From 87488db45f0a48ebe026188c2bc341c5ad5d052c Mon Sep 17 00:00:00 2001
From: Christoph Kempen <christoph@downsized.nl>
Date: Sun, 25 Oct 2026 23:00:17 +0100
Subject: [PATCH] fix: return 304 only when the file is unchanged since
 If-Modified-Since

---
 src/DocumentRoot.php      |  5 ++--
 test/DocumentRootTest.php | 57 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/src/DocumentRoot.php b/src/DocumentRoot.php
index a05a822..46548d2 100644
--- a/src/DocumentRoot.php
+++ b/src/DocumentRoot.php
@@ -306,9 +306,10 @@ private function checkPreconditions(Request $request, int $mtime, string $etag):
             return Precondition::NotModified;
         }
 
+        // If-Modified-Since must be ignored when If-None-Match is present (RFC 9110 section 13.1.3)
         $ifModifiedSince = $request->getHeader("If-Modified-Since");
-        $ifModifiedSince = $ifModifiedSince ? \strtotime($ifModifiedSince) : 0;
-        if ($ifModifiedSince && $mtime > $ifModifiedSince) {
+        $ifModifiedSince = $ifModifiedSince && !$ifNoneMatch ? \strtotime($ifModifiedSince) : 0;
+        if ($ifModifiedSince && $mtime <= $ifModifiedSince) {
             return Precondition::NotModified;
         }
 
diff --git a/test/DocumentRootTest.php b/test/DocumentRootTest.php
index f367f4b..6eaa7d7 100644
--- a/test/DocumentRootTest.php
+++ b/test/DocumentRootTest.php
@@ -250,7 +250,7 @@ public function testPreconditionNotModified(): void
 
         $request = new Request($this->createMock(Client::class), "GET", $this->createUri("/index.htm"), [
             "if-match" => $etag,
-            "if-modified-since" => "2.1.1970",
+            "if-modified-since" => \gmdate("D, d M Y H:i:s", \filemtime($diskPath))." GMT",
         ]);
 
         $response = $this->root->handleRequest($request);
@@ -260,6 +260,61 @@ public function testPreconditionNotModified(): void
         $this->assertSame($etag, $response->getHeader("etag"));
     }
 
+    public function testIfModifiedSinceOlderThanMtimeReturnsFile(): void
+    {
+        $diskPath = \realpath(self::fixturePath())."/index.htm";
+
+        $request = new Request($this->createMock(Client::class), "GET", $this->createUri("/index.htm"), [
+            "if-modified-since" => \gmdate("D, d M Y H:i:s", \filemtime($diskPath) - 3600)." GMT",
+        ]);
+
+        $response = $this->root->handleRequest($request);
+
+        $this->assertSame(HttpStatus::OK, $response->getStatus());
+        $this->assertSame(\file_get_contents($diskPath), $response->getBody()->read());
+    }
+
+    public function testIfModifiedSinceEqualToMtimeReturnsNotModified(): void
+    {
+        $diskPath = \realpath(self::fixturePath())."/index.htm";
+
+        $request = new Request($this->createMock(Client::class), "GET", $this->createUri("/index.htm"), [
+            "if-modified-since" => \gmdate("D, d M Y H:i:s", \filemtime($diskPath))." GMT",
+        ]);
+
+        $response = $this->root->handleRequest($request);
+
+        $this->assertSame(HttpStatus::NOT_MODIFIED, $response->getStatus());
+    }
+
+    public function testIfModifiedSinceNewerThanMtimeReturnsNotModified(): void
+    {
+        $diskPath = \realpath(self::fixturePath())."/index.htm";
+
+        $request = new Request($this->createMock(Client::class), "GET", $this->createUri("/index.htm"), [
+            "if-modified-since" => \gmdate("D, d M Y H:i:s", \filemtime($diskPath) + 3600)." GMT",
+        ]);
+
+        $response = $this->root->handleRequest($request);
+
+        $this->assertSame(HttpStatus::NOT_MODIFIED, $response->getStatus());
+    }
+
+    public function testIfModifiedSinceIsIgnoredWhenIfNoneMatchDoesNotMatch(): void
+    {
+        $diskPath = \realpath(self::fixturePath())."/index.htm";
+
+        $request = new Request($this->createMock(Client::class), "GET", $this->createUri("/index.htm"), [
+            "if-none-match" => "\"not-the-etag\"",
+            "if-modified-since" => \gmdate("D, d M Y H:i:s", \filemtime($diskPath) + 3600)." GMT",
+        ]);
+
+        $response = $this->root->handleRequest($request);
+
+        $this->assertSame(HttpStatus::OK, $response->getStatus());
+        $this->assertSame(\file_get_contents($diskPath), $response->getBody()->read());
+    }
+
     public function testPreconditionRangeFail(): void
     {
         $this->root->setUseEtagInode(false);