Function toolForErr

mcp/server.go:285–399

(t *Tool, h ToolHandlerFor[In, Out], cache *SchemaCache)

}

func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out], cache *SchemaCache) (*Tool, ToolHandler, error) {
	tt := *t

	// Special handling for an "any" input: treat as an empty object.
	if reflect.TypeFor[In]() == reflect.TypeFor[any]() && t.InputSchema == nil {
		tt.InputSchema = &jsonschema.Schema{Type: "object"}
	}

	var inputResolved *jsonschema.Resolved
	if _, err := setSchema[In](&tt.InputSchema, &inputResolved, cache); err != nil {
		return nil, nil, fmt.Errorf("input schema: %w", err)
	}

	// Handling for zero values:
	//
	// If Out is a pointer type and we've derived the output schema from its
	// element type, use the zero value of its element type in place of a typed
	// nil.
	var (
		elemZero       any // only non-nil if Out is a pointer type
		outputResolved *jsonschema.Resolved
	)
	if t.OutputSchema != nil || reflect.TypeFor[Out]() != reflect.TypeFor[any]() {
		var err error
		elemZero, err = setSchema[Out](&tt.OutputSchema, &outputResolved, cache)
		if err != nil {
			return nil, nil, fmt.Errorf("output schema: %v", err)
		}
	}

	th := func(ctx context.Context, req *CallToolRequest) (*CallToolResult, error) {
		var input json.RawMessage
		if req.Params.Arguments != nil {
			input = req.Params.Arguments
		}
		// Validate input and apply defaults.
		var err error
		input, err = applySchema(input, inputResolved)
		if err != nil {
			var errRes CallToolResult
			errRes.SetError(fmt.Errorf("validating \"arguments\": %v", err))
			return &errRes, nil
		}

		// Unmarshal and validate args.
		var in In
		if input != nil {
			if err := internaljson.Unmarshal(input, &in); err != nil {
				var errRes CallToolResult
				errRes.SetError(err)
				return &errRes, nil
			}
		}

		// Call typed handler.
		res, out, err := h(ctx, req, in)
		// Handle server errors appropriately:
		// - If the handler returns a structured error (like jsonrpc.Error), return it directly