static int mongo_cursor_op_query( mongo_cursor *cursor ) {
    int res;
    bson empty;
    char *data;
    mongo_message *mm;
    bson temp;
    bson_iterator it;

    /* Clear any errors. */
    mongo_clear_errors( cursor->conn );

    /* Set up default values for query and fields, if necessary. */
    if( ! cursor->query )
        cursor->query = bson_empty( &empty );
    else if( mongo_cursor_bson_valid( cursor, cursor->query ) != MONGO_OK )
        return MONGO_ERROR;

    if( ! cursor->fields )
        cursor->fields = bson_empty( &empty );
    else if( mongo_cursor_bson_valid( cursor, cursor->fields ) != MONGO_OK )
        return MONGO_ERROR;

    mm = mongo_message_create( 16 + /* header */
                               4 + /*  options */
                               strlen( cursor->ns ) + 1 + /* ns */
                               4 + 4 + /* skip,return */
                               bson_size( cursor->query ) +
                               bson_size( cursor->fields ) ,
                               0 , 0 , MONGO_OP_QUERY );

    data = &mm->data;
    data = mongo_data_append32( data , &cursor->options );
    data = mongo_data_append( data , cursor->ns , strlen( cursor->ns ) + 1 );
    data = mongo_data_append32( data , &cursor->skip );
    data = mongo_data_append32( data , &cursor->limit );
    data = mongo_data_append( data , cursor->query->data , bson_size( cursor->query ) );
    if ( cursor->fields )
        data = mongo_data_append( data , cursor->fields->data , bson_size( cursor->fields ) );

    bson_fatal_msg( ( data == ( ( char * )mm ) + mm->head.len ), "query building fail!" );

    res = mongo_message_send( cursor->conn , mm );
    if( res != MONGO_OK ) {
        return MONGO_ERROR;
    }

    res = mongo_read_response( cursor->conn, ( mongo_reply ** )&( cursor->reply ) );
    if( res != MONGO_OK ) {
        return MONGO_ERROR;
    }

    if( cursor->reply->fields.num == 1 ) {
        bson_init_data( &temp, &cursor->reply->objs );
        if( bson_find( &it, &temp, "$err" ) ) {
            mongo_set_last_error( cursor->conn, &it, &temp );
            cursor->err = MONGO_CURSOR_QUERY_FAIL;
            return MONGO_ERROR;
        }
    }

    cursor->seen += cursor->reply->fields.num;
    cursor->flags |= MONGO_CURSOR_QUERY_SENT;
    return MONGO_OK;
}
static int mongo_cursor_op_query( mongo_cursor *cursor ) {
    int res;
    bson empty;
    char *data;
    mongo_message *mm;
    bson temp;
    bson_iterator it;

     
    mongo_clear_errors( cursor->conn );

     
    if( ! cursor->query )
        cursor->query = bson_empty( &empty );
    else if( mongo_cursor_bson_valid( cursor, cursor->query ) != MONGO_OK )
        return MONGO_ERROR;

    if( ! cursor->fields )
        cursor->fields = bson_empty( &empty );
    else if( mongo_cursor_bson_valid( cursor, cursor->fields ) != MONGO_OK )
        return MONGO_ERROR;

    mm = mongo_message_create( 16 +  
                               4 +  
                               strlen( cursor->ns ) + 1 +  
                               4 + 4 +  
                               bson_size( cursor->query ) +
                               bson_size( cursor->fields ) ,
                               0 , 0 , MONGO_OP_QUERY );

    data = &mm->data;
    data = mongo_data_append32( data , &cursor->options );
    data = mongo_data_append( data , cursor->ns , strlen( cursor->ns ) + 1 );
    data = mongo_data_append32( data , &cursor->skip );
    data = mongo_data_append32( data , &cursor->limit );
    data = mongo_data_append( data , cursor->query->data , bson_size( cursor->query ) );
    if ( cursor->fields )
        data = mongo_data_append( data , cursor->fields->data , bson_size( cursor->fields ) );

    bson_fatal_msg( ( data == ( ( char * )mm ) + mm->head.len ), "query building fail!" );

    res = mongo_message_send( cursor->conn , mm );
    if( res != MONGO_OK ) {
        return MONGO_ERROR;
    }

    res = mongo_read_response( cursor->conn, ( mongo_reply ** )&( cursor->reply ) );
    if( res != MONGO_OK ) {
        return MONGO_ERROR;
    }

    if( cursor->reply->fields.num == 1 ) {
        bson_init_data( &temp, &cursor->reply->objs );
        if( bson_find( &it, &temp, "$err" ) ) {
            mongo_set_last_error( cursor->conn, &it, &temp );
            cursor->err = MONGO_CURSOR_QUERY_FAIL;
            return MONGO_ERROR;
        }
    }

    cursor->seen += cursor->reply->fields.num;
    cursor->flags |= MONGO_CURSOR_QUERY_SENT;
    return MONGO_OK;
}