cmd/serve: Add a new 'linuxkit serve' command

This simply starts a web server serving the specified directory.
It's useful for PXE booting.

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

src/cmd/linuxkit/main.go

@@ -76,6 +76,7 @@ func main() {
 		fmt.Printf("  pkg         Package building\n")
 		fmt.Printf("  push        Push a VM image to a cloud or image store\n")
 		fmt.Printf("  run         Run a VM image on a local hypervisor or remote cloud\n")
+		fmt.Printf("  serve       Run a local http server (for iPXE booting)\n")
 		fmt.Printf("  version     Print version information\n")
 		fmt.Printf("  help        Print this message\n")
 		fmt.Printf("\n")
@@ -124,6 +125,8 @@ func main() {
 		push(args[1:])
 	case "run":
 		run(args[1:])
+	case "serve":
+		serve(args[1:])
 	case "version":
 		printVersion()
 	case "help":

src/cmd/linuxkit/serve.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func logRequest(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		log.Infof("%s %s", r.Method, r.URL)
+		handler.ServeHTTP(w, r)
+	})
+}
+
+// serve starts a local web server
+func serve(args []string) {
+	flags := flag.NewFlagSet("serve", flag.ExitOnError)
+	invoked := filepath.Base(os.Args[0])
+	flags.Usage = func() {
+		fmt.Printf("USAGE: %s serve [options]\n\n", invoked)
+		fmt.Printf("Options:\n\n")
+		flags.PrintDefaults()
+	}
+	portFlag := flags.String("port", ":8080", "Local port to serve on")
+	dirFlag := flags.String("directory", ".", "Directory to serve")
+
+	http.Handle("/", http.FileServer(http.Dir(*dirFlag)))
+	log.Fatal(http.ListenAndServe(*portFlag, logRequest(http.DefaultServeMux)))
+}