Issue #11291: Add X-Sendfile support for high performance file downloads

X-Sendfile is a header that is added to the output response from PHP
that points to a local file on the disk. Upon receiving the header once
the PHP script has terminated, the web server proceeds to replace all
content in the HTTP response with the contents of the file served up
locally from the disk. Headers set in the PHP script are usually kept
in-tact (depending on the web server implementation as to what gets
changed).

This technique is meant to improve performance as it now becomes
possible for the web server to use highly efficient file serving
functions to serve up the static content. For example, a web server
could use a zero-copy splice() call on Linux platforms to prevent
unnecessary buffering, drastically improving performance.

Servers that support X-Sendfile (or equivalent, as determined by the
$g_file_download_xsendfile_header_name option) include:
* Lighttpd
* Cherokee
* Apache (with mod_xsendfile)
* nginx

config_defaults_inc.php

@@ -1655,6 +1655,26 @@
  */
 $g_absolute_path_default_upload_folder = '';
 
+/**
+ * Enable support for sending files to users via a more efficient X-Sendfile
+ * method. HTTP server software supporting this technique includes Lighttpd,
+ * Cherokee, Apache with mod_xsendfile and nginx. You may need to set the
+ * proceeding file_download_xsendfile_header_name option to suit the server you
+ * are using.
+ * @global int $g_file_download_method
+ */
+$g_file_download_xsendfile_enabled = OFF;
+
+/**
+ * The name of the X-Sendfile header to use. Each server tends to implement
+ * this functionality in a slightly different way and thus the naming
+ * conventions for the header differ between each server. Lighttpd from v1.5,
+ * Apache with mod_xsendfile and Cherokee web servers use X-Sendfile. nginx
+ * uses X-Accel-Redirect and Lighttpd v1.4 uses X-LIGHTTPD-send-file.
+ * @global string $g_file_download_xsendfile_header_name
+ */
+$g_file_download_xsendfile_header_name = 'X-Sendfile';
+
 /**************************
  * MantisBT HTML Settings *
  **************************/

docbook/adminguide/en/configuration.sgml

@@ -1353,12 +1353,12 @@
     <section id="admin.config.uploads">
         <title>File Upload</title>
 
-        <para>MantisBT allows users to upload file attachements and
-            associated them with bugs as well as projects. Bug attachments /
-            project documents can be uploaded to the webserver, database, or an
+        <para>MantisBT allows users to upload file attachments and
+            associate them with bugs as well as projects. Bug attachments /
+            project documents can be uploaded to the webserver, database or an
             FTP server. When bugs are uploaded to the webserver they are
             uploaded to the path that is configured in the project
-            properties.In case of problems getting the file upload feature to
+            properties. In case of problems getting the file upload feature to
             work, check the following resources:
             <ulink url="http://www.php.net/manual/en/features.file-upload.php">PHP
                 Manual
@@ -1478,12 +1478,35 @@
                 <term>$g_fileinfo_magic_db_file</term>
                 <listitem>
                     <para>Specify the filename of the magic database file.
-		        This is used by PHP 5.3.0 (or earlier versions with the
-		        fileinfo PECL extension) to guess what the MIME type of a
-		        file is. Usually it is safe to leave this setting as the
-		        default (blank) as PHP is usually able to find this file
-	                by itself.
-		    </para>
+                        This is used by PHP 5.3.0 (or earlier versions with the
+                        fileinfo PECL extension) to guess what the MIME type of a
+                        file is. Usually it is safe to leave this setting as the
+                        default (blank) as PHP is usually able to find this file
+                        by itself.
+                    </para>
+                </listitem>
+            </varlistentry>
+            <varlistentry>
+                <term>$g_file_download_xsendfile_enabled</term>
+                <listitem>
+                    <para>Enable support for sending files to users via a more efficient
+                        X-Sendfile method. HTTP server software supporting this technique
+                        includes Lighttpd, Cherokee, Apache with mod_xsendfile and nginx.
+                        You may need to set the proceeding file_download_xsendfile_header_name
+                        option to suit the server you are using.
+                    </para>
+                </listitem>
+            </varlistentry>
+            <varlistentry>
+                <term>$g_file_download_xsendfile_header_name</term>
+                <listitem>
+                    <para>The name of the X-Sendfile header to use. Each server tends to
+                        implement this functionality in a slightly different way and thus
+                        the naming conventions for the header differ between each server.
+                        Lighttpd from v1.5, Apache with mod_xsendfile and Cherokee web
+                        servers use X-Sendfile. nginx uses X-Accel-Redirect and Lighttpd
+                        v1.4 uses X-LIGHTTPD-send-file.
+                    </para>
                 </listitem>
             </varlistentry>
         </variablelist>

file_download.php

@@ -155,7 +155,12 @@
 				}
 
 				header( 'Content-Type: ' . $t_content_type );
-				file_send_chunk( $t_local_disk_file );
+				if ( config_get( 'file_download_xsendfile_enabled' ) ) {
+					$t_xsendfile_header_name = config_get( 'file_download_xsendfile_header_name' );
+					header( $t_xsendfile_header_name . ': ' . $t_local_disk_file );
+				} else {
+					file_send_chunk( $t_local_disk_file );
+				}
 			}
 			break;
 		case FTP: