feat: add HTTP_ADDR env var

Allow changing the bind address

README.md

@@ -22,7 +22,8 @@ Inside the provided nix shell run:
 
 This will create a small local server with live reload that emulates now.sh.
 
-Currently, the default port is 8383. You can change it by setting the `PORT` environment variable.
+Currently, the default port is 8383. You can change it by setting the `PORT`
+environment variable, or `HTTP_ADDR` to also change the bind address.
 
 ## Usage
 
@@ -45,6 +46,7 @@ You can use the following environment variables to configure nar-serve:
 | Name | Default value | Description |
 |:--   |:--            |:-- |
 | `PORT` | `8383` | Port number on which nar-service listens |
+| `HTTP_ADDR` | `:$PORT` | HTTP address to bind the server to. When set, takes precedence over $PORT. |
 | `NAR_CACHE_URL` | `https://cache.nixos.org` | The URL of the Nix store from which NARs are fetched |
 
 ## Contributing

main.go

@@ -31,17 +31,21 @@ func healthzHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func main() {
+	var (
+		port = getEnv("PORT", "8383")
+		addr = getEnv("HTTP_ADDR", "")
+	)
+
+	if addr == "" {
+		addr = ":" + port
+	}
+
 	mux := http.NewServeMux()
 	mux.HandleFunc("/", indexHandler)
 	mux.HandleFunc("/healthz", healthzHandler)
 	mux.HandleFunc("/robots.txt", robotsHandler)
 	mux.HandleFunc(unpack.MountPath, unpack.Handler)
 
-	addr := ":8383"
-	if port := os.Getenv("PORT"); port != "" {
-		addr = ":" + port
-	}
-
 	// Includes some default middlewares
 	// Serve static files from ./public
 	n := negroni.New(
@@ -51,3 +55,12 @@ func main() {
 	n.UseHandler(mux)
 	n.Run(addr)
 }
+
+func getEnv(name, def string) string {
+	value := os.Getenv(name)
+	if value == "" {
+		return def
+	}
+	return value
+}
+