[PATCH v2 15/25] selftests: tcp_authopt: Implement SNE in python

[Leonard Crestez <cdleonard@gmail.com>]

Add implementation and tests for Sequence Number Extension.

One implementation is based on an IETF draft:
https://datatracker.ietf.org/doc/draft-touch-sne/

The linux implementation is simpler and doesn't require additional
flags, it just relies on standard before/after macros.

Signed-off-by: Leonard Crestez <cdleonard@gmail.com>
---
 .../tcp_authopt/tcp_authopt_test/sne_alg.py   | 111 ++++++++++++++++++
 .../tcp_authopt_test/test_sne_alg.py          |  96 +++++++++++++++
 2 files changed, 207 insertions(+)
 create mode 100644 tools/testing/selftests/tcp_authopt/tcp_authopt_test/sne_alg.py
 create mode 100644 tools/testing/selftests/tcp_authopt/tcp_authopt_test/test_sne_alg.py

diff --git a/tools/testing/selftests/tcp_authopt/tcp_authopt_test/sne_alg.py b/tools/testing/selftests/tcp_authopt/tcp_authopt_test/sne_alg.py
new file mode 100644
index 000000000000..252356dc87a4
--- /dev/null
+++ b/tools/testing/selftests/tcp_authopt/tcp_authopt_test/sne_alg.py
@@ -0,0 +1,111 @@
+# SPDX-License-Identifier: GPL-2.0
+"""Python implementation of SNE algorithms"""
+
+
+def distance(x, y):
+    if x < y:
+        return y - x
+    else:
+        return x - y
+
+
+class SequenceNumberExtender:
+    """Based on https://datatracker.ietf.org/doc/draft-touch-sne/"""
+
+    sne: int = 0
+    sne_flag: int = 1
+    prev_seq: int = 0
+
+    def calc(self, seq):
+        """Update internal state and return SNE for certain SEQ"""
+        # use current SNE to start
+        result = self.sne
+
+        # both in same SNE range?
+        if distance(seq, self.prev_seq) < 0x80000000:
+            # jumps fwd over N/2?
+            if seq >= 0x80000000 and self.prev_seq < 0x80000000:
+                self.sne_flag = 0
+            # move prev forward if needed
+            self.prev_seq = max(seq, self.prev_seq)
+        # both in diff SNE ranges?
+        else:
+            # jumps forward over zero?
+            if seq < 0x80000000:
+                # update prev
+                self.prev_seq = seq
+                # first jump over zero? (wrap)
+                if self.sne_flag == 0:
+                    # set flag so we increment once
+                    self.sne_flag = 1
+                    # increment window
+                    self.sne = self.sne + 1
+                    # use updated SNE value
+                    result = self.sne
+            # jump backward over zero?
+            else:
+                # use pre-rollover SNE value
+                result = self.sne - 1
+
+        return result
+
+
+class SequenceNumberExtenderRFC:
+    """Based on sample code in original RFC5925 document"""
+
+    sne: int = 0
+    sne_flag: int = 1
+    prev_seq: int = 0
+
+    def calc(self, seq):
+        """Update internal state and return SNE for certain SEQ"""
+        # set the flag when the SEG.SEQ first rolls over
+        if self.sne_flag == 0 and self.prev_seq > 0x7FFFFFFF and seq < 0x7FFFFFFF:
+            self.sne = self.sne + 1
+            self.sne_flag = 1
+        # decide which SNE to use after incremented
+        if self.sne_flag and seq > 0x7FFFFFFF:
+            # use the pre-increment value
+            sne = self.sne - 1
+        else:
+            # use the current value
+            sne = self.sne
+        # reset the flag in the *middle* of the window
+        if self.prev_seq < 0x7FFFFFFF and seq > 0x7FFFFFFF:
+            self.sne_flag = 0
+        # save the current SEQ for the next time through the code
+        self.prev_seq = seq
+
+        return sne
