From 08b24620c05c6a19918202fcef2e327b8a15908c Mon Sep 17 00:00:00 2001
From: Poorna Krishnamoorthy <poorna@minio.io>
Date: Mon, 16 Nov 2020 22:52:40 -0800
Subject: [PATCH] Display storage-class of transitioned object in HEAD

---
 cmd/api-headers.go      |  3 +++
 cmd/bucket-lifecycle.go | 17 +++++++++++++++++
 cmd/erasure-object.go   | 10 ++++++++--
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/cmd/api-headers.go b/cmd/api-headers.go
index 115b39071..7b72b739b 100644
--- a/cmd/api-headers.go
+++ b/cmd/api-headers.go
@@ -200,6 +200,9 @@ func setObjectHeaders(w http.ResponseWriter, objInfo ObjectInfo, rs *HTTPRangeSp
 				fmt.Sprintf(`expiry-date="%s", rule-id="%s"`, expiryTime.Format(http.TimeFormat), ruleID),
 			}
 		}
+		if objInfo.TransitionStatus == lifecycle.TransitionComplete {
+			w.Header()[xhttp.AmzStorageClass] = []string{objInfo.StorageClass}
+		}
 	}
 
 	return nil
diff --git a/cmd/bucket-lifecycle.go b/cmd/bucket-lifecycle.go
index 90d1ccf77..03d64d4ec 100644
--- a/cmd/bucket-lifecycle.go
+++ b/cmd/bucket-lifecycle.go
@@ -168,6 +168,23 @@ func validateTransitionDestination(ctx context.Context, bucket string, targetLab
 	return sameTarget, arn.Bucket, nil
 }
 
+// transitionSC returns storage class label for this bucket
+func transitionSC(ctx context.Context, bucket string) string {
+	cfg, err := globalBucketMetadataSys.GetLifecycleConfig(bucket)
+	if err != nil {
+		return ""
+	}
+	for _, rule := range cfg.Rules {
+		if rule.Status == Disabled {
+			continue
+		}
+		if rule.Transition.StorageClass != "" {
+			return rule.Transition.StorageClass
+		}
+	}
+	return ""
+}
+
 // return true if ARN representing transition storage class is present in a active rule
 // for the lifecycle configured on this bucket
 func transitionSCInUse(ctx context.Context, lfc *lifecycle.Lifecycle, bucket, arnStr string) bool {
diff --git a/cmd/erasure-object.go b/cmd/erasure-object.go
index 94c2d2291..e88688140 100644
--- a/cmd/erasure-object.go
+++ b/cmd/erasure-object.go
@@ -424,8 +424,14 @@ func (er erasureObjects) getObjectInfo(ctx context.Context, bucket, object strin
 		// Make sure to return object info to provide extra information.
 		return objInfo, toObjectErr(errMethodNotAllowed, bucket, object)
 	}
-
-	return fi.ToObjectInfo(bucket, object), nil
+	oi := fi.ToObjectInfo(bucket, object)
+	if oi.TransitionStatus == lifecycle.TransitionComplete {
+		// overlay storage class for transitioned objects with transition tier SC Label
+		if sc := transitionSC(ctx, bucket); sc != "" {
+			oi.StorageClass = sc
+		}
+	}
+	return oi, nil
 }
 
 func undoRename(disks []StorageAPI, srcBucket, srcEntry, dstBucket, dstEntry string, isDir bool, errs []error) {