From f1bc857f66fdc7060ef3c67135fde3075029cc72 Mon Sep 17 00:00:00 2001
From: Anis Elleuch <vadmeste@users.noreply.github.com>
Date: Mon, 12 Apr 2021 17:36:15 +0100
Subject: [PATCH] Lifecycle: Accept empty <Filter> tag in XML documents
 (#12039)

Follow S3 to accept an empty filter tag inside an XML document.

<Filter> needs to be specified but it doesn't have to contain any other
XML tags inside it.
---
 pkg/bucket/lifecycle/filter.go         | 6 ++++--
 pkg/bucket/lifecycle/lifecycle_test.go | 8 +++++++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/pkg/bucket/lifecycle/filter.go b/pkg/bucket/lifecycle/filter.go
index fe1d1f661..c69d27c26 100644
--- a/pkg/bucket/lifecycle/filter.go
+++ b/pkg/bucket/lifecycle/filter.go
@@ -28,6 +28,7 @@ var (
 // Filter - a filter for a lifecycle configuration Rule.
 type Filter struct {
 	XMLName xml.Name `xml:"Filter"`
+	set     bool
 
 	Prefix Prefix
 
@@ -68,6 +69,7 @@ func (f Filter) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
 
 // UnmarshalXML - decodes XML data.
 func (f *Filter) UnmarshalXML(d *xml.Decoder, start xml.StartElement) (err error) {
+	f.set = true
 	for {
 		// Read tokens from the XML document in a stream.
 		t, err := d.Token()
@@ -111,12 +113,12 @@ func (f *Filter) UnmarshalXML(d *xml.Decoder, start xml.StartElement) (err error
 
 // IsEmpty returns true if Filter is not specified in the XML
 func (f Filter) IsEmpty() bool {
-	return !f.Prefix.set && !f.andSet && !f.tagSet
+	return !f.set
 }
 
 // Validate - validates the filter element
 func (f Filter) Validate() error {
-	if !f.Prefix.set && !f.andSet && !f.tagSet {
+	if f.IsEmpty() {
 		return errXMLNotWellFormed
 	}
 	// A Filter must have exactly one of Prefix, Tag, or And specified.
diff --git a/pkg/bucket/lifecycle/lifecycle_test.go b/pkg/bucket/lifecycle/lifecycle_test.go
index b297c40be..60bed4834 100644
--- a/pkg/bucket/lifecycle/lifecycle_test.go
+++ b/pkg/bucket/lifecycle/lifecycle_test.go
@@ -86,12 +86,18 @@ func TestParseAndValidateLifecycleConfig(t *testing.T) {
 			expectedParsingErr:    nil,
 			expectedValidationErr: errXMLNotWellFormed,
 		},
-		// Legitimate lifecycle
+		// Lifecycle with the deprecated Prefix tag
 		{
 			inputConfig:           `<LifecycleConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"><Rule><ID>rule</ID><Prefix /><Status>Enabled</Status><Expiration><Days>1</Days></Expiration></Rule></LifecycleConfiguration>`,
 			expectedParsingErr:    nil,
 			expectedValidationErr: nil,
 		},
+		// Lifecycle with empty Filter tag
+		{
+			inputConfig:           `<LifecycleConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"><Rule><ID>rule</ID><Filter></Filter><Status>Enabled</Status><Expiration><Days>1</Days></Expiration></Rule></LifecycleConfiguration>`,
+			expectedParsingErr:    nil,
+			expectedValidationErr: nil,
+		},
 	}
 
 	for i, tc := range testCases {