feature/appconnectors: start making it modular

Saves 45 KB.

Updates #12614

Change-Id: Iaeb73e69633878ce0a0f58c986024784bbe218f1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/appconnectors/appconnectors.go

@@ -0,0 +1,39 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package appconnectors registers support for Tailscale App Connectors.
+package appconnectors
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"tailscale.com/ipn/ipnlocal"
+	"tailscale.com/tailcfg"
+)
+
+func init() {
+	ipnlocal.RegisterC2N("GET /appconnector/routes", handleC2NAppConnectorDomainRoutesGet)
+}
+
+// handleC2NAppConnectorDomainRoutesGet handles returning the domains
+// that the app connector is responsible for, as well as the resolved
+// IP addresses for each domain. If the node is not configured as
+// an app connector, an empty map is returned.
+func handleC2NAppConnectorDomainRoutesGet(b *ipnlocal.LocalBackend, w http.ResponseWriter, r *http.Request) {
+	logf := b.Logger()
+	logf("c2n: GET /appconnector/routes received")
+
+	var res tailcfg.C2NAppConnectorDomainRoutesResponse
+	appConnector := b.AppConnector()
+	if appConnector == nil {
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(res)
+		return
+	}
+
+	res.Domains = appConnector.DomainRoutes()
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(res)
+}