eth/backend.go
func (b *backendInstance) HeaderByNumber(ctx context.Context,
	number *big.Int) (*types.Header, error) {
	return b.conn.ethClient().HeaderByNumber(ctx, number)
}
func (b *backendInstance) HeaderByNumber(ctx context.Context,
	number *big.Int) (*types.Header, error) {
	return b.conn.ethClient().HeaderByNumber(ctx, number)
}
// HeaderByNumber returns a Ethereum block header from the current canonical
// chain. If number is nil, the latest known header is returned.