What causes "ext onShutdown failed ({}): {}" in karatelabs/karate?

Fix the Ext.onShutdown() implementation named in the log to be idempotent and exception-safe

ext onShutdown failed

Error message

ext onShutdown failed ({}): {}

What it means

Karate 'ext' boot extensions can register an onShutdown callback invoked when the Suite finishes. Each callback is best-effort: if one throws, Karate logs this warning naming the extension class and the exception message, then keeps going (the ext's JSONL listener registration is still removed). Suite results are unaffected.

Solutions

Fix the Ext.onShutdown() implementation named in the log to be idempotent and exception-safe
Wrap external cleanup in the extension with its own try/catch and meaningful logging
Make sure onShutdown only releases resources the extension itself created
If the extension is third-party, update it or remove it from the boot binding if not needed

Example fix

// before
@Override public void onShutdown() { client.close(); files.flush(); }
// after
@Override public void onShutdown() {
  try (client) { files.flushQuietly(); }
  catch (Exception e) { logger.warn("ext cleanup failed", e); }
}

Defensive patterns

Strategy: try-catch

Validate before calling

// in your Ext: make shutdown idempotent and testable before wiring into boot binding
@Override public void onShutdown() {
    if (closed.getAndSet(true)) return;
    try { doCleanup(); } catch (Exception e) { logger.warn("cleanup failed", e); }
}

Try / catch

try { ext.onShutdown(); }
catch (Exception e) { logger.warn("ext onShutdown failed: {}", e.getMessage()); } // mirror Karate's own best-effort handling in the Ext

Prevention

Write Ext.onShutdown() to be idempotent (guard with a closed flag)
Never let shutdown-time network or remote calls throw out of onShutdown
Only release resources the extension created; don't close shared/global resources
Log the real exception inside the extension instead of relying on e.getMessage() alone

When it happens

Trigger: Suite.run() teardown iterating bootBinding.getExts() where ext.onShutdown() throws — e.g. a custom Ext whose onShutdown closes resources that are already closed, performs network cleanup that fails, or has a bug.

Common situations: Custom plugin/extension closing an HTTP client or DB pool twice; extension trying to flush data to a service that is unreachable at teardown; exceptions inside user-provided shutdown hooks.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/df328b211d08d957. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/Suite.java:613

            }

            // Close JSONL event writer
            if (jsonlWriter != null) {
                try {
                    removeJsonlListener(jsonlWriter);
                    jsonlWriter.close();
                } catch (Exception e) {
                    logger.warn("Failed to close JSONL event stream: {}", e.getMessage());
                }
            }

            // Ext onShutdown — best-effort; exceptions are logged + dropped per K43.
            if (bootBinding != null) {
                for (Ext ext : bootBinding.getExts()) {
                    try {
                        ext.onShutdown();
                    } catch (Exception e) {
                        logger.warn("ext onShutdown failed ({}): {}",
                                ext.getClass().getName(), e.getMessage());
                    }
                    removeJsonlListener(ext);
                }
            }

            // Notify listeners
            for (ResultListener listener : resultListeners) {
                listener.onSuiteEnd(result);
            }
        }

        return result;
    }

    // Thread-safe listener management for JSONL writer
    private final List<RunListener> mutableListeners = new ArrayList<>();

View on GitHub (pinned to a22eb90246)