Add WithDebugf() context option

Adds the high level WithDebugf() context option, and associated lower
level browser and dial options for setting a protocol wire debugger.
Additionally changes the conn.Conn.Read/Write implementations to be more
efficient, using direct easyjson.{Marshal,Unmarshal} calls and logging
to debug func when available.

browser.go

@@ -36,6 +36,7 @@ type Browser struct {
 	// logging funcs
 	logf func(string, ...interface{})
 	errf func(string, ...interface{})
+	dbgf func(string, ...interface{})
 
 	// The optional fields below are helpful for some tests.
 
@@ -60,32 +61,28 @@ type cmdJob struct {
 
 // NewBrowser creates a new browser.
 func NewBrowser(ctx context.Context, urlstr string, opts ...BrowserOption) (*Browser, error) {
-	conn, err := DialContext(ctx, ForceIP(urlstr))
-	if err != nil {
-		return nil, err
-	}
-
 	b := &Browser{
-		conn: conn,
-
 		tabQueue:  make(chan newTab, 1),
 		tabResult: make(chan *Target, 1),
-
-		cmdQueue: make(chan cmdJob),
-
-		logf: log.Printf,
+		cmdQueue:  make(chan cmdJob),
+		logf:      log.Printf,
 	}
-
 	// apply options
 	for _, o := range opts {
 		o(b)
 	}
-
 	// ensure errf is set
 	if b.errf == nil {
 		b.errf = func(s string, v ...interface{}) { b.logf("ERROR: "+s, v...) }
 	}
 
+	// dial
+	var err error
+	b.conn, err = DialContext(ctx, ForceIP(urlstr), WithConnDebugf(b.dbgf))
+	if err != nil {
+		return nil, err
+	}
+
 	go b.run(ctx)
 	return b, nil
 }
@@ -332,6 +329,12 @@ func WithBrowserErrorf(f func(string, ...interface{})) BrowserOption {
 	return func(b *Browser) { b.errf = f }
 }
 
+// WithBrowserDebugf is a browser option to specify a func to log actual
+// websocket messages.
+func WithBrowserDebugf(f func(string, ...interface{})) BrowserOption {
+	return func(b *Browser) { b.dbgf = f }
+}
+
 // WithConsolef is a browser option to specify a func to receive chrome log events.
 //
 // Note: NOT YET IMPLEMENTED.

chromedp.go

@@ -232,6 +232,11 @@ func WithErrorf(f func(string, ...interface{})) ContextOption {
 	return WithBrowserOption(WithBrowserErrorf(f))
 }
 
+// WithDebugf is a shortcut for WithBrowserOption(WithBrowserDebugf(f)).
+func WithDebugf(f func(string, ...interface{})) ContextOption {
+	return WithBrowserOption(WithBrowserDebugf(f))
+}
+
 // WithBrowserOption allows passing a number of browser options to the allocator
 // when allocating a new browser. As such, this context option can only be used
 // when NewContext is allocating a new browser.
@@ -248,7 +253,6 @@ func WithBrowserOption(opts ...BrowserOption) ContextOption {
 func Targets(ctx context.Context) ([]*target.Info, error) {
 	// Don't rely on Run, as that needs to be able to call Targets, and we
 	// don't want cyclic func calls.
-
 	c := FromContext(ctx)
 	if c == nil || c.Allocator == nil {
 		return nil, ErrInvalidContext

conn.go

@@ -3,11 +3,13 @@ package chromedp
 import (
 	"context"
 	"io"
+	"io/ioutil"
 	"net"
 	"strings"
 
 	"github.com/chromedp/cdproto"
 	"github.com/gorilla/websocket"
+	"github.com/mailru/easyjson"
 )
 
 var (
@@ -28,24 +30,11 @@ type Transport interface {
 // Conn wraps a gorilla/websocket.Conn connection.
 type Conn struct {
 	*websocket.Conn
-}
-
-// Read reads the next message.
-func (c *Conn) Read() (*cdproto.Message, error) {
-	msg := new(cdproto.Message)
-	if err := c.ReadJSON(msg); err != nil {
-		return nil, err
-	}
-	return msg, nil
-}
-
-// Write writes a message.
-func (c *Conn) Write(msg *cdproto.Message) error {
-	return c.WriteJSON(msg)
+	dbgf func(string, ...interface{})
 }
 
 // DialContext dials the specified websocket URL using gorilla/websocket.
-func DialContext(ctx context.Context, urlstr string) (*Conn, error) {
+func DialContext(ctx context.Context, urlstr string, opts ...DialOption) (*Conn, error) {
 	d := &websocket.Dialer{
 		ReadBufferSize:  DefaultReadBufferSize,
 		WriteBufferSize: DefaultWriteBufferSize,
@@ -57,7 +46,78 @@ func DialContext(ctx context.Context, urlstr string) (*Conn, error) {
 		return nil, err
 	}
 
-	return &Conn{conn}, nil
+	// apply opts
+	c := &Conn{
+		Conn: conn,
+	}
+	for _, o := range opts {
+		o(c)
+	}
+
+	return c, nil
+}
+
+// Read reads the next message.
+func (c *Conn) Read() (*cdproto.Message, error) {
+	// get websocket reader
+	typ, r, err := c.NextReader()
+	if err != nil {
+		return nil, err
+	}
+	if typ != websocket.TextMessage {
+		return nil, ErrInvalidWebsocketMessage
+	}
+
+	// when dbgf defined, buffer, log, unmarshal
+	if c.dbgf != nil {
+		// buffer output
+		buf, err := ioutil.ReadAll(r)
+		if err != nil {
+			return nil, err
+		}
+		c.dbgf("<- %s", string(buf))
+		msg := new(cdproto.Message)
+		if err = easyjson.Unmarshal(buf, msg); err != nil {
+			return nil, err
+		}
+		return msg, nil
+	}
+
+	// unmarshal direct from reader
+	msg := new(cdproto.Message)
+	if err = easyjson.UnmarshalFromReader(r, msg); err != nil {
+		return nil, err
+	}
+	return msg, nil
+}
+
+// Write writes a message.
+func (c *Conn) Write(msg *cdproto.Message) error {
+	w, err := c.NextWriter(websocket.TextMessage)
+	if err != nil {
+		return err
+	}
+
+	if c.dbgf != nil {
+		var buf []byte
+		buf, err = easyjson.Marshal(msg)
+		if err != nil {
+			return err
+		}
+		c.dbgf("-> %s", string(buf))
+		_, err = w.Write(buf)
+		if err != nil {
+			return err
+		}
+	} else {
+		// direct marshal
+		_, err = easyjson.MarshalToWriter(msg, w)
+		if err != nil {
+			return err
+		}
+	}
+
+	return w.Close()
 }
 
 // ForceIP forces the host component in urlstr to be an IP address.
@@ -80,3 +140,13 @@ func ForceIP(urlstr string) string {
 	}
 	return urlstr
 }
+
+// DialOption is a dial option.
+type DialOption func(*Conn)
+
+// WithConnDebugf is a dial option to set a protocol logger.
+func WithConnDebugf(f func(string, ...interface{})) DialOption {
+	return func(c *Conn) {
+		c.dbgf = f
+	}
+}

errors.go

@@ -10,6 +10,9 @@ func (err Error) Error() string {
 
 // Error types.
 const (
+	// ErrInvalidWebsocketMessage is the invalid websocket message.
+	ErrInvalidWebsocketMessage Error = "invalid websocket message"
+
 	// ErrInvalidDimensions is the invalid dimensions error.
 	ErrInvalidDimensions Error = "invalid dimensions"