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- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch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

@@ -0,0 +1,86 @@
+package surfshark
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"github.com/qdm12/gluetun-servers/pkg/updaters/providers/surfshark/servers"
+)
+
+func addServersFromAPI(ctx context.Context, client *http.Client,
+	hts hostToServers,
+) (err error) {
+	data, err := fetchAPI(ctx, client)
+	if err != nil {
+		return err
+	}
+
+	locationData := servers.LocationData()
+	hostToLocation := hostToLocation(locationData)
+
+	for _, serverData := range data {
+		locationData := hostToLocation[serverData.Host] // TODO remove in v4
+		retroLoc := locationData.RetroLoc               // empty string if the host has no retro-compatible region
+
+		tcp, udp := true, true // OpenVPN servers from API supports both TCP and UDP
+		hts.addOpenVPN(serverData.Host, serverData.Region, serverData.Country,
+			serverData.Location, retroLoc, tcp, udp)
+
+		if serverData.PubKey != "" {
+			hts.addWireguard(serverData.Host, serverData.Region, serverData.Country,
+				serverData.Location, retroLoc, serverData.PubKey)
+		}
+	}
+
+	return nil
+}
+
+type serverData struct {
+	Host     string `json:"connectionName"`
+	Region   string `json:"region"`
+	Country  string `json:"country"`
+	Location string `json:"location"`
+	PubKey   string `json:"pubKey"`
+}
+
+func fetchAPI(ctx context.Context, client *http.Client) (
+	servers []serverData, err error,
+) {
+	const url = "https://api.surfshark.com/v4/server/clusters"
+
+	for _, clustersType := range [...]string{"generic", "double", "static", "obfuscated"} {
+		request, err := http.NewRequestWithContext(ctx, http.MethodGet, url+"/"+clustersType, nil)
+		if err != nil {
+			return nil, err
+		}
+
+		response, err := client.Do(request)
+		if err != nil {
+			return nil, err
+		}
+		defer response.Body.Close()
+
+		if response.StatusCode != http.StatusOK {
+			return nil, fmt.Errorf("HTTP status code not OK: %d %s",
+				response.StatusCode, response.Status)
+		}
+
+		decoder := json.NewDecoder(response.Body)
+		var newServers []serverData
+		err = decoder.Decode(&newServers)
+		if err != nil {
+			return nil, fmt.Errorf("decoding response body: %w", err)
+		}
+
+		err = response.Body.Close()
+		if err != nil {
+			return nil, err
+		}
+
+		servers = append(servers, newServers...)
+	}
+
+	return servers, nil
+}