ReadAt does not have io.ReaderAt behavior

[ashishgandhi]

According to the io.ReaderAt documentation (https://golang.org/pkg/io/#ReaderAt). For the signature

ReadAt(p []byte, off int64) (n int, err error)

“ReadAt reads len(p) bytes into p starting at offset off in the underlying input source. It returns the number of bytes read (0 <= n <= len(p)) and any error encountered.

When ReadAt returns n < len(p), it returns a non-nil error explaining why more bytes were not returned. In this respect, ReadAt is stricter than Read.”

If you simply try playing with a file you'd quickly observe that this is not followed. Taking a real world example I have a file of size 280689401. I pass in p of length 227743. But only 214 bytes are read. And the err is nil.