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JoinDataStreamer.go
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/
JoinDataStreamer.go
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package peer
import (
"bytes"
"encoding/binary"
"io"
"github.com/DataDog/zstd"
"github.com/olebedev/emitter"
)
// RawJoinDataBuffer is a 0x83 subpacket which is functionally
// identical to Packet83_0B.
// However, its contents have been serialized ahead-of-time by JoinDataStreamer
// and hence its Serialize implementation is different
type RawJoinDataBuffer struct {
*Packet83_0B
buf []byte
}
// Serialize implements Packet83Subpacket.Serialize()
func (buf *RawJoinDataBuffer) Serialize(writer PacketWriter, stream *extendedWriter) error {
_, err := stream.Write(buf.buf)
return err
}
// MaxJoinDataBytes tells how many bytes a JoinData layer can use at most
// Generally speaking, Roblox can usually handle about 100 kB
// but we set the limit a little lower here to be safe
// TODO: Move this to JoinDataStreamer?
const MaxJoinDataBytes = 80000
type countWriter struct {
numBytes int
}
func (w *countWriter) Write(b []byte) (int, error) {
thisLen := len(b)
w.numBytes += thisLen
return thisLen, nil
}
func newCountWriter() *countWriter {
return &countWriter{}
}
// JoinDataStreamer is a helper struct that allows serialized
// JoinData objects to be created one at a time, while still constructing
// JoinData layers of appropriate length
type JoinDataStreamer struct {
// BufferEmitter emits Packet83Subpackets on channel "join-data"
// These buffers should be passed to PacketWriter.WritePacket()
BufferEmitter *emitter.Emitter
compressedBuffer *bytes.Buffer
compressor *zstd.Writer
writer *joinSerializeWriter
counter *countWriter
rawLayer *Packet83_0B
packetWriter PacketWriter
deferredStringState writeDeferredStrings
}
// NewJoinDataStreamer returns a new JoinDataStreamer object
// which emits RawJoinDataBuffer objects once their internal
// buffers reach the length specified by MaxJoinDataBytes
func NewJoinDataStreamer(writer PacketWriter) *JoinDataStreamer {
streamer := &JoinDataStreamer{
BufferEmitter: emitter.New(0),
packetWriter: writer,
}
streamer.makeNewStream()
return streamer
}
func (state *JoinDataStreamer) makeNewStream() *joinSerializeWriter {
state.compressedBuffer = bytes.NewBuffer(nil)
state.counter = newCountWriter()
state.rawLayer = &Packet83_0B{}
state.compressor = zstd.NewWriter(state.compressedBuffer)
writeMux := io.MultiWriter(state.compressor, state.counter)
state.writer = &joinSerializeWriter{&extendedWriter{writeMux}}
state.deferredStringState = newWriteDeferredStrings(state.packetWriter)
return state.writer
}
// Flush forces JoinDataStreamer to emit the RawJoinDataBuffer being
// serialized currently, unless empty
func (state *JoinDataStreamer) Flush() error {
// If there's nothing to write, skip
if len(state.rawLayer.Instances) == 0 {
return nil
}
err := state.writer.resolveDeferredStrings(state.deferredStringState)
if err != nil {
return err
}
err = state.compressor.Close()
if err != nil {
return err
}
cachedBuffer := make([]byte, state.compressedBuffer.Len()+4+4+4)
binary.BigEndian.PutUint32(cachedBuffer[:4], uint32(len(state.rawLayer.Instances)))
binary.BigEndian.PutUint32(cachedBuffer[4:8], uint32(state.compressedBuffer.Len()))
binary.BigEndian.PutUint32(cachedBuffer[8:12], uint32(state.counter.numBytes))
copy(cachedBuffer[12:], state.compressedBuffer.Bytes())
thisBuf := &RawJoinDataBuffer{
Packet83_0B: state.rawLayer,
buf: cachedBuffer,
}
<-state.BufferEmitter.Emit("join-data", thisBuf)
return nil
}
// Close flushes the JoinDataStreamer and unbinds BufferEmitter
// bindings
func (state *JoinDataStreamer) Close() error {
err := state.Flush()
if err != nil {
return err
}
state.BufferEmitter.Off("*")
return nil
}
// AddInstance add the instance to the current RawJoinDataBuffer
func (state *JoinDataStreamer) AddInstance(instance *ReplicationInstance) error {
if state.compressedBuffer.Len() > MaxJoinDataBytes {
err := state.Flush()
if err != nil {
return err
}
state.makeNewStream()
}
state.rawLayer.Instances = append(state.rawLayer.Instances, instance)
// TODO: Caching?
return instance.Serialize(state.packetWriter, state.writer, state.deferredStringState, false)
}