+
+
+def tcp_seq_before(a, b) -> bool:
+    return ((a - b) & 0xFFFFFFFF) > 0x80000000
+
+
+def tcp_seq_after(a, b) -> bool:
+    return tcp_seq_before(a, b)
+
+
+class SequenceNumberExtenderLinux:
+    """Based on linux implementation and with no extra flags"""
+
+    sne: int = 0
+    prev_seq: int = 0
+
+    def reset(self, seq, sne=0):
+        self.prev_seq = seq
+        self.sne = sne
+
+    def calc(self, seq, update=True):
+        sne = self.sne
+        if tcp_seq_before(seq, self.prev_seq):
+            if seq > self.prev_seq:
+                sne -= 1
+        else:
+            if seq < self.prev_seq:
+                sne += 1
+        if update and tcp_seq_before(self.prev_seq, seq):
+            self.prev_seq = seq
+            self.sne = sne
+        return sne
diff --git a/tools/testing/selftests/tcp_authopt/tcp_authopt_test/test_sne_alg.py b/tools/testing/selftests/tcp_authopt/tcp_authopt_test/test_sne_alg.py
new file mode 100644
index 000000000000..9b74873cff4a
--- /dev/null
+++ b/tools/testing/selftests/tcp_authopt/tcp_authopt_test/test_sne_alg.py
@@ -0,0 +1,96 @@
+# SPDX-License-Identifier: GPL-2.0
+"""Test SNE algorithm implementations"""
+
+import logging
+
+import pytest
+
+from .sne_alg import (
+    SequenceNumberExtender,
+    SequenceNumberExtenderLinux,
+    SequenceNumberExtenderRFC,
+)
+
+logger = logging.getLogger(__name__)
+
+
+# Data from https://datatracker.ietf.org/doc/draft-touch-sne/
+_SNE_TEST_DATA = [
+    (0x00000000, 0x00000000),
+    (0x00000000, 0x30000000),
+    (0x00000000, 0x90000000),
+    (0x00000000, 0x70000000),
+    (0x00000000, 0xA0000000),
+    (0x00000001, 0x00000001),
+    (0x00000000, 0xE0000000),
+    (0x00000001, 0x00000000),
+    (0x00000001, 0x7FFFFFFF),
+    (0x00000001, 0x00000000),
+    (0x00000001, 0x50000000),
+    (0x00000001, 0x80000000),
+    (0x00000001, 0x00000001),
+    (0x00000001, 0x40000000),
+    (0x00000001, 0x90000000),
+    (0x00000001, 0xB0000000),
+    (0x00000002, 0x0FFFFFFF),
+    (0x00000002, 0x20000000),
+    (0x00000002, 0x90000000),
+    (0x00000002, 0x70000000),
+    (0x00000002, 0xA0000000),
+    (0x00000003, 0x00004000),
+    (0x00000002, 0xD0000000),
+    (0x00000003, 0x20000000),
+    (0x00000003, 0x90000000),
+    (0x00000003, 0x70000000),
+    (0x00000003, 0xA0000000),
+    (0x00000004, 0x00004000),
+    (0x00000003, 0xD0000000),
+]
+
+
+# Easier test data with small jumps <= 0x30000000
+SNE_DATA_EASY = [
+    (0x00000000, 0x00000000),
+    (0x00000000, 0x30000000),
+    (0x00000000, 0x60000000),
+    (0x00000000, 0x80000000),
+    (0x00000000, 0x90000000),
+    (0x00000000, 0xC0000000),
+    (0x00000000, 0xF0000000),
+    (0x00000001, 0x10000000),
+    (0x00000000, 0xF0030000),
+    (0x00000001, 0x00030000),
+    (0x00000001, 0x10030000),
+]
+
+
+def check_sne_alg(alg, data):
+    for sne, seq in data:
+        observed_sne = alg.calc(seq)
+        logger.info(
+            "seq %08x expected sne %08x observed sne %08x", seq, sne, observed_sne
+        )
+        assert observed_sne == sne
+
+
+def test_sne_alg():
+    check_sne_alg(SequenceNumberExtender(), _SNE_TEST_DATA)
+
+
+def test_sne_alg_easy():
+    check_sne_alg(SequenceNumberExtender(), SNE_DATA_EASY)
+
+
+@pytest.mark.xfail
+def test_sne_alg_rfc():
+    check_sne_alg(SequenceNumberExtenderRFC(), _SNE_TEST_DATA)
+
+
+@pytest.mark.xfail
+def test_sne_alg_rfc_easy():
+    check_sne_alg(SequenceNumberExtenderRFC(), SNE_DATA_EASY)
+
+
+def test_sne_alg_linux():
+    check_sne_alg(SequenceNumberExtenderLinux(), _SNE_TEST_DATA)
+    check_sne_alg(SequenceNumberExtenderLinux(), SNE_DATA_EASY)
-- 
2.25.1