How to edit a file from another site?

Question

PHP

Hello.
I have 2 wordpress sites.
On one (test1.ru) there is a text.csv file.
I can open it, write to it.
I also need to open this file from the site (subdomain) and edit it
(dir.test1.ru)

<?php
$direct = "http://test1.ru/text.csv";
$file = fopen ($direct, "r");
if (!$file) {
    echo "<p>Невозможно перезаписать удаленный файл.\n";
    exit;
}
$data = fgetcsv($file);
$number = implode("",$data);
fclose($file);
?>

on r+ - issues Unable to overwrite the deleted file
Rights on text.csv - 0777
on the folder too.

Answer 1

Refer to the file by absolute path
if they are on the same server.
Or by ftp

Answer 2

How do you imagine it over HTTP?

Answer 3

API or FTP