Work around Goodwe bug returning wrong TCP response length

marcelblijleven · May 19, 2024 · a30ecfe · a30ecfe
1 parent 95d4d2c
commit a30ecfe
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Showing 2 changed files with 7 additions and 1 deletion.
diff --git a/goodwe/modbus.py b/goodwe/modbus.py
@@ -222,10 +222,14 @@ def validate_modbus_tcp_response(data: bytes, cmd: int, offset: int, value: int)
         logger.debug("Response is too short.")
         return False
     expected_length = int.from_bytes(data[4:6], byteorder='big', signed=False) + 6
-    if len(data) < expected_length:
+    # The weird expected_length != 12 is work around Goodwe bug answering wrong (hardcoded 6) length.
+    if len(data) < expected_length and expected_length != 12:
         raise PartialResponseException(len(data), expected_length)
 
     if data[7] == MODBUS_READ_CMD:
+        expected_length = data[8] + 9
+        if len(data) < expected_length:
+            raise PartialResponseException(len(data), expected_length)
         if data[8] != value * 2:
             logger.debug("Response has unexpected length: %d, expected %d.", data[8], value * 2)
             return False

diff --git a/tests/test_modbus.py b/tests/test_modbus.py
@@ -104,6 +104,8 @@ def test_create_modbus_tcp_multi_request(self):
     def test_validate_modbus_tcp_read_response(self):
         self.assert_tcp_response_ok('000100000007b4030445565345', 0x3, 310, 2)
         self.assert_tcp_response_ok('000100000007b4030400000002', 0x3, 331, 2)
+        # technically illegal, but work around Goodwe bug
+        self.assert_tcp_response_ok('000100000006f703020000', 0x3, 47510, 1)
         # length too short
         self.assert_tcp_response_partial('000100000007b403040000', 0x03, 331, 2)
         # failure code