From b17b3719958c3fb21d6a8b0d3d951a4f1688f014 Mon Sep 17 00:00:00 2001
From: Dan Fuhry <dan@fuhry.com>
Date: Tue, 19 Aug 2025 09:16:30 -0400
Subject: [PATCH] [http/s3] support `if-modified-since` and `if-none-match`

---
 http/route_action_s3.go | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/http/route_action_s3.go b/http/route_action_s3.go
index 3ab3647..4e5b6ee 100644
--- a/http/route_action_s3.go
+++ b/http/route_action_s3.go
@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/minio/minio-go/v7"
 	"github.com/minio/minio-go/v7/pkg/credentials"
@@ -75,6 +76,26 @@ func (a *S3Action) Handle(w http.ResponseWriter, r *http.Request, next http.Hand
 		return
 	}
 
+	if ims := r.Header.Get("if-modified-since"); ims != "" {
+		imsTime, err := time.Parse(http.TimeFormat, ims)
+		if err == nil && (imsTime.Equal(stat.LastModified) || imsTime.After(stat.LastModified)) {
+			w.WriteHeader(http.StatusNotModified)
+			return
+		}
+	}
+	w.Header().Set("last-modified", stat.LastModified.Format(http.TimeFormat))
+
+	if stat.ChecksumSHA1 != "" {
+		if inm := r.Header.Get("if-none-match"); inm != "" {
+			if inm == stat.ChecksumSHA1 {
+				w.WriteHeader(http.StatusNotModified)
+				return
+			}
+		}
+
+		w.Header().Set("ETag", stat.ChecksumSHA1)
+	}
+
 	var seek int64
 	var size = stat.Size
 	if rh != nil {
-- 
2.50.1