hysteria 2 prototype first public release

core/internal/frag/frag.go

@@ -0,0 +1,77 @@
+package frag
+
+import (
+	"github.com/apernet/hysteria/core/internal/protocol"
+)
+
+func FragUDPMessage(m protocol.UDPMessage, maxSize int) []protocol.UDPMessage {
+	if m.Size() <= maxSize {
+		return []protocol.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([]protocol.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 []*protocol.UDPMessage
+	count uint8
+	size  int // data size
+}
+
+func (d *Defragger) Feed(m *protocol.UDPMessage) *protocol.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([]*protocol.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
+}