Fix issue #12.

Signed-off-by: Bofu Chen (bafu) <bofu@numbersprotocol.io>

cai/jumbf.py

@@ -210,12 +210,18 @@ def get_app11_marker_segment_headers(data_bytes):
     offsets = [m.start() for m in re.finditer(marker, data_bytes)]
     headers = {}
     for offset in offsets:
-        # WORKAROUND: Reduce the probability to treat non-CAI data as
-        #             CAI metadata.
-        # check if the CI parameter equals to 0x4A50 (ASCII: 'J' 'P')
-        if data_bytes[offset + 4] != 0x4A or data_bytes[offset + 5] != 0x50:
-            continue
-        else:
+        try:
+            ci = data_bytes[offset + 4 : offset + 6].decode('utf-8')
+        except Exception as e:
+            print('Find App11 marker, and fail to get CI')
+            ci = None
+        try:
+            tbox = data_bytes[offset + 16 : offset + 20].decode('utf-8')
+        except Exception as e:
+            print('Find App11 marker, and fail to get TBox')
+            tbox = None
+
+        if ci == 'JP' and tbox == 'jumb':
             header = {}
             header['le']     = int.from_bytes(data_bytes[offset + 2 : offset + 4], byteorder='big')
             header['ci']     = data_bytes[offset + 4 : offset + 6].decode('utf-8')
@@ -228,4 +234,6 @@ def get_app11_marker_segment_headers(data_bytes):
             # passive protection to skip illegal or empty segment
             if header['le'] > 10:
                 headers[header['z']] = header
+        else:
+            print('Unknown CI ({0}) or TBox ({1}) of offset {2}'.format(ci, tbox, hex(offset)))
     return headers

cai/starling.py

@@ -125,6 +125,14 @@ def signel_claim_injection(self):
         return cai_data_bytes
 
     def multiple_claims_injection(self):
+        """Re-create a new Claim Block.
+        The high-levle idea is to
+        1. Re-construct current Claim Block by
+           concatenating the payloads in the App11 segments.
+        2. Append the new Store into the Claim Block.
+        3. Re-create App11 segments based on the updated Claim Block.
+        4. Replace the old App11 segments by the new App11 segments.
+        """
         # generate acquisition assertion
         acquisition_assertion = {
             'dc:format': 'image/jpeg',
@@ -153,6 +161,9 @@ def multiple_claims_injection(self):
 
         # re-construct Claim Block payload
         claim_block_payload = bytearray()
+        ## App11 Length of Marker Segment (the Le parameter) value is 8 ~ 65535.
+        ## App11 Packet Sequence number (the Z parameter) value is 1 ~ 2^32-1.
+        ## The Claim Block maximum size will be ~= 2^48 B ~= 280 TB.
         for i in range(1, header_number + 1):
             payload_start = self.app11_headers[i]['offset'] + 20
             payload_end = payload_start + (self.app11_headers[i]['le'] - 18)
@@ -167,8 +178,24 @@ def multiple_claims_injection(self):
         updated_app11_segment = App11Box(en=last_en)
         updated_app11_segment.payload = updated_claim_block_bytes
 
+        ## Assuming that current CAI data consists of 3 App11 segments.
+        ##
+        ## +-- starting point
+        ## v
+        ## +-------+----+----+------+-----+------+------+-------------------------------+
+        ## | APP11 | Le | CI | En=1 | Z=1 | LBox | TBox | Payload (Claim Block, part 1) |
+        ## +-------+----+----+------+-----+------+------+-------------------------------+
+        ## | APP11 | Le | CI | En=1 | Z=2 | LBox | TBox | Payload (Claim Block, part 2) |
+        ## +-------+----+----+------+-----+------+------+-------------------------------+
+        ## | APP11 | Le | CI | En=1 | Z=3 | LBox | TBox | Payload (Claim Block, part 3) |
+        ## +-------+----+----+------+-----+------+------+-------------------------------+
+        ##                                                                              ^
+        ##                                                               ending point --+
+        ##
+        ## starting point of current CAI data
         update_range_s = self.app11_headers[1]['offset']
-        update_range_e = self.app11_headers[1]['offset'] + last_lbox + 16
+        ## ending point of current CAI data
+        update_range_e = self.app11_headers[header_number]['offset'] + self.app11_headers[header_number]['le'] + 2
 
         # save CAI-injected media
         data_bytes = self.raw_bytes[:update_range_s] + updated_app11_segment.convert_bytes() + self.raw_bytes[update_range_e:]