feat(storage): generic cache interface (#8628)

# Which Problems Are Solved We identified the need of caching. Currently we have a number of places where we use different ways of caching, like go maps or LRU. We might also want shared chaches in the future, like Redis-based or in special SQL tables. # How the Problems Are Solved Define a generic Cache interface which allows different implementations. - A noop implementation is provided and enabled as. - An implementation using go maps is provided - disabled in defaults.yaml - enabled in integration tests - Authz middleware instance objects are cached using the interface. # Additional Changes - Enabled integration test command raceflag - Fix a race condition in the limits integration test client - Fix a number of flaky integration tests. (Because zitadel is super fast now!) 🎸 🚀 # Additional Context Related to https://github.com/zitadel/zitadel/issues/8648
2025-08-11 18:07:31 +00:00 · 2024-09-25 22:40:21 +03:00
parent a6ea83168d
commit 4eaa3163b6
28 changed files with 1290 additions and 78 deletions
--- a/internal/cache/cache.go
+++ b/internal/cache/cache.go
@@ -0,0 +1,106 @@
+// Package cache provides abstraction of cache implementations that can be used by zitadel.
+package cache
+
+import (
+	"context"
+	"time"
+
+	"github.com/zitadel/logging"
+)
+
+// Cache stores objects with a value of type `V`.
+// Objects may be referred to by one or more indices.
+// Implementations may encode the value for storage.
+// This means non-exported fields may be lost and objects
+// with function values may fail to encode.
+// See https://pkg.go.dev/encoding/json#Marshal for example.
+//
+// `I` is the type by which indices are identified,
+// typically an enum for type-safe access.
+// Indices are defined when calling the constructor of an implementation of this interface.
+// It is illegal to refer to an idex not defined during construction.
+//
+// `K` is the type used as key in each index.
+// Due to the limitations in type constraints, all indices use the same key type.
+//
+// Implementations are free to use stricter type constraints or fixed typing.
+type Cache[I, K comparable, V Entry[I, K]] interface {
+	// Get an object through specified index.
+	// An [IndexUnknownError] may be returned if the index is unknown.
+	// [ErrCacheMiss] is returned if the key was not found in the index,
+	// or the object is not valid.
+	Get(ctx context.Context, index I, key K) (V, bool)
+
+	// Set an object.
+	// Keys are created on each index based in the [Entry.Keys] method.
+	// If any key maps to an existing object, the object is invalidated,
+	// regardless if the object has other keys defined in the new entry.
+	// This to prevent ghost objects when an entry reduces the amount of keys
+	// for a given index.
+	Set(ctx context.Context, value V)
+
+	// Invalidate an object through specified index.
+	// Implementations may choose to instantly delete the object,
+	// defer until prune or a separate cleanup routine.
+	// Invalidated object are no longer returned from Get.
+	// It is safe to call Invalidate multiple times or on non-existing entries.
+	Invalidate(ctx context.Context, index I, key ...K) error
+
+	// Delete one or more keys from a specific index.
+	// An [IndexUnknownError] may be returned if the index is unknown.
+	// The referred object is not invalidated and may still be accessible though
+	// other indices and keys.
+	// It is safe to call Delete multiple times or on non-existing entries
+	Delete(ctx context.Context, index I, key ...K) error
+
+	// Truncate deletes all cached objects.
+	Truncate(ctx context.Context) error
+
+	// Close the cache. Subsequent calls to the cache are not allowed.
+	Close(ctx context.Context) error
+}
+
+// Entry contains a value of type `V` to be cached.
+//
+// `I` is the type by which indices are identified,
+// typically an enum for type-safe access.
+//
+// `K` is the type used as key in an index.
+// Due to the limitations in type constraints, all indices use the same key type.
+type Entry[I, K comparable] interface {
+	// Keys returns which keys map to the object in a specified index.
+	// May return nil if the index in unknown or when there are no keys.
+	Keys(index I) (key []K)
+}
+
+type CachesConfig struct {
+	Connectors struct {
+		Memory MemoryConnectorConfig
+		// SQL database.Config
+		// Redis redis.Config?
+	}
+	Instance *CacheConfig
+}
+
+type CacheConfig struct {
+	Connector string
+
+	// Age since an object was added to the cache,
+	// after which the object is considered invalid.
+	// 0 disables max age checks.
