mongoc_topology_new() selects the "localThresholdMS" URI option as an int32_t, where it is assigned to an int64_t in the struct field.

From there, it passes the value as an int64_t to mongoc_topology_description_select(). That int64_t is then passed as an size_t to mongoc_topology_description_suitable_servers(), which may also call _mongoc_try_mode_secondary() (also accepting a size_t).

There seem to be two issues with this:

• A negative "localThresholdMS" option parsed as a signed int32_t would be converted to a negative, signed int64_t value and possibly a very large unsigned size_t.
• On a 32-bit system, a int64_t is being assigned to a possibly 32-bit size_t. Aside from a possible compiler warning, this might also lead to an unexpected assignment of a negative 64-bit value to an unsigned 32-bit value. I'm uncertain if the sign bit would simply be ignored, etc.

The server selection spec does not outline a maximum value for "localThresholdMS", so I presume that is left to implementations. In that event, it might be reasonable to limit it to the maximum value of a signed 32-bit integer and always store it as a size_t after mongoc_topology_new() parses the URI option.