You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: differ.go
    path of file: ./repos/grype/grype/differ
    
    the code of the file until where you have to start completion: package differ

import (
	"encoding/json"
	"fmt"
	"io"
	"net/url"
	"path"

	"github.com/olekukonko/tablewriter"
	"github.com/wagoodman/go-partybus"
	"github.com/wagoodman/go-progress"

	"github.com/anchore/grype/grype/db"
	v5 "github.com/anchore/grype/grype/db/v5"
	"github.com/anchore/grype/grype/event"
	"github.com/anchore/grype/internal/bus"
)

type Differ struct {
	baseCurator   db.Curator
	targetCurator db.Curator
}

func NewDiffer(confi
    
func (d *Differ) setOrDownload(curator *db.Curator, filenameOrURL string) error {
	u, err := url.ParseRequestURI(filenameOrURL)

	if err != nil || u.Scheme == "" {
		*curator, err = db.NewCurator(db.Config{
			DBRootDir: filenameOrURL,
		})
		if err != nil {
			return err
		}
	} else {
		listings, err := d.baseCurator.ListingFromURL()
		if err != nil {
			return err
		}

		available := listings.Available
		dbs := available[v5.SchemaVersion]

		var listing *db.ListingEntry

		for _, d := range dbs {
			database := d
			if *d.URL == *u {
				listing = &database
			}
		}

		if listing == nil {
			return fmt.Errorf("unable to find listing for url: %s", filenameOrURL)
		}

		if err := download(curator, listing); err != nil {
			return fmt.Errorf("unable to download vulnerability database: %+v", err)
		}
	}

	return nil
}