SessionCipher: allow caller to provide fillMessageKeys limit

If options.messageKeysLimit is provided by falsey, then we don't apply
any limit at all. This can be used to set no limit for communications
from your own devices.

Why would you want that? People leave their laptops closed for weeks at
a time and get this error, since their other devices are sending
messages to it constantly:

"Too many message keys for chain"

And it seems to be really hard to fix once you're in this state. Sync
messages no longer show up from the device that got into this state.

FREEBIE

dist/libsignal-protocol.js

@@ -36032,7 +36032,14 @@ libsignal.SessionBuilder = function (storage, remoteAddress) {
   this.processV3 = builder.processV3.bind(builder);
 };
 
-function SessionCipher(storage, remoteAddress) {
+function SessionCipher(storage, remoteAddress, options) {
+  options = options || {};
+
+  if (typeof options.messageKeysLimit === 'undefined') {
+    options.messageKeysLimit = 1000;
+  }
+
+  this.messageKeysLimit = options.messageKeyLimit;
   this.remoteAddress = remoteAddress;
   this.storage = storage;
 }
@@ -36305,7 +36312,7 @@ SessionCipher.prototype = {
     });
   },
   fillMessageKeys: function(chain, counter) {
-      if (Object.keys(chain.messageKeys).length >= 1000) {
+      if (this.messageKeysLimit && Object.keys(chain.messageKeys).length >= this.messageKeysLimit) {
           console.log("Too many message keys for chain");
           return Promise.resolve(); // Stalker, much?
       }

src/SessionCipher.js

@@ -1,4 +1,11 @@
-function SessionCipher(storage, remoteAddress) {
+function SessionCipher(storage, remoteAddress, options) {
+  options = options || {};
+
+  if (typeof options.messageKeysLimit === 'undefined') {
+    options.messageKeysLimit = 1000;
+  }
+
+  this.messageKeysLimit = options.messageKeyLimit;
   this.remoteAddress = remoteAddress;
   this.storage = storage;
 }
@@ -271,7 +278,7 @@ SessionCipher.prototype = {
     });
   },
   fillMessageKeys: function(chain, counter) {
-      if (Object.keys(chain.messageKeys).length >= 1000) {
+      if (this.messageKeysLimit && Object.keys(chain.messageKeys).length >= this.messageKeysLimit) {
           console.log("Too many message keys for chain");
           return Promise.resolve(); // Stalker, much?
       }