From c88dff148b9b8da24abfde76067152c94cc629ea Mon Sep 17 00:00:00 2001
From: Jorge Antonio Diaz-Benito Soriano <jorge.diazbenitosoriano@gmail.com>
Date: Tue, 7 Nov 2023 20:21:37 +0100
Subject: [PATCH] Fix deserialization logic for mode, stratum, poll and
 precision

---
 .../internal/NtpPacketDeserializer.kt         | 44 +++++++++++++++++--
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt b/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt
index 2ace96b4..ab5bfeb2 100644
--- a/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt
+++ b/library/src/commonMain/kotlin/com/tidal/networktime/internal/NtpPacketDeserializer.kt
@@ -7,7 +7,21 @@ import kotlin.time.Duration.Companion.seconds
 
 internal class NtpPacketDeserializer {
   operator fun invoke(bytes: ByteArray): NtpPacket? {
-    val bits = bytes.flatMap { it.toString(2).asIterable() }
+    val bits = bytes.map { it.toInt() }
+      .flatMap {
+        listOf(
+          it and 1,
+          it and (1 shl 1),
+          it and (1 shl 2),
+          it and (1 shl 3),
+          it and (1 shl 4),
+          it and (1 shl 5),
+          it and (1 shl 6),
+          it and (1 shl 7),
+        ).map {
+          it != 0
+        }
+      }
     var startIndexInclusive = 0
     var endIndexExclusive = 2
     var index = 0
@@ -18,6 +32,21 @@ internal class NtpPacketDeserializer {
     startIndexInclusive = endIndexExclusive
     endIndexExclusive += 3
     val versionNumber = bits.bitRangeAsInt(startIndexInclusive until endIndexExclusive)
+    startIndexInclusive = endIndexExclusive
+    endIndexExclusive += 3
+    val mode = bits.bitRangeAsInt(startIndexInclusive until endIndexExclusive)
+    startIndexInclusive = endIndexExclusive
+    endIndexExclusive += 8
+    val stratum = bytes[1].asInt
+    if (stratum >= STRATUM_CLOCK_NOT_SYNCHRONIZED) {
+      return null
+    }
+    startIndexInclusive = endIndexExclusive
+    endIndexExclusive += 8
+    val poll = bytes[2].asInt
+    startIndexInclusive = endIndexExclusive
+    endIndexExclusive += 8
+    val precision = bytes[3].asInt
     return NtpPacket(
       (bytes[index++].toInt() shl 8) + bytes[index++],
       (bytes[index++].toInt() shl 16) + (bytes[index++].toInt() shl 24) + bytes[index++],
@@ -41,8 +70,16 @@ internal class NtpPacketDeserializer {
     )
   }
 
-  private fun List<Char>.bitRangeAsInt(intRange: IntRange) =
-    subList(intRange.first, intRange.last + 1).joinToString(separator = "").toInt(2)
+  private fun List<Boolean>.bitRangeAsInt(intRange: IntRange) =
+    subList(intRange.first, intRange.last + 1).foldIndexed(0) { i, acc, it ->
+      when (it) {
+        true -> 2F.pow(i).toInt()
+        false -> 0
+      } + acc
+    }
+
+  private val Byte.asInt
+    get() = toUByte().toInt()
 
   private val ByteArray.asNtpIntervalToInterval: Duration
     get() {
@@ -86,5 +123,6 @@ internal class NtpPacketDeserializer {
 
   companion object {
     private const val LEAP_INDICATOR_CLOCK_UNSYNCHRONIZED = 0b11
+    private const val STRATUM_CLOCK_NOT_SYNCHRONIZED = 16
   }
 }