File: Fix permanent_url with multiple permanent redirects

[jtojnar]

The File class handles redirects by calling the constructor recursively. To avoid setting the permanent_url incorrectly at the top of the constructor, the value of the property was reset after each constructor call. And since local variables were used, only the reset following the first internal constructor call would actually do anything. This was very confusing and would stop considering permanent redirects after the first one.
Let’s avoid doing stuff after popping the stack, tail recursion FTW.

Additionally, the permanent_url would only be updated when HTTP 301 Moved Permanently status code was encountered.
Let’s also support HTTP 308 Permanent Redirect.

Tracking the mutability in a property is not the cleanest but a bigger refactoring is probably not worth it with the upcoming deprecation of File.

Unfortunately, we cannot easily test this since we cannot mock curl.

[jtojnar]

I managed to test this with

--- a/tests/Unit/FileTest.php
+++ b/tests/Unit/FileTest.php
@@ -45,6 +45,7 @@ declare(strict_types=1);
 namespace SimplePie\Tests\Unit;
 
 use PHPUnit\Framework\TestCase;
+use SimplePie\File;
 
 class FileTest extends TestCase
 {
@@ -57,4 +58,13 @@ class FileTest extends TestCase
     {
         $this->assertTrue(class_exists('SimplePie_File'));
     }
+
+    public function testFoo() {
+        $file = new File(
+            url: 'http://localhost:8000/perm2',
+            redirects: 10,
+        );
+        $this->assertSame('http://localhost:8000/temp2', $file->permanent_url);
+        $this->assertSame('http://localhost:8000/final', $file->url);
+    }
 }

while running the following script with php -S localhost:8000 srv.php:

<?php

function redirect(int $status, string $location): void {
    http_response_code($status);
    header("Location: $location");
}

function output(int $status, string $text): void {
    http_response_code($status);
    echo $text;
}

match ($_SERVER['REQUEST_URI']) {
    '/perm2' => redirect(308, '/perm1'),
    '/perm1' => redirect(301, '/perm0'),
    '/perm0' => redirect(308, '/temp2'),
    '/temp2' => redirect(307, '/temp1'),
    '/temp1' => redirect(302, '/temp0'),
    '/temp0' => redirect(307, '/permA'),
    '/permA' => redirect(301, '/permB'),
    '/permB' => redirect(308, '/permC'),
    '/permC' => redirect(308, '/final'),
    '/final' => output(200, '/ok'),
    default => output(404, 'Not found'),
};

both with curl and fsockopen.

[jtojnar]

Primary motivation is to make Response::get_permanent_uri() from #774 meaningful.