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

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merged 4 commits into from
Feb 12, 2025
Merged

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

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ba8c684
Use seeded random number generator for a 100% deterministic test result
sunkup Feb 11, 2025
b26bfff
Fix typo
sunkup Feb 11, 2025
570dfdc
Rename variable
sunkup Feb 11, 2025
e2d03e4
Mock random numbers and assert corresponding record is found
sunkup Feb 12, 2025
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4 changes: 3 additions & 1 deletion app/src/androidTest/kotlin/at/bitfire/davdroid/network/DnsRecordResolverTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import org.xbill.DNS.Name
import org.xbill.DNS.SRVRecord
import org.xbill.DNS.TXTRecord
import javax.inject.Inject
import kotlin.random.Random

@HiltAndroidTest
class DnsRecordResolverTest {
Expand Down Expand Up @@ -69,8 +70,9 @@ class DnsRecordResolverTest {
// entries are selected randomly (for load balancing)
// run 1000 times to get a good distribution
val counts = IntArray(2)
val seededRandom = Random(0) // Seed of 0 ensures 100% deterministic non-failing results
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for (i in 0 until 1000) {
val result = dnsRecordResolver.bestSRVRecord(arrayOf(dns1010, dns1020))
val result = dnsRecordResolver.bestSRVRecord(arrayOf(dns1010, dns1020), seededRandom)

when (result) {
dns1010 -> counts[0]++
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12 changes: 10 additions & 2 deletions app/src/main/kotlin/at/bitfire/davdroid/network/DnsRecordResolver.kt
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Expand Up @@ -22,6 +22,7 @@ import java.util.LinkedList
import java.util.TreeMap
import java.util.logging.Logger
import javax.inject.Inject
import kotlin.random.Random

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

// 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>()
if (srvRecords.size <= 1)
return srvRecords.firstOrNull()
Expand Down Expand Up @@ -141,7 +149,7 @@ class DnsRecordResolver @Inject constructor(
map[runningWeight] = record
}

val selector = (0..runningWeight).random()
val selector = (0..runningWeight).random(randomGenerator)
return map.ceilingEntry(selector)!!.value
}

Expand Down