diff --git a/go.mod b/go.mod
index 507a22389..f863fccd1 100644
--- a/go.mod
+++ b/go.mod
@@ -10,7 +10,7 @@ require (
 	github.com/KarpelesLab/reflink v1.0.2
 	github.com/KirCute/zip v1.0.1
 	github.com/OpenListTeam/go-cache v0.1.0
-	github.com/OpenListTeam/gofakes3 v0.8.1
+	github.com/OpenListTeam/gofakes3 v0.8.2-0.20260910152701-89a46c65a7cf
 	github.com/OpenListTeam/sftpd-openlist v1.0.1
 	github.com/OpenListTeam/tache v0.2.2
 	github.com/OpenListTeam/times v0.1.0
diff --git a/go.sum b/go.sum
index b53aa8c79..878e70e64 100644
--- a/go.sum
+++ b/go.sum
@@ -51,8 +51,8 @@ github.com/OpenListTeam/115-sdk-go v0.2.6 h1:ehXyStvncvn4qRBuknor3kyGZtUmHc0+stj
 github.com/OpenListTeam/115-sdk-go v0.2.6/go.mod h1:cfvitk2lwe6036iNi2h+iNxwxWDifKZsSvNtrur5BqU=
 github.com/OpenListTeam/go-cache v0.1.0 h1:eV2+FCP+rt+E4OCJqLUW7wGccWZNJMV0NNkh+uChbAI=
 github.com/OpenListTeam/go-cache v0.1.0/go.mod h1:AHWjKhNK3LE4rorVdKyEALDHoeMnP8SjiNyfVlB+Pz4=
-github.com/OpenListTeam/gofakes3 v0.8.1 h1:uihJ7Zgb4qIafFcXhcm71BzxCyGRIqBVJYg4YOUa6uY=
-github.com/OpenListTeam/gofakes3 v0.8.1/go.mod h1:mS9Ywbo6aId6BrRzeYjOIOpK0QDVnMoKOIb0hpaQZ3U=
+github.com/OpenListTeam/gofakes3 v0.8.2-0.20260910152701-89a46c65a7cf h1:p3Wby2o00mEAZPGLZx+X6QGKoInCDBNjKpPWn0Lpprc=
+github.com/OpenListTeam/gofakes3 v0.8.2-0.20260910152701-89a46c65a7cf/go.mod h1:mS9Ywbo6aId6BrRzeYjOIOpK0QDVnMoKOIb0hpaQZ3U=
 github.com/OpenListTeam/gsync v0.1.0 h1:ywzGybOvA3lW8K1BUjKZ2IUlT2FSlzPO4DOazfYXjcs=
 github.com/OpenListTeam/gsync v0.1.0/go.mod h1:h/Rvv9aX/6CdW/7B8di3xK3xNV8dUg45Fehrd/ksZ9s=
 github.com/OpenListTeam/reflink v0.0.0-20260701021214-78760eaeafef h1:67uGHancMF/abMrnkc8abVUWQiG73Wk5d8CKt3RzkFo=
diff --git a/server/s3/backend.go b/server/s3/backend.go
index be1918d22..a79dd2285 100644
--- a/server/s3/backend.go
+++ b/server/s3/backend.go
@@ -4,9 +4,11 @@ package s3
 
 import (
 	"context"
+	"crypto/md5"
 	"encoding/hex"
 	"fmt"
 	"io"
+	"net/http"
 	"path"
 	"strings"
 	"sync"
@@ -30,7 +32,7 @@ import (
 
 var (
 	emptyPrefix = &gofakes3.Prefix{}
-	timeFormat  = "Mon, 2 Jan 2006 15:04:05 GMT"
+	timeFormat  = http.TimeFormat
 )
 
