Fixing a bug with byte order marks

Fixing a bug with byte order marks(alexwlchan.net)

5 points by surprisetalk 5 days ago | 3 comments

flohofwoe 1 hour ago |

Ugh, why are BOMs even still a thing in the 21st century? E.g. when will Windows finally arrive in the late 1990s and switch to UTF-8 for everything?

The UTF-8 BOM is especially bizarre because UTF-8 is completely endian-agnostic (so this "UTF-8 Byte Order Mark" is at most an indicator that this file is UTF-8 encoded, but guess what? Outside the Windows bubble, all text files are UTF-8 anyway).

gdwatson 21 minutes ago | |

Windows bought into Unicode hard before Unicode expanded beyond 16 bits. The consequence is that its native strings are theoretically UTF-16, but often behave like UCS-2, allowing random halves of surrogate pairs. Windows APIs reflect that, Windows filenames reflect that, and translation into UTF-8 has to reflect that -- somehow. It's not great.

Personally I'd like a world where Unicode gave up all the compromises that come with supporting UTF-16. But presumably burning all your early adopters is not a winning strategy.

mr_mitm 1 hour ago |

I hate the BOM so much. It causes so many subtle issues and I don't even understand why it's needed.

remnavi 1 hour ago |

The csv.DictReader version of this bug is the one that got me. Open a UTF-8-with-BOM CSV as plain utf-8 and your first column name comes back with an invisible U+FEFF glued to the front of it, so every lookup on that one field fails while the other columns behave perfectly. You end up suspecting the source data, the header row, anything except the encoding.

json.loads has a similar tell: a leading BOM gives you "Expecting value: line 1 column 1 (char 0)", which reads like malformed JSON when the JSON is fine.

Same fix, utf-8-sig at the open, and I think the lesson generalises past subtitles: deal with encoding once at the I/O boundary so nothing downstream ever needs to know a BOM existed. Mid-file BOMs like yours are what it looks like when that leaks.