feat: add support for flattened sessions

Chrome is deprecating non-flattened sessions (crbug.com/991325) where
commands are wrapped via Target.SendMessageToTarget. Flattened mode
includes the sessionId directly in the JSON-RPC message instead.

Add rpcc.NewSession for creating session-scoped connections that share
the parent's websocket I/O. WithSessionClose allows registering a
cleanup callback for detachment.

session.Manager now uses flattened mode by default, requiring Chrome 77+.
WithNoFlatten opts into legacy mode for older versions.

Closes #109

Author: mafredri

cdp_client.go

@@ -330,16 +330,23 @@ func (g *Generator) CdpClient(domains []proto.Domain) {
 // invoke methods or listen to events in every CDP domain. The Client consumes
 // a rpcc connection, used to invoke the methods.
 type Client struct {
+	conn *rpcc.Conn
 	%s
 }
 
 // NewClient returns a new Client that uses conn
 // for communication with the debugging target.
 func NewClient(conn *rpcc.Conn) *Client {
 	return &Client{
+		conn: conn,
 		%s
 	}
 }
+
+// Conn returns the underlying rpcc.Conn used by this Client.
+func (c *Client) Conn() *rpcc.Conn {
+	return c.conn
+}
 `, fields.buf.Bytes(), newFields.buf.Bytes())
 }
 

cmd/cdpgen/main.go

@@ -2,6 +2,8 @@ package testutil
 
 import (
 	"context"
+	"encoding/json"
+	"io"
 	"testing"
 	"time"
 
@@ -11,6 +13,41 @@ import (
 	"github.com/mafredri/cdp/rpcc"
 )
 
+// logCodec wraps an rpcc.Codec and logs all requests and responses.
+type logCodec struct {
+	t   *testing.T
+	enc *json.Encoder
+	dec *json.Decoder
+}
+
+func (c *logCodec) WriteRequest(r *rpcc.Request) error {
+	c.t.Helper()
+	data, _ := json.Marshal(r)
+	c.t.Logf("SEND: %s", data)
+	return c.enc.Encode(r)
+}
+
+func (c *logCodec) ReadResponse(r *rpcc.Response) error {
+	c.t.Helper()
+	if err := c.dec.Decode(r); err != nil {
+		return err
+	}
+	data, _ := json.Marshal(r)
+	c.t.Logf("RECV: %s", data)
+	return nil
+}
+
+// NewLogCodec returns a new rpcc codec that logs all requests and responses.
+func NewLogCodec(t *testing.T) rpcc.DialOption {
+	return rpcc.WithCodec(func(conn io.ReadWriter) rpcc.Codec {
+		return &logCodec{
+			t:   t,
+			enc: json.NewEncoder(conn),
+			dec: json.NewDecoder(conn),
+		}
+	})
+}
+
 // Client represents a test client.
 type Client struct {
 	t      *testing.T
@@ -32,7 +69,13 @@ func NewClient(ctx context.Context, t *testing.T) *Client {
 	if err != nil {
 		t.Fatal(err)
 	}
-	conn, err := rpcc.DialContext(ctx, v.WebSocketDebuggerURL)
+
+	var opts []rpcc.DialOption
+	if testing.Verbose() {
+		opts = append(opts, NewLogCodec(t))
+	}
+
+	conn, err := rpcc.DialContext(ctx, v.WebSocketDebuggerURL, opts...)
 	if err != nil {
 		t.Fatal(err)
 	}