refactor(geoip): cache tarballs as <edition>_LATEST.tar.gz

Adds geoip.TarGzName(edition) as the single source of truth for the
cache filename. The _LATEST suffix signals that the file is whatever
MaxMind served most recently (versus the dated Content-Disposition
name) and keeps httpcache's ETag sidecar tied to a stable path across
releases.

cmd/check-ip/main.go

@@ -155,13 +155,13 @@ func main() {
 	geoSet := dataset.NewSet(
 		&httpcache.Cacher{
 			URL:    geoip.DownloadBase + "/GeoLite2-City/download?suffix=tar.gz",
-			Path:   filepath.Join(maxmindDir, "GeoLite2-City.tar.gz"),
+			Path:   filepath.Join(maxmindDir, geoip.TarGzName(geoip.CityEdition)),
 			MaxAge: 3 * 24 * time.Hour,
 			Header: authHeader,
 		},
 		&httpcache.Cacher{
 			URL:    geoip.DownloadBase + "/GeoLite2-ASN/download?suffix=tar.gz",
-			Path:   filepath.Join(maxmindDir, "GeoLite2-ASN.tar.gz"),
+			Path:   filepath.Join(maxmindDir, geoip.TarGzName(geoip.ASNEdition)),
 			MaxAge: 3 * 24 * time.Hour,
 			Header: authHeader,
 		},

net/geoip/cmd/geoip-update/main.go

@@ -51,7 +51,7 @@ func main() {
 
 	exitCode := 0
 	for _, edition := range cfg.EditionIDs {
-		path := filepath.Join(outDir, edition+".tar.gz")
+		path := filepath.Join(outDir, geoip.TarGzName(edition))
 		cacher := &httpcache.Cacher{
 			URL:    geoip.DownloadBase + "/" + edition + "/download?suffix=tar.gz",
 			Path:   path,

net/geoip/databases.go

@@ -20,15 +20,15 @@ type Databases struct {
 	ASN  *geoip2.Reader
 }
 
-// Open reads <dir>/GeoLite2-City.tar.gz and <dir>/GeoLite2-ASN.tar.gz,
+// Open reads <dir>/<edition>_LATEST.tar.gz for City and ASN editions,
 // extracts the .mmdb entry from each archive in memory, and returns open
 // readers. No .mmdb files are written to disk.
 func Open(dir string) (*Databases, error) {
-	city, err := openMMDBTarGz(filepath.Join(dir, "GeoLite2-City.tar.gz"))
+	city, err := openMMDBTarGz(filepath.Join(dir, TarGzName(CityEdition)))
 	if err != nil {
 		return nil, fmt.Errorf("city: %w", err)
 	}
-	asn, err := openMMDBTarGz(filepath.Join(dir, "GeoLite2-ASN.tar.gz"))
+	asn, err := openMMDBTarGz(filepath.Join(dir, TarGzName(ASNEdition)))
 	if err != nil {
 		_ = city.Close()
 		return nil, fmt.Errorf("asn: %w", err)

net/geoip/geoip.go

@@ -15,6 +15,14 @@ const (
 	DownloadBase = "https://download.maxmind.com/geoip/databases"
 )
 
+// TarGzName returns the cache filename for edition's tar.gz archive.
+// MaxMind's Content-Disposition names include a release date
+// (e.g. GeoLite2-ASN_20260101.tar.gz); we use _LATEST so httpcache's
+// ETag sidecar stays tied to a stable path across releases.
+func TarGzName(edition string) string {
+	return edition + "_LATEST.tar.gz"
+}
+
 // DefaultConfPaths returns the standard locations where GeoIP.conf is looked
 // up: ./GeoIP.conf, then ~/.config/maxmind/GeoIP.conf.
 func DefaultConfPaths() []string {

net/geoip/geoip_integration_test.go

@@ -64,7 +64,7 @@ func TestDownload_CityAndASN(t *testing.T) {
 	td := testdataDir(t)
 
 	for _, edition := range []string{geoip.CityEdition, geoip.ASNEdition} {
-		path := filepath.Join(td, edition+".tar.gz")
+		path := filepath.Join(td, geoip.TarGzName(edition))
 		os.Remove(path)
 		os.Remove(path + ".meta")
 
@@ -96,7 +96,7 @@ func TestDownload_ConditionalGet_FreshCacher(t *testing.T) {
 	td := testdataDir(t)
 
 	for _, edition := range []string{geoip.CityEdition, geoip.ASNEdition} {
-		path := filepath.Join(td, edition+".tar.gz")
+		path := filepath.Join(td, geoip.TarGzName(edition))
 
 		if _, err := newCacher(cfg, edition, path).Fetch(); err != nil {
 			t.Fatalf("%s initial Fetch: %v", edition, err)