Add MaxNoncurrentVersions to NoncurrentExpiration action (#13580)

This unit allows users to limit the maximum number of noncurrent 
versions of an object.

To enable this rule you need the following *ilm.json*
```
cat >> ilm.json <<EOF
{
    "Rules": [
        {
            "ID": "test-max-noncurrent",
            "Status": "Enabled",
            "Filter": {
                "Prefix": "user-uploads/"
            },
            "NoncurrentVersionExpiration": {
                "MaxNoncurrentVersions": 5
            }
        }
    ]
}
EOF
mc ilm import myminio/mybucket < ilm.json
```

internal/bucket/lifecycle/lifecycle.go

@@ -29,10 +29,11 @@ import (
 )
 
 var (
-	errLifecycleTooManyRules = Errorf("Lifecycle configuration allows a maximum of 1000 rules")
-	errLifecycleNoRule       = Errorf("Lifecycle configuration should have at least one rule")
-	errLifecycleDuplicateID  = Errorf("Lifecycle configuration has rule with the same ID. Rule ID must be unique.")
-	errXMLNotWellFormed      = Errorf("The XML you provided was not well-formed or did not validate against our published schema")
+	errLifecycleTooManyRules                = Errorf("Lifecycle configuration allows a maximum of 1000 rules")
+	errLifecycleNoRule                      = Errorf("Lifecycle configuration should have at least one rule")
+	errLifecycleDuplicateID                 = Errorf("Lifecycle configuration has rule with the same ID. Rule ID must be unique.")
+	errXMLNotWellFormed                     = Errorf("The XML you provided was not well-formed or did not validate against our published schema")
+	errLifecycleInvalidNoncurrentExpiration = Errorf("Exactly one of NoncurrentDays (positive integer) or MaxNoncurrentVersions should be specified in a NoncurrentExpiration rule.")
 )
 
 const (
@@ -140,6 +141,9 @@ func (lc Lifecycle) HasActiveRules(prefix string, recursive bool) bool {
 		if rule.NoncurrentVersionExpiration.NoncurrentDays > 0 {
 			return true
 		}
+		if rule.NoncurrentVersionExpiration.MaxNoncurrentVersions > 0 {
+			return true
+		}
 		if !rule.NoncurrentVersionTransition.IsNull() {
 			return true
 		}
@@ -234,6 +238,10 @@ func (lc Lifecycle) FilterActionableRules(obj ObjectOpts) []Rule {
 			rules = append(rules, rule)
 			continue
 		}
+		if rule.NoncurrentVersionExpiration.MaxNoncurrentVersions > 0 {
+			rules = append(rules, rule)
+			continue
+		}
 		// The NoncurrentVersionTransition action requests MinIO to transition
 		// noncurrent versions of objects x days after the objects become
 		// noncurrent.
@@ -468,3 +476,32 @@ func (lc Lifecycle) TransitionTier(obj ObjectOpts) string {
 	}
 	return ""
 }
+
+// NoncurrentVersionsExpirationLimit returns the minimum limit on number of
+// noncurrent versions across rules.
+func (lc Lifecycle) NoncurrentVersionsExpirationLimit(obj ObjectOpts) int {
+	var lim int
+	for _, rule := range lc.FilterActionableRules(obj) {
+		if rule.NoncurrentVersionExpiration.MaxNoncurrentVersions == 0 {
+			continue
+		}
+		if lim == 0 || lim > rule.NoncurrentVersionExpiration.MaxNoncurrentVersions {
+			lim = rule.NoncurrentVersionExpiration.MaxNoncurrentVersions
+		}
+	}
+	return lim
+}
+
+// HasMaxNoncurrentVersions returns true if there exists a rule with
+// MaxNoncurrentVersions limit set.
+func (lc Lifecycle) HasMaxNoncurrentVersions() bool {
+	for _, rule := range lc.Rules {
+		if rule.Status == Disabled {
+			continue
+		}
+		if rule.NoncurrentVersionExpiration.MaxNoncurrentVersions > 0 {
+			return true
+		}
+	}
+	return false
+}