 // s3Backend implements the gofakes3.Backend interface to make an S3
@@ -117,9 +119,13 @@ func (b *s3Backend) HeadObject(ctx context.Context, bucketName, objectName strin
 
 	fp := path.Join(bucketPath, objectName)
 	fmeta, _ := op.GetNearestMeta(fp)
-	node, err := fs.Get(context.WithValue(ctx, conf.MetaKey, fmeta), fp, &fs.GetArgs{})
+	ctx = context.WithValue(ctx, conf.MetaKey, fmeta)
+	node, err := fs.Get(ctx, fp, &fs.GetArgs{})
 	if err != nil {
-		return nil, gofakes3.KeyNotFound(objectName)
+		if errs.IsObjectNotFound(err) {
+			return nil, gofakes3.KeyNotFound(objectName)
+		}
+		return nil, err
 	}
 
 	if node.IsDir() {
@@ -127,23 +133,27 @@ func (b *s3Backend) HeadObject(ctx context.Context, bucketName, objectName strin
 	}
 
 	size := node.GetSize()
-	// hash := getFileHashByte(fobj)
+	hash, err := getObjectHash(ctx, fp, node)
+	if err != nil {
+		return nil, err
+	}
 
 	meta := map[string]string{
-		"Last-Modified": node.ModTime().Format(timeFormat),
+		"Last-Modified": node.ModTime().UTC().Format(timeFormat),
 		"Content-Type":  utils.GetMimeType(fp),
 	}
 
-	if val, ok := b.meta.Load(fp); ok {
-		metaMap := val.(map[string]string)
-		for k, v := range metaMap {
+	stored, etag := b.loadMetadata(fp, hash)
+	for k, v := range stored {
+		if k != "Last-Modified" {
 			meta[k] = v
 		}
 	}
 
 	return &gofakes3.Object{
-		Name: objectName,
-		// Hash:     hash,
+		Name:     objectName,
+		Hash:     hash,
+		ETag:     etag,
 		Metadata: meta,
 		Size:     size,
 		Contents: noOpReadCloser{},
@@ -160,15 +170,24 @@ func (b *s3Backend) GetObject(ctx context.Context, bucketName, objectName string
 
 	fp := path.Join(bucketPath, objectName)
 	fmeta, _ := op.GetNearestMeta(fp)
-	node, err := fs.Get(context.WithValue(ctx, conf.MetaKey, fmeta), fp, &fs.GetArgs{})
+	ctx = context.WithValue(ctx, conf.MetaKey, fmeta)
+	node, err := fs.Get(ctx, fp, &fs.GetArgs{})
 	if err != nil {
-		return nil, gofakes3.KeyNotFound(objectName)
+		if errs.IsObjectNotFound(err) {
+			return nil, gofakes3.KeyNotFound(objectName)
+		}
+		return nil, err
 	}
 
 	if node.IsDir() {
 		return nil, gofakes3.KeyNotFound(objectName)
 	}
 
+	hash, err := getObjectHash(ctx, fp, node)
+	if err != nil {
+		return nil, err
+	}
+
 	link, file, err := fs.Link(ctx, fp, model.LinkArgs{})
 	if err != nil {
 		return nil, err
@@ -193,7 +212,7 @@ func (b *s3Backend) GetObject(ctx context.Context, bucketName, objectName string
 		return nil, fmt.Errorf("the remote storage driver need to be enhanced to support s3")
 	}
 
-	var rd io.Reader
+	var rd io.ReadCloser
 	if rnge != nil {
 		rd, err = rrf.RangeRead(ctx, http_range.Range(*rnge))
 	} else {
@@ -204,26 +223,34 @@ func (b *s3Backend) GetObject(ctx context.Context, bucketName, objectName string
 	}
 
 	meta := map[string]string{
-		"Last-Modified":       node.ModTime().Format(timeFormat),
+		"Last-Modified":       node.ModTime().UTC().Format(timeFormat),
 		"Content-Disposition": utils.GenerateContentDisposition(file.GetName()),
 		"Content-Type":        utils.GetMimeType(fp),
 	}
 
