From 5a149fcad086de94792ef1a6b4e41313c0cb903b Mon Sep 17 00:00:00 2001
From: Jernej Kos <jernej@kos.mx>
Date: Thu, 1 Sep 2022 10:09:07 +0200
Subject: [PATCH] go/genesis: Cache computed genesis document hash

---
 .changelog/4919.feature.md |  1 +
 go/genesis/api/api.go      | 12 +++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/4919.feature.md

diff --git a/.changelog/4919.feature.md b/.changelog/4919.feature.md
new file mode 100644
index 00000000000..7a64388fd67
--- /dev/null
+++ b/.changelog/4919.feature.md
@@ -0,0 +1 @@
+go/genesis: Cache computed genesis document hash
diff --git a/go/genesis/api/api.go b/go/genesis/api/api.go
index 1d2d48f8ba6..25faf6fe2ba 100644
--- a/go/genesis/api/api.go
+++ b/go/genesis/api/api.go
@@ -51,11 +51,21 @@ type Document struct {
 	// Extra data is arbitrary extra data that is part of the
 	// genesis block but is otherwise ignored by the protocol.
 	ExtraData map[string][]byte `json:"extra_data"`
+
+	cachedHash *hash.Hash
 }
 
 // Hash returns the cryptographic hash of the encoded genesis document.
+//
+// Calling this method will cause the computed hash to be cached so make sure
+// that the document is not modified later.
 func (d *Document) Hash() hash.Hash {
-	return hash.NewFrom(d)
+	if d.cachedHash != nil {
+		return *d.cachedHash
+	}
+	h := hash.NewFrom(d)
+	d.cachedHash = &h
+	return h
 }
 
 // ChainContext returns a string that can be used as a chain domain separation