Hysteria: Upgrade to official v2.8.2 (#6041)

https://github.com/XTLS/Xray-core/pull/6041#issuecomment-4357417742

And fixes https://github.com/XTLS/Xray-core/issues/6039

proxy/hysteria/protocol.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/apernet/quic-go/quicvarint"
 	"github.com/xtls/xray-core/common/errors"
+	"github.com/xtls/xray-core/transport/internet/hysteria"
 )
 
 const (
@@ -17,8 +18,6 @@ const (
 	MaxMessageLength = 2048
 	MaxPaddingLength = 4096
 
-	MaxUDPSize = 4096
-
 	maxVarInt1 = 63
 	maxVarInt2 = 16383
 	maxVarInt4 = 1073741823
@@ -62,7 +61,7 @@ func ReadTCPRequest(r io.Reader) (string, error) {
 }
 
 func WriteTCPRequest(w io.Writer, addr string) error {
-	padding := tcpRequestPadding.String()
+	padding := hysteria.TcpRequestPadding.String()
 	paddingLen := len(padding)
 	addrLen := len(addr)
 	sz := int(quicvarint.Len(uint64(addrLen))) + addrLen +
@@ -122,7 +121,7 @@ func ReadTCPResponse(r io.Reader) (bool, string, error) {
 }
 
 func WriteTCPResponse(w io.Writer, ok bool, msg string) error {
-	padding := tcpResponsePadding.String()
+	padding := hysteria.TcpResponsePadding.String()
 	paddingLen := len(padding)
 	msgLen := len(msg)
 	sz := 1 + int(quicvarint.Len(uint64(msgLen))) + msgLen +
@@ -247,3 +246,75 @@ func varintPut(b []byte, i uint64) int {
 	}
 	panic(fmt.Sprintf("%#x doesn't fit into 62 bits", i))
 }
+
+func FragUDPMessage(m *UDPMessage, maxSize int) []UDPMessage {
+	if m.Size() <= maxSize {
+		return []UDPMessage{*m}
+	}
+	fullPayload := m.Data
+	maxPayloadSize := maxSize - m.HeaderSize()
+	off := 0
+	fragID := uint8(0)
+	fragCount := uint8((len(fullPayload) + maxPayloadSize - 1) / maxPayloadSize) // round up
+	frags := make([]UDPMessage, fragCount)
+	for off < len(fullPayload) {
+		payloadSize := len(fullPayload) - off
+		if payloadSize > maxPayloadSize {
+			payloadSize = maxPayloadSize
+		}
+		frag := *m
+		frag.FragID = fragID
+		frag.FragCount = fragCount
+		frag.Data = fullPayload[off : off+payloadSize]
+		frags[fragID] = frag
+		off += payloadSize
+		fragID++
+	}
+	return frags
+}
+
+// Defragger handles the defragmentation of UDP messages.
+// The current implementation can only handle one packet ID at a time.
+// If another packet arrives before a packet has received all fragments
+// in their entirety, any previous state is discarded.
+type Defragger struct {
+	pktID uint16
+	frags []*UDPMessage
+	count uint8
+	size  int // data size
+}
+
+func (d *Defragger) Feed(m *UDPMessage) *UDPMessage {
+	if m.FragCount <= 1 {
+		return m
+	}
+	if m.FragID >= m.FragCount {
+		// wtf is this?
+		return nil
+	}
+	if m.PacketID != d.pktID || m.FragCount != uint8(len(d.frags)) {
+		// new message, clear previous state
+		d.pktID = m.PacketID
+		d.frags = make([]*UDPMessage, m.FragCount)
+		d.frags[m.FragID] = m
+		d.count = 1
+		d.size = len(m.Data)
+	} else if d.frags[m.FragID] == nil {
+		d.frags[m.FragID] = m
+		d.count++
+		d.size += len(m.Data)
+		if int(d.count) == len(d.frags) {
+			// all fragments received, assemble
+			data := make([]byte, d.size)
+			off := 0
+			for _, frag := range d.frags {
+				off += copy(data[off:], frag.Data)
+			}
+			m.Data = data
+			m.FragID = 0
+			m.FragCount = 1
+			return m
+		}
+	}
+	return nil
+}