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protocol.go
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protocol.go
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package gotalk
import (
"bytes"
"encoding/binary"
"errors"
"io"
"strconv"
"time"
)
// Version of this protocol
const ProtocolVersion = uint8(1)
// Protocol message types
const (
MsgTypeSingleReq = MsgType('r')
MsgTypeStreamReq = MsgType('s')
MsgTypeStreamReqPart = MsgType('p')
MsgTypeSingleRes = MsgType('R')
MsgTypeStreamRes = MsgType('S')
MsgTypeErrorRes = MsgType('E')
MsgTypeRetryRes = MsgType('e')
MsgTypeNotification = MsgType('n')
MsgTypeHeartbeat = MsgType('h')
MsgTypeProtocolError = MsgType('f')
)
// ProtocolError codes
const (
ProtocolErrorAbnormal = 0
ProtocolErrorUnsupported = 1
ProtocolErrorInvalidMsg = 2
ProtocolErrorTimeout = 3
)
// Protocol message type
type MsgType byte
// Write the version this protocol implements to `s`
func WriteVersion(s io.Writer) (int, error) {
return s.Write(protocolVersionBuf[:])
}
// Read the version the other end implements. Returns an error if this side's protocol
// is incompatible with the other side's version.
func ReadVersion(s io.Reader) (uint8, error) {
b := make([]byte, 2)
if _, err := readn(s, b); err != nil {
return 0, err
}
n, err := strconv.ParseUint(string(b), 16, 8)
if err != nil {
return 0, err
}
if n != uint64(ProtocolVersion) {
return 0, errors.New("unsupported protocol version \"" + string(b) + "\"")
}
return uint8(n), nil
}
// Maximum value of a heartbeat's "load"
var HeartbeatMsgMaxLoad = 0xffff
// Create a slice of bytes representing a heartbeat message
func MakeHeartbeatMsg(load uint16, b []byte) []byte {
// b := []byte{byte(MsgTypeHeartbeat), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
b[0] = byte(MsgTypeHeartbeat)
z := 1
copyFixnum(b[z:z+4], 4, uint64(load), 16)
z += 4
copyFixnum(b[z:z+8], 8, uint64(time.Now().UTC().Unix()), 16)
return b[0:13]
}
// Create a slice of bytes representing a message (w/o any payload)
func MakeMsg(t MsgType, id, name3 string, wait, size uint32) []byte {
// calculate buffer size
bz := 9 // minimum size, fitting type and payload size
name3z := 0
if t == MsgTypeRetryRes {
bz = 21 // e.g. "e00010000000100000001"
} else {
if id != "" {
bz += 4 // msg with id e.g. "R000100000005"
}
name3z = len(name3)
if name3z != 0 {
bz += 3 + name3z // msg w/ name3 e.g. "r0001004echo00000005"
}
}
b := make([]byte, bz)
b[0] = byte(t) // type e.g. "R"
z := 1
if id != "" {
b[1] = id[0]
b[2] = id[1]
b[3] = id[2]
b[4] = id[3] // id e.g. "abcd"
z += 4
}
if name3z != 0 {
copyFixnum(b[z:z+3], 3, uint64(name3z), 16) // name3 size e.g. "004"
z += 3
copy(b[z:], []byte(name3))
z += name3z
}
if t == MsgTypeRetryRes {
copyFixnum(b[z:z+8], 8, uint64(wait), 16)
z += 8
}
if size == 0 {
copy(b[z:], zeroes[:8])
} else {
copyFixnum(b[z:z+8], 8, uint64(size), 16) // payload size e.g. "0000005"
}
return b[:z+8]
}
// Read a message from `s`
// If t is MsgTypeHeartbeat, wait==load, size==time
func ReadMsg(s io.Reader, b []byte) (t MsgType, id, name3 string, wait, size uint32, err error) {
// "r0001004echo00000005" => ('r', "0001", "echo", 0, 5, nil)
