Add stub client-api-load-balancer binary

src/github.com/matrix-org/dendrite/cmd/client-api-load-balancer/main.go

@@ -0,0 +1,58 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+const usage = `Usage: %s
+
+Create a single endpoint URL which clients can be pointed at.
+
+The client-server API in Dendrite is split across multiple processes
+which listen on multiple ports. You cannot point a Matrix client at
+any of those ports, as there will be unimplemented functionality.
+In addition, all client-server API processes start with the additional
+path prefix '/api', which Matrix clients will be unaware of.
+
+This tool will proxy requests for all client-server URLs and forward
+them to their respective process. It will also add the '/api' path
+prefix to incoming requests.
+
+Arguments:
+
+`
+
+var (
+	syncServerURL = flag.String("sync-server-url", "", "The base URL of the listening 'dendrite-sync-server' process. E.g. 'http://localhost:4200'")
+	clientAPIURL  = flag.String("client-api-url", "", "The base URL of the listening 'dendrite-client-api' process. E.g. 'http://localhost:4321'")
+	bindAddress   = flag.String("bind-address", ":8008", "The listening port for the proxy.")
+)
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, usage, os.Args[0])
+		flag.PrintDefaults()
+	}
+
+	flag.Parse()
+
+	if *syncServerURL == "" {
+		flag.Usage()
+		fmt.Fprintln(os.Stderr, "no --sync-server-url specified.")
+		os.Exit(1)
+	}
+
+	if *clientAPIURL == "" {
+		flag.Usage()
+		fmt.Fprintln(os.Stderr, "no --client-api-url specified.")
+		os.Exit(1)
+	}
+
+	fmt.Println("Proxying requests to:")
+	fmt.Println("  /_matrix/client/r0/sync  => ", *syncServerURL+"/api/_matrix/client/r0/sync")
+	fmt.Println("  /*                       => ", *clientAPIURL+"/api/*")
+	fmt.Println("Listening on %s", *bindAddress)
+
+}