Remove netRPC based plugins (#6173)

* Remove netRPC backend plugins

* Remove netRPC database plugins

* Fix tests and comments

builtin/logical/database/dbplugin/client.go

@@ -35,11 +35,12 @@ func NewPluginClient(ctx context.Context, sys pluginutil.RunnerUtil, pluginRunne
 
 	// pluginSets is the map of plugins we can dispense.
 	pluginSets := map[int]plugin.PluginSet{
-		// Version 3 supports both protocols
+		// Version 3 used to supports both protocols. We want to keep it around
+		// since it's possible old plugins built against this version will still
+		// work with gRPC. There is currently no difference between version 3
+		// and version 4.
 		3: plugin.PluginSet{
-			"database": &DatabasePlugin{
-				GRPCDatabasePlugin: new(GRPCDatabasePlugin),
-			},
+			"database": new(GRPCDatabasePlugin),
 		},
 		// Version 4 only supports gRPC
 		4: plugin.PluginSet{
@@ -76,9 +77,6 @@ func NewPluginClient(ctx context.Context, sys pluginutil.RunnerUtil, pluginRunne
 	switch raw.(type) {
 	case *gRPCClient:
 		db = raw.(*gRPCClient)
-	case *databasePluginRPCClient:
-		logger.Warn("plugin is using deprecated netRPC transport, recompile plugin to upgrade to gRPC", "plugin", pluginRunner.Name)
-		db = raw.(*databasePluginRPCClient)
 	default:
 		return nil, errors.New("unsupported client type")
 	}

builtin/logical/database/dbplugin/plugin.go

@@ -3,7 +3,6 @@ package dbplugin
 import (
 	"context"
 	"fmt"
-	"net/rpc"
 	"time"
 
 	"google.golang.org/grpc"
@@ -73,8 +72,6 @@ func PluginFactory(ctx context.Context, pluginName string, sys pluginutil.LookRu
 		switch db.(*DatabasePluginClient).Database.(type) {
 		case *gRPCClient:
 			transport = "gRPC"
-		case *databasePluginRPCClient:
-			transport = "netRPC"
 		}
 
 	}
@@ -111,17 +108,9 @@ var handshakeConfig = plugin.HandshakeConfig{
 	MagicCookieValue: "926a0820-aea2-be28-51d6-83cdf00e8edb",
 }
 
-var _ plugin.Plugin = &DatabasePlugin{}
-var _ plugin.GRPCPlugin = &DatabasePlugin{}
 var _ plugin.Plugin = &GRPCDatabasePlugin{}
 var _ plugin.GRPCPlugin = &GRPCDatabasePlugin{}
 
-// DatabasePlugin implements go-plugin's Plugin interface. It has methods for
-// retrieving a server and a client instance of the plugin.
-type DatabasePlugin struct {
-	*GRPCDatabasePlugin
-}
-
 // GRPCDatabasePlugin is the plugin.Plugin implementation that only supports GRPC
 // transport
 type GRPCDatabasePlugin struct {
@@ -131,17 +120,6 @@ type GRPCDatabasePlugin struct {
 	plugin.NetRPCUnsupportedPlugin
 }
 
-func (d DatabasePlugin) Server(*plugin.MuxBroker) (interface{}, error) {
-	impl := &DatabaseErrorSanitizerMiddleware{
-		next: d.Impl,
-	}
-	return &databasePluginRPCServer{impl: impl}, nil
-}
-
-func (DatabasePlugin) Client(b *plugin.MuxBroker, c *rpc.Client) (interface{}, error) {
-	return &databasePluginRPCClient{client: c}, nil
-}
-
 func (d GRPCDatabasePlugin) GRPCServer(_ *plugin.GRPCBroker, s *grpc.Server) error {
 	impl := &DatabaseErrorSanitizerMiddleware{
 		next: d.Impl,