chore(all): return concrete types, accept interfaces

- Remove exported interfaces unused locally
- Define interfaces to accept arguments
- Return concrete types, not interfaces

internal/provider/custom/connection.go

@@ -8,7 +8,6 @@ import (
 	"github.com/qdm12/gluetun/internal/constants"
 	"github.com/qdm12/gluetun/internal/constants/vpn"
 	"github.com/qdm12/gluetun/internal/models"
-	"github.com/qdm12/gluetun/internal/openvpn/extract"
 )
 
 var (
@@ -28,7 +27,7 @@ func (p *Provider) GetConnection(selection settings.ServerSelection) (
 	}
 }
 
-func getOpenVPNConnection(extractor extract.Interface,
+func getOpenVPNConnection(extractor extractor,
 	selection settings.ServerSelection) (
 	connection models.Connection, err error) {
 	_, connection, err = extractor.Data(*selection.OpenVPN.ConfFile)

internal/provider/custom/interfaces.go

@@ -0,0 +1,8 @@
+package custom
+
+import "github.com/qdm12/gluetun/internal/models"
+
+type extractor interface {
+	Data(filepath string) (lines []string,
+		connection models.Connection, err error)
+}

internal/provider/custom/provider.go

@@ -8,7 +8,7 @@ import (
 )
 
 type Provider struct {
-	extractor extract.Interface
+	extractor extractor
 	utils.NoPortForwarder
 	common.Fetcher
 }