virtualfile.read can lead to infinite loops

[ghost]

I had an issue while using Packr with Gomigrate. The issue being that file content was being output twice which is a combination of how Gomigrate reads files and that virtaulfile(s) reset their internal cursror/file position to 0 after a complete read. The correct behaviour here is return 0 bytes and EOF when a file has been completely read.

The issue is better explained in the link below but can be recreated exactly in Packr.

GeertJohan/go.rice#108

Code (largely copied from the above link)

`var DefaultBufferSize = uint(1000000)

func main() {
box := packr.Folder("./embedded-migrate/migrations")

f, err := box.Open("1_tabOne_up.sql")
if err != nil {
	panic(err)
}
defer f.Close()

b := bufio.NewReaderSize(f, int(DefaultBufferSize))
b.Peek(int(DefaultBufferSize))

bs, err := ioutil.ReadAll(b)
if err != nil {
	panic(err)
}
log.Printf("%s", bs)

}`

Which outputs the file content twice.