Add initial prototype (#1)

* Add survey library to select server

* Add speedtest

* Add --random flag to connect

* Add list command

* Cache server list

* Tail the openvpn logs so that it appears in vpngate logs

* Add goreleaser action

* Add golangci-lint action

pkg/vpn/cache.go

@@ -0,0 +1,89 @@
+package vpn
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"path"
+	"time"
+
+	"github.com/rs/zerolog/log"
+	"github.com/spf13/afero"
+)
+
+const serverCachefile = "servers.json"
+
+func getCacheDir() string {
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		log.Error().Msgf("Failed to get user's home directory: %s ", err)
+		return ""
+	}
+	cacheDir := path.Join(homeDir, ".vpngate", "cache")
+	return cacheDir
+}
+
+func createCacheDir() error {
+	cacheDir := getCacheDir()
+	var AppFs = afero.NewOsFs()
+	return AppFs.MkdirAll(cacheDir, 0700)
+}
+
+func getVpnListCache() (*[]Server, error) {
+	cacheFile := path.Join(getCacheDir(), serverCachefile)
+	serversFile, err := os.Open(cacheFile)
+
+	if err != nil {
+		return nil, err
+	}
+
+	byteValue, err := ioutil.ReadAll(serversFile)
+
+	if err != nil {
+		return nil, err
+	}
+
+	var servers []Server
+
+	err = json.Unmarshal(byteValue, &servers)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return &servers, nil
+}
+
+func writeVpnListToCache(servers []Server) error {
+
+	err := createCacheDir()
+
+	if err != nil {
+		return err
+	}
+
+	f, err := json.MarshalIndent(servers, "", " ")
+
+	if err != nil {
+		return err
+	}
+
+	cacheFile := path.Join(getCacheDir(), serverCachefile)
+
+	err = ioutil.WriteFile(cacheFile, f, 0644)
+
+	return err
+
+}
+
+func vpnListCacheIsExpired() bool {
+	file, err := os.Stat(path.Join(getCacheDir(), serverCachefile))
+
+	if err != nil {
+		return true
+	}
+
+	lastModified := file.ModTime()
+
+	return (time.Since(lastModified)) > time.Duration(24*time.Hour)
+}