Configuration

DahoConfig controls the server's behavior. Pass it when creating the Daho instance:

final app = Daho(
  config: const DahoConfig(
    bodyLimit: 8 * 1024 * 1024,
    concurrency: 4,
    trustProxy: true,
  ),
);

Options Reference

Option	Type	Default	Description
bodyLimit	int	4 MB	Max request body in bytes. Oversized requests get 413 before the body is read.
concurrency	int?	CPU cores	Worker Isolate count. Clamped to [1, 64].
requestTimeout	Duration	Duration.zero	Per-request timeout. Zero keeps H2O's default.
idleTimeout	Duration	Duration.zero	Keep-alive idle timeout. Zero keeps H2O's default.
shutdownGracePeriod	Duration	5 seconds	Drain time after SIGINT/SIGTERM.
errorHandler	ErrorHandler	defaultErrorHandler	Called when a handler/middleware throws.
notFoundHandler	NotFoundHandler	defaultNotFoundHandler	Called when no route matches.
trustProxy	bool	false	Use X-Forwarded-For / X-Real-IP for req.ip.
disableStartupMessage	bool	false	Silence startup/shutdown log lines.

Body Limit

Controls the maximum request body size. Enforced by H2O before the body is read, so oversized requests are rejected early with 413 Payload Too Large.

// 8 MB body limit (for file uploads)
config: const DahoConfig(bodyLimit: 8 * 1024 * 1024)

Concurrency

By default, Daho spawns one worker per CPU core. In containers with CPU quotas, Platform.numberOfProcessors may report the host's core count rather than the cgroup limit — set concurrency explicitly:

// 4 workers regardless of host core count
config: const DahoConfig(concurrency: 4)

Trust Proxy

When running behind a reverse proxy (nginx, Cloudflare, AWS ALB), enable trustProxy so req.ip reflects the real client IP from X-Forwarded-For or X-Real-IP:

config: const DahoConfig(trustProxy: true)

WARNING

Only enable trustProxy behind a trusted reverse proxy. Without a proxy, clients can spoof their IP via these headers.

Custom Error Handler

Define a custom error handler to control what clients see when a handler throws:

void myErrorHandler(
  DahoRequest req,
  DahoResponse res,
  Object error,
  StackTrace stackTrace,
) {
  // Log the error server-side
  stderr.writeln('[ERROR] ${req.method} ${req.path}: $error');

  // Return a safe response to the client
  res.status(500).json({'error': 'Internal Server Error'});
}

final app = Daho(
  config: DahoConfig(errorHandler: myErrorHandler),
);

INFO

Error and not-found handlers must be top-level or static functions — not closures. The config is sent across Isolate boundaries, and Dart cannot transfer closures.

Custom Not-Found Handler

void myNotFoundHandler(DahoRequest req, DahoResponse res) {
  res.status(404).json({
    'error': 'Not Found',
    'path': req.path,
  });
}

final app = Daho(
  config: DahoConfig(notFoundHandler: myNotFoundHandler),
);

Shutdown Grace Period

When the server receives SIGINT or SIGTERM, it waits this duration for in-flight requests to finish before exiting:

config: const DahoConfig(shutdownGracePeriod: Duration(seconds: 10))

You can also run cleanup logic via the onShutdown callback:

app.listen(
  8080,
  routes: setupRoutes,
  onShutdown: () async {
    print('Cleaning up...');
    // Close database connections, flush buffers, etc.
  },
);