Express

If you have an existing Express application, Katman can be mounted as middleware alongside your REST routes.

Setup

import express from "express"
import { katmanExpress } from "katman/express"

const app = express()
app.use(express.json()) // Required for POST body parsing

// Existing routes
app.get("/api/health", (req, res) => res.json({ status: "ok" }))

// Katman RPC under /rpc
app.use("/rpc", katmanExpress(appRouter, {
  context: (req) => ({
    db: getDB(),
    user: req.user,
    ip: req.ip,
  }),
}))

app.listen(3000)

Context from Express

The context function receives the Express request object. Bridge your existing auth middleware, IP detection, and headers:

katmanExpress(appRouter, {
  context: (req) => ({
    user: req.user,           // from passport or similar
    ip: req.ip,
    headers: req.headers,
  }),
})

Route behavior

• Procedures are matched by the path after the mount prefix
• POST /rpc/users/list → calls users.list with the JSON body as input
• GET /rpc/users/list?data={"limit":10} → calls users.list with parsed query data
• Unmatched paths pass through to the next Express middleware (next())

What's next?

• Fastify — Fastify plugin adapter
• Server — standalone serve() as an alternative
• Integrations — other available integrations