Custom options in middleware

[sebcomeau]

Is it possible to pass custom options (such as metadata) to the openapi-fetch middleware? I need to collect HTTP status metrics for each fetch call, and for that, every defined method should be able to pass a custom option like meta.metricPrefix. My instrumentation middleware should then be able to access this meta option in order to record the status code using our OpenTelemetry backend.

Here’s an example of how the client and middleware would look:

// Example client call
const { data } = await client.GET('/users', {
  meta: {
    metricPrefix: 'http.client.api.users',
  },
});

// Instrumentation middleware
export function instrumentationMiddleware(): Middleware {
  const instrumentationService = new InstrumentationService();
  return {
    onResponse: ({ options, response }) => {
      if (typeof options.meta?.metricPrefix !== 'string') return; // skip if not set
      instrumentationService.countHttpStatus(options.meta.metricPrefix, response.status);
    }
  };
}