Improve go/rpc API (github#905)

* improve go/rpc API

* fix TestMultiClient

* code review feedback

Author: qmuntal

go/internal/e2e/multi_client_test.go

@@ -16,11 +16,8 @@ import (
 func TestMultiClient(t *testing.T) {
 	// Use TCP mode so a second client can connect to the same CLI process
 	ctx := testharness.NewTestContext(t)
-	client1 := copilot.NewClient(&copilot.ClientOptions{
-		CLIPath:  ctx.CLIPath,
-		Cwd:      ctx.WorkDir,
-		Env:      ctx.Env(),
-		UseStdio: copilot.Bool(false),
+	client1 := ctx.NewClient(func(opts *copilot.ClientOptions) {
+		opts.UseStdio = copilot.Bool(false)
 	})
 	t.Cleanup(func() { client1.ForceStop() })
 

go/internal/e2e/testharness/context.go

@@ -158,7 +158,8 @@ func (c *TestContext) Env() []string {
 }
 
 // NewClient creates a CopilotClient configured for this test context.
-func (c *TestContext) NewClient() *copilot.Client {
+// Optional overrides can be applied to the default ClientOptions via the opts function.
+func (c *TestContext) NewClient(opts ...func(*copilot.ClientOptions)) *copilot.Client {
 	options := &copilot.ClientOptions{
 		CLIPath: c.CLIPath,
 		Cwd:     c.WorkDir,
@@ -170,6 +171,10 @@ func (c *TestContext) NewClient() *copilot.Client {
 		options.GitHubToken = "fake-token-for-e2e-tests"
 	}
 
+	for _, opt := range opts {
+		opt(options)
+	}
+
 	return copilot.NewClient(options)
 }
 

go/internal/jsonrpc2/jsonrpc2.go

@@ -214,17 +214,23 @@ func (c *Client) Request(method string, params any) (json.RawMessage, error) {
 		}
 	}
 
-	paramsData, err := json.Marshal(params)
-	if err != nil {
-		return nil, fmt.Errorf("failed to marshal params: %w", err)
+	var paramsData json.RawMessage
+	if params == nil {
+		paramsData = json.RawMessage("{}")
+	} else {
+		var err error
+		paramsData, err = json.Marshal(params)
+		if err != nil {
+			return nil, fmt.Errorf("failed to marshal params: %w", err)
+		}
 	}
 
 	// Send request
 	request := Request{
 		JSONRPC: "2.0",
 		ID:      json.RawMessage(`"` + requestID + `"`),
 		Method:  method,
-		Params:  json.RawMessage(paramsData),
+		Params:  paramsData,
 	}
 
 	if err := c.sendMessage(request); err != nil {
@@ -261,15 +267,19 @@ func (c *Client) Request(method string, params any) (json.RawMessage, error) {
 
 // Notify sends a JSON-RPC notification (no response expected)
 func (c *Client) Notify(method string, params any) error {
-	paramsData, err := json.Marshal(params)
-	if err != nil {
-		return fmt.Errorf("failed to marshal params: %w", err)
+	var paramsData json.RawMessage
+	if params != nil {
+		var err error
+		paramsData, err = json.Marshal(params)
+		if err != nil {
+			return fmt.Errorf("failed to marshal params: %w", err)
+		}
 	}
 
 	notification := Request{
 		JSONRPC: "2.0",
 		Method:  method,
-		Params:  json.RawMessage(paramsData),
+		Params:  paramsData,
 	}
 	return c.sendMessage(notification)
 }