package network import ( "bytes" "crypto/sha256" "encoding/binary" "errors" "fmt" "io" "github.com/anthdm/neo-go/pkg/core" "github.com/anthdm/neo-go/pkg/network/payload" ) const ( // The minimum size of a valid message. minMessageSize = 24 cmdSize = 12 ) var ( errChecksumMismatch = errors.New("checksum mismatch") ) // NetMode type that is compatible with netModes below. type NetMode uint32 // String implements the stringer interface. func (n NetMode) String() string { switch n { case ModeDevNet: return "devnet" case ModeTestNet: return "testnet" case ModeMainNet: return "mainnet" default: return "" } } // Values used for the magic field, according to the docs. const ( ModeMainNet NetMode = 0x00746e41 // 7630401 ModeTestNet = 0x74746e41 // 1953787457 ModeDevNet = 56753 // docker privnet ) // Message is the complete message send between nodes. type Message struct { Magic NetMode // Command is utf8 code, of which the length is 12 bytes, // the extra part is filled with 0. Command [cmdSize]byte // Length of the payload Length uint32 // Checksum is the first 4 bytes of the value that two times SHA256 // hash of the payload Checksum uint32 // Payload send with the message. Payload payload.Payload } type commandType string // valid commands used to send between nodes. const ( cmdVersion commandType = "version" cmdVerack = "verack" cmdGetAddr = "getaddr" cmdAddr = "addr" cmdGetHeaders = "getheaders" cmdHeaders = "headers" cmdGetBlocks = "getblocks" cmdInv = "inv" cmdGetData = "getdata" cmdBlock = "block" cmdTX = "tx" cmdConsensus = "consensus" ) func newMessage(magic NetMode, cmd commandType, p payload.Payload) *Message { var ( size uint32 checksum []byte ) if p != nil { buf := new(bytes.Buffer) if err := p.EncodeBinary(buf); err != nil { panic(err) } size = uint32(buf.Len()) checksum = sumSHA256(sumSHA256(buf.Bytes())) } else { checksum = sumSHA256(sumSHA256([]byte{})) } return &Message{ Magic: magic, Command: cmdToByteArray(cmd), Length: size, Payload: p, Checksum: binary.LittleEndian.Uint32(checksum[:4]), } } // Converts the 12 byte command slice to a commandType. func (m *Message) commandType() commandType { cmd := cmdByteArrayToString(m.Command) switch cmd { case "version": return cmdVersion case "verack": return cmdVerack case "getaddr": return cmdGetAddr case "addr": return cmdAddr case "getheaders": return cmdGetHeaders case "header": return cmdHeaders case "getblocks": return cmdGetBlocks case "inv": return cmdInv case "getdata": return cmdGetData case "block": return cmdBlock case "tx": return cmdTX case "consensus": return cmdConsensus default: return "" } } // decode a Message from the given reader. func (m *Message) decode(r io.Reader) error { binary.Read(r, binary.LittleEndian, &m.Magic) binary.Read(r, binary.LittleEndian, &m.Command) binary.Read(r, binary.LittleEndian, &m.Length) binary.Read(r, binary.LittleEndian, &m.Checksum) // return if their is no payload. if m.Length == 0 { return nil } return m.decodePayload(r) } func (m *Message) decodePayload(r io.Reader) error { buf := make([]byte, m.Length) n, err := r.Read(buf) if err != nil { return err } if uint32(n) != m.Length { return fmt.Errorf("expected to have read exactly %d bytes got %d", m.Length, n) } // Compare the checksum of the payload. if !compareChecksum(m.Checksum, buf) { return errChecksumMismatch } r = bytes.NewReader(buf) var p payload.Payload switch m.commandType() { case cmdVersion: p = &payload.Version{} if err := p.DecodeBinary(r); err != nil { return err } case cmdInv: p = &payload.Inventory{} if err := p.DecodeBinary(r); err != nil { return err } case cmdAddr: p = &payload.AddressList{} if err := p.DecodeBinary(r); err != nil { return err } case cmdBlock: p = &core.Block{} if err := p.DecodeBinary(r); err != nil { return err } } m.Payload = p return nil } // encode a Message to any given io.Writer. func (m *Message) encode(w io.Writer) error { binary.Write(w, binary.LittleEndian, m.Magic) binary.Write(w, binary.LittleEndian, m.Command) binary.Write(w, binary.LittleEndian, m.Length) binary.Write(w, binary.LittleEndian, m.Checksum) if m.Payload != nil { return m.Payload.EncodeBinary(w) } return nil } // convert a command (string) to a byte slice filled with 0 bytes till // size 12. func cmdToByteArray(cmd commandType) [cmdSize]byte { cmdLen := len(cmd) if cmdLen > cmdSize { panic("exceeded command max length of size 12") } // The command can have max 12 bytes, rest is filled with 0. b := [cmdSize]byte{} for i := 0; i < cmdLen; i++ { b[i] = cmd[i] } return b } func cmdByteArrayToString(cmd [cmdSize]byte) string { buf := []byte{} for i := 0; i < cmdSize; i++ { if cmd[i] != 0 { buf = append(buf, cmd[i]) } } return string(buf) } func sumSHA256(b []byte) []byte { h := sha256.New() h.Write(b) return h.Sum(nil) } func compareChecksum(have uint32, b []byte) bool { sum := sumSHA256(sumSHA256(b))[:4] want := binary.LittleEndian.Uint32(sum) return have == want }