1 files changed, 64 insertions, 0 deletions
diff --git a/network/receivepack/hooks/reject_force_push.go b/network/receivepack/hooks/reject_force_push.go
new file mode 100644
index 00000000..79714c8b
--- /dev/null
+++ b/network/receivepack/hooks/reject_force_push.go
@@ -0,0 +1,64 @@
+package hooks
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/commitquery"
+	objectid "codeberg.org/lindenii/furgit/object/id"
+	objectmix "codeberg.org/lindenii/furgit/object/storer/mix"
+	receivepack "codeberg.org/lindenii/furgit/network/receivepack"
+	refstore "codeberg.org/lindenii/furgit/ref/store"
+)
+
+// RejectForcePush rejects updates whose new value is not a fast-forward of the
+// currently resolved reference.
+func RejectForcePush() receivepack.Hook {
+	return func(
+		ctx context.Context,
+		req receivepack.HookRequest,
+	) ([]receivepack.UpdateDecision, error) {
+		_ = ctx
+
+		objects := objectmix.New(req.QuarantinedObjects, req.ExistingObjects)
+
+		decisions := make([]receivepack.UpdateDecision, len(req.Updates))
+		for i := range decisions {
+			decisions[i].Accept = true
+		}
+
+		for i, update := range req.Updates {
+			if update.OldID == objectid.Zero(update.OldID.Algorithm()) || update.NewID == objectid.Zero(update.NewID.Algorithm()) {
+				continue
+			}
+
+			current, err := req.Refs.ResolveToDetached(update.Name)
+			switch {
+			case err == nil:
+			case errors.Is(err, refstore.ErrReferenceNotFound):
+				continue
+			default:
+				return nil, fmt.Errorf("resolve %s: %w", update.Name, err)
+			}
+
+			if current.ID == update.NewID {
+				continue
+			}
+
+			ok, err := commitquery.New(objects, nil).IsAncestor(current.ID, update.NewID)
+			if err != nil {
+				return nil, fmt.Errorf("check fast-forward %s: %w", update.Name, err)
+			}
+
+			if !ok {
+				decisions[i] = receivepack.UpdateDecision{
+					Accept:  false,
+					Message: "non-fast-forward",
+				}
+			}
+		}
+
+		return decisions, nil
+	}
+}