vfs: make -ve sized files appear as 0 size. #320

This means that Google docs will no longer appear as huge files in
`rclone mount`.  They will not be downloadable, though sometimes
trying twice will work.

docs/content/drive.md

@@ -382,6 +382,14 @@ see User rate limit exceeded errors, wait at least 24 hours and retry.
 You can disable server side copies with `--disable copy` to download
 and upload the files if you prefer.
 
+Google docs will appear as size -1 in `rclone ls` and as size 0 in
+anything which uses the VFS layer, eg `rclone mount`, `rclone serve
+XXX`.  This is because rclone can't find out the size of the Google
+Documents until they are downloaded.  An unfortunate consequence of
+this is that you can't download Google docs using `rclone mount` - you
+will get a 0 sized file.  If you try again the doc may gain its
+correct size and be downloadable.
+
 ### Duplicated files ###
 
 Sometimes, for no reason I've been able to track down, drive will

vfs/file.go

@@ -144,6 +144,14 @@ func (f *File) ModTime() (modTime time.Time) {
 	return f.d.modTime
 }
 
+// nonNegative returns 0 if i is -ve, i otherwise
+func nonNegative(i int64) int64 {
+	if i >= 0 {
+		return i
+	}
+	return 0
+}
+
 // Size of the file
 func (f *File) Size() int64 {
 	f.mu.Lock()
@@ -153,7 +161,7 @@ func (f *File) Size() int64 {
 	if f.o == nil || len(f.writers) != 0 {
 		return atomic.LoadInt64(&f.size)
 	}
-	return f.o.Size()
+	return nonNegative(f.o.Size())
 }
 
 // SetModTime sets the modtime for the file

vfs/read.go

@@ -51,7 +51,7 @@ func newReadFileHandle(f *File, o fs.Object) (*ReadFileHandle, error) {
 		noSeek: f.d.vfs.Opt.NoSeek,
 		file:   f,
 		hash:   mhash,
-		size:   o.Size(),
+		size:   nonNegative(o.Size()),
 	}
 	return fh, nil
 }