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- // Copyright (C) 2016 The Protocol Authors.
- package protocol
- import (
- "encoding/binary"
- "errors"
- "io"
- )
- var (
- // ErrTooOldVersion is returned by ExchangeHello when the other side
- // speaks an older, incompatible version of the protocol.
- ErrTooOldVersion = errors.New("the remote device speaks an older version of the protocol not compatible with this version")
- // ErrUnknownMagic is returned by ExchangeHello 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 Hello) (Hello, error) {
- if h.Timestamp == 0 {
- panic("bug: missing timestamp in outgoing hello")
- }
- if err := writeHello(c, h); err != nil {
- return Hello{}, 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 ErrTooOldVersion, ErrUnknownMagic:
- return true
- default:
- return false
- }
- }
- func readHello(c io.Reader) (Hello, error) {
- header := make([]byte, 4)
- if _, err := io.ReadFull(c, header); err != nil {
- return Hello{}, 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 Hello{}, err
- }
- msgSize := binary.BigEndian.Uint16(header[:2])
- if msgSize > 32767 {
- return Hello{}, errors.New("hello message too big")
- }
- buf := make([]byte, msgSize)
- if _, err := io.ReadFull(c, buf); err != nil {
- return Hello{}, err
- }
- var hello Hello
- if err := hello.Unmarshal(buf); err != nil {
- return Hello{}, err
- }
- return Hello(hello), nil
- case 0x00010001, 0x00010000, Version13HelloMagic:
- // This is the first word of an older cluster config message or an
- // old magic number. (Version 0, message ID 1, message type 0,
- // compression enabled or disabled)
- return Hello{}, ErrTooOldVersion
- }
- return Hello{}, ErrUnknownMagic
- }
- func writeHello(c io.Writer, h Hello) 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, 6+len(msg))
- 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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