Rework generate_name() logic

Adds a new config option POMF_FILES_LENGTH. This will allow the user to
adjust the length of filenames. Defaults to 6.

The filename generator never used character z in new filenames. There
are 27 characters in a-z, but the old code uses a magic number of 26
characters. This bug was introduced in commit
5b77a4eaab418836820b2a0bad7c88f0b88136a0.

Instead of relying on magic numbers like with mt_rand(), conveniently
use arrays with array_rand() instead. More characters can be added with
array_merge() in future if desired.

2 files changed, 9 insertions, 7 deletions

diff --git a/static/includes/settings.inc.php b/static/includes/settings.inc.php
index e909b9a..9751cff 100644
--- a/static/includes/settings.inc.php
+++ b/static/includes/settings.inc.php
@@ -9,8 +9,10 @@ define('POMF_DB_PASS', '***');
 
 // Root location of files
 define('POMF_FILES_ROOT', '/mnt/pantsu/http/files/');
-// Maximum number of iterations while generating a new name
+// Maximum number of iterations while generating a new filename
 define('POMF_FILES_RETRIES', 15);
+// Number of random characters to use in a new filename
+define('POMF_FILES_LENGTH', 6);
 // URL to prepend to output (include trailing slash)
 define('POMF_URL', 'https://i.pantsu.cat/');
 
diff --git a/static/upload.php b/static/upload.php
index 8aac02c..6e54ae1 100644
--- a/static/upload.php
+++ b/static/upload.php
@@ -23,8 +23,9 @@ function generate_name ($file) {
 	global $doubledots;
 
 	// We start at N retries, and --N until we give up
-	$tries = POMF_FILES_RETRIES;
-	$ext   = pathinfo($file->name, PATHINFO_EXTENSION);
+   $tries  = POMF_FILES_RETRIES;
+   $length = POMF_FILES_LENGTH;
+   $ext    = pathinfo($file->name, PATHINFO_EXTENSION);
 
 	// Check if extension is a double-dot extension and, if true, override $ext
 	$revname = strrev($file->name);
@@ -39,11 +40,10 @@ function generate_name ($file) {
 		// Iterate until we reach the maximum number of retries
 		if ($tries-- == 0) throw new Exception('Gave up trying to find an unused name', 500);
 
-		$chars = 'abcdefghijklmnopqrstuvwxyz';
+       $chars = range('a', 'z');
 		$name  = '';
-		for ($i = 0; $i < 6; $i++) {
-			$name .= $chars[mt_rand(0, 25)];
-			// $chars string length is hardcoded, should use a variable to store it?
+       for ($i = 0; $i < $length; $i++) {
+           $name .= $chars[array_rand($chars)];
 		}
 
 		// Add the extension to the file name