vfs: fix renaming/deleting open files with cache mode "writes" under Windows

Before this change, renaming and deleting of open files (which can
easily happen due to the asynchronous nature of file systems) would
produce an error, for example saving files with Firefox.

After this change we open files with the flags necessary for open
files to be renamed or deleted.

Fixes #2730

vfs/make_open_tests.go

@@ -15,6 +15,8 @@ import (
 	"log"
 	"os"
 	"strings"
+
+	"github.com/ncw/rclone/lib/file"
 )
 
 // Interprets err into a vfs error
@@ -45,7 +47,7 @@ func test(fileName string, flags int, mode string) {
 	if !os.IsNotExist(err) {
 		log.Fatalf("File must not exist")
 	}
-	f, openNonExistentErr := os.OpenFile(fileName, flags, 0666)
+	f, openNonExistentErr := file.OpenFile(fileName, flags, 0666)
 
 	var readNonExistentErr error
 	var writeNonExistentErr error
@@ -65,7 +67,7 @@ func test(fileName string, flags int, mode string) {
 	}
 
 	// write the file
-	f, err = os.Create(fileName)
+	f, err = file.Create(fileName)
 	if err != nil {
 		log.Fatalf("failed to create: %v", err)
 	}
@@ -81,7 +83,7 @@ func test(fileName string, flags int, mode string) {
 
 	// then open file and try with file existing
 
-	f, openExistingErr := os.OpenFile(fileName, flags, 0666)
+	f, openExistingErr := file.OpenFile(fileName, flags, 0666)
 	var readExistingErr error
 	var writeExistingErr error
 	if openExistingErr == nil {
@@ -100,7 +102,7 @@ func test(fileName string, flags int, mode string) {
 	}
 
 	// read the file
-	f, err = os.Open(fileName)
+	f, err = file.Open(fileName)
 	if err != nil {
 		log.Fatalf("failed to open: %v", err)
 	}

vfs/read_write.go

@@ -12,6 +12,7 @@ import (
 	"github.com/ncw/rclone/fs/accounting"
 	"github.com/ncw/rclone/fs/log"
 	"github.com/ncw/rclone/fs/operations"
+	"github.com/ncw/rclone/lib/file"
 	"github.com/pkg/errors"
 )
 
@@ -124,7 +125,7 @@ func (fh *RWFileHandle) openPending(truncate bool) (err error) {
 		}
 
 		// try to open a exising cache file
-		fd, err = os.OpenFile(fh.osPath, cacheFileOpenFlags&^os.O_CREATE, 0600)
+		fd, err = file.OpenFile(fh.osPath, cacheFileOpenFlags&^os.O_CREATE, 0600)
 		if os.IsNotExist(err) {
 			// cache file does not exist, so need to fetch it if we have an object to fetch
 			// it from
@@ -185,7 +186,7 @@ func (fh *RWFileHandle) openPending(truncate bool) (err error) {
 
 	if fd == nil {
 		fs.Debugf(fh.logPrefix(), "Opening cached copy with flags=%s", decodeOpenFlags(fh.flags))
-		fd, err = os.OpenFile(fh.osPath, cacheFileOpenFlags, 0600)
+		fd, err = file.OpenFile(fh.osPath, cacheFileOpenFlags, 0600)
 		if err != nil {
 			return errors.Wrap(err, "cache open file failed")
 		}

vfs/test_vfs/test_vfs.go

@@ -16,6 +16,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"github.com/ncw/rclone/lib/file"
 )
 
 var (
@@ -194,7 +196,7 @@ func (t *Test) close() {
 func (t *Test) open() {
 	t.close()
 	t.logf("open")
-	handle, err := os.OpenFile(t.path(), os.O_RDWR|os.O_CREATE, 0666)
+	handle, err := file.OpenFile(t.path(), os.O_RDWR|os.O_CREATE, 0666)
 	if err != nil {
 		t.errorf("failed to open: %v", err)
 		return