Add example test for null and omitted params

conn.go

@@ -69,10 +69,10 @@ func (c *Conn) Close() error {
 	return c.close(nil)
 }
 
-// Call initiates a JSON-RPC call using the specified method and
-// params, and waits for the response. If the response is successful,
-// its result is stored in result (a pointer to a value that can be
-// JSON-unmarshaled into); otherwise, a non-nil error is returned.
+// Call initiates a JSON-RPC call using the specified method and params, and
+// waits for the response. If the response is successful, its result is stored
+// in result (a pointer to a value that can be JSON-unmarshaled into);
+// otherwise, a non-nil error is returned. See DispatchCall for more details.
 func (c *Conn) Call(ctx context.Context, method string, params, result interface{}, opts ...CallOption) error {
 	call, err := c.DispatchCall(ctx, method, params, opts...)
 	if err != nil {
@@ -87,11 +87,14 @@ func (c *Conn) DisconnectNotify() <-chan struct{} {
 	return c.disconnect
 }
 
-// DispatchCall dispatches a JSON-RPC call using the specified method
-// and params, and returns a call proxy or an error. Call Wait()
-// on the returned proxy to receive the response. Only use this
-// function if you need to do work after dispatching the request,
-// otherwise use Call.
+// DispatchCall dispatches a JSON-RPC call using the specified method and
+// params, and returns a call proxy or an error. Call Wait() on the returned
+// proxy to receive the response. Only use this function if you need to do work
+// after dispatching the request, otherwise use Call.
+//
+// The params member is omitted from the JSON-RPC request if the given params is
+// nil. Use json.RawMessage("null") to send a JSON-RPC request with its params
+// member set to null.
 func (c *Conn) DispatchCall(ctx context.Context, method string, params interface{}, opts ...CallOption) (Waiter, error) {
 	req := &Request{Method: method}
 	for _, opt := range opts {
@@ -114,9 +117,13 @@ func (c *Conn) DispatchCall(ctx context.Context, method string, params interface
 	return Waiter{call: call}, nil
 }
 
-// Notify is like Call, but it returns when the notification request
-// is sent (without waiting for a response, because JSON-RPC
-// notifications do not have responses).
+// Notify is like Call, but it returns when the notification request is sent
+// (without waiting for a response, because JSON-RPC notifications do not have
+// responses).
+//
+// The params member is omitted from the JSON-RPC request if the given params is
+// nil. Use json.RawMessage("null") to send a JSON-RPC request with its params
+// member set to null.
 func (c *Conn) Notify(ctx context.Context, method string, params interface{}, opts ...CallOption) error {
 	req := &Request{Method: method, Notif: true}
 	for _, opt := range opts {

example_test.go

@@ -0,0 +1,78 @@
+package jsonrpc2_test
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/sourcegraph/jsonrpc2"
+)
+
+// Send a JSON-RPC notification with its params member omitted.
+func ExampleConn_Notify_paramsOmitted() {
+	ctx := context.Background()
+
+	connA, connB := net.Pipe()
+	defer connA.Close()
+	defer connB.Close()
+
+	rpcConn := jsonrpc2.NewConn(ctx, jsonrpc2.NewPlainObjectStream(connA), nil)
+
+	// Send the JSON-RPC notification.
+	go func() {
+		// Set params to nil.
+		if err := rpcConn.Notify(ctx, "foo", nil); err != nil {
+			fmt.Fprintln(os.Stderr, "notify:", err)
+		}
+	}()
+
+	// Read the raw JSON-RPC notification on connB.
+	//
+	// Reading the raw JSON-RPC request is for the purpose of this example only.
+	// Use a jsonrpc2.Handler to read parsed requests.
+	buf := make([]byte, 64)
+	n, err := connB.Read(buf)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "read:", err)
+	}
+
+	fmt.Printf("%s\n", buf[:n])
+
+	// Output: {"jsonrpc":"2.0","method":"foo"}
+}
+
+// Send a JSON-RPC notification with its params member set to null.
+func ExampleConn_Notify_nullParams() {
+	ctx := context.Background()
+
+	connA, connB := net.Pipe()
+	defer connA.Close()
+	defer connB.Close()
+
+	rpcConn := jsonrpc2.NewConn(ctx, jsonrpc2.NewPlainObjectStream(connA), nil)
+
+	// Send the JSON-RPC notification.
+	go func() {
+		// Set params to the JSON null value.
+		params := json.RawMessage("null")
+		if err := rpcConn.Notify(ctx, "foo", params); err != nil {
+			fmt.Fprintln(os.Stderr, "notify:", err)
+		}
+	}()
+
+	// Read the raw JSON-RPC notification on connB.
+	//
+	// Reading the raw JSON-RPC request is for the purpose of this example only.
+	// Use a jsonrpc2.Handler to read parsed requests.
+	buf := make([]byte, 64)
+	n, err := connB.Read(buf)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "read:", err)
+	}
+
+	fmt.Printf("%s\n", buf[:n])
+
+	// Output: {"jsonrpc":"2.0","method":"foo","params":null}
+}