load extensions during compile time using go build tags

cmd/kwild/server/build.go

@@ -198,9 +198,13 @@ func buildDatasetsModule(d *coreDependencies, eng datasets.Engine, accs datasets
 }
 
 func buildEngine(d *coreDependencies, a *sessions.AtomicCommitter) *engine.Engine {
-	extensions, err := connectExtensions(d.ctx, d.cfg.AppCfg.ExtensionEndpoints)
+	extensions, err := getExtensions(d.ctx, d.cfg.AppCfg.ExtensionEndpoints)
 	if err != nil {
-		failBuild(err, "failed to connect to extensions")
+		failBuild(err, "failed to get extensions")
+	}
+
+	for _, ext := range extensions {
+		d.log.Debug("registered extension", zap.String("name", ext.Name()))
 	}
 
 	sqlCommitRegister := &sqlCommittableRegister{

cmd/kwild/server/utils.go

@@ -11,10 +11,11 @@ import (
 	"github.com/kwilteam/kwil-db/core/log"
 	types "github.com/kwilteam/kwil-db/core/types/admin"
 	"github.com/kwilteam/kwil-db/core/types/transactions"
-	extensions "github.com/kwilteam/kwil-db/extensions/actions"
+	extActions "github.com/kwilteam/kwil-db/extensions/actions"
 	"github.com/kwilteam/kwil-db/internal/abci"
 	"github.com/kwilteam/kwil-db/internal/abci/cometbft/privval"
 	"github.com/kwilteam/kwil-db/internal/engine"
+	"github.com/kwilteam/kwil-db/internal/extensions"
 	"github.com/kwilteam/kwil-db/internal/kv"
 	"github.com/kwilteam/kwil-db/internal/sessions"
 	sqlSessions "github.com/kwilteam/kwil-db/internal/sessions/sql-session"
@@ -28,9 +29,18 @@ import (
 	cmttypes "github.com/cometbft/cometbft/types"
 )
 
-// connectExtensions connects to the provided extension urls.
-func connectExtensions(ctx context.Context, urls []string) (map[string]*extensions.Extension, error) {
-	exts := make(map[string]*extensions.Extension, len(urls))
+// getExtensions returns both the local and remote extensions. Remote extensions are identified by
+// connecting to the specified extension URLs.
+func getExtensions(ctx context.Context, urls []string) (map[string]extActions.Extension, error) {
+	exts := make(map[string]extActions.Extension)
+
+	for name, ext := range extActions.RegisteredExtensions() {
+		_, ok := exts[name]
+		if ok {
+			return nil, fmt.Errorf("duplicate extension name: %s", name)
+		}
+		exts[name] = ext
+	}
 
 	for _, url := range urls {
 		ext := extensions.New(url)
@@ -46,15 +56,17 @@ func connectExtensions(ctx context.Context, urls []string) (map[string]*extensio
 
 		exts[ext.Name()] = ext
 	}
-
 	return exts, nil
 }
 
-func adaptExtensions(exts map[string]*extensions.Extension) map[string]engine.ExtensionInitializer {
+func adaptExtensions(exts map[string]extActions.Extension) map[string]engine.ExtensionInitializer {
 	adapted := make(map[string]engine.ExtensionInitializer, len(exts))
 
 	for name, ext := range exts {
-		adapted[name] = extensionInitializeFunc(ext.CreateInstance)
+		initializer := &extensions.ExtensionInitializer{
+			Extension: ext,
+		}
+		adapted[name] = extensionInitializeFunc(initializer.CreateInstance)
 	}
 
 	return adapted

extensions/actions/extension_registry.go

@@ -0,0 +1,28 @@
+package extensions
+
+import (
+	"context"
+	"strings"
+)
+
+type Extension interface {
+	Name() string
+	Initialize(ctx context.Context, metadata map[string]string) (map[string]string, error)
+	Execute(ctx context.Context, metadata map[string]string, method string, args ...any) ([]any, error)
+}
+
+var registeredExtensions = make(map[string]Extension)
+
+func RegisterExtension(name string, ext Extension) error {
+	name = strings.ToLower(name)
+	if _, ok := registeredExtensions[name]; ok {
+		panic("extension of same name already registered: " + name)
+	}
+
+	registeredExtensions[name] = ext
+	return nil
+}
+
+func RegisteredExtensions() map[string]Extension {
+	return registeredExtensions
+}