example.go

// Example usage:
// Triggers an io.ErrUnexpectedEOF on the last read
func TestCanDiffWhenOldlistIsCorrupted(t *testing.T) {
	log.SetOutput(testwriter(t)) // log to testing.Log

	oldKeys := []s3.Key{{ETag: "1"}, {ETag: "3"}}
	newKeys := []s3.Key{{ETag: "1"}, {ETag: "2"}, {ETag: "3"}}
	want := []s3.Key{{ETag: "2"}}

	oldList := encodeKeys(oldKeys)
	newList := encodeKeys(newKeys)

	errOldList := lastErrReader(oldList, io.ErrUnexpectedEOF)

	testDiffReaders(t, errOldList, newList, want)
}

last_read_error.go

// io.Reader implementer
type reader func(p []byte) (int, error)

func (r reader) Read(p []byte) (int, error) { return r(p) }

func lastErrReader(r io.Reader, lastReadErr error) io.Reader {
	return reader(func(p []byte) (int, error) {
		n, err := r.Read(p)
		if err == io.EOF {
			return n, lastReadErr
		}
		return n, err
	})
}