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126 lines
3.5 KiB
Go
126 lines
3.5 KiB
Go
package multiplex
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import (
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"container/heap"
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//"log"
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)
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// The data is multiplexed through several TCP connections, therefore the
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// order of arrival is not guaranteed. A stream's first packet may be sent through
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// connection0 and its second packet may be sent through connection1. Although both
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// packets are transmitted reliably (as TCP is reliable), packet1 may arrive to the
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// remote side before packet0. Cloak have to therefore sequence the packets so that they
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// arrive in order as they were sent by the proxy software
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//
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// Cloak packets will have a 32-bit sequence number on them, so we know in which order
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// they should be sent to the proxy software. The code in this file provides buffering and sorting.
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//
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// Similar to TCP, the next seq number after 2^32-1 is 0. This is called wrap around.
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//
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// Note that in golang, integer overflow results in wrap around
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//
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// Stream.nextRecvSeq is the expected sequence number of the next packet
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// Stream.rev counts the amount of time the sequence number gets wrapped
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type frameNode struct {
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trueSeq uint64
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frame *Frame
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}
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type sorterHeap []*frameNode
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func (sh sorterHeap) Less(i, j int) bool {
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return sh[i].trueSeq < sh[j].trueSeq
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}
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func (sh sorterHeap) Len() int {
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return len(sh)
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}
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func (sh sorterHeap) Swap(i, j int) {
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sh[i], sh[j] = sh[j], sh[i]
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}
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func (sh *sorterHeap) Push(x interface{}) {
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*sh = append(*sh, x.(*frameNode))
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}
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func (sh *sorterHeap) Pop() interface{} {
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old := *sh
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n := len(old)
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x := old[n-1]
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*sh = old[0 : n-1]
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return x
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}
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func (s *Stream) writeNewFrame(f *Frame) {
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s.newFrameCh <- f
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}
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// recvNewFrame is a forever running loop which receives frames unordered,
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// cache and order them and send them into sortedBufCh
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func (s *Stream) recvNewFrame() {
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for {
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f := <-s.newFrameCh
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if f == nil {
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return
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}
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// when there's no ooo packages in heap and we receive the next package in order
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if len(s.sh) == 0 && f.Seq == s.nextRecvSeq {
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if f.Closing == 1 {
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// empty data indicates closing signal
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s.passiveClose()
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return
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} else {
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s.sortedBuf.Write(f.Payload)
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s.nextRecvSeq += 1
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if s.nextRecvSeq == 0 { // getting wrapped
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s.rev += 1
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s.wrapMode = false
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}
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}
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continue
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}
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fs := &frameNode{
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trueSeq: 0,
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frame: f,
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}
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if f.Seq < s.nextRecvSeq {
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// For the ease of demonstration, assume seq is uint8, i.e. it wraps around after 255
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// e.g. we are on rev=0 (wrap has not happened yet)
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// and we get the order of recv as 253 254 0 1
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// after 254, nextN should be 255, but 0 is received and 0 < 255
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// now 0 should have a trueSeq of 256
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if !s.wrapMode {
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// wrapMode is true when the latest seq is wrapped but nextN is not
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s.wrapMode = true
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}
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fs.trueSeq = uint64(1<<32)*uint64(s.rev+1) + uint64(f.Seq) + 1
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// +1 because wrapped 0 should have trueSeq of 256 instead of 255
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// when this bit was run on 1, the trueSeq of 1 would become 256
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} else {
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fs.trueSeq = uint64(1<<32)*uint64(s.rev) + uint64(f.Seq)
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// when this bit was run on 255, the trueSeq of 255 would be 255
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}
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heap.Push(&s.sh, fs)
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// Keep popping from the heap until empty or to the point that the wanted seq was not received
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for len(s.sh) > 0 && s.sh[0].frame.Seq == s.nextRecvSeq {
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f = heap.Pop(&s.sh).(*frameNode).frame
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if f.Closing == 1 {
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// empty data indicates closing signal
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s.passiveClose()
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return
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} else {
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s.sortedBuf.Write(f.Payload)
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s.nextRecvSeq += 1
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if s.nextRecvSeq == 0 { // getting wrapped
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s.rev += 1
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s.wrapMode = false
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}
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}
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}
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}
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}
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