What causes "Filename not found" in quarkusio/quarkus?

Ensure every part inside multipart/mixed includes a filename parameter in Content-Disposition.

quarkusio/quarkus · error · ErrorDataDecoderException

Filename not found

Error message

Filename not found

What it means

In mixed multipart mode, the decoder found a form field (name attribute) without a filename attribute. Only file uploads are supported inside multipart/mixed sections, so parsing fails with 'Filename not found'. This enforces that every part within a mixed block is a file upload.

Source

Thrown at independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/multipart/QuarkusMultipartResponseDecoder.java:824

                // FileUpload
                currentStatus = MultiPartStatus.FILEUPLOAD;
                // do not change the buffer position
                return decodeMultipart(MultiPartStatus.FILEUPLOAD);
            } else {
                // Field
                currentStatus = MultiPartStatus.FIELD;
                // do not change the buffer position
                return decodeMultipart(MultiPartStatus.FIELD);
            }
        } else {
            if (filenameAttribute != null) {
                // FileUpload
                currentStatus = MultiPartStatus.MIXEDFILEUPLOAD;
                // do not change the buffer position
                return decodeMultipart(MultiPartStatus.MIXEDFILEUPLOAD);
            } else {
                // Field is not supported in MIXED mode
                throw new ErrorDataDecoderException("Filename not found");
            }
        }
    }

    private static final String FILENAME_ENCODED = HttpHeaderValues.FILENAME.toString() + '*';

    private Attribute getContentDispositionAttribute(String... values) {
        String name = cleanString(values[0]);
        String value = values[1];

        // Filename can be token, quoted or encoded. See https://tools.ietf.org/html/rfc5987
        if (HttpHeaderValues.FILENAME.contentEquals(name)) {
            // Value is quoted or token. Strip if quoted:
            int last = value.length() - 1;
            if (last > 0 &&
                    value.charAt(0) == HttpConstants.DOUBLE_QUOTE &&
                    value.charAt(last) == HttpConstants.DOUBLE_QUOTE) {
                value = value.substring(1, last);

View on GitHub (pinned to e1c734241f)

Solutions

Ensure every part inside multipart/mixed includes a filename parameter in Content-Disposition.
Move plain (non-file) fields out of the mixed section into the outer multipart body.
Fix the server serializer so mixed sections only contain file attachments.
If the payload is legitimate, handle it with a custom parser instead of the built-in decoder.

Example fix

// before (field inside mixed, no filename)
Content-Disposition: form-data; name="note"
// after
Content-Disposition: form-data; name="attachment"; filename="note.txt"

Defensive patterns

Strategy: validation

Validate before calling

// Ensure every part inside multipart/mixed carries a filename
mixedParts.forEach(p -> {
    if (p.filename() == null || p.filename().isBlank()) {
        throw new IllegalStateException("Part '" + p.name() + "' in multipart/mixed must have a filename");
    }
});

Type guard

static boolean isFilePart(DispositionPart p) {
    return p != null && p.filename() != null && !p.filename().isBlank();
}

Try / catch

try {
    return decoder.decodeMultipart(MIXEDDELIMITER);
} catch (ErrorDataDecoderException e) {
    if ("Filename not found".equals(e.getMessage())) {
        throw new UnsupportedMixedFieldException("Plain fields are not allowed inside multipart/mixed", e);
    }
    throw e;
}

Prevention

Only place file uploads inside multipart/mixed sections.
Put plain form fields at the outer multipart/form-data level.
Enforce filename presence in the server serializer API.
Test mixed payloads against the Quarkus client in CI.

When it happens

Trigger: Inside a multipart/mixed section, a part's Content-Disposition has a 'name' but no 'filename' parameter, so the MIXEDFILEUPLOAD transition cannot complete.

Common situations: Servers embedding plain fields inside multipart/mixed blocks; hand-written multipart serializers mixing fields and files in a mixed section; email-style bodies reused over HTTP.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/8c225da270598fa3. Report an issue: GitHub.