RUBY-3435 Don't overflow the 4-bytes allotted to an ObjectID's timest…

…amp portion (#327)

* final tweaks for BSON 5 release

* RUBY-3435 constrain timestamp to 4-bytes

ext/bson/util.c

@@ -65,7 +65,7 @@ VALUE rb_bson_object_id_generator_next(int argc, VALUE* args, VALUE self)
    * obtaining the timestamp value." */
 
   timestamp = rb_funcall(rb_bson_object_id_class, rb_intern("timestamp"), 0);
-  time_component = BSON_UINT32_TO_BE(NUM2INT(timestamp));
+  time_component = BSON_UINT32_TO_BE(NUM2UINT(timestamp));
 
   /* "A 5-byte field consisting of a random value generated once per process.
    * This random value is unique to the machine and process.

lib/bson/object_id.rb

@@ -356,12 +356,22 @@ def repair(object)
         block_given? ? yield(object) : object
       end
 
+      # The largest numeric value that can be converted to an integer by MRI's
+      # NUM2UINT. Further, the spec dictates that the time component of an
+      # ObjectID must be no more than 4 bytes long, so the spec itself is
+      # constrained in this regard.
+      MAX_INTEGER = 2 ** 32
+
       # Returns an integer timestamp (seconds since the Epoch). Primarily used
       # by the generator to produce object ids.
       #
+      # @note This value is guaranteed to be no more than 4 bytes in length. A
+      #   time value far enough in the future to require a larger integer than
+      #   4 bytes will be truncated to 4 bytes.
+      #
       # @return [ Integer ] the number of seconds since the Epoch.
       def timestamp
-        ::Time.now.to_i
+        ::Time.now.to_i % MAX_INTEGER
       end
     end
 

spec/bson/object_id_spec.rb

@@ -622,6 +622,20 @@
     end
   end
 
+  context 'when the timestamp is larger than a 32-bit integer' do
+    let(:distant_future) { Time.at(2 ** 32) }
+
+    before do
+      allow(Time).to receive(:now).and_return(distant_future)
+    end
+
+    let(:object_id) { BSON::ObjectId.new }
+
+    it 'wraps the timestamp to 0' do
+      expect(object_id.to_time).to be == Time.at(0)
+    end
+  end
+
   context 'when fork changes the pid' do
     before do
       skip 'requires Process.fork' unless Process.respond_to?(:fork)