fix(env): Retro-compatible precedence order for variables with defaults set in Dockerfile

- `BLOCK_NSA` has precedence over `BLOCK_SURVEILLANCE`
- `HEALTH_OPENVPN_DURATION_ADDITION` has precedence over `HEALTH_VPN_DURATION_ADDITION`
- `HEALTH_OPENVPN_DURATION_INITIAL` has precendence over `HEALTH_VPN_DURATION_INITIAL`
- Chain of precedence: `PROXY` > `TINYPROXY` > `HTTPPROXY`
- Chain of precedence: `PROXY_LOG_LEVEL` > `TINYPROXY_LOG` > `HTTPPROXY_LOG`
- `PROTOCOL` has precendence over `OPENVPN_PROTOCOL`
- `IP_STATUS_FILE` has precendence over `PUBLICIP_FILE`
- `SHADOWSOCKS_PORT` has precedence over `SHADOWSOCKS_LISTENING_ADDRESS`
- `SHADOWSOCKS_METHOD` has precedence over `SHADOWSOCKS_CIPHER`

internal/configuration/sources/env/openvpnselection.go

@@ -36,16 +36,17 @@ func (r *Reader) readOpenVPNSelection() (
 var ErrOpenVPNProtocolNotValid = errors.New("OpenVPN protocol is not valid")
 
 func (r *Reader) readOpenVPNProtocol() (tcp *bool, err error) {
-	envKey := "OPENVPN_PROTOCOL"
-	protocol := strings.ToLower(os.Getenv("OPENVPN_PROTOCOL"))
-	if protocol == "" {
 		// Retro-compatibility
-		protocol = strings.ToLower(os.Getenv("PROTOCOL"))
+	envKey := "PROTOCOL"
+	protocol := strings.ToLower(os.Getenv("PROTOCOL"))
+	if protocol == "" {
+		protocol = strings.ToLower(os.Getenv("OPENVPN_PROTOCOL"))
 		if protocol != "" {
-			envKey = "PROTOCOL"
+			envKey = "OPENVPN_PROTOCOL"
+		}
+	} else {
 			r.onRetroActive("PROTOCOL", "OPENVPN_PROTOCOL")
 		}
-	}
 
 	switch protocol {
 	case "":