quarkusio/quarkus · error · IllegalStateException

Reading MultiByteHttpData as String is not supported

Error message

Reading MultiByteHttpData as String is not supported

What it means

getString() decodes the whole part content into a String in standard Netty HttpData. MultiByteHttpData is a streaming adapter that cannot (and must not) materialize all bytes into a String, so it always throws IllegalStateException. This is an intentional unsupported-operation guard, not a state error.

Solutions

  1. Read content incrementally via getChunk(int) after isReady(...) and decode chunks yourself if you truly need text.
  2. If the body is textual, send a String part instead of a Multi<Byte> streaming part.
  3. Collect the source Multi<Byte> upstream and decode from the collected bytes, not from the adapter.
  4. Branch on concrete type before calling getString on InterfaceHttpData instances.

Example fix

// before
String text = httpData.getString();
// after
if (httpData instanceof MultiByteHttpData) {
    // read via getChunk after isReady, decode chunk by chunk
} else {
    String text = httpData.getString();
}
Defensive patterns

Strategy: type-guard

Validate before calling

String safeGetString(InterfaceHttpData data) {
    if (data instanceof MultiByteHttpData) {
        throw new IllegalArgumentException("Read streaming parts via getChunk(); getString is unsupported");
    }
    return data.getString();
}

Type guard

boolean supportsString(InterfaceHttpData data) {
    return !(data instanceof MultiByteHttpData);
}

Try / catch

try {
    String s = data.getString();
} catch (IllegalStateException e) {
    if (e.getMessage() != null && e.getMessage().contains("not supported")) {
        // decode incrementally from getChunk() instead
    } else {
        throw e;
    }
}

Prevention

When it happens

Trigger: Calling getString() on a MultiByteHttpData - typically from logging, debugging, or generic InterfaceHttpData iteration code that stringifies every part of a multipart request/response.

Common situations: Printing multipart parts for diagnostics (including MultiByteHttpData.toString users who then call getString); generic form-data decoders on the server or on response handling; test assertions that read part content as text.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/1a7036dc4927bfae. Report an issue: GitHub.

Appendix: source

Thrown at independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/multipart/MultiByteHttpData.java:221

        ByteBuf result = VertxByteBufAllocator.DEFAULT.heapBuffer(toRead, toRead);

        // finish if the whole buffer is filled
        // or we hit the end, `done` && buffer.readableBytes == 0
        while (toRead > 0 && !(buffer.readableBytes() == 0 && done)) {
            int readBytes = Math.min(buffer.readableBytes(), toRead);
            result.writeBytes(buffer.readBytes(readBytes));
            buffer.discardReadBytes();
            subscription.request(readBytes);

            toRead -= readBytes;
        }
        return result;
    }

    @Override
    public String getString() {
        throw new IllegalStateException("Reading MultiByteHttpData as String is not supported");
    }

    @Override
    public String getString(Charset encoding) {
        throw new IllegalStateException("Reading MultiByteHttpData as String is not supported");
    }

    @Override
    public boolean renameTo(File dest) {
        throw new IllegalStateException("Renaming destination file for MultiByteHttpData is not supported");
    }

    @Override
    public boolean isInMemory() {
        return true;
    }

    @Override

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