-	if val, ok := b.meta.Load(fp); ok {
-		metaMap := val.(map[string]string)
-		for k, v := range metaMap {
+	stored, etag := b.loadMetadata(fp, hash)
+	for k, v := range stored {
+		if k != "Last-Modified" {
 			meta[k] = v
 		}
 	}
 
 	return &gofakes3.Object{
 		// Name: gofakes3.URLEncode(objectName),
-		Name: objectName,
-		// Hash:     "",
+		Name:     objectName,
+		Hash:     hash,
+		ETag:     etag,
 		Metadata: meta,
 		Size:     size,
 		Range:    rnge,
-		Contents: utils.ReadCloser{Reader: rd, Closer: link},
+		Contents: utils.NewReadCloser(rd, func() error {
+			readErr := rd.Close()
+			linkErr := link.Close()
+			if readErr != nil {
+				return readErr
+			}
+			return linkErr
+		}),
 	}, nil
 }
 
@@ -239,7 +266,7 @@ func (b *s3Backend) PutObject(
 	meta map[string]string,
 	input io.Reader, size int64,
 ) (result gofakes3.PutObjectResult, err error) {
-	return result, b.putStream(ctx, bucketName, objectName, meta, input, size)
+	return result, b.putStream(ctx, bucketName, objectName, meta, input, size, "")
 }
 
 // putStream stores the given object into the underlying storage. It is shared
@@ -249,6 +276,7 @@ func (b *s3Backend) putStream(
 	ctx context.Context, bucketName, objectName string,
 	meta map[string]string,
 	input io.Reader, size int64,
+	etag string,
 ) error {
 	bucket, err := getBucketByName(bucketName)
 	if err != nil {
@@ -314,9 +342,10 @@ func (b *s3Backend) putStream(
 	if setting.GetBool(conf.IgnoreSystemFiles) && utils.IsSystemFile(obj.Name) {
 		return errs.IgnoredSystemFile
 	}
+	hash := md5.New()
 	stream := &stream.FileStream{
 		Obj:      &obj,
-		Reader:   input,
+		Reader:   io.TeeReader(input, hash),
 		Mimetype: meta["Content-Type"],
 	}
 	if stream.Mimetype == "" {
@@ -328,7 +357,7 @@ func (b *s3Backend) putStream(
 		return err
 	}
 
-	b.meta.Store(fp, meta)
+	b.meta.Store(fp, objectMetadata{headers: meta, hash: hash.Sum(nil), etag: etag})
 
 	return nil
 }
@@ -374,7 +403,10 @@ func (b *s3Backend) deleteObject(ctx context.Context, bucketName, objectName str
 		return err
 	}
 
-	fs.Remove(ctx, fp)
+	if err := fs.Remove(ctx, fp); err != nil {
+		return err
+	}
+	b.meta.Delete(fp)
 	return nil
 }
 
@@ -418,6 +450,9 @@ func (b *s3Backend) CopyObject(ctx context.Context, srcBucket, srcKey, dstBucket
 	srcFp := path.Join(srcBucketPath, srcKey)
 	fmeta, _ := op.GetNearestMeta(srcFp)
 	srcNode, err := fs.Get(context.WithValue(ctx, conf.MetaKey, fmeta), srcFp, &fs.GetArgs{})
+	if err != nil {
+		return result, err
+	}
 