+	MaxAge time.Duration
+
+	// Age since last use (Get) of an object,
+	// after which the object is considered invalid.
+	// 0 disables last use age checks.
+	LastUseAge time.Duration
+
+	// Log allows logging of the specific cache.
+	// By default only errors are logged to stdout.
+	Log *logging.Config
+}
+
+type MemoryConnectorConfig struct {
+	Enabled   bool
+	AutoPrune AutoPruneConfig
+}
--- a/internal/cache/error.go
+++ b/internal/cache/error.go
@@ -0,0 +1,29 @@
+package cache
+
+import (
+	"errors"
+	"fmt"
+)
+
+type IndexUnknownError[I comparable] struct {
+	index I
+}
+
+func NewIndexUnknownErr[I comparable](index I) error {
+	return IndexUnknownError[I]{index}
+}
+
+func (i IndexUnknownError[I]) Error() string {
+	return fmt.Sprintf("index %v unknown", i.index)
+}
+
+func (a IndexUnknownError[I]) Is(err error) bool {
+	if b, ok := err.(IndexUnknownError[I]); ok {
+		return a.index == b.index
+	}
+	return false
+}
+
+var (
+	ErrCacheMiss = errors.New("cache miss")
+)
--- a/internal/cache/gomap/gomap.go
+++ b/internal/cache/gomap/gomap.go
@@ -0,0 +1,204 @@
+package gomap
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+	"maps"
+	"os"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/zitadel/zitadel/internal/cache"
+)
+
+type mapCache[I, K comparable, V cache.Entry[I, K]] struct {
+	config   *cache.CacheConfig
+	indexMap map[I]*index[K, V]
+	logger   *slog.Logger
+}
+
+// NewCache returns an in-memory Cache implementation based on the builtin go map type.
+// Object values are stored as-is and there is no encoding or decoding involved.
+func NewCache[I, K comparable, V cache.Entry[I, K]](background context.Context, indices []I, config cache.CacheConfig) cache.PrunerCache[I, K, V] {
+	m := &mapCache[I, K, V]{
+		config:   &config,
+		indexMap: make(map[I]*index[K, V], len(indices)),
+		logger: slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+			AddSource: true,
+			Level:     slog.LevelError,
+		})),
+	}
+	if config.Log != nil {
+		m.logger = config.Log.Slog()
+	}
+	m.logger.InfoContext(background, "map cache logging enabled")
+
+	for _, name := range indices {
+		m.indexMap[name] = &index[K, V]{
+			config:  m.config,
+			entries: make(map[K]*entry[V]),
+		}
+	}
+	return m
+}
+
+func (c *mapCache[I, K, V]) Get(ctx context.Context, index I, key K) (value V, ok bool) {
+	i, ok := c.indexMap[index]
+	if !ok {
+		c.logger.ErrorContext(ctx, "map cache get", "err", cache.NewIndexUnknownErr(index), "index", index, "key", key)
+		return value, false
+	}
+	entry, err := i.Get(key)
+	if err == nil {
+		c.logger.DebugContext(ctx, "map cache get", "index", index, "key", key)
+		return entry.value, true
+	}
+	if errors.Is(err, cache.ErrCacheMiss) {
+		c.logger.InfoContext(ctx, "map cache get", "err", err, "index", index, "key", key)
+		return value, false
+	}
+	c.logger.ErrorContext(ctx, "map cache get", "err", cache.NewIndexUnknownErr(index), "index", index, "key", key)
+	return value, false
+}
+
+func (c *mapCache[I, K, V]) Set(ctx context.Context, value V) {
+	now := time.Now()
+	entry := &entry[V]{
+		value:   value,
+		created: now,
+	}
+	entry.lastUse.Store(now.UnixMicro())
+
+	for name, i := range c.indexMap {
+		keys := value.Keys(name)
+		i.Set(keys, entry)
+		c.logger.DebugContext(ctx, "map cache set", "index", name, "keys", keys)
+	}
+}
+
+func (c *mapCache[I, K, V]) Invalidate(ctx context.Context, index I, keys ...K) error {
+	i, ok := c.indexMap[index]
+	if !ok {
+		return cache.NewIndexUnknownErr(index)
+	}
+	i.Invalidate(keys)
+	c.logger.DebugContext(ctx, "map cache invalidate", "index", index, "keys", keys)
+	return nil
+}
+
+func (c *mapCache[I, K, V]) Delete(ctx context.Context, index I, keys ...K) error {