// "R000100000005" => ('R', "0001", "", 0, 5, nil)
// "e00010000138800000014" => ('e', "0001", "", 5000, 20, nil)
// A message has a minimum size of 13, so read first 13 bytes
// e.g. "n001a00000000" = <notification> <short name> <no payload>
readz := 13
readz, err = readn(s, b[:readz])
if err != nil {
if err == io.EOF && readz >= 9 && b[0] == byte(MsgTypeProtocolError) {
// OK to read until EOF for MsgTypeProtocolError as they are shorter than other messages
err = nil
} else {
return
}
}
// type
t = MsgType(b[0])
z := 1
if t == MsgTypeHeartbeat {
// load
var n uint64
n, err = strconv.ParseUint(string(b[z:z+4]), 16, 16)
z += 4
if err != nil {
return
}
wait = uint32(n)
} else if t != MsgTypeNotification && t != MsgTypeProtocolError {
// requestID
id = string(b[z : z+4])
z += 4
}
if t == MsgTypeSingleReq || t == MsgTypeStreamReq || t == MsgTypeNotification {
// name
// text3Size
name3z, e := strconv.ParseUint(string(b[z:z+3]), 16, 16)
z += 3
if e != nil {
err = e
return
}
// Read remainder of message
newz := z + int(name3z) + 8 // 8 = payload size
if cap(b) < newz {
// Grow buffer (only happens with really long name3)
newb := make([]byte, newz)
copy(newb, b)
b = newb
}
if newz > readz {
if _, err = readn(s, b[readz:newz]); err != nil {
return
}
}
// text3Value
name3 = string(b[z : z+int(name3z)])
z += int(name3z)
} else if t == MsgTypeRetryRes {
// wait
n, e := strconv.ParseUint(string(b[z:z+8]), 16, 32)
if e != nil {
err = e
return
}
wait = uint32(n)
z += 8
// read remainding 8 bytes of the message
if _, err = readn(s, b[z:z+8]); err != nil {
return
}
}
// payloadSize (or time if t==MsgTypeHeartbeat)
n, e := strconv.ParseUint(string(b[z:z+8]), 16, 32)
if e != nil {
err = e
return
}
size = uint32(n)
return
}
// Returns a 4-byte representation of a 32-bit integer, suitable an integer-based request ID.
func FormatRequestID(n uint32) []byte {
buf := bytes.NewBuffer(make([]byte, 4)[:0])
err := binary.Write(buf, binary.LittleEndian, n)
if err != nil {
panic(err)
}
return buf.Bytes()
}
// =============================================================================
var protocolVersionBuf [2]byte // version as fixnum2 ([H,H] where H is any of 0-9a-fA-F)
var zeroes = [...]byte{48, 48, 48, 48, 48, 48, 48, 48}
func init() {
copyFixnum(protocolVersionBuf[:0], 2, uint64(ProtocolVersion), 16)
}
func copyFixnum(buf []byte, ndigits int, n uint64, base int) {
z := len(strconv.AppendUint(buf[:0], n, base))
rShiftSlice(buf[:ndigits], ndigits-z, byte(48))
}
// func makeFixnumBuf(ndigits int, n uint64, base int) []byte {
// zb := make([]byte, ndigits)
// z := len(strconv.AppendUint(zb[:0], n, base))
// rShiftSlice(zb, ndigits-z, byte(48))
// return zb
// }
func rShiftSlice(b []byte, n int, padb byte) {
if n != 0 {
bz := len(b)
wi := bz - 1
for ; wi >= n; wi-- {
b[wi] = b[wi-n]
b[wi-n] = padb
}
zn := bz - n - 1
for ; wi > zn; wi-- {
b[wi] = padb
}
}
}
// Read exactly len(b) bytes from s, blocking if needed
func readn(s io.Reader, b []byte) (int, error) {
// behaves similar to io.ReadFull, but simpler and allowing EOF<len(b)
p := 0
n := len(b)
for p < n {
z, err := s.Read(b[p:])
p += z
if err != nil {
return p, err
}
}
return p, nil
}