Apply Gilles' suggestions

util/netutil/file_server.go

@@ -4,13 +4,35 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"os"
 	"time"
 
+	"github.com/eluv-io/common-go/util/testutil"
+	"github.com/eluv-io/errors-go"
 	"github.com/eluv-io/log-go"
 )
 
-// NewFileServer creates a lightweight file server.
-func NewFileServer(fsRoot string, port int) *FileServer {
+// NewFileServer creates a lightweight file server, which is a very thin wrapper around go's
+// `http.FileServer`. If port is zero, a free port is used.
+//
+// This implementation is probably not safe for production use, but good for testing.
+func NewFileServer(fsRoot string, port int) (*FileServer, error) {
+	stat, err := os.Stat(fsRoot)
+	if err != nil {
+		return nil, errors.E("NewFileServer", errors.K.IO, err)
+	}
+	if !stat.IsDir() {
+		return nil, errors.E("NewFileServer", errors.K.Invalid,
+			"reason", "fs_root is not a directory",
+			"fs_root", fsRoot)
+	}
+	if port == 0 {
+		port, err = testutil.FreePort()
+		if err != nil {
+			return nil, errors.E("NewFileServer", errors.K.IO, err)
+		}
+	}
+
 	h := http.FileServer(http.Dir(fsRoot))
 	s := &http.Server{
 		Addr:    fmt.Sprintf(":%d", port),
@@ -22,7 +44,11 @@ func NewFileServer(fsRoot string, port int) *FileServer {
 		root: fsRoot,
 		s:    s,
 		log:  log.Get("/eluvio/file_server"),
-	}
+	}, nil
+}
+
+func (fs *FileServer) Port() int {
+	return fs.port
 }
 
 type FileServer struct {
@@ -37,13 +63,20 @@ func (fs *FileServer) SetLog(l *log.Log) {
 	fs.log = l
 }
 
+func (fs *FileServer) doLog(msg string, args ...interface{}) {
+	if fs.log == nil {
+		return
+	}
+	fs.log.Info(msg, args...)
+}
+
 func (fs *FileServer) Start() {
-	fs.log.Info("starting file server", "root", fs.root, "port", fs.port)
-	go func() { fs.log.Info("http server shutdown", fs.s.ListenAndServe()) }()
+	fs.doLog("starting file server", "root", fs.root, "port", fs.port)
+	go func() { fs.doLog("file server shutdown", fs.s.ListenAndServe()) }()
 }
 
 func (fs *FileServer) Stop() error {
-	fs.log.Info("shutting down file server", "root", fs.root, "port", fs.port)
+	fs.doLog("shutting down file server", "root", fs.root, "port", fs.port)
 	c, cancel := context.WithTimeout(context.Background(), time.Second*5)
 	defer cancel()
 	return fs.s.Shutdown(c)