+	i, ok := c.indexMap[index]
+	if !ok {
+		return cache.NewIndexUnknownErr(index)
+	}
+	i.Delete(keys)
+	c.logger.DebugContext(ctx, "map cache delete", "index", index, "keys", keys)
+	return nil
+}
+
+func (c *mapCache[I, K, V]) Prune(ctx context.Context) error {
+	for name, index := range c.indexMap {
+		index.Prune()
+		c.logger.DebugContext(ctx, "map cache prune", "index", name)
+	}
+	return nil
+}
+
+func (c *mapCache[I, K, V]) Truncate(ctx context.Context) error {
+	for name, index := range c.indexMap {
+		index.Truncate()
+		c.logger.DebugContext(ctx, "map cache clear", "index", name)
+	}
+	return nil
+}
+
+func (c *mapCache[I, K, V]) Close(ctx context.Context) error {
+	return ctx.Err()
+}
+
+type index[K comparable, V any] struct {
+	mutex   sync.RWMutex
+	config  *cache.CacheConfig
+	entries map[K]*entry[V]
+}
+
+func (i *index[K, V]) Get(key K) (*entry[V], error) {
+	i.mutex.RLock()
+	entry, ok := i.entries[key]
+	i.mutex.RUnlock()
+	if ok && entry.isValid(i.config) {
+		return entry, nil
+	}
+	return nil, cache.ErrCacheMiss
+}
+
+func (c *index[K, V]) Set(keys []K, entry *entry[V]) {
+	c.mutex.Lock()
+	for _, key := range keys {
+		c.entries[key] = entry
+	}
+	c.mutex.Unlock()
+}
+
+func (i *index[K, V]) Invalidate(keys []K) {
+	i.mutex.RLock()
+	for _, key := range keys {
+		if entry, ok := i.entries[key]; ok {
+			entry.invalid.Store(true)
+		}
+	}
+	i.mutex.RUnlock()
+}
+
+func (c *index[K, V]) Delete(keys []K) {
+	c.mutex.Lock()
+	for _, key := range keys {
+		delete(c.entries, key)
+	}
+	c.mutex.Unlock()
+}
+
+func (c *index[K, V]) Prune() {
+	c.mutex.Lock()
+	maps.DeleteFunc(c.entries, func(_ K, entry *entry[V]) bool {
+		return !entry.isValid(c.config)
+	})
+	c.mutex.Unlock()
+}
+
+func (c *index[K, V]) Truncate() {
+	c.mutex.Lock()
+	c.entries = make(map[K]*entry[V])
+	c.mutex.Unlock()
+}
+
+type entry[V any] struct {
+	value   V
+	created time.Time
+	invalid atomic.Bool
+	lastUse atomic.Int64 // UnixMicro time
+}
+
+func (e *entry[V]) isValid(c *cache.CacheConfig) bool {
+	if e.invalid.Load() {
+		return false
+	}
+	now := time.Now()
+	if c.MaxAge > 0 {
+		if e.created.Add(c.MaxAge).Before(now) {
+			e.invalid.Store(true)
+			return false
+		}
+	}
+	if c.LastUseAge > 0 {
+		lastUse := e.lastUse.Load()
+		if time.UnixMicro(lastUse).Add(c.LastUseAge).Before(now) {
+			e.invalid.Store(true)
+			return false
+		}
+		e.lastUse.CompareAndSwap(lastUse, now.UnixMicro())
+	}
+	return true
+}
--- a/internal/cache/gomap/gomap_test.go
+++ b/internal/cache/gomap/gomap_test.go
@@ -0,0 +1,334 @@
+package gomap
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/zitadel/logging"
+
+	"github.com/zitadel/zitadel/internal/cache"
+)
+
+type testIndex int
+
+const (
+	testIndexID testIndex = iota
+	testIndexName
+)
+
+var testIndices = []testIndex{
+	testIndexID,
+	testIndexName,
+}
+
+type testObject struct {
+	id    string
+	names []string
+}
+
+func (o *testObject) Keys(index testIndex) []string {
+	switch index {
+	case testIndexID:
+		return []string{o.id}
+	case testIndexName:
+		return o.names
+	default:
+		return nil
+	}
+}
+
+func Test_mapCache_Get(t *testing.T) {
+	c := NewCache[testIndex, string, *testObject](context.Background(), testIndices, cache.CacheConfig{
+		MaxAge:     time.Second,
+		LastUseAge: time.Second / 4,
+		Log: &logging.Config{
+			Level:     "debug",
+			AddSource: true,
+		},
+	})
+	defer c.Close(context.Background())
+	obj := &testObject{
+		id:    "id",
+		names: []string{"foo", "bar"},
+	}
+	c.Set(context.Background(), obj)
+
+	type args struct {
+		index testIndex
+		key   string
+	}
+	tests := []struct {
+		name   string
