MDL-59960 core_files: improve mimetype detection

Improve mimetype detection for remote files that
have no file extension.  The mimetype detection
that makes use of the file, only works with local
files, so do not use the remote path which can be
a URL or stream.

lib/filestorage/file_system.php

@@ -514,14 +514,13 @@ protected static function get_file_handle_for_path($path, $type = stored_file::F
      * @return string The MIME type.
      */
     public function mimetype_from_hash($contenthash, $filename) {
-        $pathname = $this->get_remote_path_from_hash($contenthash);
+        $pathname = $this->get_local_path_from_hash($contenthash);
         $mimetype = file_storage::mimetype($pathname, $filename);
 
-        if (!$this->is_file_readable_locally_by_hash($contenthash, false) && $mimetype === 'document/unknown') {
+        if ($mimetype === 'document/unknown' && !$this->is_file_readable_locally_by_hash($contenthash)) {
             // The type is unknown, but the full checks weren't completed because the file isn't locally available.
             // Ensure we have a local copy and try again.
             $pathname = $this->get_local_path_from_hash($contenthash, true);
-
             $mimetype = file_storage::mimetype_from_file($pathname);
         }
 
@@ -539,18 +538,7 @@ public function mimetype_from_storedfile($file) {
             // Files with an empty filesize are treated as directories and have no mimetype.
             return null;
         }
-        $pathname = $this->get_remote_path_from_storedfile($file);
-        $mimetype = file_storage::mimetype($pathname, $file->get_filename());
-
-        if (!$this->is_file_readable_locally_by_storedfile($file) && $mimetype === 'document/unknown') {
-            // The type is unknown, but the full checks weren't completed because the file isn't locally available.
-            // Ensure we have a local copy and try again.
-            $pathname = $this->get_local_path_from_storedfile($file, true);
-
-            $mimetype = file_storage::mimetype_from_file($pathname);
-        }
-
-        return $mimetype;
+        return $this->mimetype_from_hash($file->get_contenthash(), $file->get_filename());
     }
 
     /**

lib/filestorage/tests/file_system_test.php

@@ -951,14 +951,13 @@ public function test_mimetype_from_hash_using_filename() {
      * a locally available file whose filename does not suggest mimetype.
      */
     public function test_mimetype_from_hash_using_file_content() {
-        $filepath = '/path/to/file/not/currently/on/disk';
         $filecontent = 'example content';
         $contenthash = file_storage::hash_from_string($filecontent);
         $filename = 'example';
 
         $filepath = __DIR__ . "/fixtures/testimage.jpg";
-        $fs = $this->get_testable_mock(['get_remote_path_from_hash']);
-        $fs->method('get_remote_path_from_hash')->willReturn($filepath);
+        $fs = $this->get_testable_mock(['get_local_path_from_hash']);
+        $fs->method('get_local_path_from_hash')->willReturn($filepath);
 
         $result = $fs->mimetype_from_hash($contenthash, $filename);
         $this->assertEquals('image/jpeg', $result);
@@ -1023,8 +1022,8 @@ public function test_mimetype_from_storedfile_using_filename() {
      */
     public function test_mimetype_from_storedfile_using_file_content() {
         $filepath = __DIR__ . "/fixtures/testimage.jpg";
-        $fs = $this->get_testable_mock(['get_remote_path_from_storedfile']);
-        $fs->method('get_remote_path_from_storedfile')->willReturn($filepath);
+        $fs = $this->get_testable_mock(['get_local_path_from_hash']);
+        $fs->method('get_local_path_from_hash')->willReturn($filepath);
 
         $file = $this->get_stored_file('example content');
 
@@ -1040,14 +1039,12 @@ public function test_mimetype_from_storedfile_using_file_content_remote() {
         $filepath = __DIR__ . "/fixtures/testimage.jpg";
 
         $fs = $this->get_testable_mock([
-            'get_remote_path_from_storedfile',
-            'is_file_readable_locally_by_storedfile',
-            'get_local_path_from_storedfile',
+            'is_file_readable_locally_by_hash',
+            'get_local_path_from_hash',
         ]);
 
-        $fs->method('get_remote_path_from_storedfile')->willReturn('/path/to/remote/file');
-        $fs->method('is_file_readable_locally_by_storedfile')->willReturn(false);
-        $fs->method('get_local_path_from_storedfile')->willReturn($filepath);
+        $fs->method('is_file_readable_locally_by_hash')->willReturn(false);
+        $fs->method('get_local_path_from_hash')->will($this->onConsecutiveCalls('/path/to/remote/file', $filepath));
 
         $file = $this->get_stored_file('example content');