bring in khatru and eventstore.

khatru/docs/cookbook/dynamic.md

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+---
+outline: deep
+---
+
+# Generating `khatru` relays dynamically and serving them from the same path
+
+Suppose you want to expose a different relay interface depending on the subdomain that is accessed. I don't know, maybe you want to serve just events with pictures on `pictures.example.com` and just events with audio files on `audios.example.com`; maybe you want just events in English on `en.example.com` and just examples in Portuguese on `pt.example.com`, there are many possibilities.
+
+You could achieve that with a scheme like the following
+
+```go
+var topLevelHost = "example.com"
+var mainRelay = khatru.NewRelay() // we're omitting all the configuration steps for brevity
+var subRelays = xsync.NewMapOf[string, *khatru.Relay]()
+
+func main () {
+	handler := http.HandlerFunc(dynamicRelayHandler)
+
+	log.Printf("listening at http://0.0.0.0:8080")
+	http.ListenAndServe("0.0.0.0:8080", handler)
+}
+
+func dynamicRelayHandler(w http.ResponseWriter, r *http.Request) {
+	var relay *khatru.Relay
+	subdomain := r.Host[0 : len(topLevelHost)-len(topLevelHost)]
+	if subdomain == "" {
+		// no subdomain, use the main top-level relay
+		relay = mainRelay
+	} else {
+		// call on subdomain, so get a dynamic relay
+		subdomain = subdomain[0 : len(subdomain)-1] // remove dangling "."
+		// get a dynamic relay
+		relay, _ = subRelays.LoadOrCompute(subdomain, func () *khatru.Relay {
+			return makeNewRelay(subdomain)
+		})
+	}
+
+	relay.ServeHTTP(w, r)
+}
+
+func makeNewRelay (subdomain string) *khatru.Relay {
+	// somehow use the subdomain to generate a relay with specific configurations
+	relay := khatru.NewRelay()
+	switch subdomain {
+	case "pictures":
+		// relay configuration shenanigans go here
+	case "audios":
+		// relay configuration shenanigans go here
+	case "en":
+		// relay configuration shenanigans go here
+	case "pt":
+		// relay configuration shenanigans go here
+	}
+	return relay
+}
+```
+
+In practice you could come up with a way that allows all these dynamic relays to share a common underlying datastore, but this is out of the scope of this example.