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balance predicted ports around the center between maxPort and minPort

master
Christian Ulrich 2020-11-18 23:04:17 +01:00
parent 81a39f32c1
commit 3f9d7a7671
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GPG Key ID: 8241BE099775A097
1 changed files with 20 additions and 8 deletions
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28
port_prediction.nim
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@ -1,10 +1,9 @@
import algorithm
import net
import random
import sequtils
import unittest
const RandomPortCount = 10000
const RandomPortCount = 10000'u16
proc min(a, b: uint16): uint16 =
min(a.int32, b.int32).uint16
@ -81,11 +80,13 @@ proc predictPortRange*(localPort: uint16, probedPorts: seq[uint16]): seq[uint16]
result.add(maxPort.subtractOffset(i))
return
# assume symmetric NAT with random port mapping
randomize()
let first = if maxPort <= uint16.high - RandomPortCount - 1000'u16:
maxPort + 1000'u16
assert(RandomPortCount mod 2 == 0)
let center = minPort + (maxPort - minPort) div 2
let half = RandomPortCount div 2
let first = if (1024'u16 + half) < center:
min(center - half, uint16.high - RandomPortCount + 1)
else:
uint16.high - RandomPortCount
1024'u16
result = newSeq[uint16](RandomPortCount)
for i in 0'u16 .. RandomPortCount - 1'u16:
result[i] = first + i
@ -155,5 +156,16 @@ suite "port prediction tests":
check(predicted == @[Port(65533)])
test "random mapping":
let predicted = predictPortRange(Port(1234), @[Port(3546), Port(7624)])
check(predicted.len == RandomPortCount)
let predicted = predictPortRange(Port(1234), @[Port(20000), Port(24000)])
let half = RandomPortCount div 2'u16
check(predicted == toSeq(countup(22000'u16 - half, 22000'u16 + half - 1)).map(toPort))
test "random mapping, low":
let predicted = predictPortRange(Port(1234), @[Port(1200), Port(1600)])
check(predicted.len == RandomPortCount.int)
check(predicted == toSeq(countup(1024'u16, 1024'u16 + RandomPortCount - 1)).map(toPort))
test "random mapping, high":
let predicted = predictPortRange(Port(1234), @[Port(65000), Port(65400)])
check(predicted.len == RandomPortCount.int)
check(predicted == toSeq(countup(uint16.high - RandomPortCount + 1, uint16.high)).map(toPort))