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server.go
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server.go
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package tcprelay
import (
"bufio"
"crypto/tls"
"encoding/hex"
"fmt"
"io"
"log"
"net"
"tcprelay/relaytarget"
"time"
)
type tcpRelayServer struct {
addr string
target relaytarget.TcpRelayTarget
tlsCfg *tls.Config
}
func NewTcpRelayServer(port int, target relaytarget.TcpRelayTarget, tlsCfg *tls.Config) *tcpRelayServer {
return &tcpRelayServer{
addr: fmt.Sprintf(":%d", port),
target: target,
tlsCfg: tlsCfg,
}
}
func (s *tcpRelayServer) listener() (l net.Listener, err error) {
if s.tlsCfg != nil {
l, err = tls.Listen("tcp", s.addr, s.tlsCfg)
log.Printf("using TLS connection\n")
} else {
l, err = net.Listen("tcp4", s.addr)
}
if err != nil {
return nil, err
}
log.Printf("middle server is listening on address %s\n", s.addr)
return l, nil
}
func (s *tcpRelayServer) Listen() {
l, err := s.listener()
if err != nil {
log.Fatal(err)
}
err = s.target.Prepare()
if err != nil {
log.Printf("target server is not ready: %+v", err)
return
}
for {
client, err := l.Accept()
if err != nil {
log.Println(err)
continue
}
go handleConnection(client, s.target)
}
}
func handleConnection(client net.Conn, target relaytarget.TcpRelayTarget) {
defer func() {
log.Printf("connections terminated\n\n")
client.Close()
}()
log.Printf("client connected from %s\n", client.RemoteAddr().String())
err := target.Dial()
if err != nil {
log.Printf("can't dial target server: %+v\n", err)
return
}
log.Printf("successfully dial target server %s\n\n", target.Conn().RemoteAddr().String())
defer target.Close()
for {
var data []byte
data, err = copy(target.Conn(), client)
if err != nil {
log.Printf("error when send data by client: %+v\n", err)
return
}
log.Printf("%s ==========> %s\n", client.RemoteAddr().String(), target.Conn().RemoteAddr().String())
log.Printf("transmitted packet length: %d\n%s\n\n", len(data), hex.EncodeToString(data))
data, err = copy(client, target.Conn())
if err != nil {
log.Printf("error when send data back to client: %+v\n", err)
return
}
log.Printf("%s <========== %s\n", client.RemoteAddr().String(), target.Conn().RemoteAddr().String())
log.Printf("received packet length: %d\n%s\n\n", len(data), hex.EncodeToString(data))
}
}
func copy(dst net.Conn, src net.Conn) (writtenData []byte, err error) {
src.SetReadDeadline(time.Now().Add(time.Second * 30))
r := bufio.NewReader(src)
w := bufio.NewWriter(dst)
buf := make([]byte, 1024)
buf[0], err = r.ReadByte()
if err != nil {
return writtenData, fmt.Errorf("read first byte error: %+v", err)
}
err = w.WriteByte(buf[0])
if err != nil {
return writtenData, fmt.Errorf("write first byte error: %+v", err)
}
writtenData = append(writtenData, buf[0])
for r.Buffered() > 0 {
nr, er := r.Read(buf[:])
if nr > 0 {
nw, ew := w.Write(buf[:nr])
if ew != nil {
err = fmt.Errorf("write data error: %+v", ew)
break
}
writtenData = append(writtenData, buf[:nw]...)
if nr != nw {
err = io.ErrShortWrite
break
}
}
if er != nil {
if er != io.EOF {
err = fmt.Errorf("read data error: %+v", er)
}
break
}
}
w.Flush()
return writtenData, err
}