Fixed JS parsing of unspecified map keys

We need to use a default of 0 when parsing unspecified map keys, instead
of failing an assertion.

This change was written by Michael Aaron (michaelaaron@google.com) but I
am cherry-picking it directly instead of waiting for the next sync of
Google-internal changes.

1 files changed, 11 insertions, 4 deletions

diff --git a/js/map.js b/js/map.js
index 7b5b2c38..2fb14837 100644
--- a/js/map.js
+++ b/js/map.js
@@ -443,7 +443,8 @@ jspb.Map.prototype.serializeBinary = function(
 /**
  * Read one key/value message from the given BinaryReader. Compatible as the
  * `reader` callback parameter to jspb.BinaryReader.readMessage, to be called
- * when a key/value pair submessage is encountered.
+ * when a key/value pair submessage is encountered. If the Key is undefined,
+ * we should default it to 0.
  * @template K, V
  * @param {!jspb.Map} map
  * @param {!jspb.BinaryReader} reader
@@ -457,12 +458,17 @@ jspb.Map.prototype.serializeBinary = function(
  *    readMessage, in which case the second callback arg form is used.
  *
  * @param {?function(V,!jspb.BinaryReader)=} opt_valueReaderCallback
- *    The BinaryReader parsing callback for type V, if V is a message type.
+ *    The BinaryReader parsing callback for type V, if V is a message type
+ *
+ * @param {K=} opt_defaultKey
+ *    The default value for the type of map keys. Accepting map
+ *    entries with unset keys is required for maps to be backwards compatible
+ *    with the repeated message representation described here: goo.gl/zuoLAC
  *
  */
 jspb.Map.deserializeBinary = function(map, reader, keyReaderFn, valueReaderFn,
-                                      opt_valueReaderCallback) {
-  var key = undefined;
+                                      opt_valueReaderCallback, opt_defaultKey) {
+  var key = opt_defaultKey;
   var value = undefined;
 
   while (reader.nextField()) {
@@ -470,6 +476,7 @@ jspb.Map.deserializeBinary = function(map, reader, keyReaderFn, valueReaderFn,
       break;
     }
     var field = reader.getFieldNumber();
+
     if (field == 1) {
       // Key.
       key = keyReaderFn.call(reader);