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Fix db_get/db_fill failing on S7-1200 PLCs with incorrect MC7Size #608

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Fix db_get/db_fill failing on S7-1200 PLCs with incorrect MC7Size #608

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28 changes: 22 additions & 6 deletions snap7/client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -269,8 +269,9 @@ def db_get(self, db_number: int, size: int = 0) -> bytearray:
Get entire DB.
Uses get_block_info() to determine the DB size automatically.
If the PLC does not support get_block_info(), pass the size
parameter explicitly.
If the PLC does not support get_block_info() or reports an
incorrect size (common on S7-1200/1500), pass the size parameter
explicitly.
Args:
db_number: DB number to read
Expand All @@ -283,15 +284,23 @@ def db_get(self, db_number: int, size: int = 0) -> bytearray:
if size <= 0:
block_info = self.get_block_info(Block.DB, db_number)
size = block_info.MC7Size if block_info.MC7Size > 0 else 65536
return self.db_read(db_number, 0, size)
try:
return self.db_read(db_number, 0, size)
except S7Error:
raise S7Error(
f"db_get failed for DB{db_number} with auto-detected size {size}. "
f"Some PLCs (e.g. S7-1200) report incorrect MC7Size in block info. "
f"Try passing the actual DB size explicitly: client.db_get({db_number}, size=<actual_size>)"
)

def db_fill(self, db_number: int, filler: int, size: int = 0) -> int:
"""
Fill a DB with a filler byte.
Uses get_block_info() to determine the DB size automatically.
If the PLC does not support get_block_info(), pass the size
parameter explicitly.
If the PLC does not support get_block_info() or reports an
incorrect size (common on S7-1200/1500), pass the size parameter
explicitly.
Args:
db_number: DB number to fill
Expand All @@ -306,7 +315,14 @@ def db_fill(self, db_number: int, filler: int, size: int = 0) -> int:
block_info = self.get_block_info(Block.DB, db_number)
size = block_info.MC7Size if block_info.MC7Size > 0 else 65536
data = bytearray([filler] * size)
return self.db_write(db_number, 0, data)
try:
return self.db_write(db_number, 0, data)
except S7Error:
raise S7Error(
f"db_fill failed for DB{db_number} with auto-detected size {size}. "
f"Some PLCs (e.g. S7-1200) report incorrect MC7Size in block info. "
f"Try passing the actual DB size explicitly: client.db_fill({db_number}, {filler}, size=<actual_size>)"
)

def read_area(self, area: Area, db_number: int, start: int, size: int, word_len: Optional[WordLen] = None) -> bytearray:
"""
Expand Down
5 changes: 3 additions & 2 deletions tests/test_client_e2e.py
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Original file line number Diff line number Diff line change
Expand Up @@ -492,8 +492,9 @@ def test_db_get(self) -> None:
try:
data = self.client.db_get(DB_READ_ONLY)
except Exception as e:
if "does not exist" in str(e).lower() or "block info failed" in str(e).lower():
pytest.skip(f"get_block_info not supported on this PLC: {e}")
err_msg = str(e).lower()
if "does not exist" in err_msg or "block info failed" in err_msg or "auto-detected size" in err_msg:
pytest.skip(f"db_get with auto-detect not supported on this PLC: {e}")
raise
self.assertIsInstance(data, bytearray)
self.assertGreater(len(data), 0)
Expand Down