internal/bucket/lifecycle/lifecycle_test.go

@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -111,6 +112,12 @@ func TestParseAndValidateLifecycleConfig(t *testing.T) {
 			expectedParsingErr:    nil,
 			expectedValidationErr: nil,
 		},
+		// Lifecycle with max noncurrent versions
+		{
+			inputConfig:           `<LifecycleConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"><Rule><ID>rule</ID>><Status>Enabled</Status><Filter></Filter><NoncurrentVersionExpiration><MaxNoncurrentVersions>5</MaxNoncurrentVersions></NoncurrentVersionExpiration></Rule></LifecycleConfiguration>`,
+			expectedParsingErr:    nil,
+			expectedValidationErr: nil,
+		},
 	}
 
 	for i, tc := range testCases {
@@ -619,3 +626,24 @@ func TestTransitionTier(t *testing.T) {
 		t.Fatalf("Expected TIER-2 but got %s", got)
 	}
 }
+
+func TestNoncurrentVersionsLimit(t *testing.T) {
+	// test that the lowest max noncurrent versions limit is returned among
+	// matching rules
+	var rules []Rule
+	for i := 1; i <= 10; i++ {
+		rules = append(rules, Rule{
+			ID:     strconv.Itoa(i),
+			Status: "Enabled",
+			NoncurrentVersionExpiration: NoncurrentVersionExpiration{
+				MaxNoncurrentVersions: i,
+			},
+		})
+	}
+	lc := Lifecycle{
+		Rules: rules,
+	}
+	if lim := lc.NoncurrentVersionsExpirationLimit(ObjectOpts{Name: "obj"}); lim != 1 {
+		t.Fatalf("Expected max noncurrent versions limit to be 1 but got %d", lim)
+	}
+}

internal/bucket/lifecycle/noncurrentversion.go

@@ -24,14 +24,15 @@ import (
 
 // NoncurrentVersionExpiration - an action for lifecycle configuration rule.
 type NoncurrentVersionExpiration struct {
-	XMLName        xml.Name       `xml:"NoncurrentVersionExpiration"`
-	NoncurrentDays ExpirationDays `xml:"NoncurrentDays,omitempty"`
-	set            bool
+	XMLName               xml.Name       `xml:"NoncurrentVersionExpiration"`
+	NoncurrentDays        ExpirationDays `xml:"NoncurrentDays,omitempty"`
+	MaxNoncurrentVersions int            `xml:"MaxNoncurrentVersions,omitempty"`
+	set                   bool
 }
 
 // MarshalXML if non-current days not set to non zero value
 func (n NoncurrentVersionExpiration) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
-	if n.IsDaysNull() {
+	if n.IsNull() {
 		return nil
 	}
 	type noncurrentVersionExpirationWrapper NoncurrentVersionExpiration
@@ -51,6 +52,11 @@ func (n *NoncurrentVersionExpiration) UnmarshalXML(d *xml.Decoder, startElement
 	return nil
 }
 
+// IsNull returns if both NoncurrentDays and NoncurrentVersions are empty
+func (n NoncurrentVersionExpiration) IsNull() bool {
+	return n.IsDaysNull() && n.MaxNoncurrentVersions == 0
+}
+
 // IsDaysNull returns true if days field is null
 func (n NoncurrentVersionExpiration) IsDaysNull() bool {
 	return n.NoncurrentDays == ExpirationDays(0)
@@ -62,8 +68,17 @@ func (n NoncurrentVersionExpiration) Validate() error {
 		return nil
 	}
 	val := int(n.NoncurrentDays)
-	if val <= 0 {
+	switch {
+	case val == 0 && n.MaxNoncurrentVersions == 0:
+		// both fields can't be zero
 		return errXMLNotWellFormed
+
+	case val > 0 && n.MaxNoncurrentVersions > 0:
+		// both tags can't be non-zero simultaneously
+		return errLifecycleInvalidNoncurrentExpiration
+
+	case val < 0, n.MaxNoncurrentVersions < 0:
+		// negative values are not supported
 	}
 	return nil
 }