+		args   args
+		want   *testObject
+		wantOk bool
+	}{
+		{
+			name: "ok",
+			args: args{
+				index: testIndexID,
+				key:   "id",
+			},
+			want:   obj,
+			wantOk: true,
+		},
+		{
+			name: "miss",
+			args: args{
+				index: testIndexID,
+				key:   "spanac",
+			},
+			want:   nil,
+			wantOk: false,
+		},
+		{
+			name: "unknown index",
+			args: args{
+				index: 99,
+				key:   "id",
+			},
+			want:   nil,
+			wantOk: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := c.Get(context.Background(), tt.args.index, tt.args.key)
+			assert.Equal(t, tt.want, got)
+			assert.Equal(t, tt.wantOk, ok)
+		})
+	}
+}
+
+func Test_mapCache_Invalidate(t *testing.T) {
+	c := NewCache[testIndex, string, *testObject](context.Background(), testIndices, cache.CacheConfig{
+		MaxAge:     time.Second,
+		LastUseAge: time.Second / 4,
+		Log: &logging.Config{
+			Level:     "debug",
+			AddSource: true,
+		},
+	})
+	defer c.Close(context.Background())
+	obj := &testObject{
+		id:    "id",
+		names: []string{"foo", "bar"},
+	}
+	c.Set(context.Background(), obj)
+	err := c.Invalidate(context.Background(), testIndexName, "bar")
+	require.NoError(t, err)
+	got, ok := c.Get(context.Background(), testIndexID, "id")
+	assert.Nil(t, got)
+	assert.False(t, ok)
+}
+
+func Test_mapCache_Delete(t *testing.T) {
+	c := NewCache[testIndex, string, *testObject](context.Background(), testIndices, cache.CacheConfig{
+		MaxAge:     time.Second,
+		LastUseAge: time.Second / 4,
+		Log: &logging.Config{
+			Level:     "debug",
+			AddSource: true,
+		},
+	})
+	defer c.Close(context.Background())
+	obj := &testObject{
+		id:    "id",
+		names: []string{"foo", "bar"},
+	}
+	c.Set(context.Background(), obj)
+	err := c.Delete(context.Background(), testIndexName, "bar")
+	require.NoError(t, err)
+
+	// Shouldn't find object by deleted name
+	got, ok := c.Get(context.Background(), testIndexName, "bar")
+	assert.Nil(t, got)
+	assert.False(t, ok)
+
+	// Should find object by other name
+	got, ok = c.Get(context.Background(), testIndexName, "foo")
+	assert.Equal(t, obj, got)
+	assert.True(t, ok)
+
+	// Should find object by id
+	got, ok = c.Get(context.Background(), testIndexID, "id")
+	assert.Equal(t, obj, got)
+	assert.True(t, ok)
+}
+
+func Test_mapCache_Prune(t *testing.T) {
+	c := NewCache[testIndex, string, *testObject](context.Background(), testIndices, cache.CacheConfig{
+		MaxAge:     time.Second,
+		LastUseAge: time.Second / 4,
+		Log: &logging.Config{
+			Level:     "debug",
+			AddSource: true,
+		},
+	})
+	defer c.Close(context.Background())
+
+	objects := []*testObject{
+		{
+			id:    "id1",
+			names: []string{"foo", "bar"},
+		},
+		{
+			id:    "id2",
+			names: []string{"hello"},
+		},
+	}
+	for _, obj := range objects {
+		c.Set(context.Background(), obj)
+	}
+	// invalidate one entry
+	err := c.Invalidate(context.Background(), testIndexName, "bar")
+	require.NoError(t, err)
+
+	err = c.(cache.Pruner).Prune(context.Background())
+	require.NoError(t, err)
+
+	// Other object should still be found
+	got, ok := c.Get(context.Background(), testIndexID, "id2")
+	assert.Equal(t, objects[1], got)
+	assert.True(t, ok)
+}
+
+func Test_mapCache_Truncate(t *testing.T) {
+	c := NewCache[testIndex, string, *testObject](context.Background(), testIndices, cache.CacheConfig{
+		MaxAge:     time.Second,
+		LastUseAge: time.Second / 4,
+		Log: &logging.Config{
+			Level:     "debug",
+			AddSource: true,
+		},
+	})
+	defer c.Close(context.Background())
+	objects := []*testObject{
+		{
+			id:    "id1",
+			names: []string{"foo", "bar"},
+		},
+		{
+			id:    "id2",
+			names: []string{"hello"},
+		},
+	}
+	for _, obj := range objects {
