add experimental plugin system

sdk/plugin/notifier/notifier.go

@@ -0,0 +1,57 @@
+// Package notifier defines the implementation for event notifier plugin.
+// Notifier plugins allow to receive filesystem events such as file uploads,
+// downloads etc. and user events such as add, update, delete.
+package notifier
+
+import (
+	"context"
+
+	"github.com/hashicorp/go-plugin"
+	"google.golang.org/grpc"
+
+	"github.com/drakkan/sftpgo/v2/sdk/plugin/notifier/proto"
+)
+
+const (
+	// PluginName defines the name for a notifier plugin
+	PluginName = "notifier"
+)
+
+// Handshake is a common handshake that is shared by plugin and host.
+var Handshake = plugin.HandshakeConfig{
+	ProtocolVersion:  1,
+	MagicCookieKey:   "SFTPGO_NOTIFIER_PLUGIN",
+	MagicCookieValue: "c499b98b-cd59-4df2-92b3-6268817f4d80",
+}
+
+// PluginMap is the map of plugins we can dispense.
+var PluginMap = map[string]plugin.Plugin{
+	PluginName: &Plugin{},
+}
+
+// Notifier defines the interface for notifiers plugins
+type Notifier interface {
+	NotifyFsEvent(action, username, fsPath, fsTargetPath, sshCmd, protocol string, fileSize int64, status int) error
+	NotifyUserEvent(action string, user []byte) error
+}
+
+// Plugin defines the implementation to serve/connect to a notifier plugin
+type Plugin struct {
+	plugin.Plugin
+	Impl Notifier
+}
+
+// GRPCServer defines the GRPC server implementation for this plugin
+func (p *Plugin) GRPCServer(broker *plugin.GRPCBroker, s *grpc.Server) error {
+	proto.RegisterNotifierServer(s, &GRPCServer{
+		Impl: p.Impl,
+	})
+	return nil
+}
+
+// GRPCClient defines the GRPC client implementation for this plugin
+func (p *Plugin) GRPCClient(ctx context.Context, broker *plugin.GRPCBroker, c *grpc.ClientConn) (interface{}, error) {
+	return &GRPCClient{
+		client: proto.NewNotifierClient(c),
+	}, nil
+}