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// Copyright (C) 2016 The Protocol Authors.
package protocol
import (
"encoding/binary"
"errors"
"fmt"
"io"
)
// The HelloIntf interface is implemented by the version specific hello
// message. It knows its magic number and how to serialize itself to a byte
// buffer.
type HelloIntf interface {
Magic() uint32
Marshal() ([]byte, error)
}
// The HelloResult is the non version specific interpretation of the other
// side's Hello message.
type HelloResult struct {
DeviceName string
ClientName string
ClientVersion string
}
var (
// ErrTooOldVersion12 is returned by ExchangeHello when the other side
// speaks the older, incompatible version 0.12 of the protocol.
ErrTooOldVersion12 = errors.New("the remote device speaks an older version of the protocol (v0.12) not compatible with this version")
// ErrTooOldVersion13 is returned by ExchangeHello when the other side
// speaks the older, incompatible version 0.12 of the protocol.
ErrTooOldVersion13 = errors.New("the remote device speaks an older version of the protocol (v0.13) not compatible with this version")
// ErrUnknownMagic is returned by ExchangeHellow when the other side
// speaks something entirely unknown.
ErrUnknownMagic = errors.New("the remote device speaks an unknown (newer?) version of the protocol")
)
func ExchangeHello(c io.ReadWriter, h HelloIntf) (HelloResult, error) {
if err := writeHello(c, h); err != nil {
return HelloResult{}, err
}
return readHello(c)
}
// IsVersionMismatch returns true if the error is a reliable indication of a
// version mismatch that we might want to alert the user about.
func IsVersionMismatch(err error) bool {
switch err {
case ErrTooOldVersion12, ErrTooOldVersion13, ErrUnknownMagic:
return true
default:
return false
}
}
func readHello(c io.Reader) (HelloResult, error) {
header := make([]byte, 4)
if _, err := io.ReadFull(c, header); err != nil {
return HelloResult{}, err
}
switch binary.BigEndian.Uint32(header) {
case HelloMessageMagic:
// This is a v0.14 Hello message in proto format
if _, err := io.ReadFull(c, header[:2]); err != nil {
return HelloResult{}, err
}
msgSize := binary.BigEndian.Uint16(header[:2])
if msgSize > 32767 {
return HelloResult{}, fmt.Errorf("hello message too big")
}
buf := make([]byte, msgSize)
if _, err := io.ReadFull(c, buf); err != nil {
return HelloResult{}, err
}
var hello Hello
if err := hello.Unmarshal(buf); err != nil {
return HelloResult{}, err
}
res := HelloResult{
DeviceName: hello.DeviceName,
ClientName: hello.ClientName,
ClientVersion: hello.ClientVersion,
}
return res, nil
case Version13HelloMagic:
// This is a v0.13 Hello message in XDR format
if _, err := io.ReadFull(c, header[:4]); err != nil {
return HelloResult{}, err
}
msgSize := binary.BigEndian.Uint32(header[:4])
if msgSize > 1024 {
return HelloResult{}, fmt.Errorf("hello message too big")
}
buf := make([]byte, msgSize)
if _, err := io.ReadFull(c, buf); err != nil {
return HelloResult{}, err
}
var hello Version13HelloMessage
if err := hello.UnmarshalXDR(buf); err != nil {
return HelloResult{}, err
}
res := HelloResult(hello)
return res, ErrTooOldVersion13
case 0x00010001, 0x00010000:
// This is the first word of a v0.12 cluster config message.
// (Version 0, message ID 1, message type 0, compression enabled or disabled)
return HelloResult{}, ErrTooOldVersion12
}
return HelloResult{}, ErrUnknownMagic
}
func writeHello(c io.Writer, h HelloIntf) error {
msg, err := h.Marshal()
if err != nil {
return err
}
if len(msg) > 32767 {
// The header length must be a positive signed int16
panic("bug: attempting to serialize too large hello message")
}
header := make([]byte, 6)
binary.BigEndian.PutUint32(header[:4], h.Magic())
binary.BigEndian.PutUint16(header[4:], uint16(len(msg)))
_, err = c.Write(append(header, msg...))
return err
}
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