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Add support to read/write space-padded fixed-length strings #378

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merged 1 commit into from
Aug 3, 2022
Merged

Add support to read/write space-padded fixed-length strings #378

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84 changes: 83 additions & 1 deletion snap7/util.py
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Original file line number Diff line number Diff line change
Expand Up @@ -411,6 +411,44 @@ def get_real(bytearray_: bytearray, byte_index: int) -> float:
return real


def set_fstring(bytearray_: bytearray, byte_index: int, value: str, max_length: int):
"""Set space-padded fixed-length string value

Args:
bytearray_: buffer to write to.
byte_index: byte index to start writing from.
value: string to write.
max_length: maximum string length, i.e. the fixed size of the string.

Raises:
:obj:`TypeError`: if the `value` is not a :obj:`str`.
:obj:`ValueError`: if the length of the `value` is larger than the `max_size`
or 'value' contains non-ascii characters.

Examples:
>>> data = bytearray(20)
>>> snap7.util.set_fstring(data, 0, "hello world", 15)
>>> data
bytearray(b'hello world \x00\x00\x00\x00\x00')
"""
if not value.isascii():
raise ValueError("Value contains non-ascii values.")
# FAIL HARD WHEN trying to write too much data into PLC
size = len(value)
if size > max_length:
raise ValueError(f'size {size} > max_length {max_length} {value}')

i = 0

# fill array which chr integers
for i, c in enumerate(value):
bytearray_[byte_index + i] = ord(c)

# fill the rest with empty space
for r in range(i + 1, max_length):
bytearray_[byte_index + r] = ord(' ')


def set_string(bytearray_: bytearray, byte_index: int, value: str, max_size: int = 255):
"""Set string value

Expand Down Expand Up @@ -461,6 +499,37 @@ def set_string(bytearray_: bytearray, byte_index: int, value: str, max_size: int
bytearray_[byte_index + 2 + r] = ord(' ')


def get_fstring(bytearray_: bytearray, byte_index: int, max_length: int, remove_padding: bool = True) -> str:
"""Parse space-padded fixed-length string from bytearray

Notes:
This function supports fixed-length ASCII strings, right-padded with spaces.

Args:
bytearray_: buffer from where to get the string.
byte_index: byte index from where to start reading.
max_length: the maximum length of the string.
remove_padding: whether to remove the right-padding.

Returns:
String value.

Examples:
>>> data = [ord(letter) for letter in "hello world "]
>>> snap7.util.get_fstring(data, 0, 15)
'hello world'
>>> snap7.util.get_fstring(data, 0, 15, remove_padding=false)
'hello world '
"""
data = map(chr, bytearray_[byte_index:byte_index + max_length])
string = "".join(data)

if remove_padding:
return string.rstrip(' ')
else:
return string


def get_string(bytearray_: bytearray, byte_index: int) -> str:
"""Parse string from bytearray

Expand Down Expand Up @@ -1532,7 +1601,12 @@ def get_value(self, byte_index: Union[str, int], type_: str) -> Union[ValueError
# first 4 bytes are used by db
byte_index = self.get_offset(byte_index)

if type_.startswith('STRING'):
if type_.startswith('FSTRING'):
max_size = re.search(r'\d+', type_)
if max_size is None:
raise ValueError("Max size could not be determinate. re.search() returned None")
return get_fstring(bytearray_, byte_index, int(max_size[0]))
elif type_.startswith('STRING'):
max_size = re.search(r'\d+', type_)
if max_size is None:
raise ValueError("Max size could not be determinate. re.search() returned None")
Expand Down Expand Up @@ -1594,6 +1668,14 @@ def set_value(self, byte_index: Union[str, int], type_: str, value: Union[bool,

byte_index = self.get_offset(byte_index)

if type_.startswith('FSTRING') and isinstance(value, str):
max_size = re.search(r'\d+', type_)
if max_size is None:
raise ValueError("Max size could not be determinate. re.search() returned None")
max_size_grouped = max_size.group(0)
max_size_int = int(max_size_grouped)
return set_fstring(bytearray_, byte_index, value, max_size_int)

if type_.startswith('STRING') and isinstance(value, str):
max_size = re.search(r'\d+', type_)
if max_size is None:
Expand Down
45 changes: 41 additions & 4 deletions test/test_util.py
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,7 @@
80 testDate DATE
82 testTod TOD
86 testDtl DTL
98 testFstring FSTRING[8]
"""

test_spec_indented = """
Expand Down Expand Up @@ -72,6 +73,7 @@
80 testDate DATE
82 testTod TOD
86 testDtl DTL
98 testFstring FSTRING[8]
"""


Expand All @@ -95,14 +97,15 @@
143, 255, 255, 255, # test time
254, # test byte 0xFE
48, 57, # test uint 12345
7, 91, 205, 21, # test udint 123456789
7, 91, 205, 21, # test udint 123456789
65, 157, 111, 52, 84, 126, 107, 117, # test lreal 123456789.123456789
65, # test char A
3, 169, # test wchar Ω
0, 4, 0, 4, 3, 169, 0, ord('s'), 0, ord('t'), 0, 196, # test wstring Ω s t Ä
45, 235, # test date 09.03.2022
2, 179, 41, 128, # test tod 12:34:56
7, 230, 3, 9, 4, 12, 34, 45, 0, 0, 0, 0 # test dtl 09.03.2022 12:34:56
45, 235, # test date 09.03.2022
2, 179, 41, 128, # test tod 12:34:56
7, 230, 3, 9, 4, 12, 34, 45, 0, 0, 0, 0, # test dtl 09.03.2022 12:34:56
116, 101, 115, 116, 32, 32, 32, 32 # test fstring 'test '
])

_new_bytearray = bytearray(100)
Expand Down Expand Up @@ -232,6 +235,40 @@ def test_write_string(self):
except ValueError:
pass

def test_get_fstring(self):
data = [ord(letter) for letter in "hello world "]
self.assertEqual(util.get_fstring(data, 0, 15), 'hello world')
self.assertEqual(util.get_fstring(data, 0, 15, remove_padding=False), 'hello world ')

def test_get_fstring_name(self):
test_array = bytearray(_bytearray)
row = util.DB_Row(test_array, test_spec, layout_offset=4)
value = row['testFstring']
self.assertEqual(value, 'test')

def test_get_fstring_index(self):
test_array = bytearray(_bytearray)
row = util.DB_Row(test_array, test_spec, layout_offset=4)
value = row.get_value(98, 'FSTRING[8]') # get value
self.assertEqual(value, 'test')

def test_set_fstring(self):
data = bytearray(20)
util.set_fstring(data, 0, "hello world", 15)
self.assertEqual(data, bytearray(b'hello world \x00\x00\x00\x00\x00'))

def test_set_fstring_name(self):
test_array = bytearray(_bytearray)
row = util.DB_Row(test_array, test_spec, layout_offset=4)
row['testFstring'] = 'TSET'
self.assertEqual(row['testFstring'], 'TSET')

def test_set_fstring_index(self):
test_array = bytearray(_bytearray)
row = util.DB_Row(test_array, test_spec, layout_offset=4)
row.set_value(98, 'FSTRING[8]', 'TSET')
self.assertEqual(row['testFstring'], 'TSET')

def test_get_int(self):
test_array = bytearray(_bytearray)
row = util.DB_Row(test_array, test_spec, layout_offset=4)
Expand Down