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tstest/natlab: add latency & loss simulation

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A simple implementation of latency and loss simulation, applied to
writes to the ethernet interface of the NIC. The latency implementation
could be optimized substantially later if necessary.

Updates #13355
Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker
2024-09-13 11:35:47 -07:00
committed by James Tucker
parent 41aac26106
commit c0a1ed86cb
3 changed files with 56 additions and 3 deletions
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23
tstest/natlab/vnet/vnet.go
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@ -515,6 +515,8 @@ type network struct {
wanIP4 netip.Addr // router's LAN IPv4, if any
lanIP4 netip.Prefix // router's LAN IP + CIDR (e.g. 192.168.2.1/24)
breakWAN4 bool // break WAN IPv4 connectivity
latency time.Duration // latency applied to interface writes
lossRate float64 // probability of dropping a packet (0.0 to 1.0)
nodesByIP4 map[netip.Addr]*node // by LAN IPv4
nodesByMAC map[MAC]*node
logf func(format string, args ...any)
@ -977,7 +979,7 @@ func (n *network) writeEth(res []byte) bool {
for mac, nw := range n.writers.All() {
if mac != srcMAC {
num++
nw.write(res)
n.conditionedWrite(nw, res)
}
}
return num > 0
@ -987,7 +989,7 @@ func (n *network) writeEth(res []byte) bool {
return false
}
if nw, ok := n.writers.Load(dstMAC); ok {
nw.write(res)
n.conditionedWrite(nw, res)
return true
}
@ -1000,6 +1002,23 @@ func (n *network) writeEth(res []byte) bool {
return false
}
func (n *network) conditionedWrite(nw networkWriter, packet []byte) {
if n.lossRate > 0 && rand.Float64() < n.lossRate {
// packet lost
return
}
if n.latency > 0 {
// copy the packet as there's no guarantee packet is owned long enough.
// TODO(raggi): this could be optimized substantially if necessary,
// a pool of buffers and a cheaper delay mechanism are both obvious improvements.
var pkt = make([]byte, len(packet))
copy(pkt, packet)
time.AfterFunc(n.latency, func() { nw.write(pkt) })
} else {
nw.write(packet)
}
}
var (
macAllNodes = MAC{0: 0x33, 1: 0x33, 5: 0x01}
macAllRouters = MAC{0: 0x33, 1: 0x33, 5: 0x02}