apache/druid · error · ParseException

Unable to parse row [ ]

Error message

Unable to parse row [%s]

What it means

JavaScriptParser wraps any exception raised while executing the user-supplied JavaScript function into a ParseException with message "Unable to parse row [%s]". The parser compiles a JS script and calls it to turn each input row into a {key: value} Map; if the script throws, returns a non-Map, or compilation fails, this error is thrown for the offending row.

Solutions

1. Inspect the wrapped cause in the ParseException stack trace to find the actual JS error
2. Verify the JavaScript function returns a plain object ({key: value}), not a string, array, or null
3. Check that JavaScript is enabled (druid.javascript.enabled=true) in the runtime properties of the involved service
4. Test the function logic on a sample row locally before deploying the ingestion spec

Example fix

// before
"parseSpec": {"type":"javascript", "function":"function(str) { return JSON.stringify(JSON.parse(str)); }"}
// after
"parseSpec": {"type":"javascript", "function":"function(str) { return JSON.parse(str); }"}

// validate before ingesting
if (!script.trim().startsWith("function")) throw new IllegalArgumentException("JS must be a function returning {key: value}");
// smoke-test: JSON.parse(functionResult) must yield a plain object

function returnsMap(Object v) { return v instanceof java.util.Map; }

try { map = parser.parseToMap(row); } catch (ParseException e) { log.error("Row rejected: {} cause: {}", row, e.getCause()); throw e; }

When it happens

Trigger: Calling parseToMap(String) on a row where the configured JavaScript function throws an exception, returns null/non-Map value, or the script itself failed to compile (which surfaces as a ParseException for the first row processed).

Common situations: Ingestion specs using type:'javascript' parseSpec with a buggy or truncated function; script returns a JSON string or array instead of an object; JavaScript engine disabled in runtime.properties (druid.javascript.enabled=false) causing script initialization failure; JS syntax errors after copy-paste.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• JavaScript parsed value
• Size of rawColumnsList
• AggregatorFactoryNotMergeableException
• Attempt to add row to swapped-out sink for segment
• authResult.getErrorMessage()

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/ea88fb7a2265647b. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/java/util/common/parsers/JavaScriptParser.java:83

      final String function
  )
  {
    this.fn = compile(function);
  }

  @Override
  public Map<String, Object> parseToMap(String input)
  {
    try {
      final Object compiled = fn.apply(input);
      if (!(compiled instanceof Map)) {
        throw new ParseException(input, "JavaScript parsed value [%s] must be in {key: value} format!", input);
      }

      return (Map) compiled;
    }
    catch (Exception e) {
      throw new ParseException(input, e, "Unable to parse row [%s]", input);
    }
  }

  @Override
  public void setFieldNames(Iterable<String> fieldNames)
  {
    throw new UnsupportedOperationException();
  }

  @Override
  public List<String> getFieldNames()
  {
    throw new UnsupportedOperationException();
  }
}

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