+		c.Set(context.Background(), obj)
+	}
+
+	err := c.Truncate(context.Background())
+	require.NoError(t, err)
+
+	mc := c.(*mapCache[testIndex, string, *testObject])
+	for _, index := range mc.indexMap {
+		index.mutex.RLock()
+		assert.Len(t, index.entries, 0)
+		index.mutex.RUnlock()
+	}
+}
+
+func Test_entry_isValid(t *testing.T) {
+	type fields struct {
+		created time.Time
+		invalid bool
+		lastUse time.Time
+	}
+	tests := []struct {
+		name   string
+		fields fields
+		config *cache.CacheConfig
+		want   bool
+	}{
+		{
+			name: "invalid",
+			fields: fields{
+				created: time.Now(),
+				invalid: true,
+				lastUse: time.Now(),
+			},
+			config: &cache.CacheConfig{
+				MaxAge:     time.Minute,
+				LastUseAge: time.Second,
+			},
+			want: false,
+		},
+		{
+			name: "max age exceeded",
+			fields: fields{
+				created: time.Now().Add(-(time.Minute + time.Second)),
+				invalid: false,
+				lastUse: time.Now(),
+			},
+			config: &cache.CacheConfig{
+				MaxAge:     time.Minute,
+				LastUseAge: time.Second,
+			},
+			want: false,
+		},
+		{
+			name: "max age disabled",
+			fields: fields{
+				created: time.Now().Add(-(time.Minute + time.Second)),
+				invalid: false,
+				lastUse: time.Now(),
+			},
+			config: &cache.CacheConfig{
+				LastUseAge: time.Second,
+			},
+			want: true,
+		},
+		{
+			name: "last use age exceeded",
+			fields: fields{
+				created: time.Now().Add(-(time.Minute / 2)),
+				invalid: false,
+				lastUse: time.Now().Add(-(time.Second * 2)),
+			},
+			config: &cache.CacheConfig{
+				MaxAge:     time.Minute,
+				LastUseAge: time.Second,
+			},
+			want: false,
+		},
+		{
+			name: "last use age disabled",
+			fields: fields{
+				created: time.Now().Add(-(time.Minute / 2)),
+				invalid: false,
+				lastUse: time.Now().Add(-(time.Second * 2)),
+			},
+			config: &cache.CacheConfig{
+				MaxAge: time.Minute,
+			},
+			want: true,
+		},
+		{
+			name: "valid",
+			fields: fields{
+				created: time.Now(),
+				invalid: false,
+				lastUse: time.Now(),
+			},
+			config: &cache.CacheConfig{
+				MaxAge:     time.Minute,
+				LastUseAge: time.Second,
+			},
+			want: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			e := &entry[any]{
+				created: tt.fields.created,
+			}
+			e.invalid.Store(tt.fields.invalid)
+			e.lastUse.Store(tt.fields.lastUse.UnixMicro())
+			got := e.isValid(tt.config)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
--- a/internal/cache/noop/noop.go
+++ b/internal/cache/noop/noop.go
@@ -0,0 +1,22 @@
+package noop
+
+import (
+	"context"
+
+	"github.com/zitadel/zitadel/internal/cache"
+)
+
+type noop[I, K comparable, V cache.Entry[I, K]] struct{}
+
+// NewCache returns a cache that does nothing
+func NewCache[I, K comparable, V cache.Entry[I, K]]() cache.Cache[I, K, V] {
+	return noop[I, K, V]{}
+}
+
+func (noop[I, K, V]) Set(context.Context, V)                          {}
+func (noop[I, K, V]) Get(context.Context, I, K) (value V, ok bool)    { return }
+func (noop[I, K, V]) Invalidate(context.Context, I, ...K) (err error) { return }
+func (noop[I, K, V]) Delete(context.Context, I, ...K) (err error)     { return }
+func (noop[I, K, V]) Prune(context.Context) (err error)               { return }
+func (noop[I, K, V]) Truncate(context.Context) (err error)            { return }
+func (noop[I, K, V]) Close(context.Context) (err error)               { return }
--- a/internal/cache/pruner.go
+++ b/internal/cache/pruner.go
@@ -0,0 +1,76 @@
+package cache
+
+import (
+	"context"
+	"math/rand"
+	"time"
+
+	"github.com/jonboulle/clockwork"
+	"github.com/zitadel/logging"
+)
+
+// Pruner is an optional [Cache] interface.
