Make sure the mount point exists before trying to mount.

Otherwise we get confusing EOF errors when we later call out to osxfuse.

mount.go

+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fuse
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/net/context"
+)
+
+// A type that knows how to serve ops read from a connection.
+type Server interface {
+	// Read and serve ops from the supplied connection until EOF. Do not return
+	// until all operations have been responded to. Must not be called more than
+	// once.
+	ServeOps(*Connection)
+}
+
+// Attempt to mount a file system on the given directory, using the supplied
+// Server to serve connection requests. This function blocks until the file
+// system is successfully mounted.
+func Mount(
+	dir string,
+	server Server,
+	config *MountConfig) (mfs *MountedFileSystem, err error) {
+	// Sanity check: make sure the mount point exists and is a directory. This
+	// saves us from some confusing errors later on OS X.
+	fi, err := os.Stat(dir)
+	switch {
+	case os.IsNotExist(err):
+		return
+
+	case err != nil:
+		err = fmt.Errorf("Statting mount point: %v", err)
+		return
+
+	case !fi.IsDir():
+		err = fmt.Errorf("Mount point %s is not a directory", dir)
+		return
+	}
+
+	// Initialize the struct.
+	mfs = &MountedFileSystem{
+		dir:                 dir,
+		joinStatusAvailable: make(chan struct{}),
+	}
+
+	// Begin the mounting process, which will continue in the background.
+	ready := make(chan error, 1)
+	dev, err := mount(dir, config, ready)
+	if err != nil {
+		err = fmt.Errorf("mount: %v", err)
+		return
+	}
+
+	// Choose a parent context for ops.
+	opContext := config.OpContext
+	if opContext == nil {
+		opContext = context.Background()
+	}
+
+	// Create a Connection object wrapping the device.
+	connection, err := newConnection(
+		opContext,
+		config.DebugLogger,
+		config.ErrorLogger,
+		dev)
+
+	if err != nil {
+		err = fmt.Errorf("newConnection: %v", err)
+		return
+	}
+
+	// Serve the connection in the background. When done, set the join status.
+	go func() {
+		server.ServeOps(connection)
+		mfs.joinStatus = connection.close()
+		close(mfs.joinStatusAvailable)
+	}()
+
+	// Wait for the mount process to complete.
+	if err = <-ready; err != nil {
+		err = fmt.Errorf("mount (background): %v", err)
+		return
+	}
+
+	return
+}

mounted_file_system.go

@@ -14,19 +14,7 @@
 
 package fuse
 
-import (
-	"fmt"
-
-	"golang.org/x/net/context"
-)
-
-// A type that knows how to serve ops read from a connection.
-type Server interface {
-	// Read and serve ops from the supplied connection until EOF. Do not return
-	// until all operations have been responded to. Must not be called more than
-	// once.
-	ServeOps(*Connection)
-}
+import "golang.org/x/net/context"
 
 // A struct representing the status of a mount operation, with a method that
 // waits for unmounting.
@@ -58,58 +46,3 @@ func (mfs *MountedFileSystem) Join(ctx context.Context) error {
 		return ctx.Err()
 	}
 }
-
-// Attempt to mount a file system on the given directory, using the supplied
-// Server to serve connection requests. This function blocks until the file
-// system is successfully mounted.
-func Mount(
-	dir string,
-	server Server,
-	config *MountConfig) (mfs *MountedFileSystem, err error) {
-	// Initialize the struct.
-	mfs = &MountedFileSystem{
-		dir:                 dir,
-		joinStatusAvailable: make(chan struct{}),
-	}
-
-	// Begin the mounting process, which will continue in the background.
-	ready := make(chan error, 1)
-	dev, err := mount(dir, config, ready)
-	if err != nil {
-		err = fmt.Errorf("mount: %v", err)
-		return
-	}
-
-	// Choose a parent context for ops.
-	opContext := config.OpContext
-	if opContext == nil {
-		opContext = context.Background()
-	}
-
-	// Create a Connection object wrapping the device.
-	connection, err := newConnection(
-		opContext,
-		config.DebugLogger,
-		config.ErrorLogger,
-		dev)
-
-	if err != nil {
-		err = fmt.Errorf("newConnection: %v", err)
-		return
-	}
-
-	// Serve the connection in the background. When done, set the join status.
-	go func() {
-		server.ServeOps(connection)
-		mfs.joinStatus = connection.close()
-		close(mfs.joinStatusAvailable)
-	}()
-
-	// Wait for the mount process to complete.
-	if err = <-ready; err != nil {
-		err = fmt.Errorf("mount (background): %v", err)
-		return
-	}
-
-	return
-}