diff --git a/go.mod b/go.mod
index 3c8bc79..3f71120 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,7 @@ module opcua-go
 go 1.21
 
 require (
-	github.com/shoothzj/gox v0.0.3-0.20240914162741-a7541b79fa6f
+	github.com/shoothzj/gox v0.0.3-0.20240915030409-0ff3ac4e657c
 	github.com/stretchr/testify v1.9.0
 )
 
diff --git a/go.sum b/go.sum
index 8170fd8..3aa2062 100644
--- a/go.sum
+++ b/go.sum
@@ -2,8 +2,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/shoothzj/gox v0.0.3-0.20240914162741-a7541b79fa6f h1:a70I1OcxVdGGIN7hnt4p/22afJ16tFvOkjlTfV9aK8o=
-github.com/shoothzj/gox v0.0.3-0.20240914162741-a7541b79fa6f/go.mod h1:W8vthsaC2LWvu1zy/B9znKuOOSrFUqWCMHkdbqZJE04=
+github.com/shoothzj/gox v0.0.3-0.20240915030409-0ff3ac4e657c h1:bGa8KCyniEJwV1IF6BKSwjKlexk5If8cXp3M17JOfa4=
+github.com/shoothzj/gox v0.0.3-0.20240915030409-0ff3ac4e657c/go.mod h1:W8vthsaC2LWvu1zy/B9znKuOOSrFUqWCMHkdbqZJE04=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
diff --git a/opcua/client.go b/opcua/client.go
index 0767d7e..7a1edce 100644
--- a/opcua/client.go
+++ b/opcua/client.go
@@ -1,20 +1,176 @@
 package opcua
 
-import "log/slog"
+import (
+	"crypto/tls"
+	"fmt"
+	"github.com/shoothzj/gox/buffer"
+	"github.com/shoothzj/gox/netx"
+	"log/slog"
+	"net"
+	"sync"
+)
 
 type ClientConfig struct {
-	logger *slog.Logger
+	Address          netx.Address
+	BufferMax        int
+	SendQueueSize    int
+	PendingQueueSize int
+	TlsConfig        *tls.Config
+
+	Logger *slog.Logger
+}
+
+type sendRequest struct {
+	bytes    []byte
+	callback func([]byte, error)
 }
 
 type Client struct {
 	config *ClientConfig
 	logger *slog.Logger
+
+	conn         net.Conn
+	eventsChan   chan *sendRequest
+	pendingQueue chan *sendRequest
+	buffer       *buffer.Buffer
+	closeCh      chan struct{}
+}
+
+func (c *Client) Send(bytes []byte) ([]byte, error) {
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+	var result []byte
+	var err error
+	c.sendAsync(bytes, func(resp []byte, e error) {
+		result = resp
+		err = e
+		wg.Done()
+	})
+	wg.Wait()
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+func (c *Client) sendAsync(bytes []byte, callback func([]byte, error)) {
+	sr := &sendRequest{
+		bytes:    bytes,
+		callback: callback,
+	}
+	c.eventsChan <- sr
+}
+
+func (c *Client) read() {
+	for {
+		select {
+		case req := <-c.pendingQueue:
+			n, err := c.conn.Read(c.buffer.WritableSlice())
+			if err != nil {
+				req.callback(nil, err)
+				c.closeCh <- struct{}{}
+				break
+			}
+			err = c.buffer.AdjustWriteCursor(n)
+			if err != nil {
+				req.callback(nil, err)
+				c.closeCh <- struct{}{}
+				break
+			}
+			if c.buffer.Size() < 4 {
+				continue
+			}
+			bytes := make([]byte, 4)
+			err = c.buffer.ReadExactly(bytes)
+			c.buffer.Compact()
+			if err != nil {
+				req.callback(nil, err)
+				c.closeCh <- struct{}{}
+				break
+			}
+			length := int(bytes[3]) | int(bytes[2])<<8 | int(bytes[1])<<16 | int(bytes[0])<<24
+			if c.buffer.Size() < length {
+				continue
+			}
+			// in case ddos attack
+			if length > c.buffer.Capacity() {
+				req.callback(nil, fmt.Errorf("response length %d is too large", length))
+				c.closeCh <- struct{}{}
+				break
+			}
+			data := make([]byte, length)
+			err = c.buffer.ReadExactly(data)
+			if err != nil {
+				req.callback(nil, err)
+				c.closeCh <- struct{}{}
+				break
+			}
+			c.buffer.Compact()
+			req.callback(data, nil)
+		case <-c.closeCh:
+			return
+		}
+	}
+}
+
+func (c *Client) write() {
+	for {
+		select {
+		case req := <-c.eventsChan:
+			n, err := c.conn.Write(req.bytes)
+			if err != nil {
+				req.callback(nil, err)
+				c.closeCh <- struct{}{}
+				break
+			}
+			if n != len(req.bytes) {
+				req.callback(nil, fmt.Errorf("write %d bytes, but expect %d bytes", n, len(req.bytes)))
+				c.closeCh <- struct{}{}
+				break
+			}
+			c.pendingQueue <- req
+		case <-c.closeCh:
+			return
+		}
+	}
 }
 
-func NewClient(config *ClientConfig) *Client {
+func (c *Client) Close() {
+	_ = c.conn.Close()
+	c.closeCh <- struct{}{}
+}
+
+func NewClient(config *ClientConfig) (*Client, error) {
+	conn, err := netx.Dial(config.Address, config.TlsConfig)
+
+	if err != nil {
+		return nil, err
+	}
+	if config.SendQueueSize == 0 {
+		config.SendQueueSize = 1000
+	}
+	if config.PendingQueueSize == 0 {
+		config.PendingQueueSize = 1000
+	}
+	if config.BufferMax == 0 {
+		config.BufferMax = 512 * 1024
+	}
+
 	client := &Client{
 		config: config,
-		logger: config.logger,
+		logger: config.Logger,
+
+		conn:         conn,
+		eventsChan:   make(chan *sendRequest, config.SendQueueSize),
+		pendingQueue: make(chan *sendRequest, config.PendingQueueSize),
+		buffer:       buffer.NewBuffer(config.BufferMax),
+		closeCh:      make(chan struct{}),
 	}
-	return client
+	go func() {
+		client.read()
+	}()
+	go func() {
+		client.write()
+	}()
+	return client, nil
 }