From 29e0287ef381ff674edc85bee403c0e95a9fd91c Mon Sep 17 00:00:00 2001
From: Hubert Chathi <hubertc@matrix.org>
Date: Fri, 19 Nov 2021 21:43:27 -0500
Subject: [PATCH] add function to forget the old fallback key

---
 include/olm/account.hh | 3 +++
 include/olm/olm.h      | 9 +++++++++
 javascript/olm_post.js | 4 ++--
 src/account.cpp        | 7 +++++++
 src/olm.cpp            | 7 +++++++
 5 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/olm/account.hh b/include/olm/account.hh
index 88302ba..dd115f5 100644
--- a/include/olm/account.hh
+++ b/include/olm/account.hh
@@ -169,6 +169,9 @@ struct Account {
         std::uint8_t * fallback_json, std::size_t fallback_json_length
     );
 
+    /** Forget about the old fallback key */
+    void forget_old_fallback_key();
+
     /** Lookup a one time key with the given public key */
     OneTimeKey const * lookup_key(
         _olm_curve25519_public_key const & public_key
diff --git a/include/olm/olm.h b/include/olm/olm.h
index cdb35a2..9e02440 100644
--- a/include/olm/olm.h
+++ b/include/olm/olm.h
@@ -310,6 +310,15 @@ OLM_EXPORT size_t olm_account_unpublished_fallback_key(
     void * fallback_key, size_t fallback_key_size
 );
 
+/** Forget about the old fallback key.  This should be called once you are
+ * reasonably certain that you will not receive any more messages that use
+ * the old fallback key (e.g. 5 minutes after the new fallback key has been
+ * published).
+ */
+OLM_EXPORT void olm_account_forget_old_fallback_key(
+    OlmAccount * account
+);
+
 
 /** The number of random bytes needed to create an outbound session */
 OLM_EXPORT size_t olm_create_outbound_session_random_length(
diff --git a/javascript/olm_post.js b/javascript/olm_post.js
index 305e4c5..634753c 100644
--- a/javascript/olm_post.js
+++ b/javascript/olm_post.js
@@ -194,8 +194,8 @@ Account.prototype['unpublished_fallback_key'] = restore_stack(function() {
     return UTF8ToString(keys, keys_length);
 });
 
-Account.prototype['forget_previous_fallback'] = restore_stack(function() {
-    account_method(Module['_olm_account_forget_previous_fallback_key'])(
+Account.prototype['forget_old_fallback'] = restore_stack(function() {
+    account_method(Module['_olm_account_forget_old_fallback_key'])(
         this.ptr
     );
 });
diff --git a/src/account.cpp b/src/account.cpp
index 80768ae..5056d5f 100644
--- a/src/account.cpp
+++ b/src/account.cpp
@@ -398,6 +398,13 @@ std::size_t olm::Account::get_unpublished_fallback_key_json(
     return pos - fallback_json;
 }
 
+void olm::Account::forget_old_fallback_key(
+) {
+    if (num_fallback_keys >= 2) {
+        num_fallback_keys = 1;
+    }
+}
+
 namespace olm {
 
 static std::size_t pickle_length(
diff --git a/src/olm.cpp b/src/olm.cpp
index f7fbc42..3a30f7a 100644
--- a/src/olm.cpp
+++ b/src/olm.cpp
@@ -512,6 +512,13 @@ size_t olm_account_unpublished_fallback_key(
 }
 
 
+void olm_account_forget_old_fallback_key(
+    OlmAccount * account
+) {
+    return from_c(account)->forget_old_fallback_key();
+}
+
+
 size_t olm_create_outbound_session_random_length(
     OlmSession const * session
 ) {