quarkusio/quarkus · error · ErrorDataDecoderException

Illegal charset in multipart response Content-Type (wrapped)

Error message

Illegal charset in multipart response Content-Type (wrapped)

What it means

When the Content-Type header of a multipart response declares a charset parameter whose name is not a legal charset name, Charset.forName throws IllegalCharsetNameException, which is wrapped into an ErrorDataDecoderException. This indicates a malformed charset= parameter in the response's Content-Type header.

Source

Thrown at independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/multipart/QuarkusMultipartResponseDecoder.java:227

            Charset charset) {
        this.response = checkNotNull(response, "request");
        this.charset = checkNotNull(charset, "charset");
        this.factory = checkNotNull(factory, "factory");
        // Fill default values

        String contentTypeValue = this.response.headers().get(HttpHeaderNames.CONTENT_TYPE);
        if (contentTypeValue == null) {
            throw new ErrorDataDecoderException("No '" + HttpHeaderNames.CONTENT_TYPE + "' header present.");
        }

        String[] dataBoundary = getMultipartDataBoundary(contentTypeValue);
        if (dataBoundary != null) {
            multipartDataBoundary = dataBoundary[0];
            if (dataBoundary.length > 1 && dataBoundary[1] != null) {
                try {
                    this.charset = Charset.forName(dataBoundary[1]);
                } catch (IllegalCharsetNameException e) {
                    throw new ErrorDataDecoderException(e);
                }
            }
        } else {
            destroy();
            throw new ErrorDataDecoderException("Unable to parse multipart response - No delimiter specified");
        }
        currentStatus = MultiPartStatus.HEADERDELIMITER;

        try {
            if (this.response instanceof HttpContent) {
                // Offer automatically if the given request is als type of HttpContent
                // See #1089
                offer((HttpContent) this.response);
            } else {
                parseBody();
            }
        } catch (Throwable e) {
            destroy();

View on GitHub (pinned to e1c734241f)

Solutions

1. Fix the server to emit a valid charset name such as UTF-8
2. Log the raw Content-Type header to identify the malformed value
3. Catch ErrorDataDecoderException and re-try decoding with a forced default charset if the library API allows
4. Reject or sanitize the response at the proxy/gateway layer

Example fix

// before (server)
Content-Type: multipart/mixed; boundary=xyz; charset=utf 8
// after
Content-Type: multipart/mixed; boundary=xyz; charset=UTF-8

String ct = response.headers().get(HttpHeaderNames.CONTENT_TYPE);
for (String p : ct.split(";")) {
    p = p.trim();
    if (p.startsWith("charset=")) {
        String name = p.substring(8).replace("\"", "");
        if (!Charset.isSupported(name)) throw new IllegalArgumentException("Illegal charset: " + name);
    }
}

try { new QuarkusMultipartResponseDecoder(response, factory, charset); } catch (ErrorDataDecoderException e) { log.error("Bad charset in Content-Type", e.getCause()); }

When it happens

Trigger: Response Content-Type like multipart/mixed; boundary=...; charset=<invalid name> where the charset name contains characters that are not legal charset-name syntax (e.g. spaces, '*', '=') — not merely an unknown charset.

Common situations: Server frameworks or custom code emitting a malformed charset parameter (e.g. charset=UTF_8 or charset="utf 8"); proxies rewriting Content-Type incorrectly.

Related errors

• Error decoding multipart field charset (wrapped IOException/
• Cannot create a Encoder if request is a TRACE
• Needs a boundary value
• No 'Content-Type' header present.
• Unable to parse multipart response - No delimiter specified

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/a958f73f0c3893d9. Report an issue: GitHub.