Add function to share megolm keys for historical messages, take 2

src/client.js

@@ -2303,6 +2303,39 @@ MatrixClient.prototype.deleteKeysFromBackup = function(roomId, sessionId, versio
     );
 };
 
+/**
+ * Share shared-history decryption keys with the given users.
+ *
+ * @param {string} roomId the room for which keys should be shared.
+ * @param {array} userIds a list of users to share with.  The keys will be sent to
+ *     all of the user's current devices.
+ */
+MatrixClient.prototype.sendSharedHistoryKeys = async function(roomId, userIds) {
+    if (this._crypto === null) {
+        throw new Error("End-to-end encryption disabled");
+    }
+
+    const roomEncryption = this._roomList.getRoomEncryption(roomId);
+    if (!roomEncryption) {
+        // unknown room, or unencrypted room
+        logger.error("Unknown room.  Not sharing decryption keys");
+        return;
+    }
+
+    const deviceInfos = await this._crypto.downloadKeys(userIds);
+    const devicesByUser = {};
+    for (const [userId, devices] of Object.entries(deviceInfos)) {
+        devicesByUser[userId] = Object.values(devices);
+    }
+
+    const alg = this._crypto._getRoomDecryptor(roomId, roomEncryption.algorithm);
+    if (alg.sendSharedHistoryInboundSessions) {
+        await alg.sendSharedHistoryInboundSessions(devicesByUser);
+    } else {
+        logger.warning("Algorithm does not support sharing previous keys", roomEncryption.algorithm);
+    }
+};
+
 // Group ops
 // =========
 // Operations on groups that come down the sync stream (ie. ones the

src/crypto/OlmDevice.js

@@ -1048,6 +1048,7 @@ OlmDevice.prototype.addInboundGroupSession = async function(
         'readwrite', [
             IndexedDBCryptoStore.STORE_INBOUND_GROUP_SESSIONS,
             IndexedDBCryptoStore.STORE_INBOUND_GROUP_SESSIONS_WITHHELD,
+            IndexedDBCryptoStore.STORE_SHARED_HISTORY_INBOUND_GROUP_SESSIONS,
         ], (txn) => {
             /* if we already have this session, consider updating it */
             this._getInboundGroupSession(
@@ -1104,6 +1105,12 @@ OlmDevice.prototype.addInboundGroupSession = async function(
                         this._cryptoStore.storeEndToEndInboundGroupSession(
                             senderKey, sessionId, sessionData, txn,
                         );
+
+                        if (!existingSession && extraSessionData.sharedHistory) {
+                            this._cryptoStore.addSharedHistoryInboundGroupSession(
+                                roomId, senderKey, sessionId, txn,
+                            );
+                        }
                     } finally {
                         session.free();
                     }
@@ -1383,6 +1390,7 @@ OlmDevice.prototype.getInboundGroupSessionKey = async function(
                         "forwarding_curve25519_key_chain":
                             sessionData.forwardingCurve25519KeyChain || [],
                         "sender_claimed_ed25519_key": senderEd25519Key,
+                        "shared_history": sessionData.sharedHistory || false,
                     };
                 },
             );
@@ -1415,10 +1423,24 @@ OlmDevice.prototype.exportInboundGroupSession = function(
             "session_key": session.export_session(messageIndex),
             "forwarding_curve25519_key_chain": session.forwardingCurve25519KeyChain || [],
             "first_known_index": session.first_known_index(),
+            "org.matrix.msc3061.shared_history": sessionData.sharedHistory || false,
         };
     });
 };
 
+OlmDevice.prototype.getSharedHistoryInboundGroupSessions = async function(roomId) {
+    let result;
+    await this._cryptoStore.doTxn(
+        'readonly', [
+            IndexedDBCryptoStore.STORE_SHARED_HISTORY_INBOUND_GROUP_SESSIONS,
+        ], (txn) => {
+            result = this._cryptoStore.getSharedHistoryInboundGroupSessions(roomId, txn);
+        },
+        logger.withPrefix("[getSharedHistoryInboundGroupSessionsForRoom]"),
+    );
+    return result;
+};
+
 // Utilities
 // =========