apache/druid · error · ISE

Unsupported content encoding

Error message

Unsupported content encoding [%s]

What it means

When HttpEmitterConfig.contentEncoding is set, the EmittingThread encodes each batch payload in a switch; only GZIP is supported besides NONE/identity. Any other configured encoding hits the default branch and throws IllegalStateException('Unsupported content encoding [%s]'). The config value failed validation at send time rather than at config load.

Solutions

  1. Set contentEncoding to GZIP (or leave unset/identity) in HttpEmitterConfig.
  2. Validate config values at startup; only GZIP compression is implemented.
  3. Remove the contentEncoding field entirely if compression is not needed.
  4. Upgrade Druid if a newly added encoding is expected — older versions support only GZIP.

Example fix

// before
HttpEmitterConfig.builder().setContentEncoding("DEFLATE")...
// after
HttpEmitterConfig.builder().setContentEncoding("gzip")...
Defensive patterns

Strategy: validation

Validate before calling

HttpEmitterConfig config = ...;
String enc = String.valueOf(config.getContentEncoding());
if (!enc.isEmpty() && !"GZIP".equalsIgnoreCase(enc.trim())) {
  throw new IllegalArgumentException("Only GZIP content encoding is supported, got: " + enc);
}

Try / catch

try {
  emitter.emit(event);
} catch (IllegalStateException e) {
  if (e.getMessage().contains("Unsupported content encoding")) {
    log.error(e, "Fix contentEncoding in emitter config to GZIP or unset");
  }
}

Prevention

When it happens

Trigger: Setting HttpEmitterConfig.contentEncoding to a value other than GZIP (e.g. 'gzip ' case variants handled elsewhere, DEFLATE, BR) and then emitting; copy-pasting encoding names from other HTTP clients.

Common situations: Users assuming compression options like deflate/brotli are supported; typos in emitter JSON config ('contentEncoding': 'GZIP ' vs other names); older configs migrated from other systems.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/f3c92740871628cd. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/java/util/emitter/core/HttpPostEmitter.java:757

      long sendingStartMs = System.currentTimeMillis();

      final RequestBuilder request = new RequestBuilder("POST");
      request.setUrl(url);
      byte[] payload;
      int payloadLength;
      ContentEncoding contentEncoding = config.getContentEncoding();
      if (contentEncoding != null) {
        switch (contentEncoding) {
          case GZIP:
            try (GZIPOutputStream gzipOutputStream = acquireGzipOutputStream(length)) {
              gzipOutputStream.write(buffer, 0, length);
            }
            payload = gzipBaos.getBuffer();
            payloadLength = gzipBaos.size();
            request.setHeader(HttpHeaders.Names.CONTENT_ENCODING, HttpHeaders.Values.GZIP);
            break;
          default:
            throw new ISE("Unsupported content encoding [%s]", contentEncoding.name());
        }
      } else {
        payload = buffer;
        payloadLength = length;
      }

      request.setHeader(HttpHeaders.Names.CONTENT_TYPE, "application/json");
      request.setHeader(HttpHeaders.Names.CONTENT_LENGTH, String.valueOf(payloadLength));
      request.setBody(ByteBuffer.wrap(payload, 0, payloadLength));

      if (config.getBasicAuthentication() != null) {
        final String[] parts = config.getBasicAuthentication().getPassword().split(":", 2);
        final String user = parts[0];
        final String password = parts.length > 1 ? parts[1] : "";
        String encoded = StringUtils.encodeBase64String((user + ':' + password).getBytes(StandardCharsets.UTF_8));
        request.setHeader(HttpHeaders.Names.AUTHORIZATION, "Basic " + encoded);
      }

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