Allow customization of the message sent in recordRpc (express-middleware)

Hello! At the moment, message sent in recordRpc is a combination of req.method and req.route.path as can be seen here: https://github.com/openzipkin/zipkin-js/blob/aeb5d09beaa3b3dd634200625f236c76ea4630d0/packages/zipkin-instrumentation-express/src/expressMiddleware.js#L58

It would be a great improvement to allow the customization of this message. Maybe through a method passed as an argument of expressMiddleware function (like tracer, servicename and port). This method could accept req object as argument to have access to properties like req.originalUrl or req.baseUrl With this improvement examples like this could be achieved.

const customMessage = function customMessage(req) {
     return 'Custom message: '.concat(serviceName, ' ').concat(req.method, ' ')
     .concat(req.baseUrl).concat(req.route.path);
};
// Add zipkin middleware
app.use(zipkinMiddleware({ tracer, serviceName, customMessage }));

Thanks in advance.

[DavidGarNav]

Thanks for your responses @jcchavezs and @ghermeto. I will try to explain the need to customize the Rpc.

Our API framework does not allow us to include the whole endpoint inside req.route.path in consequence we are not able to distinguise two endpoints from two different services in Zipkin.

Lets say:

• Service 1:

  • method = post
  • originaUrl = api/servcie1/get
  • req.baseUrl = api/service1
  • req.route.path = /add

• Service 2:

  • method = post
  • originaUrl = api/servcie2/get
  • req.baseUrl = api/service2
  • req.route.path = /add

With the actual behaviour of express-middleware recordRpc method will send the same message for both services (post /add). If we want to apply metrics based on this field both services will be considered the same, which is a mistake. Unfortunately recode our routing system to avoid this problem is not possible, that’s why we request this change.

I can’t see how the spanCustomizer could help to solve this problem becuse if recordRpc method is not replaced, the same message will be sent anyway.

A possible implementation of the change that we request could be: Add customMessage argument to https://github.com/openzipkin/zipkin-js/blob/aeb5d09beaa3b3dd634200625f236c76ea4630d0/packages/zipkin-instrumentation-express/src/expressMiddleware.js#L30

Result:

module.exports = function expressMiddleware({tracer, serviceName, port = 0, customMessage = null}) {

Replace code inside if statement at https://github.com/openzipkin/zipkin-js/blob/aeb5d09beaa3b3dd634200625f236c76ea4630d0/packages/zipkin-instrumentation-express/src/expressMiddleware.js#L57-L59

Result:

if (req.route) {
    if (customMessage) {
        tracer.recordRpc(customMessage(req));
    } else {
        tracer.recordRpc(`${req.method} ${req.route.path}`);
    }
}

I hope that this explanation helps to understand our request.

Thank you

[jcchavezs]

Awesome @DavidGarNav!