remove casting and update comment property to take first item of list

Author: bkayranci

scapy/packet.py

@@ -227,8 +227,8 @@ def __init__(self,
     def comment(self):
         # type: () -> Optional[bytes]
         """Get the comment of the packet"""
-        if self.comments is not None and len(self.comments) > 0:
-            return self.comments[-1]
+        if self.comments and len(self.comments):
+            return self.comments[0]
         return None
 
     @comment.setter

scapy/utils.py

@@ -1805,7 +1805,7 @@ def _read_options(self, options):
                 if code in [1, 2988, 2989, 19372, 19373]:  # https://www.ietf.org/archive/id/draft-tuexen-opsawg-pcapng-05.html#name-options-format
                     if code not in opts:
                         opts[code] = []
-                    cast(List[bytes], opts[code]).append(options[4:4 + length])
+                    opts[code].append(options[4:4 + length])
                 else:
                     opts[code] = options[4:4 + length]
             if code == 0:
@@ -1827,9 +1827,9 @@ def _read_block_idb(self, block, _):
         options = self.default_options.copy()  # type: Dict[str, Any]
         for c, v in options_raw.items():
             if isinstance(v, list):
-                # If the option is a list, we take the last value
-                # (as per pcapng spec)
-                v = v[-1]
+                # Spec allows multiple occurrences (see https://www.ietf.org/archive/id/draft-tuexen-opsawg-pcapng-05.html#section-4.2-8.6)
+                # but does not define which to use. We take the first for backward compatibility.
+                v = v[0]
             if c == 9:
                 length = len(v)
                 if length == 1:
@@ -1886,7 +1886,6 @@ def _read_block_epb(self, block, size):
         process_information = {}
         for code, value in options.items():
             if code in [0x8001, 0x8003]:  # PCAPNG_EPB_PIB_INDEX, PCAPNG_EPB_E_PIB_INDEX
-                value = cast(bytes, value)
                 try:
                     proc_index = struct.unpack(self.endian + "I", value)[0]
                 except struct.error:
@@ -1903,7 +1902,6 @@ def _read_block_epb(self, block, size):
         comments = options.get(1, None)
         epb_flags_raw = options.get(2, None)
         if epb_flags_raw:
-            epb_flags_raw = cast(bytes, epb_flags_raw)
             try:
                 epb_flags, = struct.unpack(self.endian + "I", epb_flags_raw)
             except struct.error:
@@ -2049,7 +2047,6 @@ def _read_block_pib(self, block, _):
         # Get Options
         options = self._read_options(block)
         for code, value in options.items():
-            value = cast(bytes, value)
             if code == 2:
                 process_information["name"] = value.decode("ascii", "backslashreplace")
             elif code == 4:
@@ -2588,7 +2585,7 @@ def _write_block_epb(self,
 
         # Options
         opts = b''
-        if comments is not None and len(comments) > 0:
+        if comments and len(comments):
             for c in comments:
                 comment = bytes_encode(c)
                 opts += struct.pack(self.endian + "HH", 1, len(comment))