 	c, err := b.GetObject(ctx, srcBucket, srcKey, nil)
 	if err != nil {
diff --git a/server/s3/etag.go b/server/s3/etag.go
new file mode 100644
index 000000000..f88a8ac02
--- /dev/null
+++ b/server/s3/etag.go
@@ -0,0 +1,73 @@
+package s3
+
+import (
+	"bytes"
+	"context"
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+	"io"
+
+	"github.com/OpenListTeam/OpenList/v4/internal/fs"
+	"github.com/OpenListTeam/OpenList/v4/internal/model"
+	"github.com/OpenListTeam/OpenList/v4/internal/stream"
+	"github.com/OpenListTeam/OpenList/v4/pkg/http_range"
+	"github.com/OpenListTeam/OpenList/v4/pkg/utils"
+)
+
+type objectMetadata struct {
+	headers map[string]string
+	hash    []byte
+	etag    string
+}
+
+// Only reuse upload metadata when it still describes the current content.
+func (b *s3Backend) loadMetadata(name string, hash []byte) (map[string]string, string) {
+	if value, ok := b.meta.Load(name); ok {
+		metadata := value.(objectMetadata)
+		if bytes.Equal(metadata.hash, hash) {
+			return metadata.headers, metadata.etag
+		}
+	}
+	return nil, ""
+}
+
+// Metadata alone cannot identify content: clients can preserve both file size
+// and modification time when overwriting an object. Use the driver's MD5 when
+// available, otherwise hash the complete content, including for HEAD and ranges.
+func getObjectHash(ctx context.Context, name string, obj model.Obj) ([]byte, error) {
+	if value := obj.GetHash().GetHash(utils.MD5); value != "" {
+		hash, err := hex.DecodeString(value)
+		if err != nil || len(hash) != md5.Size {
+			return nil, fmt.Errorf("invalid object MD5: %q", value)
+		}
+		return hash, nil
+	}
+	link, file, err := fs.Link(ctx, name, model.LinkArgs{})
+	if err != nil {
+		return nil, err
+	}
+	defer link.Close()
+	size := link.ContentLength
+	if size <= 0 {
+		size = file.GetSize()
+	}
+	ranges, err := stream.GetRangeReaderFromLink(size, link)
+	if err != nil {
+		return nil, err
+	}
+	reader, err := ranges.RangeRead(ctx, http_range.Range{Length: -1})
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+	hash := md5.New()
+	n, err := utils.CopyWithBuffer(hash, reader)
+	if err != nil {
+		return nil, err
+	}
+	if n != size {
+		return nil, io.ErrUnexpectedEOF
+	}
+	return hash.Sum(nil), nil
+}
diff --git a/server/s3/etag_test.go b/server/s3/etag_test.go
new file mode 100644
index 000000000..439359000
--- /dev/null
+++ b/server/s3/etag_test.go
@@ -0,0 +1,64 @@
+package s3
+
+import (
+	"context"
+	"crypto/md5"
+	"encoding/hex"
+	"net/http/httptest"
+	"sync"
+	"testing"
+
+	"github.com/OpenListTeam/OpenList/v4/internal/model"
+	"github.com/OpenListTeam/OpenList/v4/pkg/utils"
+)
+
+func TestObjectHashFromDriver(t *testing.T) {
+	sum := md5.Sum([]byte("content"))
+	obj := &model.Object{HashInfo: utils.NewHashInfo(utils.MD5, hex.EncodeToString(sum[:]))}
+	hash, err := getObjectHash(context.Background(), "object", obj)
+	if err != nil || hex.EncodeToString(hash) != hex.EncodeToString(sum[:]) {
+		t.Fatalf("hash = %x, err = %v", hash, err)
+	}
+	for _, value := range []string{"invalid", "ab"} {
+		obj.HashInfo = utils.NewHashInfo(utils.MD5, value)
+		if _, err := getObjectHash(context.Background(), "object", obj); err == nil {
+			t.Fatalf("accepted invalid MD5 %q", value)
+		}
+	}
+}
+
+func TestMultipartMetadataMatchesCurrentContent(t *testing.T) {
+	b := &s3Backend{meta: new(sync.Map)}
+	oldHash := md5.Sum([]byte("old"))
+	newHash := md5.Sum([]byte("new"))
+	b.meta.Store("object", objectMetadata{
+		headers: map[string]string{"Content-Type": "text/plain"},
+		hash:    oldHash[:],
+		etag:    `"multipart-2"`,
+	})
+	meta, etag := b.loadMetadata("object", oldHash[:])
+	if etag != `"multipart-2"` || meta["Content-Type"] != "text/plain" {
+		t.Fatal("lost metadata for unchanged multipart content")
+	}
+	meta, etag = b.loadMetadata("object", newHash[:])
+	if meta != nil || etag != "" {
+		t.Fatal("reused a multipart validator after a same-size content change")
+	}
+}
+
+func TestConditionalRequestsDoNotRedirect(t *testing.T) {
+	for _, method := range []string{"GET", "PUT"} {
+		for _, name := range []string{"If-Match", "If-None-Match", "If-Modified-Since", "If-Unmodified-Since", "If-Range"} {
+			for _, value := range []string{"*", ""} {
+				r := httptest.NewRequest(method, "/bucket/object", nil)
+				r.Header.Set(name, value)
+				if url, ok := directObjectURL(r, nil); ok || url != "" {
+					t.Fatalf("redirected %s with %s", method, name)
+				}
+				if url, ok := directUploadURL(r, nil); ok || url != "" {
+					t.Fatalf("redirected %s with %s", method, name)
+				}
+			}
+		}
+	}
+}
diff --git a/server/s3/multipart.go b/server/s3/multipart.go
index 7261ea361..37e89617d 100644
--- a/server/s3/multipart.go
+++ b/server/s3/multipart.go
@@ -234,7 +234,9 @@ func (b *s3Backend) CompleteMultipartUpload(ctx context.Context, bucket, object
 
