refactor(storage): new storage file structure

- new directory structure containing manifest.json and one json file per provider, by default.
- the manifest.json file can specify a filepath for each vpn provider
- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch
- `STORAGE_SERVERS_DIRECTORY_PATH` replaces `STORAGE_FILEPATH` (which is now a migration source only). It sets the directory where server manifest and per-provider JSON files are stored (default: `/gluetun/servers/`).
- First-run migration: On startup, gluetun checks for the old /gluetun/servers.json file; if found and no new manifest exists, it automatically migrates all data to /gluetun/servers/ directory structure
- Silent fallback: If legacy file isn't found, uses the new directory path normally
- Legacy cleanup: After successful migration, attempts to remove the old fat JSON file (logs warning only if removal fails, e.g., read-only bind mounts)

gluetun-servers/pkg/updaters/providers/mullvad/hosttoserver.go

@@ -0,0 +1,78 @@
+package mullvad
+
+import (
+	"errors"
+	"fmt"
+	"net/netip"
+	"strings"
+
+	"github.com/qdm12/gluetun-servers/pkg/constants"
+	"github.com/qdm12/gluetun-servers/pkg/models"
+)
+
+type hostToServer map[string]models.Server
+
+func (hts hostToServer) add(data serverData) (err error) {
+	if !data.Active {
+		return nil
+	}
+
+	if data.IPv4 == "" && data.IPv6 == "" {
+		return errors.New("no IP address for VPN server")
+	}
+
+	server, ok := hts[data.Hostname]
+	if ok { // API returns a server per hostname at most
+		return nil
+	}
+
+	switch data.Type {
+	case "wireguard":
+		server.VPN = constants.Wireguard
+	case "bridge":
+		// ignore bridge servers
+		return nil
+	default:
+		return fmt.Errorf("VPN type not supported: %s", data.Type)
+	}
+
+	if data.IPv4 != "" {
+		ipv4, err := netip.ParseAddr(data.IPv4)
+		if err != nil {
+			return fmt.Errorf("parsing IPv4 address: %w", err)
+		} else if !ipv4.Is4() {
+			return fmt.Errorf("IP address is not IPv4: %s", data.IPv4)
+		}
+		server.IPs = append(server.IPs, ipv4)
+	}
+
+	if data.IPv6 != "" {
+		ipv6, err := netip.ParseAddr(data.IPv6)
+		if err != nil {
+			return fmt.Errorf("parsing IPv6 address: %w", err)
+		} else if !ipv6.Is6() {
+			return fmt.Errorf("IP address is not IPv6: %s", data.IPv6)
+		}
+		server.IPs = append(server.IPs, ipv6)
+	}
+
+	server.Country = data.Country
+	server.City = strings.ReplaceAll(data.City, ",", "")
+	server.Hostname = data.Hostname
+	server.ISP = data.Provider
+	server.Owned = data.Owned
+	server.WgPubKey = data.PubKey
+
+	hts[data.Hostname] = server
+
+	return nil
+}
+
+func (hts hostToServer) toServersSlice() (servers []models.Server) {
+	servers = make([]models.Server, 0, len(hts))
+	for _, server := range hts {
+		server.IPs = uniqueSortedIPs(server.IPs)
+		servers = append(servers, server)
+	}
+	return servers
+}