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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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/privateinternetaccess/servers.go

@@ -0,0 +1,99 @@
+package privateinternetaccess
+
+import (
+	"context"
+	"fmt"
+	"sort"
+	"time"
+
+	"github.com/qdm12/gluetun-servers/pkg/models"
+	"github.com/qdm12/gluetun-servers/pkg/updaters/common"
+)
+
+func (u *Updater) FetchServers(ctx context.Context, minServers int) (
+	servers []models.Server, err error,
+) {
+	nts := make(nameToServer)
+
+	noChangeCounter := 0
+	const maxNoChange = 10
+	const betweenDuration = 200 * time.Millisecond
+	const maxDuration = time.Minute
+
+	maxTimer := time.NewTimer(maxDuration)
+
+	for {
+		data, err := fetchAPI(ctx, u.client)
+		if err != nil {
+			return nil, err
+		}
+
+		change := addData(data.Regions, nts)
+
+		if !change {
+			noChangeCounter++
+			if noChangeCounter == maxNoChange {
+				break
+			}
+		} else {
+			noChangeCounter = 0
+		}
+
+		timer := time.NewTimer(betweenDuration)
+		maxTimeout := false
+		select {
+		case <-ctx.Done():
+			if !timer.Stop() {
+				<-timer.C
+			}
+			if !maxTimer.Stop() {
+				<-timer.C
+			}
+			return nil, ctx.Err()
+		case <-timer.C:
+		case <-maxTimer.C:
+			if !timer.Stop() {
+				<-timer.C
+			}
+			maxTimeout = true
+		}
+
+		if maxTimeout {
+			break
+		}
+	}
+
+	servers = nts.toServersSlice()
+
+	if len(servers) < minServers {
+		return nil, fmt.Errorf("%w: %d and expected at least %d",
+			common.ErrNotEnoughServers, len(servers), minServers)
+	}
+
+	sort.Sort(models.SortableServers(servers))
+
+	return servers, nil
+}
+
+func addData(regions []regionData, nts nameToServer) (change bool) {
+	for _, region := range regions {
+		if region.Offline {
+			continue
+		}
+		for _, server := range region.Servers.UDP {
+			const tcp, udp = false, true
+			if nts.add(server.CN, region.DNS, region.Name, tcp, udp, region.PortForward, server.IP) {
+				change = true
+			}
+		}
+
+		for _, server := range region.Servers.TCP {
+			const tcp, udp = true, false
+			if nts.add(server.CN, region.DNS, region.Name, tcp, udp, region.PortForward, server.IP) {
+				change = true
+			}
+		}
+	}
+
+	return change
+}