Command.get raises TypeError on the first lowercase FTP command, so a valid RFC 959 request cannot be parsed

[JarryShaw]

Command.get normalises the key it registers but not the key it looks up, so the first lowercase or mixed-case FTP command in a capture raises TypeError instead of parsing.

Mechanism

pcapkit/const/ftp/command.py:297-298:

if key not in Command._member_map_:
    return extend_enum(Command, key.upper(), default if default is not None else key)
return Command[key]

The membership test uses key, the registration uses key.upper(). For key='retr' the test misses — _member_map_ holds RETR — so it calls extend_enum(Command, 'RETR', ...), and RETR is already a member.

This is reachable from real wire data, not just from a direct get() call. pcapkit/protocols/application/ftp.py:36 compiles the request pattern with re.I:

FTP_REQUEST = re.compile(rb'^(?P<cmmd>[A-Z]{3,4})( +(?P<args>.*))?\r\n$', re.I)

so a lowercase command matches, and ftp.py:99 passes the matched text verbatim: cmmd_val = Enum_Command.get(cmmd).

RFC 959 section 5.3 defines FTP commands as case-insensitive -- "Upper and lower case alphabetic characters are to be treated identically", so retr file.txt is a valid request that this library cannot parse.

Reproduction

>>> from pcapkit.const.ftp.command import Command
>>> Command.get('retr')
TypeError: 'RETR' already in use as <Command.RETR: Retrieve>

Executed on origin/main (9c240a60e), CPython 3.14.7, aenum 3.1.17. It fails on the first call, not on a second — the collision is against the statically defined member, so nothing needs to have been registered first.

Notes

• The fix is to normalise once and use the same normalised key for both the test and the lookup, rather than testing the raw key.
• pcapkit/const/http/method.py:175-176 has the identical mismatch and is filed separately.
• Found while investigating Profile by self time: aenum.extend_enum is 16.7% of extraction, dispatch and imports under 1% #575; it is a correctness defect, not a performance one.