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Unverified Commit d3c1dbb5 authored by Sunik Kupfer's avatar Sunik Kupfer Committed by GitHub
Browse files

`DnsRecordResolverTest`: Use seeded random number generator for deterministic test result (#1306) 

* Use seeded random number generator for a 100% deterministic test result

* Fix typo

* Rename variable

* Mock random numbers and assert corresponding record is found
parent cd554d88

app/src/androidTest/kotlin/at/bitfire/davdroid/network/DnsRecordResolverTest.kt

+17 −17
Original line number Original line Diff line number Diff line
@@ -6,6 +6,8 @@ package at.bitfire.davdroid.network 




import dagger.hilt.android.testing.HiltAndroidRule

import dagger.hilt.android.testing.HiltAndroidRule

import dagger.hilt.android.testing.HiltAndroidTest

import dagger.hilt.android.testing.HiltAndroidTest

import io.mockk.every

import io.mockk.mockk

import org.junit.Assert.assertArrayEquals

import org.junit.Assert.assertArrayEquals

import org.junit.Assert.assertEquals

import org.junit.Assert.assertEquals

import org.junit.Assert.assertNull

import org.junit.Assert.assertNull
@@ -18,6 +20,7 @@ import org.xbill.DNS.Name 
import org.xbill.DNS.SRVRecord

import org.xbill.DNS.SRVRecord

import org.xbill.DNS.TXTRecord

import org.xbill.DNS.TXTRecord

import javax.inject.Inject

import javax.inject.Inject

import kotlin.random.Random





@HiltAndroidTest

@HiltAndroidTest

class DnsRecordResolverTest {

class DnsRecordResolverTest {
@@ -65,25 +68,22 @@ class DnsRecordResolverTest { 
            Name.fromString("_caldavs._tcp.example.com."),

            Name.fromString("_caldavs._tcp.example.com."),

            DClass.IN, 3600, 10, 20, 8443, Name.fromString("dav1020.example.com.")

            DClass.IN, 3600, 10, 20, 8443, Name.fromString("dav1020.example.com.")

        )

        )



        val dns1030 = SRVRecord(

        // entries are selected randomly (for load balancing)

            Name.fromString("_caldavs._tcp.example.com."),

        // run 1000 times to get a good distribution

            DClass.IN, 3600, 10, 30, 8443, Name.fromString("dav1030.example.com.")

        val counts = IntArray(2)

        )

        for (i in 0 until 1000) {

        val records = arrayOf(dns1010, dns1020, dns1030)

            val result = dnsRecordResolver.bestSRVRecord(arrayOf(dns1010, dns1020))





        val randomNumberGenerator = mockk<Random>()

            when (result) {

        for (i in 0..60) {

                dns1010 -> counts[0]++

            every { randomNumberGenerator.nextInt(0, 61) } returns i

                dns1020 -> counts[1]++

            val expected = when (i) {

                in 0..10 -> dns1010

                in 11..30 -> dns1020

                else -> dns1030

            }

            }

            assertEquals(expected, dnsRecordResolver.bestSRVRecord(records, randomNumberGenerator))

        }

        }



        /* We had weights 10 and 20, so the distribution of 1000 tries should be roughly

            weight 10   fraction 1/3   expected count 333   binomial distribution (p=1/3) with 99.99% in [275..393]

            weight 20   fraction 2/3   expected count 667   binomial distribution (p=2/3) with 99.99% in [607..725]

         */

        assertTrue(counts[0] in 275..393)

        assertTrue(counts[1] in 607..725)

    }

    }





    @Test

    @Test

app/src/main/kotlin/at/bitfire/davdroid/network/DnsRecordResolver.kt

+10 −2
Original line number Original line Diff line number Diff line
@@ -22,6 +22,7 @@ import java.util.LinkedList 
import java.util.TreeMap

import java.util.TreeMap

import java.util.logging.Logger

import java.util.logging.Logger

import javax.inject.Inject

import javax.inject.Inject

import kotlin.random.Random





/**

/**

 * Allows to resolve SRV/TXT records. Chooses the correct resolver, DNS servers etc.

 * Allows to resolve SRV/TXT records. Chooses the correct resolver, DNS servers etc.
@@ -102,7 +103,14 @@ class DnsRecordResolver @Inject constructor( 




    // record selection

    // record selection





    fun bestSRVRecord(records: Array<out Record>): SRVRecord? {

    /**

     * Selects the best SRV record from a list of records, based on algorithm from RFC 2782.

     *

     * @param records the records to choose from

     * @param randomGenerator a random number generator to use for random selection

     * @return the best SRV record, or `null` if no SRV record is available

     */

    fun bestSRVRecord(records: Array<out Record>, randomGenerator: Random = Random.Default): SRVRecord? {

        val srvRecords = records.filterIsInstance<SRVRecord>()

        val srvRecords = records.filterIsInstance<SRVRecord>()

        if (srvRecords.size <= 1)

        if (srvRecords.size <= 1)

            return srvRecords.firstOrNull()

            return srvRecords.firstOrNull()
@@ -141,7 +149,7 @@ class DnsRecordResolver @Inject constructor( 
            map[runningWeight] = record

            map[runningWeight] = record

        }

        }





        val selector = (0..runningWeight).random()

        val selector = (0..runningWeight).random(randomGenerator)

        return map.ceilingEntry(selector)!!.value

        return map.ceilingEntry(selector)!!.value

    }

    }