From 5f38019f3cf6fc942fd3c65fddd6193946e24e7a Mon Sep 17 00:00:00 2001
From: Matt Rice <3780536+mattrice@users.noreply.github.com>
Date: Fri, 18 Feb 2022 15:30:29 -0500
Subject: [PATCH] MDL-72582 core_files: Update readfile_accel error handling

Correct the error handling in readfile_accel to properly log errors when
working on a stored_file, rather than hiding the true error behind the
incorrect "Object of class stored_file could not be converted to
string."

Co-authored-by: Simey Lameze <simey@moodle.com>
Co-authored-by: Trisha Milan <trishamilan@catalyst-au.net>
---
 lib/filelib.php | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/lib/filelib.php b/lib/filelib.php
index a5d62cc0aeb..edd075ed3b3 100644
--- a/lib/filelib.php
+++ b/lib/filelib.php
@@ -2226,10 +2226,11 @@ function readfile_accel($file, $mimetype, $accelerate) {
         header('Content-Type: '.$mimetype);
     }
 
-    $lastmodified = is_object($file) ? $file->get_timemodified() : filemtime($file);
+    $isfileobj = is_object($file);
+    $lastmodified = $isfileobj ? $file->get_timemodified() : filemtime($file);
     header('Last-Modified: '. gmdate('D, d M Y H:i:s', $lastmodified) .' GMT');
 
-    if (is_object($file)) {
+    if ($isfileobj) {
         header('Etag: "' . $file->get_contenthash() . '"');
         if (isset($_SERVER['HTTP_IF_NONE_MATCH']) and trim($_SERVER['HTTP_IF_NONE_MATCH'], '"') === $file->get_contenthash()) {
             header('HTTP/1.1 304 Not Modified');
@@ -2238,7 +2239,7 @@ function readfile_accel($file, $mimetype, $accelerate) {
     }
 
     // if etag present for stored file rely on it exclusively
-    if (!empty($_SERVER['HTTP_IF_MODIFIED_SINCE']) and (empty($_SERVER['HTTP_IF_NONE_MATCH']) or !is_object($file))) {
+    if (!empty($_SERVER['HTTP_IF_MODIFIED_SINCE']) && (empty($_SERVER['HTTP_IF_NONE_MATCH']) || !$isfileobj)) {
         // get unixtime of request header; clip extra junk off first
         $since = strtotime(preg_replace('/;.*$/', '', $_SERVER["HTTP_IF_MODIFIED_SINCE"]));
         if ($since && $since >= $lastmodified) {
@@ -2254,7 +2255,7 @@ function readfile_accel($file, $mimetype, $accelerate) {
     }
 
     if ($accelerate) {
-        if (is_object($file)) {
+        if ($isfileobj) {
             $fs = get_file_storage();
             if ($fs->supports_xsendfile()) {
                 if ($fs->xsendfile_file($file)) {
@@ -2271,7 +2272,8 @@ function readfile_accel($file, $mimetype, $accelerate) {
         }
     }
 
-    $filesize = is_object($file) ? $file->get_filesize() : filesize($file);
+    $filesize = $isfileobj ? $file->get_filesize() : filesize($file);
+    $filename = $isfileobj ? $file->get_filename() : $file;
 
     header('Last-Modified: '. gmdate('D, d M Y H:i:s', $lastmodified) .' GMT');
 
@@ -2305,10 +2307,10 @@ function readfile_accel($file, $mimetype, $accelerate) {
                 $ranges = false;
             }
             if ($ranges) {
-                if (is_object($file)) {
+                if ($isfileobj) {
                     $handle = $file->get_content_file_handle();
                     if ($handle === false) {
-                        throw new file_exception('storedfilecannotreadfile', $file->get_filename());
+                        throw new file_exception('storedfilecannotreadfile', $filename);
                     }
                 } else {
                     $handle = fopen($file, 'rb');
@@ -2334,7 +2336,12 @@ function readfile_accel($file, $mimetype, $accelerate) {
             // We do not expect any content in the buffer when we are serving files.
             $buffercontents = ob_get_clean();
             if ($buffercontents !== '') {
-                error_log('Non-empty default output handler buffer detected while serving the file ' . $file);
+                // Include a preview of the first 20 characters of the output buffer to help identify
+                // what's causing it to be non-empty. This is useful for diagnosing unexpected output
+                // without exposing full content.
+                $buffercontentspreview = substr($buffercontents, 0, 20);
+                debugging("Non-empty default output handler buffer detected while serving the file {$filename}. " .
+                    "Buffer contents (first 20 characters): {$buffercontentspreview}", DEBUG_DEVELOPER);
             }
         } else {
             // Some handlers such as zlib output compression may have file signature buffered - flush it.
@@ -2343,7 +2350,7 @@ function readfile_accel($file, $mimetype, $accelerate) {
     }
 
     // send the whole file content
-    if (is_object($file)) {
+    if ($isfileobj) {
         $file->readfile();
     } else {
         if (readfile_allow_large($file, $filesize) === false) {