Add plugin's support for provider

Co-authored-by: Julien Salleyron <julien@traefik.io>

cmd/internal/gen/main.go

@@ -0,0 +1,124 @@
+package main
+
+import (
+	"fmt"
+	"go/build"
+	"go/types"
+	"io/ioutil"
+	"log"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+const rootPkg = "github.com/traefik/traefik/v2/pkg/config/dynamic"
+
+const (
+	destModuleName = "github.com/traefik/genconf"
+	destPkg        = "dynamic"
+)
+
+const marsh = `package %s
+
+import "encoding/json"
+
+type JSONPayload struct {
+	*Configuration
+}
+
+func (c JSONPayload) MarshalJSON() ([]byte, error) {
+	if c.Configuration == nil {
+		return nil, nil
+	}
+
+	return json.Marshal(c.Configuration)
+}
+`
+
+// main generate Go Structures from Go structures.
+// Allows to create an external module (destModuleName) used by the plugin's providers
+// that contains Go structs of the dynamic configuration and nothing else.
+// These Go structs do not have any non-exported fields and do not rely on any external dependencies.
+func main() {
+	dest := filepath.Join(path.Join(build.Default.GOPATH, "src"), destModuleName, destPkg)
+
+	log.Println("Output:", dest)
+
+	err := run(dest)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func run(dest string) error {
+	centrifuge, err := NewCentrifuge(rootPkg)
+	if err != nil {
+		return err
+	}
+
+	centrifuge.IncludedImports = []string{
+		"github.com/traefik/traefik/v2/pkg/tls",
+		"github.com/traefik/traefik/v2/pkg/types",
+	}
+
+	centrifuge.ExcludedTypes = []string{
+		// tls
+		"CertificateStore", "Manager",
+		// dynamic
+		"Message", "Configurations",
+		// types
+		"HTTPCodeRanges", "HostResolverConfig",
+	}
+
+	centrifuge.ExcludedFiles = []string{
+		"github.com/traefik/traefik/v2/pkg/types/logs.go",
+		"github.com/traefik/traefik/v2/pkg/types/metrics.go",
+	}
+
+	centrifuge.TypeCleaner = cleanType
+	centrifuge.PackageCleaner = cleanPackage
+
+	err = centrifuge.Run(dest, destPkg)
+	if err != nil {
+		return err
+	}
+
+	return ioutil.WriteFile(filepath.Join(dest, "marshaler.go"), []byte(fmt.Sprintf(marsh, destPkg)), 0666)
+}
+
+func cleanType(typ types.Type, base string) string {
+	if typ.String() == "github.com/traefik/traefik/v2/pkg/tls.FileOrContent" {
+		return "string"
+	}
+
+	if typ.String() == "[]github.com/traefik/traefik/v2/pkg/tls.FileOrContent" {
+		return "[]string"
+	}
+
+	if typ.String() == "github.com/traefik/paerser/types.Duration" {
+		return "string"
+	}
+
+	if strings.Contains(typ.String(), base) {
+		return strings.ReplaceAll(typ.String(), base+".", "")
+	}
+
+	if strings.Contains(typ.String(), "github.com/traefik/traefik/v2/pkg/") {
+		return strings.ReplaceAll(typ.String(), "github.com/traefik/traefik/v2/pkg/", "")
+	}
+
+	return typ.String()
+}
+
+func cleanPackage(src string) string {
+	switch src {
+	case "github.com/traefik/paerser/types":
+		return ""
+	case "github.com/traefik/traefik/v2/pkg/tls":
+		return path.Join(destModuleName, destPkg, "tls")
+	case "github.com/traefik/traefik/v2/pkg/types":
+		return path.Join(destModuleName, destPkg, "types")
+	default:
+		return src
+	}
+}