CDRIVER-3732 document correct read preference behavior for mongoc_client_select_server

Author: samantharitter

src/libmongoc/doc/mongoc_client_select_server.rst

@@ -23,7 +23,7 @@ Parameters
 
 * ``client``: A :symbol:`mongoc_client_t`.
 * ``for_writes``: Whether to choose a server suitable for writes or reads.
-* ``prefs``: An optional :symbol:`mongoc_read_prefs_t`. If ``for_writes`` is true, ``prefs`` must be NULL. Otherwise, use ``prefs`` to customize server selection, or pass NULL to use the read preference configured on the client.
+* ``prefs``: An optional :symbol:`mongoc_read_prefs_t`. If ``for_writes`` is true, ``prefs`` must be NULL. Otherwise, use ``prefs`` to customize server selection, or pass NULL to use read preference PRIMARY.
 * ``error``: An optional location for a :symbol:`bson_error_t <errors>` or ``NULL``.
 
 Returns

src/libmongoc/tests/test-mongoc-client.c

@@ -2528,6 +2528,22 @@ _test_mongoc_client_select_server (bool pooled)
       client = test_framework_client_new ();
    }
 
+   sd = mongoc_client_select_server (client,
+                                     true, /* for writes */
+                                     NULL,
+                                     &error);
+
+   ASSERT (sd);
+   server_type = mongoc_server_description_type (sd);
+   ASSERT (!strcmp (server_type, "Standalone") ||
+           !strcmp (server_type, "RSPrimary") ||
+           !strcmp (server_type, "Mongos"));
+
+   /* Do not inherit read prefs from the client. */
+   prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
+   mongoc_client_set_read_prefs (client, prefs);
+
+   mongoc_server_description_destroy (sd);
    sd = mongoc_client_select_server (client,
                                      true, /* for writes */
                                      NULL,
@@ -2552,7 +2568,6 @@ _test_mongoc_client_select_server (bool pooled)
            !strcmp (server_type, "Mongos"));
 
    mongoc_server_description_destroy (sd);
-   prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
    sd = mongoc_client_select_server (client,
                                      false, /* for reads */
                                      prefs,