Filter Expires header from user metadata (#7269)

Instead save it as a struct field in ObjectInfo as it is
a standard HTTP header - Fixes minio/mc#2690

cmd/fs-v1-metadata.go

@@ -22,8 +22,10 @@ import (
 	"encoding/json"
 	"io"
 	"io/ioutil"
+	"net/http"
 	"os"
 	pathutil "path"
+	"time"
 
 	"github.com/minio/minio/cmd/logger"
 	"github.com/minio/minio/pkg/lock"
@@ -169,7 +171,15 @@ func (m fsMetaV1) ToObjectInfo(bucket, object string, fi os.FileInfo) ObjectInfo
 	} else {
 		objInfo.StorageClass = globalMinioDefaultStorageClass
 	}
-
+	var (
+		t time.Time
+		e error
+	)
+	if exp, ok := m.Meta["expires"]; ok {
+		if t, e = time.Parse(http.TimeFormat, exp); e == nil {
+			objInfo.Expires = t.UTC()
+		}
+	}
 	// etag/md5Sum has already been extracted. We need to
 	// remove to avoid it from appearing as part of
 	// response headers. e.g, X-Minio-* or X-Amz-*.