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Tag parse refactor
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@mikhail-iurkov
mikhail-iurkov committed Jan 19, 2022
1 parent 2fa6876 commit 755df22
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Showing 3 changed files with 69 additions and 106 deletions.
22 changes: 22 additions & 0 deletions piexif/_exif.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,6 @@
from struct import calcsize


class TYPES:
Byte = 1
Ascii = 2
Expand All @@ -13,6 +16,25 @@ class TYPES:
DFloat = 12


TYPE_FORMAT = {
TYPES.Byte: 'B',
TYPES.Ascii: None,
TYPES.Short: 'H',
TYPES.Long: 'L',
TYPES.Rational: 'LL',
TYPES.SByte: 'b',
TYPES.Undefined: None,
TYPES.SShort: 'h',
TYPES.SLong: 'l',
TYPES.SRational: 'll',
TYPES.Float: 'f',
TYPES.DFloat: 'd',
}


TYPE_LENGTH = {t: calcsize('=' + f) for t, f in TYPE_FORMAT.items() if f}


SIMPLE_NUMERICS = [
TYPES.Byte,
TYPES.Short,
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148 changes: 47 additions & 101 deletions piexif/_load.py
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,42 @@ def get_ifd_dict(self, pointer, ifd_name, read_unknown=False):
result = {}
return result

def _read_tag(self, pointer):
tag, value_type, value_num = unpack_from(
self.endian_mark + "HHL", self.tiftag, pointer
)
# Treat unknown types as `Undefined`
value_length = TYPE_LENGTH.get(value_type, 1)
value_length_total = value_length * value_num
if value_length_total > 4:
data_pointer = unpack_from(
self.endian_mark + "L", self.tiftag, pointer + 8
)[0]
else:
data_pointer = pointer + 8

format = TYPE_FORMAT.get(value_type, None)

if format is None:
# Ascii, Undefined and unknown types
if value_type == TYPES.Ascii:
# Crop ending zero
value_length_total = max(0, value_length_total - 1)
raw_value = self.tiftag[data_pointer:data_pointer+value_length_total]
values = (raw_value, )
else:
# Unpacked types
values = unpack_from(
self.endian_mark + format * value_num, self.tiftag, data_pointer
)
# Collate rationals
if len(format) > 1:
stride = len(format)
values = tuple(
values[i*stride:(i+1)*stride] for i in range(value_num)
)
return tag, value_type, tuple(values)

def _do_get_ifd_dict(self, pointer, ifd_name, read_unknown=False):
ifd_dict = {}
tag_count = unpack_from(self.endian_mark + "H",
Expand All @@ -122,24 +158,24 @@ def _do_get_ifd_dict(self, pointer, ifd_name, read_unknown=False):
t = ifd_name
for x in range(tag_count):
pointer = offset + 12 * x
tag, value_type, value_num = unpack_from(
self.endian_mark + "HHL", self.tiftag, pointer)
value = self.tiftag[pointer+8: pointer+12]
v_set = (value_type, value_num, value, tag)
tag, value_type, values = self._read_tag(pointer)
if tag in TAGS[t]:
converted = self.convert_value(v_set)
expected_value_type = TAGS[t][tag]['type']
if value_type != expected_value_type:
try:
converted = coerce(converted, value_type, expected_value_type)
values = coerce(values, value_type, expected_value_type)
except ValueError:
# Skip if coercion failed
continue
if isinstance(converted, tuple) and (len(converted) == 1):
converted = converted[0]
ifd_dict[tag] = converted
if len(values) == 1:
values = values[0]
ifd_dict[tag] = values
elif read_unknown:
ifd_dict[tag] = (v_set[0], v_set[1], v_set[2], self.tiftag)
value_num, = unpack_from(
self.endian_mark + "L", self.tiftag, pointer + 4
)
pointer_or_value = self.tiftag[pointer + 8: pointer + 12]
ifd_dict[tag] = value_type, value_num, pointer_or_value, self.tiftag
else:
pass

