Packetimpact test for ACK to OTW Seq segments behavior in CLOSING

TCP, in CLOSING state, MUST send an ACK with next expected SEQ number after
receiving any segment with OTW SEQ number and remain in the same state.
While I am here, I also changed shutdown to behave the same as other calls
in posix_server.

PiperOrigin-RevId: 362976955

1 files changed, 21 insertions, 0 deletions

diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index bafc45d3b..8ad9040ff 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -823,6 +823,27 @@ func (conn *TCPIPv4) LocalAddr(t *testing.T) *unix.SockaddrInet4 {
 	return sa
 }
 
+// GenerateOTWSeqSegment generates a segment with
+// seqnum = RCV.NXT + RCV.WND + seqNumOffset, the generated segment is only
+// acceptable when seqNumOffset is 0, otherwise an ACK is expected from the
+// receiver.
+func GenerateOTWSeqSegment(t *testing.T, conn *TCPIPv4, seqNumOffset seqnum.Size, windowSize seqnum.Size) TCP {
+	t.Helper()
+	lastAcceptable := conn.LocalSeqNum(t).Add(windowSize)
+	otwSeq := uint32(lastAcceptable.Add(seqNumOffset))
+	return TCP{SeqNum: Uint32(otwSeq), Flags: TCPFlags(header.TCPFlagAck)}
+}
+
+// GenerateUnaccACKSegment generates a segment with
+// acknum = SND.NXT + seqNumOffset, the generated segment is only acceptable
+// when seqNumOffset is 0, otherwise an ACK is expected from the receiver.
+func GenerateUnaccACKSegment(t *testing.T, conn *TCPIPv4, seqNumOffset seqnum.Size, windowSize seqnum.Size) TCP {
+	t.Helper()
+	lastAcceptable := conn.RemoteSeqNum(t)
+	unaccAck := uint32(lastAcceptable.Add(seqNumOffset))
+	return TCP{AckNum: Uint32(unaccAck), Flags: TCPFlags(header.TCPFlagAck)}
+}
+
 // IPv4Conn maintains the state for all the layers in a IPv4 connection.
 type IPv4Conn struct {
 	Connection