 	defer combined.Close()
 
-	err := b.putStream(ctx, bucket, object, state.meta, combined, total)
+	sum := md5.Sum(concat)
+	etag := fmt.Sprintf("%q", fmt.Sprintf("%s-%d", hex.EncodeToString(sum[:]), len(ordered)))
+	err := b.putStream(ctx, bucket, object, state.meta, combined, total, etag)
 	if err != nil {
 		// Leave the upload in place so the client may retry completion, per
 		// the gofakes3 MultipartBackend contract.
@@ -244,8 +246,6 @@ func (b *s3Backend) CompleteMultipartUpload(ctx context.Context, bucket, object
 	// Success: drop bookkeeping and clean up part files.
 	b.removeUpload(uploadID)
 
-	sum := md5.Sum(concat)
-	etag := fmt.Sprintf("%q", fmt.Sprintf("%s-%d", hex.EncodeToString(sum[:]), len(ordered)))
 	log.Debugf("s3 multipart: completed upload %s -> %s/%s (%d bytes)", uploadID, bucket, object, total)
 	return "", etag, nil
 }
diff --git a/server/s3/preconditions.go b/server/s3/preconditions.go
new file mode 100644
index 000000000..930fffbcf
--- /dev/null
+++ b/server/s3/preconditions.go
@@ -0,0 +1,12 @@
+package s3
+
+import "net/http"
+
+func hasPreconditions(r *http.Request) bool {
+	for _, name := range []string{"If-Match", "If-None-Match", "If-Modified-Since", "If-Unmodified-Since", "If-Range"} {
+		if _, ok := r.Header[name]; ok {
+			return true
+		}
+	}
+	return false
+}
diff --git a/server/s3/redirect.go b/server/s3/redirect.go
index 6d8d430bc..5696314ef 100644
--- a/server/s3/redirect.go
+++ b/server/s3/redirect.go
@@ -38,7 +38,7 @@ func redirectHandler(next http.Handler, authPairs map[string]string) http.Handle
 }
 
 func directObjectURL(r *http.Request, authPairs map[string]string) (string, bool) {
-	if r.Method != http.MethodGet {
+	if r.Method != http.MethodGet || hasPreconditions(r) {
 		return "", false
 	}
 	if hasNonObjectQuery(r) || !s3RequestAuthorized(r, authPairs) {
@@ -75,7 +75,7 @@ func directObjectURL(r *http.Request, authPairs map[string]string) (string, bool
 }
 
 func directUploadURL(r *http.Request, authPairs map[string]string) (string, bool) {
-	if r.Method != http.MethodPut || r.ContentLength < 0 {
+	if r.Method != http.MethodPut || r.ContentLength < 0 || hasPreconditions(r) {
 		return "", false
 	}
 	if hasNonObjectQuery(r) || !s3RequestAuthorized(r, authPairs) {