP
   class Tool
@@ -27,6 +28,29 @@ module MCP
         input_schema = InputSchema.new(properties: { message: { type: "string" } }, required: [:message])
         assert_empty input_schema.missing_required_arguments({ message: "Hello, world!" })
       end
+
+      test "valid schema initialization" do
+        schema = InputSchema.new(properties: { foo: { type: "string" } }, required: [:foo])
+        assert_equal({ type: "object", properties: { foo: { type: "string" } }, required: [:foo] }, schema.to_h)
+      end
+
+      test "invalid schema raises argument error" do
+        assert_raises(ArgumentError) do
+          InputSchema.new(properties: { foo: { type: "invalid_type" } }, required: [:foo])
+        end
+      end
+
+      test "validate arguments with valid data" do
+        schema = InputSchema.new(properties: { foo: { type: "string" } }, required: [:foo])
+        assert_nil(schema.validate_arguments({ foo: "bar" }))
+      end
+
+      test "validate arguments with invalid data" do
+        schema = InputSchema.new(properties: { foo: { type: "string" } }, required: [:foo])
+        assert_raises(InputSchema::ValidationError) do
+          schema.validate_arguments({ foo: 123 })
+        end
+      end
     end
   end
 end

test/mcp/tool_test.rb

@@ -82,6 +82,23 @@ module MCP
       assert_equal expected, tool.input_schema.to_h
     end
 
+    test "raises detailed error message for invalid schema" do
+      error = assert_raises(ArgumentError) do
+        Class.new(MCP::Tool) do
+          input_schema(
+            properties: {
+              count: { type: "integer", minimum: "not a number" },
+            },
+            required: [:count],
+          )
+        end
+      end
+
+      assert_includes error.message, "Invalid JSON Schema"
+      assert_includes error.message, "#/properties/count/minimum"
+      assert_includes error.message, "string did not match the following type: number"
+    end
+
     test ".define allows definition of simple tools with a block" do
       tool = Tool.define(name: "mock_tool", description: "a mock tool for testing") do |_|
         Tool::Response.new([{ type: "text", content: "OK" }])
@@ -226,5 +243,23 @@ module MCP
       assert_equal response.content, [{ type: "text", content: "OK" }]
       assert_equal response.is_error, false
     end
+
+    test "input_schema rejects any $ref in schema" do
+      schema_with_ref = {
+        properties: {
+          foo: { "$ref" => "#/definitions/bar" },
+        },
+        required: [],
+        definitions: {
+          bar: { type: "string" },
+        },
+      }
+      error = assert_raises(ArgumentError) do
+        Class.new(MCP::Tool) do
+          input_schema schema_with_ref
+        end
+      end
+      assert_match(/Invalid JSON Schema/, error.message)
+    end
   end
 end