From 6252cff1e5f674dc86fa231e92beec9a3d589c5f Mon Sep 17 00:00:00 2001
From: Alex Cabal <alex@alexcabal.com>
Date: Wed, 24 Jun 2020 21:28:15 -0500
Subject: [PATCH] Only write the OPDS feed and updated timestamp if the feeds
 actually changed

---
 lib/OpdsFeed.php            | 38 ++++++++++++++++++++++++++++---------
 scripts/deploy-ebook-to-www |  2 +-
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/lib/OpdsFeed.php b/lib/OpdsFeed.php
index df1954a1..05193dce 100644
--- a/lib/OpdsFeed.php
+++ b/lib/OpdsFeed.php
@@ -19,6 +19,20 @@ class OpdsFeed{
 		$this->IsCrawlable = $isCrawlable;
 	}
 
+	private function Sha1Entries(string $xmlString): string{
+		$xml = new SimpleXMLElement(str_replace('xmlns=', 'ns=', $xmlString));
+		$xml->registerXPathNamespace('dc', 'http://purl.org/dc/elements/1.1/');
+		$xml->registerXPathNamespace('schema', 'http://schema.org/');
+		$entries = $xml->xpath('/feed/entry') ?? [];
+
+		$output = '';
+		foreach($entries as $entry){
+			$output .= $entry->asXml();
+		}
+
+		return sha1(preg_replace('/\s/ius', '', $output));
+	}
+
 	public function Save(string $filename): void{
 		$updatedTimestamp = gmdate('Y-m-d\TH:i:s\Z');
 
@@ -28,16 +42,22 @@ class OpdsFeed{
 		file_put_contents($tempFilename, $feed);
 		exec('se clean ' . escapeshellarg($tempFilename));
 
-		rename($tempFilename, $filename);
+		// Did we actually update the feed? If so, write to file and update the index
+		if(!is_file($filename)){
+			// File doesn't exist, write it out
+			rename($tempFilename, $filename);
+		}
+		elseif($this->Sha1Entries($feed) != $this->Sha1Entries(file_get_contents($filename))){
+			// Files don't match, save the file and update the index feed with the last updated timestamp
+			$xml = new SimpleXMLElement(str_replace('xmlns=', 'ns=', file_get_contents(WEB_ROOT . '/opds/index.xml')));
+			$xml->registerXPathNamespace('dc', 'http://purl.org/dc/elements/1.1/');
+			$xml->registerXPathNamespace('schema', 'http://schema.org/');
 
-		// Update the index feed with the last updated timestamp
-		$xml = new SimpleXMLElement(str_replace('xmlns=', 'ns=', file_get_contents(WEB_ROOT . '/opds/index.xml')));
-		$xml->registerXPathNamespace('dc', 'http://purl.org/dc/elements/1.1/');
-		$xml->registerXPathNamespace('schema', 'http://schema.org/');
+			$feedEntry = ($xml->xpath('/feed/entry[id="' . $this->Id . '"]/updated') ?? [])[0];
+			$feedEntry[0] = $updatedTimestamp;
+			file_put_contents(WEB_ROOT . '/opds/index.xml', str_replace(" ns=", " xmlns=", $xml->asXml() ?? ''));
 
-		$feedEntry = ($xml->xpath('/feed/entry[id="' . $this->Id . '"]/updated') ?? [])[0];
-		$feedEntry[0] = $updatedTimestamp;
-		file_put_contents(WEB_ROOT . '/opds/index.xml', str_replace(" ns=", " xmlns=", $xml->asXml() ?? ''));
-		exec('se clean ' . WEB_ROOT . '/opds/index.xml');
+			rename($tempFilename, $filename);
+		}
 	}
 }
diff --git a/scripts/deploy-ebook-to-www b/scripts/deploy-ebook-to-www
index 1178af4b..9cba8e56 100755
--- a/scripts/deploy-ebook-to-www
+++ b/scripts/deploy-ebook-to-www
@@ -227,7 +227,7 @@ if [ "${verbose}" = "true" ]; then
 	printf "Rebuilding OPDS catalog ... "
 fi
 
-bash -c "php \"${scriptsDir}\"/generate-opds.php --webroot \"${webRoot}\" --weburl \"${webUrl}\" > \"${webRoot}\"/www/opds/all.xml"
+bash -c "php \"${scriptsDir}\"/generate-opds.php --webroot \"${webRoot}\" --weburl \"${webUrl}\""
 
 if [ "${verbose}" = "true" ]; then
 	printf "Done.\n"