allow hosting on alternate port.

cmd/smweb/main.go

@@ -1,8 +1,10 @@
 package main
 
 import (
+	"fmt"
 	"net/http"
 	"os"
+	"strconv"
 
 	"github.com/elazarl/go-bindata-assetfs"
 	"mcquay.me/web"
@@ -20,13 +22,23 @@ func main() {
 	} else {
 		fs = http.Dir(os.Getenv("SM_STATIC"))
 	}
+	port := 8000
+	if os.Getenv("PORT") != "" {
+		p, err := strconv.Atoi(os.Getenv("PORT"))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "couldn't parse port: %v\n", err)
+			os.Exit(1)
+		}
+		port = p
+	}
 	// XXX: beware: I've copy/pasted this twice now and been confused because
 	// I ought to have been using my own servemux
 	http.Handle(
 		"/",
 		http.FileServer(fs),
 	)
-	if err := http.ListenAndServe(":8000", nil); err != nil {
+	if err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil); err != nil {
-		panic(err)
+		fmt.Fprintf(os.Stderr, "problem serving: %v\n", err)
+		os.Exit(1)
 	}
 }