Fixed equal starting seq / ack case, added more tests

Author: compscidr

src/main/kotlin/com/jasonernst/knet/transport/tcp/TcpHeader.kt

@@ -355,10 +355,10 @@ data class TcpHeader(
 
     override fun toString(): String =
         "TcpHeader{" +
-            "sourcePort=" + Integer.toUnsignedString(sourcePort.toInt() and 0xFFFF) +
-            ", destinationPort=" + Integer.toUnsignedString(destinationPort.toInt() and 0xFFFF) +
-            ", sequenceNumber=" + sequenceNumber +
-            ", acknowledgementNumber=" + acknowledgementNumber +
+            "srcPort=" + Integer.toUnsignedString(sourcePort.toInt() and 0xFFFF) +
+            ", dstPort=" + Integer.toUnsignedString(destinationPort.toInt() and 0xFFFF) +
+            ", seq=" + sequenceNumber +
+            ", ack=" + acknowledgementNumber +
             ", dataOffset=" + Integer.toUnsignedString(getDataOffset().toInt()) +
             ", cwr=" + cwr +
             ", ece=" + ece +
@@ -379,25 +379,27 @@ data class TcpHeader(
         startingAcknowledgement: UInt,
     ): String {
         val seq =
-            if (sequenceNumber > startingSequenceNumber) {
+            if (sequenceNumber >= startingSequenceNumber) {
                 sequenceNumber - startingSequenceNumber
             } else {
                 UInt.MAX_VALUE - startingSequenceNumber + sequenceNumber
             }
         val ack =
-            if (acknowledgementNumber > startingAcknowledgement) {
+            if (acknowledgementNumber >= startingAcknowledgement) {
                 acknowledgementNumber - startingAcknowledgement
             } else {
                 UInt.MAX_VALUE - startingAcknowledgement + acknowledgementNumber
             }
 
         return "TcpHeader{" +
-            "sourcePort=" + Integer.toUnsignedString(sourcePort.toInt() and 0xFFFF) +
-            ", destinationPort=" + Integer.toUnsignedString(destinationPort.toInt() and 0xFFFF) +
-            ", sequenceNumber=" + seq +
-            ", acknowledgementNumber=" + ack +
-            ", rawSequenceNumber=" + sequenceNumber +
-            ", rawAcknowledgementNumber=" + acknowledgementNumber +
+            "srcPort=" + Integer.toUnsignedString(sourcePort.toInt() and 0xFFFF) +
+            ", dstPort=" + Integer.toUnsignedString(destinationPort.toInt() and 0xFFFF) +
+            ", seq=" + seq +
+            ", ack=" + ack +
+            ", rawSeq=" + sequenceNumber +
+            ", rawAck=" + acknowledgementNumber +
+            ", rawStartSeq=" + startingSequenceNumber +
+            ", rawStartAck=" + startingAcknowledgement +
             ", dataOffset=" + Integer.toUnsignedString(getDataOffset().toInt()) +
             ", cwr=" + cwr +
             ", ece=" + ece +

src/test/kotlin/com/jasonernst/knet/transport/tcp/TcpTests.kt

@@ -76,9 +76,25 @@ class TcpTests {
     @Test fun toStringWithSequenceAndAck() {
         val tcpHeader = TcpHeader(sequenceNumber = 1000u, acknowledgementNumber = 2000u)
 
+        // ensure the sequence is correct in the good case without wraparound
         val headerString = tcpHeader.toString(startingSequenceNumber = 10u, startingAcknowledgement = 1500u)
         println(headerString)
-        assertTrue(headerString.contains("sequenceNumber=990"))
-        assertTrue(headerString.contains("acknowledgementNumber=500"))
+        assertTrue(headerString.contains("seq=990"))
+        assertTrue(headerString.contains("ack=500"))
+
+        // make sure when we have the same starting seq and ack to the header, we get 0s
+        val headerString2 = tcpHeader.toString(startingSequenceNumber = 1000u, startingAcknowledgement = 2000u)
+        println(headerString2)
+        assertTrue(headerString2.contains("seq=0"))
+        assertTrue(headerString2.contains("ack=0"))
+
+        // make sure the wraparound case works
+        val headerString3 = tcpHeader.toString(startingSequenceNumber = 1001u, startingAcknowledgement = 2002u)
+        println(headerString3)
+        val expectedSeq = UInt.MAX_VALUE - 1001u + tcpHeader.sequenceNumber
+        println(expectedSeq)
+        assertTrue(headerString3.contains("seq=$expectedSeq"))
+        val expectedAck = UInt.MAX_VALUE - 2002u + tcpHeader.acknowledgementNumber
+        assertTrue(headerString3.contains("ack=$expectedAck"))
     }
 }