Cloak/internal/multiplex/streamBuffer.go

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package multiplex
// The data is multiplexed through several TCP connections, therefore the
// order of arrival is not guaranteed. A stream's first packet may be sent through
// connection0 and its second packet may be sent through connection1. Although both
// packets are transmitted reliably (as TCP is reliable), packet1 may arrive to the
// remote side before packet0. Cloak have to therefore sequence the packets so that they
// arrive in order as they were sent by the proxy software
//
// Cloak packets will have a 32-bit sequence number on them, so we know in which order
// they should be sent to the proxy software. The code in this file provides buffering and sorting.
import (
"container/heap"
"fmt"
"sync"
)
type sorterHeap []*Frame
func (sh sorterHeap) Less(i, j int) bool {
return sh[i].Seq < sh[j].Seq
}
func (sh sorterHeap) Len() int {
return len(sh)
}
func (sh sorterHeap) Swap(i, j int) {
sh[i], sh[j] = sh[j], sh[i]
}
func (sh *sorterHeap) Push(x interface{}) {
*sh = append(*sh, x.(*Frame))
}
func (sh *sorterHeap) Pop() interface{} {
old := *sh
n := len(old)
x := old[n-1]
*sh = old[0 : n-1]
return x
}
type streamBuffer struct {
recvM sync.Mutex
nextRecvSeq uint64
rev int
sh sorterHeap
buf *bufferedPipe
}
func NewStreamBuffer() *streamBuffer {
sb := &streamBuffer{
sh: []*Frame{},
rev: 0,
buf: NewBufferedPipe(),
}
return sb
}
// recvNewFrame is a forever running loop which receives frames unordered,
// cache and order them and send them into sortedBufCh
func (sb *streamBuffer) Write(f Frame) error {
sb.recvM.Lock()
defer sb.recvM.Unlock()
// when there'fs no ooo packages in heap and we receive the next package in order
if len(sb.sh) == 0 && f.Seq == sb.nextRecvSeq {
if f.Closing == 1 {
sb.buf.Close()
return nil
} else {
sb.buf.Write(f.Payload)
sb.nextRecvSeq += 1
}
return nil
}
if f.Seq < sb.nextRecvSeq {
return fmt.Errorf("seq %v is smaller than nextRecvSeq %v", f.Seq, sb.nextRecvSeq)
}
heap.Push(&sb.sh, &f)
// Keep popping from the heap until empty or to the point that the wanted seq was not received
for len(sb.sh) > 0 && sb.sh[0].Seq == sb.nextRecvSeq {
f = *heap.Pop(&sb.sh).(*Frame)
if f.Closing == 1 {
// empty data indicates closing signal
sb.buf.Close()
return nil
} else {
sb.buf.Write(f.Payload)
sb.nextRecvSeq += 1
}
}
return nil
}
func (sb *streamBuffer) Read(buf []byte) (int, error) {
return sb.buf.Read(buf)
}
func (sb *streamBuffer) Close() error {
return sb.buf.Close()
}