git.r.bdr.sh - rbdr/mobius/blob - hotline/handshake.go

   1 package hotline
   2
   3 import (
   4         "bytes"
   5         "encoding/binary"
   6         "errors"
   7         "io"
   8 )
   9
  10 type handshake struct {
  11         Protocol    [4]byte // Must be 0x54525450 TRTP
  12         SubProtocol [4]byte
  13         Version     [2]byte // Always 1
  14         SubVersion  [2]byte
  15 }
  16
  17 // Handshake
  18 // After establishing TCP connection, both client and server start the handshake process
  19 // in order to confirm that each of them comply with requirements of the other.
  20 // The information provided in this initial data exchange identifies protocols,
  21 // and their versions, used in the communication. In the case where, after inspection,
  22 // the capabilities of one of the subjects do not comply with the requirements of the other,
  23 // the connection is dropped.
  24 //
  25 // The following information is sent to the server:
  26 // Description          Size    Data    Note
  27 // Protocol ID          4               TRTP    0x54525450
  28 // Sub-protocol ID      4               HOTL    User defined
  29 // VERSION                      2               1               Currently 1
  30 // Sub-version          2               2               User defined
  31 //
  32 // The server replies with the following:
  33 // Description          Size    Data    Note
  34 // Protocol ID          4               TRTP
  35 // Error code           4                               Error code returned by the server (0 = no error)
  36 func Handshake(conn io.ReadWriter) error {
  37         handshakeBuf := make([]byte, 12)
  38         if _, err := io.ReadFull(conn, handshakeBuf); err != nil {
  39                 return err
  40         }
  41
  42         var h handshake
  43         r := bytes.NewReader(handshakeBuf)
  44         if err := binary.Read(r, binary.BigEndian, &h); err != nil {
  45                 return err
  46         }
  47
  48         if h.Protocol != [4]byte{0x54, 0x52, 0x54, 0x50} {
  49                 return errors.New("invalid handshake")
  50         }
  51
  52         _, err := conn.Write([]byte{84, 82, 84, 80, 0, 0, 0, 0})
  53         return err
  54 }