nfsmount: fix exit after external unmount #7503

Before this change, if a user unmounted externally (for example, via the Finder
UI), rclone would not be aware of this and wait forever to exit -- effectively
causing a deadlock that would require Ctrl+C to terminate.

After this change, when the handler detects an external unmount, it calls a
function which allows rclone to cleanly shutdown the VFS and exit.

cmd/nfsmount/nfsmount.go

@@ -81,6 +81,9 @@ func mount(VFS *vfs.VFS, mountpoint string, opt *mountlib.Options) (asyncerrors
 	}
 	asyncerrors = errChan
 	unmount = func() error {
+		if s.UnmountedExternally {
+			return nil
+		}
 		var umountErr error
 		var out []byte
 		if runtime.GOOS == "darwin" {
@@ -98,5 +101,12 @@ func mount(VFS *vfs.VFS, mountpoint string, opt *mountlib.Options) (asyncerrors
 		}
 		return nil
 	}
+
+	nfs.OnUnmountFunc = func() {
+		s.UnmountedExternally = true
+		errChan <- nil
+		VFS.Shutdown()
+	}
+
 	return
 }

cmd/serve/nfs/handler.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"strings"
 
 	"github.com/go-git/go-billy/v5"
 	"github.com/rclone/rclone/fs"
@@ -100,6 +101,16 @@ func (o *Options) Limit() int {
 	return o.HandleLimit
 }
 
+// OnUnmountFunc registers a function to call when externally unmounted
+var OnUnmountFunc func()
+
+func onUnmount() {
+	fs.Infof(nil, "unmount detected")
+	if OnUnmountFunc != nil {
+		OnUnmountFunc()
+	}
+}
+
 // LogIntercepter intercepts noisy go-nfs logs and reroutes them to DEBUG
 type LogIntercepter struct {
 	Level nfs.LogLevel
@@ -114,6 +125,12 @@ func (l *LogIntercepter) Intercept(args ...interface{}) {
 
 // Interceptf intercepts go-nfs logs and calls fs.Debugf instead
 func (l *LogIntercepter) Interceptf(format string, args ...interface{}) {
+	argsS := fmt.Sprint(args...)
+	// bit of a workaround... the real fix is probably https://github.com/willscott/go-nfs/pull/28
+	if strings.Contains(argsS, "mount.Umnt") {
+		onUnmount()
+	}
+
 	fs.Debugf(nil, "[NFS DEBUG] "+format, args...)
 }
 

cmd/serve/nfs/server.go

@@ -16,10 +16,11 @@ import (
 
 // Server contains everything to run the Server
 type Server struct {
-	opt      Options
+	opt                 Options
-	handler  nfs.Handler
+	handler             nfs.Handler
-	ctx      context.Context // for global config
+	ctx                 context.Context // for global config
-	listener net.Listener
+	listener            net.Listener
+	UnmountedExternally bool
 }
 
 // NewServer creates a new server