Just take a -port arg instead of a -listen address

This will simplify deployment on some platforms (e.g. heroku)

README.md

@@ -15,12 +15,12 @@ variables:
 ```
 $ go-httpbin -help
 Usage of ./dist/go-httpbin:
-  -listen string
-        Listen address (default ":8080")
   -max-duration duration
         Maximum duration a response may take (default 10s)
   -max-memory int
         Maximum size of request or response, in bytes (default 1048576)
+  -port int
+        Port to listen on (default 8080)
 ```
 
 ## Installation
@@ -37,22 +37,10 @@ go get github.com/mccutchen/go-httpbin/...
 
 ## Development
 
-### Building
-
 ```
 make
-```
-
-### Testing
-
-```
 make test
 make testcover
-```
-
-### Running
-
-```
 make run
 ```
 

cmd/go-httpbin/main.go

@@ -4,6 +4,7 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"net"
 	"net/http"
 	"os"
 	"strconv"
@@ -12,16 +13,16 @@ import (
 	"github.com/mccutchen/go-httpbin/httpbin"
 )
 
-const defaultListenAddr = ":8080"
+const defaultPort = 8080
 
 var (
-	listenAddr  string
+	port        int
 	maxMemory   int64
 	maxDuration time.Duration
 )
 
 func main() {
-	flag.StringVar(&listenAddr, "listen", ":8080", "Listen address")
+	flag.IntVar(&port, "port", defaultPort, "Port to listen on")
 	flag.Int64Var(&maxMemory, "max-memory", httpbin.DefaultMaxMemory, "Maximum size of request or response, in bytes")
 	flag.DurationVar(&maxDuration, "max-duration", httpbin.DefaultMaxDuration, "Maximum duration a response may take")
 	flag.Parse()
@@ -46,14 +47,21 @@ func main() {
 			os.Exit(1)
 		}
 	}
-	if listenAddr == defaultListenAddr && os.Getenv("LISTEN") != "" {
-		listenAddr = os.Getenv("LISTEN")
+	if port == defaultPort && os.Getenv("PORT") != "" {
+		port, err = strconv.Atoi(os.Getenv("PORT"))
+		if err != nil {
+			fmt.Printf("invalid value %#v for env var PORT: %s\n", os.Getenv("PORT"), err)
+			flag.Usage()
+			os.Exit(1)
+		}
 	}
 
 	h := httpbin.NewHTTPBinWithOptions(&httpbin.Options{
 		MaxMemory:   maxMemory,
 		MaxDuration: maxDuration,
 	})
-	log.Printf("listening on %s", listenAddr)
+
+	listenAddr := net.JoinHostPort("0.0.0.0", strconv.Itoa(port))
+	log.Printf("listening on port %s", listenAddr)
 	log.Fatal(http.ListenAndServe(listenAddr, h.Handler()))
 }