CDRIVER-735 only test allowDiskUse on new mongods

The "aggregate" command only accepts allowDiskUse in mongod 2.6+.

Author: ajdavis

tests/test-libmongoc.c

@@ -847,6 +847,24 @@ test_framework_is_mongos (void)
    return is_mongos;
 }
 
+
+bool
+test_framework_max_wire_version_at_least (int version)
+{
+   bson_t reply;
+   bson_iter_t iter;
+   bool at_least;
+
+   call_ismaster (&reply);
+
+   at_least = (bson_iter_init_find (&iter, &reply, "maxWireVersion")
+                && bson_iter_as_int64 (&iter) >= version);
+
+   bson_destroy (&reply);
+
+   return at_least;
+}
+
 int
 main (int   argc,
       char *argv[])

tests/test-libmongoc.h

@@ -37,6 +37,7 @@ mongoc_uri_t *test_framework_get_uri (void);
 mongoc_client_t *test_framework_client_new (void);
 mongoc_client_pool_t *test_framework_client_pool_new (void);
 bool test_framework_is_mongos (void);
+bool test_framework_max_wire_version_at_least (int version);
 
 typedef struct _debug_stream_stats_t {
     int n_destroyed;

tests/test-mongoc-collection.c

@@ -1227,9 +1227,14 @@ test_aggregate (void)
          ASSERT (cursor);
       } else {
          bson_init (&opts);
-         BSON_APPEND_INT32 (&opts, "batchSize", 10);
-         BSON_APPEND_BOOL (&opts, "allowDiskUse", true);
 
+         /* servers < 2.6 error is passed allowDiskUse */
+         if (test_framework_max_wire_version_at_least (2)) {
+            BSON_APPEND_BOOL (&opts, "allowDiskUse", true);
+         }
+
+         /* this is ok, the driver silently omits batchSize if server < 2.6 */
+         BSON_APPEND_INT32 (&opts, "batchSize", 10);
          cursor = mongoc_collection_aggregate(collection, MONGOC_QUERY_NONE, pipeline, &opts, NULL);
          ASSERT (cursor);