+type Pruner interface {
+	// Prune deletes all invalidated or expired objects.
+	Prune(ctx context.Context) error
+}
+
+type PrunerCache[I, K comparable, V Entry[I, K]] interface {
+	Cache[I, K, V]
+	Pruner
+}
+
+type AutoPruneConfig struct {
+	// Interval at which the cache is automatically pruned.
+	// 0 or lower disables automatic pruning.
+	Interval time.Duration
+
+	// Timeout for an automatic prune.
+	// It is recommended to keep the value shorter than AutoPruneInterval
+	// 0 or lower disables automatic pruning.
+	Timeout time.Duration
+}
+
+func (c AutoPruneConfig) StartAutoPrune(background context.Context, pruner Pruner, name string) (close func()) {
+	return c.startAutoPrune(background, pruner, name, clockwork.NewRealClock())
+}
+
+func (c *AutoPruneConfig) startAutoPrune(background context.Context, pruner Pruner, name string, clock clockwork.Clock) (close func()) {
+	if c.Interval <= 0 {
+		return func() {}
+	}
+	background, cancel := context.WithCancel(background)
+	// randomize the first interval
+	timer := clock.NewTimer(time.Duration(rand.Int63n(int64(c.Interval))))
+	go c.pruneTimer(background, pruner, name, timer)
+	return cancel
+}
+
+func (c *AutoPruneConfig) pruneTimer(background context.Context, pruner Pruner, name string, timer clockwork.Timer) {
+	defer func() {
+		if !timer.Stop() {
+			<-timer.Chan()
+		}
+	}()
+
+	for {
+		select {
+		case <-background.Done():
+			return
+		case <-timer.Chan():
+			timer.Reset(c.Interval)
+			err := c.doPrune(background, pruner)
+			logging.OnError(err).WithField("name", name).Error("cache auto prune")
+		}
+	}
+}
+
+func (c *AutoPruneConfig) doPrune(background context.Context, pruner Pruner) error {
+	ctx, cancel := context.WithCancel(background)
+	defer cancel()
+	if c.Timeout > 0 {
+		ctx, cancel = context.WithTimeout(background, c.Timeout)
+		defer cancel()
+	}
+	return pruner.Prune(ctx)
+}
--- a/internal/cache/pruner_test.go
+++ b/internal/cache/pruner_test.go
@@ -0,0 +1,43 @@
+package cache
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/jonboulle/clockwork"
+	"github.com/stretchr/testify/assert"
+)
+
+type testPruner struct {
+	called chan struct{}
+}
+
+func (p *testPruner) Prune(context.Context) error {
+	p.called <- struct{}{}
+	return nil
+}
+
+func TestAutoPruneConfig_startAutoPrune(t *testing.T) {
+	c := AutoPruneConfig{
+		Interval: time.Second,
+		Timeout:  time.Millisecond,
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	pruner := testPruner{
+		called: make(chan struct{}),
+	}
+	clock := clockwork.NewFakeClock()
+	close := c.startAutoPrune(ctx, &pruner, "foo", clock)
+	defer close()
+	clock.Advance(time.Second)
+
+	select {
+	case _, ok := <-pruner.called:
+		assert.True(t, ok)
+	case <-ctx.Done():
+		t.Fatal(ctx.Err())
+	}
+}