The previous comment claimed defParamCharset:'utf8' fixed multipart
filename header decoding. It doesn't - that option only fires for the
RFC 5987 encoded filename*=utf-8''... form, which clients rarely send.
The actual UTF-8 recovery happens in the storage.filename callback
(added in d679ca8) via Buffer.from(name,'latin1').toString('utf8').
The option is kept set for the rare RFC 5987 case but the comment no
longer overclaims what it does.
busboy reads the Content-Disposition filename="..." header value as
latin1 by default - even with defParamCharset:'utf8' set, that option
only applies to RFC 5987 encoded filename*=... params, which most
clients (browsers, curl, programmatic HTTP) don't send. Modern clients
send raw UTF-8 bytes for non-ASCII filenames; busboy interprets those
bytes one-byte-per-char as latin1, producing a JS string like 'A-tilde
+ quarter-mark' for 'u-umlaut'. JS then re-encodes that string as UTF-8
on the way to SQLite, yielding 4 bytes (c3 83 c2 bc) for what should be
2 bytes (c3 bc). Classic double-encoding mojibake - shows up in the UI
as 'BegrA-tilde...' instead of 'Begru-umlaut...'.
Fix: in the multer filename callback, re-decode file.originalname from
latin1 to utf8 to recover the original byte sequence. Mutating
originalname here propagates to every route handler reading
req.file.originalname (POST /, PUT /:id/replace, and any future upload
route using the same middleware).
This is the actual visible-mojibake bug semetra22 reported. The prior
commit b677752 (NFC normalize in safeFilename) handles a separate but
related case (macOS NFD clients sending decomposed forms); both fixes
compose correctly - latin1->utf8 first restores the byte sequence,
then NFC normalize collapses NFD into composed form.
Smoke verified by sending raw UTF-8 multipart from a Node https client
(no shell escaping). NFC input 'Begru-umlaut-essungsscreens.jpg' with
bytes c3bc c39f arrives clean (was c383c2bc c383c29f before). NFD input
'u + combining diaeresis' arrives as composed NFC c3bc after both fixes.
multer/busboy decode multipart filename headers as latin1 by default,
which mangled umlauts and other non-ASCII characters end-to-end
(Größe.jpg arrived as Größe.jpg and was stored that way). Setting
defParamCharset: 'utf8' on the multer options makes the entire
upload pipeline consistent UTF-8.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ScreenTinker - open source digital signage management software.
MIT License, all features included, no license gates.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
