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Write a middleware that runs before (or after) the processor, and register it in the Message Dispatcher. A middleware uses the same gRPC contract and the same @routr/processor library as a processor. The difference is its job: a processor computes the route, while a middleware makes a small change or causes a side effect, then passes the message along. Typical uses are authentication, logging, tracing, request normalization, and driving RTPEngine. Routr ships two: SimpleAuth (pre-processor) and RTPRelay (post-processor).

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Prerequisites

  • Node.js and npm.
  • A running Routr deployment that uses the Message Dispatcher. Middlewares only run through the Dispatcher; EdgePort never calls them directly.

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How the Dispatcher calls middlewares

For each request, the Dispatcher:
  1. Runs every middleware with postProcessor: false, in the order listed.
  2. Sends the result to the matching processor.
  3. Runs every middleware with postProcessor: true, in the order listed, on the processor’s output.
Each middleware receives the output of the previous one. The Dispatcher keeps only the message field of a middleware’s reply. If a middleware returns a SIP response (for example 401 Unauthorized), the Dispatcher skips the remaining middlewares in that phase and carries the response forward. Use postProcessor: true when your middleware needs data the processor adds, such as the final Route headers or the SDP that the callee sends. RTPRelay runs post-processor for this reason.

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Write the middleware

1

Install the library

Create a project and install @routr/processor:
2

Implement the handler

Create index.js. This middleware tags every INVITE with an X-Tenant header and passes all other messages through untouched. The default middleware port in Routr is 51903:
index.js
Always call res.send(req) for messages you don’t change. To reject a request, return a SIP response instead. SimpleAuth does this with CommonResponse.createUnauthorizedResponse() from @routr/common when the digest check fails.
3

Run it

Start the middleware:
4

Register it in the Dispatcher

Add the middleware under spec.middlewares in dispatcher.yaml:
dispatcher.yaml
Set postProcessor explicitly to true or false. The Dispatcher compares it strictly, so a middleware with no postProcessor value never runs.
On Kubernetes, add the entry under dispatcher.middlewares in the Helm values (ref, serviceName, postProcessor); the chart points it at port 51903.

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Verify

Restart the Dispatcher and place a call. Capture the INVITE that leaves Routr (for example with sngrep) and confirm it carries X-Tenant: acme.

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Pitfalls

  • An unreachable middleware fails the request. If the Dispatcher can’t reach a middleware, it returns an error instead of skipping it.
  • Keep it fast and stateless. Every listed middleware runs on every request.
  • Filter early. Check the method or message type first and pass everything else through, as SimpleAuth does with its METHODS list.

Build a processor

The full processor walkthrough and the Response API.

Alterations API

Helpers for editing SIP messages.

Message Dispatcher

Dispatcher configuration reference.

Message flow

Where middlewares sit in a request’s path.