vhost

packet/packet.go

@@ -0,0 +1,119 @@
+package packet
+
+import (
+	"encoding/binary"
+	"iter"
+	"net/netip"
+	"slices"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+const Size = 0xffff
+
+type Packet struct {
+	Payload []byte
+	Control []byte
+	Name    []byte
+	SegSize int
+
+	//todo should this hold out as well?
+	OutLen int
+
+	wasSegmented bool
+	isV4         bool
+}
+
+func New(isV4 bool) *Packet {
+	return &Packet{
+		Payload: make([]byte, Size),
+		Control: make([]byte, unix.CmsgSpace(2)),
+		Name:    make([]byte, unix.SizeofSockaddrInet6),
+		isV4:    isV4,
+	}
+}
+
+func (p *Packet) AddrPort() netip.AddrPort {
+	var ip netip.Addr
+	// Its ok to skip the ok check here, the slicing is the only error that can occur and it will panic
+	if p.isV4 {
+		ip, _ = netip.AddrFromSlice(p.Name[4:8])
+	} else {
+		ip, _ = netip.AddrFromSlice(p.Name[8:24])
+	}
+	return netip.AddrPortFrom(ip.Unmap(), binary.BigEndian.Uint16(p.Name[2:4]))
+}
+
+func (p *Packet) updateCtrl(ctrlLen int) {
+	p.SegSize = len(p.Payload)
+	p.wasSegmented = false
+	if ctrlLen == 0 {
+		return
+	}
+	if len(p.Control) == 0 {
+		return
+	}
+	cmsgs, err := unix.ParseSocketControlMessage(p.Control)
+	if err != nil {
+		return // oh well
+	}
+
+	for _, c := range cmsgs {
+		if c.Header.Level == unix.SOL_UDP && c.Header.Type == unix.UDP_GRO && len(c.Data) >= 2 {
+			p.wasSegmented = true
+			p.SegSize = int(binary.LittleEndian.Uint16(c.Data[:2]))
+			return
+		}
+	}
+}
+
+// Update sets a Packet into "just received, not processed" state
+func (p *Packet) Update(ctrlLen int) {
+	p.OutLen = -1
+	p.updateCtrl(ctrlLen)
+}
+
+func (p *Packet) SetSegSizeForTX() {
+	p.SegSize = len(p.Payload)
+	hdr := (*unix.Cmsghdr)(unsafe.Pointer(&p.Control[0]))
+	hdr.Level = unix.SOL_UDP
+	hdr.Type = unix.UDP_SEGMENT
+	hdr.SetLen(syscall.CmsgLen(2))
+	binary.NativeEndian.PutUint16(p.Control[unix.CmsgLen(0):unix.CmsgLen(0)+2], uint16(p.SegSize))
+}
+
+func (p *Packet) CompatibleForSegmentationWith(otherP *Packet, currentTotalSize int) bool {
+	//same dest
+	if !slices.Equal(p.Name, otherP.Name) {
+		return false
+	}
+
+	//don't get too big
+	if len(p.Payload)+currentTotalSize >= 0xffff {
+		return false
+	}
+
+	//same body len
+	//todo allow single different size at end
+	if len(p.Payload) != len(otherP.Payload) {
+		return false //todo technically you can cram one extra in
+	}
+	return true
+}
+
+func (p *Packet) Segments() iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		//cursor := 0
+		for offset := 0; offset < len(p.Payload); offset += p.SegSize {
+			end := offset + p.SegSize
+			if end > len(p.Payload) {
+				end = len(p.Payload)
+			}
+			if !yield(p.Payload[offset:end]) {
+				return
+			}
+		}
+	}
+}