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[WIP] Add support for large UDP packets #29

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transport/udp: send large data in fragmented IPv4 packets
Signed-off-by: Björn Svensson <bjorn.a.svensson@est.tech>
bjosv committed Jan 26, 2024
commit 254916b3c2d311aaf43b66db293fd44fc12ad307
98 changes: 95 additions & 3 deletions src/emu/plugins/transport/udp.go
Original file line number Diff line number Diff line change
@@ -99,9 +99,48 @@ func (o *UdpSocket) Write(buf []byte) (res SocketErr, queued bool) {
}
var pkt udpPkt

if uint16(len(buf)) > o.GetL7MTU() {
o.ctx.udpStats.udp_drop_msg_bigger_mtu++
return SeENOBUFS, false
mtu := o.GetL7MTU()
if uint16(len(buf)) > mtu {
if o.ipv6 {
o.ctx.udpStats.udp_drop_msg_bigger_mtu++
return SeENOBUFS, false
}
// Send large data in multiple IPv4 packets, fragmented

// The payload size in a fragment need to be a multiple of 8
maxPayloadSize := uint16(mtu/8) * 8
payload := buf[:maxPayloadSize]
payloadSize := uint16(len(payload))
pkt.datalen = uint16(len(buf))

// Send first fragment containing UDP header
o.buildDpktFirstFragment(&pkt, payload)
o.ctx.udpStats.udp_sndpack++
o.ctx.udpStats.udp_sndbyte += uint64(payloadSize)
o.tctx.Veth.Send(pkt.m)
dataSent := payloadSize

// Send trailing segments
for {
if dataSent+maxPayloadSize > pkt.datalen {
payload = buf[dataSent:]
} else {
payload = buf[dataSent : dataSent+maxPayloadSize]
}
payloadSize = uint16(len(payload))

o.buildDpktTrailingFragment(&pkt, payload, dataSent+UDP_HEADER_LEN)
o.ctx.udpStats.udp_sndpack++
o.ctx.udpStats.udp_sndbyte += uint64(payloadSize)
o.tctx.Veth.Send(pkt.m)

dataSent += payloadSize
if dataSent >= pkt.datalen {
break // All data is sent
}
}

return SeOK, true
}

o.buildDpkt(&pkt, buf)
@@ -157,6 +196,59 @@ func (o *UdpSocket) send(pkt *udpPkt) int {
return 0
}

func (o *UdpSocket) buildDpktFirstFragment(pkt *udpPkt, data []byte) int {
tl := uint16(len(o.pktTemplate))
dl := uint16(len(data))
m := o.ns.AllocMbuf(tl + dl)
m.Append(o.pktTemplate) // template with IP and UDP header
m.Append(data)
pkt.m = m

p := m.GetData()
l3 := o.l3Offset

// Update fragment flags
f := (uint16(layers.IPv4MoreFragments) << 13)
binary.BigEndian.PutUint16(p[l3+6:l3+8], f)

// Update UDP header length
binary.BigEndian.PutUint16(p[l3+24:l3+26], pkt.datalen+UDP_HEADER_LEN)

// Update IPv4 header
ipv4 := layers.IPv4Header(p[l3 : l3+20])
ipv4.SetLength(20 + uint16(len(data)) + UDP_HEADER_LEN)
ipv4.UpdateChecksum()

return 0
}

func (o *UdpSocket) buildDpktTrailingFragment(pkt *udpPkt, data []byte, dataSent uint16) int {
tl := uint16(len(o.pktTemplate)) - UDP_HEADER_LEN
dl := uint16(len(data))
m := o.ns.AllocMbuf(tl + dl)
m.Append(o.pktTemplate[:tl]) // template without UDP header
m.Append(data)
pkt.m = m

p := m.GetData()
l3 := o.l3Offset
payload_size := uint16(len(data))

// Update fragment offset and flag if more fragments are required
f := dataSent / 8
if dataSent+payload_size < pkt.datalen {
f += (uint16(layers.IPv4MoreFragments) << 13)
}
binary.BigEndian.PutUint16(p[l3+6:l3+8], f)

// Update IPv4 header
ipv4 := layers.IPv4Header(p[l3 : l3+20])
ipv4.SetLength(20 + payload_size)
ipv4.UpdateChecksum()

return 0
}

func (o *UdpSocket) buildDpkt(pkt *udpPkt, data []byte) int {
dl := uint16(len(data))
m := o.ns.AllocMbuf(uint16(len(o.pktTemplate)) + dl)