File: thumbspage/piexif/_common.py

import struct
from ._exceptions import InvalidImageDataError
def split_into_segments(data):
 """Slices JPEG meta data into a list from JPEG binary data.
 """
 if data[0:2] != b"\xff\xd8":
 raise InvalidImageDataError("Given data isn't JPEG.")
 head = 2
 segments = [b"\xff\xd8"]
 while 1:
 if data[head: head + 2] == b"\xff\xda":
 segments.append(data[head:])
 break
 else:
 length = struct.unpack(">H", data[head + 2: head + 4])[0]
 endPoint = head + length + 2
 seg = data[head: endPoint]
 segments.append(seg)
 head = endPoint
 if (head >= len(data)):
 raise InvalidImageDataError("Wrong JPEG data.")
 return segments
def read_exif_from_file(filename):
 """Slices JPEG meta data into a list from JPEG binary data.
 """
 f = open(filename, "rb")
 data = f.read(6)
 if data[0:2] != b"\xff\xd8":
 raise InvalidImageDataError("Given data isn't JPEG.")
 head = data[2:6]
 HEAD_LENGTH = 4
 exif = None
 while len(head) == HEAD_LENGTH:
 length = struct.unpack(">H", head[2: 4])[0]
 if head[:2] == b"\xff\xe1":
 segment_data = f.read(length - 2)
 if segment_data[:4] != b'Exif':
 head = f.read(HEAD_LENGTH)
 continue
 exif = head + segment_data
 break
 elif head[0:1] == b"\xff":
 f.read(length - 2)
 head = f.read(HEAD_LENGTH)
 else:
 break
 f.close()
 return exif
def get_exif_seg(segments):
 """Returns Exif from JPEG meta data list
 """
 for seg in segments:
 if seg[0:2] == b"\xff\xe1" and seg[4:10] == b"Exif\x00\x00":
 return seg
 return None
def merge_segments(segments, exif=b""):
 """Merges Exif with APP0 and APP1 manipulations.
 """
 if segments[1][0:2] == b"\xff\xe0" and \
 segments[2][0:2] == b"\xff\xe1" and \
 segments[2][4:10] == b"Exif\x00\x00":
 if exif:
 segments[2] = exif
 segments.pop(1)
 elif exif is None:
 segments.pop(2)
 else:
 segments.pop(1)
 elif segments[1][0:2] == b"\xff\xe0":
 if exif:
 segments[1] = exif
 elif segments[1][0:2] == b"\xff\xe1" and \
 segments[1][4:10] == b"Exif\x00\x00":
 if exif:
 segments[1] = exif
 elif exif is None:
 segments.pop(1)
 else:
 if exif:
 segments.insert(1, exif)
 return b"".join(segments)