feat: add Register function to DA registry (cosmos#721)

Resolves cosmos#715.

da/registry/registry.go

@@ -1,12 +1,23 @@
 package registry
 
 import (
+	"fmt"
+
 	"github.com/rollkit/rollkit/da"
 	"github.com/rollkit/rollkit/da/celestia"
 	"github.com/rollkit/rollkit/da/grpc"
 	"github.com/rollkit/rollkit/da/mock"
 )
 
+// ErrAlreadyRegistered is used when user tries to register DA using a name already used in registry.
+type ErrAlreadyRegistered struct {
+	name string
+}
+
+func (e *ErrAlreadyRegistered) Error() string {
+	return fmt.Sprintf("Data Availability Layer '%s' already registered", e.name)
+}
+
 // this is a central registry for all Data Availability Layer Clients
 var clients = map[string]func() da.DataAvailabilityLayerClient{
 	"mock":     func() da.DataAvailabilityLayerClient { return &mock.DataAvailabilityLayerClient{} },
@@ -23,6 +34,17 @@ func GetClient(name string) da.DataAvailabilityLayerClient {
 	return f()
 }
 
+// Register adds a Data Availability Layer Client to registry.
+//
+// If name was previously used in the registry, error is returned.
+func Register(name string, constructor func() da.DataAvailabilityLayerClient) error {
+	if _, found := clients[name]; !found {
+		clients[name] = constructor
+		return nil
+	}
+	return &ErrAlreadyRegistered{name: name}
+}
+
 // RegisteredClients returns names of all DA clients in registry.
 func RegisteredClients() []string {
 	registered := make([]string, 0, len(clients))

da/registry/registry_test.go

@@ -4,6 +4,9 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"github.com/rollkit/rollkit/da"
+	"github.com/rollkit/rollkit/da/mock"
 )
 
 func TestRegistery(t *testing.T) {
@@ -14,7 +17,21 @@ func TestRegistery(t *testing.T) {
 
 	assert.ElementsMatch(expected, actual)
 
-	for _, e := range expected {
+	constructor := func() da.DataAvailabilityLayerClient {
+		return &mock.DataAvailabilityLayerClient{} // cheating, only for tests :D
+	}
+	err := Register("testDA", constructor)
+	assert.NoError(err)
+
+	// re-registration should fail
+	err = Register("celestia", constructor)
+	regErr := &ErrAlreadyRegistered{}
+	assert.ErrorAs(err, &regErr)
+	assert.Equal("celestia", regErr.name)
+
+	assert.Contains(RegisteredClients(), "testDA")
+
+	for _, e := range RegisteredClients() {
 		dalc := GetClient(e)
 		assert.NotNil(dalc)
 	}