@sgspecker This allows to create a new photo with updated caption in camera roll if you share an existing photo which has already a caption
import appex
import console
import os
import photos
def main():
if appex.is_running_extension():
fil = appex.get_attachments()[0]
else:
fil = 'a.jpg'
with open(fil, mode='rb') as fin:
b = fin.read()
#b'\xff\xed\xllllPhotoshop 3.0\x00' = marker APP1
# -----
#b'8BIM\x04\x04\x00\x00\x00\x00\x00\x17\x1c\x01Z\x00\x03\x1b%G\x1c\x02\x0\x0\x02
# ---
#b'\x00\x02\x1c\x02x\x00\x03Cap\x00
ip = b.find(b'Photoshop')
if ip >= 0:
#print(b[ip-6:ip+100])
lip = int.from_bytes(b[ip-2:ip], "big")
i8 = b.find(b'8BIM',ip)
if i8 >= 0:
l8 = int.from_bytes(b[i8+10:i8+12], "big")
i = b.find(b'\x1c\x02x', i8)
# caption field identified by x'1c0278' then length in 2 bytes x'0005' = 5
l = int.from_bytes(b[i+3:i+5], "big")
caption = b[i+5:i+5+l].decode("utf-8")
#print(caption)
#return # if no update
#
caption = console.input_alert('new caption?','', caption, 'ok', hide_cancel_button=True)
lu = len(caption)
bl = lu.to_bytes(2,'big') # x'000l'
# store new caption
b = b[:i+3] + bl + caption.encode('utf-8') + b[i+5+l:]
# change length of 8BIM marker
l8aft = l8 - l + lu
bl8aft = l8aft.to_bytes(2,'big') # x'000l'
b = b[:i8+10] + bl8aft + b[i8+12:]
# change length of Photoshop marker at ip-2
lipaft = lip - l + lu
blaft = lipaft.to_bytes(2,'big') # x'000l'
b = b[:ip-2] + blaft + b[ip:]
tmp = '_temp.jpg'
with open(tmp, mode='wb') as fout:
fout.write(b)
asset = photos.create_image_asset(tmp)
os.remove(tmp)
appex.finish()
if __name__ == '__main__':
main()
