From e2332f3163795cd2a4a5907112f01dece2e09144 Mon Sep 17 00:00:00 2001
From: Aurora Gaffney <aurora@blinklabs.io>
Date: Sat, 14 Jun 2025 22:58:12 -0400
Subject: [PATCH] fix: handle rollback from chain iterator in chainsync server

Fixes #769

Signed-off-by: Aurora Gaffney <aurora@blinklabs.io>
---
 chainsync.go | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/chainsync.go b/chainsync.go
index 34847ae2..3d18f4c4 100644
--- a/chainsync.go
+++ b/chainsync.go
@@ -151,11 +151,19 @@ func (n *Node) chainsyncServerRequestNext(
 		}
 	}
 	if next != nil {
-		return ctx.Server.RollForward(
-			next.Block.Type,
-			next.Block.Cbor,
-			tip,
-		)
+		if next.Rollback {
+			err = ctx.Server.RollBackward(
+				next.Point,
+				tip,
+			)
+		} else {
+			err = ctx.Server.RollForward(
+				next.Block.Type,
+				next.Block.Cbor,
+				tip,
+			)
+		}
+		return err
 	}
 	// Send AwaitReply
 	if err := ctx.Server.AwaitReply(); err != nil {
@@ -168,11 +176,18 @@ func (n *Node) chainsyncServerRequestNext(
 			return
 		}
 		tip := n.ledgerState.Tip()
-		_ = ctx.Server.RollForward(
-			next.Block.Type,
-			next.Block.Cbor,
-			tip,
-		)
+		if next.Rollback {
+			_ = ctx.Server.RollBackward(
+				next.Point,
+				tip,
+			)
+		} else {
+			_ = ctx.Server.RollForward(
+				next.Block.Type,
+				next.Block.Cbor,
+				tip,
+			)
+		}
 	}()
 	return nil
 }