Expand All @@ -148,96 +184,6 @@ def _do_get_ifd_dict(self, pointer, ifd_name, read_unknown=False):
ifd_dict["first_ifd_pointer"] = self.tiftag[pointer:pointer + 4]
return ifd_dict

def convert_value(self, val):
data = None
t = val[0]
length = val[1]
value = val[2]

if t == TYPES.Byte: # BYTE
if length > 4:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from("B" * length, self.tiftag, pointer)
else:
data = unpack_from("B" * length, value)
elif t == TYPES.Ascii: # ASCII
if length > 4:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = self.tiftag[pointer: pointer+length - 1]
else:
data = value[0: length - 1]
elif t == TYPES.Short: # SHORT
if length > 2:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "H" * length,
self.tiftag, pointer)
else:
data = unpack_from(self.endian_mark + "H" * length, value)
elif t == TYPES.Long: # LONG
if length > 1:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "L" * length,
self.tiftag, pointer)
else:
data = unpack_from(self.endian_mark + "L" * length, value)
elif t == TYPES.Rational: # RATIONAL
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = tuple(
unpack_from(self.endian_mark + "LL",
self.tiftag, pointer + x * 8)
for x in range(length)
)
elif t == TYPES.SByte: # SIGNED BYTES
if length > 4:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from("b" * length, self.tiftag, pointer)
else:
data = unpack_from("b" * length, value)
elif t == TYPES.Undefined: # UNDEFINED BYTES
if length > 4:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = self.tiftag[pointer: pointer+length]
else:
data = value[0: length]
elif t == TYPES.SShort: # SIGNED SHORT
if length > 2:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "h" * length,
self.tiftag, pointer)
else:
data = unpack_from(self.endian_mark + "h" * length, value)
elif t == TYPES.SLong: # SLONG
if length > 1:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "l" * length,
self.tiftag, pointer)
else:
data = unpack_from(self.endian_mark + "l" * length, value)
elif t == TYPES.SRational: # SRATIONAL
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = tuple(
unpack_from(self.endian_mark + "ll",
self.tiftag, pointer + x * 8)
for x in range(length)
)
elif t == TYPES.Float: # FLOAT
if length > 1:
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "f" * length,
self.tiftag, pointer)
else:
data = unpack_from(self.endian_mark + "f" * length, value)
elif t == TYPES.DFloat: # DOUBLE
pointer = unpack_from(self.endian_mark + "L", value)[0]
data = unpack_from(self.endian_mark + "d" * length,
self.tiftag, pointer)
else:
raise ValueError("Exif might be wrong. Got incorrect value " +
"type to decode.\n" +
"tag: " + str(val[3]) + "\ntype: " + str(t))

return data


def _get_key_name_dict(exif_dict):
new_dict = {
Expand All @@ -254,7 +200,7 @@ def coerce(value, type, target):
if target == TYPES.Undefined:
if type == TYPES.Byte:
# Interpret numbers as byte values, to fit Pillow behaviour
return b''.join(min(x, 255).to_bytes(1, 'big') for x in value)
return ( b''.join(min(x, 255).to_bytes(1, 'big') for x in value), )
elif target in SIMPLE_NUMERICS:
if type in SIMPLE_NUMERICS:
return value
Expand Down
5 changes: 0 additions & 5 deletions tests/s_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -657,11 +657,6 @@ def test_ExifReader_return_unknown(self):
self.assertEqual(ifd[65535][1], 0)
self.assertEqual(ifd[65535][2], b"\x00\x00")

def test_ExifReader_convert_value_fail(self):
er = piexif._load._ExifReader(I1)
with self.assertRaises(ValueError):
er.convert_value((None, None, None, None))

def test_split_into_segments_fail1(self):
with self.assertRaises(InvalidImageDataError):
_common.split_into_segments(b"I'm not JPEG")
Expand Down

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