feat: add url shortener

shortener/.gitignore

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+links/

shortener/README.md

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+# ash.ley
+
+A simple link shortener. Its a single PHP script which requires a small about of webserver configuration. Adding new links just requires adding a file to the `links/` folder containing the URL to link to.
+
+## Webserver configuration
+
+```nginx
+server {
+    server_name ash.ley;
+    root /var/www/ash.ley;
+    
+    location ~ ^/links {
+        deny all;
+    }
+    
+    location / {
+        try_files @ashdotley;
+    }
+    
+    location @ashdotley {
+        rewrite ^/(.*) /index.php?id=$1&$args last;
+    }
+    
+    location ~ ^/index.php$ {
+        include fastcgi_params;
+        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
+        fastcgi_param REDIRECT_STATUS 200;
+        fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
+    }
+}
+```
+

shortener/index.php

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+<?php
+if (isset($_GET['l'])) {
+    $l = $_GET['l'];
+    if (str_contains($l, '/') || str_contains($l, '~') || str_contains($l, '.')) {
+        http_response_code(400);
+        echo "hehe no you don't";
+        die;
+    }
+    $path = 'links/'.$l;
+    if (file_exists($path)) {
+        $target = file_get_contents($path);
+        header('Location: ' . $target);
+    } else {
+        http_response_code(404);
+        echo "<h1>not found</h1>";
+        echo 'nyy-a?';
+    }
+} else {
+    echo "<h1>nyaaaa!</h1>";
+    echo "~w~\n";
+}
+?>