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 var trtp = [4]byte{0x54, 0x52, 0x54, 0x50}
  18
  19 // Handshake
  20 // After establishing TCP connection, both client and server start the handshake process
  21 // in order to confirm that each of them comply with requirements of the other.
  22 // The information provided in this initial data exchange identifies protocols,
  23 // and their versions, used in the communication. In the case where, after inspection,
  24 // the capabilities of one of the subjects do not comply with the requirements of the other,
  25 // the connection is dropped.
  26 //
  27 // The following information is sent to the server:
  28 // Description          Size    Data    Note
  29 // Protocol ID          4               TRTP    0x54525450
  30 // Sub-protocol ID      4               HOTL    User defined
  31 // VERSION                      2               1               Currently 1
  32 // Sub-version          2               2               User defined
  33 //
  34 // The server replies with the following:
  35 // Description          Size    Data    Note
  36 // Protocol ID          4               TRTP
  37 // Error code           4                               Error code returned by the server (0 = no error)
  38 func Handshake(rw io.ReadWriter) error {
  39         handshakeBuf := make([]byte, 12)
  40         if _, err := io.ReadFull(rw, handshakeBuf); err != nil {
  41                 return err
  42         }
  43
  44         var h handshake
  45         r := bytes.NewReader(handshakeBuf)
  46         if err := binary.Read(r, binary.BigEndian, &h); err != nil {
  47                 return err
  48         }
  49
  50         if h.Protocol != trtp {
  51                 return errors.New("invalid handshake")
  52         }
  53
  54         _, err := rw.Write([]byte{84, 82, 84, 80, 0, 0, 0, 0})
  55         return err
  56 }