microcluster/rest/resources: Compare the joining node's extensions ag…

…ainst the leader's

During a cluster join, the joining node communicate its extensions as seen earlier.
When received (by the leader), we make sure that the target extensions (the joining node ones) and the source
extensions (the leader ones) by comparing them. If they the target ones are supported, we add a serialized view
of both the `internal` and `external` part to the `internal_cluster_members` tables.

Signed-off-by: Gabriel Mougard <[email protected]>

internal/rest/resources/cluster.go

@@ -22,6 +22,7 @@ import (
 
 	"github.com/canonical/microcluster/client"
 	"github.com/canonical/microcluster/cluster"
+	"github.com/canonical/microcluster/internal/db"
 	"github.com/canonical/microcluster/internal/rest/access"
 	internalClient "github.com/canonical/microcluster/internal/rest/client"
 	internalTypes "github.com/canonical/microcluster/internal/rest/types"
@@ -129,14 +130,30 @@ func clusterPost(s *state.State, r *http.Request) response.Response {
 		return response.SyncResponse(true, tokenResponse)
 	}
 
+	// Check if the joining node's extensions are compatible with the leader's.
+	targetExtensions, err := db.NewExtensionRegistryFromList(req.Extensions)
+	if err != nil {
+		return response.SmartError(err)
+	}
+
+	err = s.Extensions.Supports(targetExtensions)
+	if err != nil {
+		return response.SmartError(err)
+	}
+
+	// Then add the new member's extensions to the database.
+	internalExtensions, externalExtensions := targetExtensions.SerializeForDB()
+
 	err = s.Database.Transaction(s.Context, func(ctx context.Context, tx *sql.Tx) error {
 		dbClusterMember := cluster.InternalClusterMember{
-			Name:        req.Name,
-			Address:     req.Address.String(),
-			Certificate: req.Certificate.String(),
-			Schema:      req.SchemaVersion,
-			Heartbeat:   time.Time{},
-			Role:        cluster.Pending,
+			Name:                  req.Name,
+			Address:               req.Address.String(),
+			Certificate:           req.Certificate.String(),
+			Schema:                req.SchemaVersion,
+			InternalAPIExtensions: internalExtensions,
+			ExternalAPIExtensions: externalExtensions,
+			Heartbeat:             time.Time{},
+			Role:                  cluster.Pending,
 		}
 
 		record, err := cluster.GetInternalTokenRecord(ctx, tx, req.Secret)