Fix deserialization logic for several fields

* leap indicator * version number * mode * stratum * poll * precision Fix version number deserialization logic Fix deserialization logic for mode, stratum, poll and precision
tidal-music · Nov 7, 2023 · 389976c · 389976c
1 parent 4356f9e
commit 389976c
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Showing 2 changed files with 27 additions and 2 deletions.
diff --git a/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpExchanger.kt b/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpExchanger.kt
@@ -27,7 +27,7 @@ internal class NtpExchanger(
         NTP_PORT_NUMBER.toByte(),
       )
       val responseTime = referenceClock.referenceEpochTime - requestTime
-      NtpExchangeResult(responseTime, ntpPacketDeserializer(buffer))
+      ntpPacketDeserializer(buffer)?.let { NtpExchangeResult(responseTime, it) }
     } catch (_: Throwable) {
       null
     } finally {

diff --git a/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt b/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt
@@ -6,8 +6,24 @@ import kotlin.time.Duration.Companion.milliseconds
 import kotlin.time.Duration.Companion.seconds
 
 internal class NtpPacketDeserializer {
-  operator fun invoke(bytes: ByteArray): NtpPacket {
+  operator fun invoke(bytes: ByteArray): NtpPacket? {
     var index = 0
+    val leapIndicator = (bytes[index].toInt() shr 6) and 0b11
+    if (leapIndicator == LEAP_INDICATOR_CLOCK_UNSYNCHRONIZED) {
+      return null
+    }
+    val versionNumber = (bytes[index].toInt() shr 3) and 0b111
+    val mode = bytes[index].toInt() and 0b111
+    if (mode != MODE_SERVER) {
+      return null
+    }
+    ++index
+    val stratum = bytes[index++].asIntResolvingSign
+    if (stratum >= STRATUM_CLOCK_NOT_SYNCHRONIZED) {
+      return null
+    }
+    val poll = bytes[index++].asIntResolvingSign
+    val precision = bytes[index++].asIntResolvingSign
     return NtpPacket(
       (bytes[index++].toInt() shl 8) + bytes[index++],
       (bytes[index++].toInt() shl 16) + (bytes[index++].toInt() shl 24) + bytes[index++],
@@ -31,6 +47,9 @@ internal class NtpPacketDeserializer {
     )
   }
 
+  private val Byte.asIntResolvingSign
+    get() = toUByte().toInt()
+
   private val ByteArray.asNtpIntervalToInterval: Duration
     get() {
       var index = 0
@@ -70,4 +89,10 @@ internal class NtpPacketDeserializer {
         NtpPacket.NTP_EPOCH_OFFSET_WITH_EPOCH +
         fraction.milliseconds
     }
+
+  companion object {
+    private const val LEAP_INDICATOR_CLOCK_UNSYNCHRONIZED = 0b11
+    private const val MODE_SERVER = 4
+    private const val STRATUM_CLOCK_NOT_SYNCHRONIZED = 16
+  }
 }