[#373] pruning: add optional regex field to last_n rule

fixes #373

config/config.go

@@ -324,6 +324,7 @@ type PruneKeepNotReplicated struct {
 type PruneKeepLastN struct {
 	Type  string `yaml:"type"`
 	Count int    `yaml:"count"`
+	Regex string `yaml:"regex,optional"`
 }
 
 type PruneKeepRegex struct { // FIXME rename to KeepRegex

docs/configuration/prune.rst

@@ -175,9 +175,11 @@ Policy ``last_n``
          keep_receiver:
          - type: last_n
            count: 10
+           regex: ^zrepl_.*$ # optional
      ...
 
-``last_n`` keeps the last ``count`` snapshots (last = youngest = most recent creation date).
+``last_n`` filters the snapshot list by ``regex``, then keeps the last ``count`` snapshots in that list (last = youngest = most recent creation date)
+All snapshots that don't match ``regex`` or exceed ``count`` in the filtered list are destroyed unless matched by other rules.
 
 .. _prune-keep-regex:
 

pruning/keep_last_n.go

@@ -1,6 +1,7 @@
 package pruning
 
 import (
+	"regexp"
 	"sort"
 	"strings"
 
@@ -8,14 +9,27 @@ import (
 )
 
 type KeepLastN struct {
-	n int
+	n  int
+	re *regexp.Regexp
 }
 
-func NewKeepLastN(n int) (*KeepLastN, error) {
+func MustKeepLastN(n int, regex string) *KeepLastN {
+	k, err := NewKeepLastN(n, regex)
+	if err != nil {
+		panic(err)
+	}
+	return k
+}
+
+func NewKeepLastN(n int, regex string) (*KeepLastN, error) {
 	if n <= 0 {
 		return nil, errors.Errorf("must specify positive number as 'keep last count', got %d", n)
 	}
-	return &KeepLastN{n}, nil
+	re, err := regexp.Compile(regex)
+	if err != nil {
+		return nil, errors.Errorf("invalid regex %q: %s", regex, err)
+	}
+	return &KeepLastN{n, re}, nil
 }
 
 func (k KeepLastN) KeepRule(snaps []Snapshot) (destroyList []Snapshot) {
@@ -24,17 +38,25 @@ func (k KeepLastN) KeepRule(snaps []Snapshot) (destroyList []Snapshot) {
 		return []Snapshot{}
 	}
 
-	res := shallowCopySnapList(snaps)
+	matching, notMatching := partitionSnapList(snaps, func(snapshot Snapshot) bool {
+		return k.re.MatchString(snapshot.Name())
+	})
+	// snaps that don't match the regex are not kept by this rule
+	destroyList = append(destroyList, notMatching...)
 
-	sort.Slice(res, func(i, j int) bool {
+	if len(matching) == 0 {
+		return destroyList
+	}
+
+	sort.Slice(matching, func(i, j int) bool {
 		// by date (youngest first)
-		id, jd := res[i].Date(), res[j].Date()
+		id, jd := matching[i].Date(), matching[j].Date()
 		if !id.Equal(jd) {
 			return id.After(jd)
 		}
 		// then lexicographically descending (e.g. b, a)
-		return strings.Compare(res[i].Name(), res[j].Name()) == 1
+		return strings.Compare(matching[i].Name(), matching[j].Name()) == 1
 	})
-
+	destroyList = append(destroyList, matching[k.n:]...)
-	return res[k.n:]
+	return destroyList
 }

pruning/keep_last_n_test.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestKeepLastN(t *testing.T) {
@@ -28,7 +29,7 @@ func TestKeepLastN(t *testing.T) {
 		"keep2": {
 			inputs: inputs["s1"],
 			rules: []KeepRule{
-				KeepLastN{2},
+				MustKeepLastN(2, ""),
 			},
 			expDestroy: map[string]bool{
 				"1": true, "2": true, "3": true,
@@ -37,34 +38,66 @@ func TestKeepLastN(t *testing.T) {
 		"keep1OfTwoWithSameTime": { // Keep one of two with same time
 			inputs: inputs["s1"],
 			rules: []KeepRule{
-				KeepLastN{1},
+				MustKeepLastN(1, ""),
 			},
 			expDestroy: map[string]bool{"1": true, "2": true, "3": true, "4": true},
 		},
 		"keepMany": {
 			inputs: inputs["s1"],
 			rules: []KeepRule{
-				KeepLastN{100},
+				MustKeepLastN(100, ""),
 			},
 			expDestroy: map[string]bool{},
 		},
-		"empty": {
+		"empty_input": {
 			inputs: inputs["s2"],
 			rules: []KeepRule{
-				KeepLastN{100},
+				MustKeepLastN(100, ""),
 			},
 			expDestroy: map[string]bool{},
 		},
+		"empty_regex": {
+			inputs: inputs["s1"],
+			rules: []KeepRule{
+				MustKeepLastN(4, ""),
+			},
+			expDestroy: map[string]bool{
+				"1": true,
+			},
+		},
+		"multiple_regexes": {
+			inputs: []Snapshot{
+				stubSnap{"a1", false, o(10)},
+				stubSnap{"b1", false, o(11)},
+				stubSnap{"a2", false, o(20)},
+				stubSnap{"b2", false, o(21)},
+				stubSnap{"a3", false, o(30)},
+				stubSnap{"b3", false, o(31)},
+			},
+			rules: []KeepRule{
+				MustKeepLastN(2, "^a"),
+				MustKeepLastN(2, "^b"),
+			},
+			expDestroy: map[string]bool{
+				"a1": true,
+				"b1": true,
+			},
+		},
 	}
 
 	testTable(tcs, t)
 
 	t.Run("mustBePositive", func(t *testing.T) {
 		var err error
-		_, err = NewKeepLastN(0)
+		_, err = NewKeepLastN(0, "foo")
 		assert.Error(t, err)
-		_, err = NewKeepLastN(-5)
+		_, err = NewKeepLastN(-5, "foo")
 		assert.Error(t, err)
 	})
 
+	t.Run("emptyRegexAllowed", func(t *testing.T) {
+		_, err := NewKeepLastN(23, "")
+		require.NoError(t, err)
+	})
+
 }

pruning/pruning.go

@@ -60,7 +60,7 @@ func RuleFromConfig(in config.PruningEnum) (KeepRule, error) {
 	case *config.PruneKeepNotReplicated:
 		return NewKeepNotReplicated(), nil
 	case *config.PruneKeepLastN:
-		return NewKeepLastN(v.Count)
+		return NewKeepLastN(v.Count, v.Regex)
 	case *config.PruneKeepRegex:
 		return NewKeepRegex(v.Regex, v.Negate)
 	case *config.PruneGrid: