From 31dd581438f67f724286191fb0abc0e3b9da4d81 Mon Sep 17 00:00:00 2001
From: jan iversen <jancasacondor@gmail.com>
Date: Mon, 11 Nov 2024 16:04:30 +0100
Subject: [PATCH] RTU frame problem, when received split. (#2452)

---
 pymodbus/framer/rtu.py                         |  4 ++--
 test/framer/test_framer.py                     |  8 ++++----
 test/framer/test_multidrop.py                  | 18 ++++++++++++++++++
 test/sub_client/test_client_faulty_response.py |  2 +-
 4 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/pymodbus/framer/rtu.py b/pymodbus/framer/rtu.py
index 28ba1ff52..b19876d90 100644
--- a/pymodbus/framer/rtu.py
+++ b/pymodbus/framer/rtu.py
@@ -103,7 +103,7 @@ def decode(self, data: bytes) -> tuple[int, int, int, bytes]:
         for used_len in range(data_len):
             if data_len - used_len < self.MIN_SIZE:
                 Log.debug("Short frame: {} wait for more data", data, ":hex")
-                return used_len, 0, 0, self.EMPTY
+                return 0, 0, 0, self.EMPTY
             dev_id = int(data[used_len])
             if not (pdu_class := self.decoder.lookupPduClass(data[used_len:])):
                 continue
@@ -111,7 +111,7 @@ def decode(self, data: bytes) -> tuple[int, int, int, bytes]:
                 size = data_len +1
             if data_len < used_len +size:
                 Log.debug("Frame - not ready")
-                return used_len, dev_id, 0, self.EMPTY
+                return 0, dev_id, 0, self.EMPTY
             for test_len in range(data_len, used_len + size - 1, -1):
                 start_crc = test_len -2
                 crc = data[start_crc : start_crc + 2]
diff --git a/test/framer/test_framer.py b/test/framer/test_framer.py
index 20dde385b..5838e3d8d 100644
--- a/test/framer/test_framer.py
+++ b/test/framer/test_framer.py
@@ -327,19 +327,19 @@ async def test_decode_type(self, entry, test_framer, data, dev_id, tr_id, expect
                  (9, b'\x83\x02'),
             ]),
             (FramerType.RTU, b'\x00\x83\x02\x91\x21', [ # bad crc
-                 (1, b''),
+                 (0, b''),
                  (0, b''),
             ]),
             (FramerType.RTU, b'\x00\x83\x02\xf0\x91\x31', [ # dummy char in stream, bad crc
-                 (1, b''),
+                 (0, b''),
                  (0, b''),
             ]),
             (FramerType.RTU, b'\x00\x83\x02\x91\x21\x00\x83\x02\x91\x31', [ # bad crc + good CRC
-                (1, b''),
+                (0, b''),
                 (0, b''),
             ]),
             (FramerType.RTU, b'\x00\x83\x02\xf0\x91\x31\x00\x83\x02\x91\x31', [ # dummy char in stream, bad crc  + good CRC
-                 (1, b''),
+                 (0, b''),
                  (0, b''),
             ]),
         ]
diff --git a/test/framer/test_multidrop.py b/test/framer/test_multidrop.py
index 19a42bb43..736572935 100644
--- a/test/framer/test_multidrop.py
+++ b/test/framer/test_multidrop.py
@@ -165,3 +165,21 @@ def test_getFrameStart(self, framer):
         used_len, pdu = framer.processIncomingFrame(framer_2ok)
         assert pdu
         assert used_len == len(framer_2ok)
+
+    def test_rtu_split_frame(self, framer):
+        """Test test_rtu_split_frame."""
+        msg1 = (b'\x01\x08\x00\x00\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb'
+                b'\xcc\xdd\xee\xff\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99')
+        msg2 = (b'\xaa\xbb\xcc\xdd\xee\xff\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99'
+                b'\xaa\xbb\xcc\xdd\xee\xff\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99'
+                b'\xaa\xbb\xcc\xdd\xee\xff\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99'
+                b'\xaa\xbb\xcc\xdd\xee\xff\xe7\x65')
+        used_len, pdu = framer.processIncomingFrame(msg1+msg2)
+        assert pdu
+        assert used_len == len(msg1 + msg2)
+        used_len, pdu = framer.processIncomingFrame(msg1)
+        assert not pdu
+        assert not used_len
+        used_len, pdu = framer.processIncomingFrame(msg1+msg2)
+        assert pdu
+        assert used_len == len(msg1 + msg2)
diff --git a/test/sub_client/test_client_faulty_response.py b/test/sub_client/test_client_faulty_response.py
index 8beaf4c6d..2974f7773 100644
--- a/test/sub_client/test_client_faulty_response.py
+++ b/test/sub_client/test_client_faulty_response.py
@@ -29,7 +29,7 @@ def test_1917_frame(self):
         framer = FramerRTU(DecodePDU(False))
         used_len, pdu = framer.processIncomingFrame(recv)
         assert not pdu
-        assert used_len
+        assert not used_len
 
     def test_faulty_frame1(self, framer):
         """Test ok frame."""