commit 89f692395e61983bfedb2d5acc48907274a30ae5
Author: achmizs <said@saidachmiz.net>
Date:   Mon Jan 28 10:51:01 2019 -0500

    Initial commit

diff --git a/versioned-assets.php b/versioned-assets.php
new file mode 100644
index 0000000..7b2b141
--- /dev/null
+++ b/versioned-assets.php
@@ -0,0 +1,51 @@
+<?php
+/** \versioned_assets.php
+  * \Copyright (c) 2017 Said Achmiz
+  * \Licensed under the MIT License
+  * \brief Adds versions (modification timestamps) to attachment URLs, so that browser
+  *  caches invalidate properly when attachments are updated.
+  */
+$RecipeInfo['VersionedAssets']['Version'] = '2017-12-13';
+
+global $LinkFunctions;
+$LinkFunctions['Attach:'] = 'LinkUploadVersioned';
+
+SDV($VersionedAssetsReattachFileExtension, true);
+
+function LinkUploadVersioned($pagename, $imap, $path, $alt, $txt, $fmt=NULL) {
+	global $FmtV, $UploadFileFmt, $LinkUploadCreateFmt,
+		$UploadUrlFmt, $UploadPrefixFmt, $EnableDirectDownload;
+	if (preg_match('!^(.*)/([^/]+)$!', $path, $match)) {
+		$pagename = MakePageName($pagename, $match[1]);
+		$path = $match[2];
+	}
+	$upname = MakeUploadName($pagename, $path);
+	$encname = rawurlencode($upname);
+	$filepath = FmtPageName("$UploadFileFmt/$upname", $pagename);
+	$FmtV['$LinkUpload'] =
+		FmtPageName("\$PageUrl?action=upload&amp;upname=$encname", $pagename);
+	$FmtV['$LinkText'] = $txt;
+	if (!file_exists($filepath)) 
+		return FmtPageName($LinkUploadCreateFmt, $pagename);
+	$path = PUE(FmtPageName(IsEnabled($EnableDirectDownload, 1) 
+								? "$UploadUrlFmt$UploadPrefixFmt/$encname"
+								: "{\$PageUrl}?action=download&amp;upname=$encname",
+							$pagename));
+	
+	## Append the modification time to the URL as a GET parameter; this should be ignored
+	## by the web server, but is seen as part of the unique URL of the remote resource by
+	## the browser; when it changes (because the attachment has been modified), the 
+	## browser will see that it doesn’t have a cached version of the resource under the
+	## new URL, and will retrieve the updated version.
+	$versioned_path = $path . "?v=" . filemtime($filepath);
+	
+	global $VersionedAssetsReattachFileExtension;
+	if ($VersionedAssetsReattachFileExtension == true) {
+		## Re-attach the file extension, so that LinkIcons and such things work properly.
+		preg_match("/\\.[^\\.]+$/", $path, $matches);
+		$versioned_path .= $matches[0];
+	}
+	
+	return LinkIMap($pagename, $imap, $versioned_path, $alt, $txt, $fmt);
+}
+