Added a cached loader for xload (#21)

* Added a cached loader

* Added examples & tests

* Added DisableEmptyValueHit option

* Used sync.Map for cache

---------

Co-authored-by: ajatprabha <[email protected]>

xload/providers/cached/cache.go

@@ -0,0 +1,68 @@
+package cached
+
+import (
+	"sync"
+	"time"
+)
+
+// Cacher is the interface for custom cache implementations.
+//
+//go:generate mockery --name Cacher --structname MockCache --filename mock_test.go --outpkg cached --output .
+type Cacher interface {
+	Get(key string) (string, error)
+	Set(key, value string, ttl time.Duration) error
+}
+
+type mv struct {
+	val string
+	ttl time.Time
+}
+
+// MapCache is a simple cache implementation using a map.
+type MapCache struct {
+	m sync.Map
+
+	now func() time.Time
+}
+
+// NewMapCache returns a new MapCache.
+func NewMapCache() *MapCache {
+	return &MapCache{
+		m:   sync.Map{},
+		now: time.Now,
+	}
+}
+
+// Get returns the value for the given key, if cached.
+func (c *MapCache) Get(key string) (string, error) {
+	v, ok := c.m.Load(key)
+	if !ok {
+		return "", nil
+	}
+
+	mv, ok := v.(*mv)
+
+	if !ok || c.now().After(mv.ttl) {
+		c.delete(key)
+
+		return "", nil
+	}
+
+	return mv.val, nil
+}
+
+// Set sets the value for the given key.
+func (c *MapCache) Set(key, value string, ttl time.Duration) error {
+	v := &mv{
+		val: value,
+		ttl: c.now().Add(ttl),
+	}
+
+	c.m.Store(key, v)
+
+	return nil
+}
+
+func (c *MapCache) delete(key string) {
+	c.m.Delete(key)
+}

xload/providers/cached/cache_test.go

@@ -0,0 +1,43 @@
+package cached
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMapCache(t *testing.T) {
+	cache := NewMapCache()
+
+	err := cache.Set("foo", "bar", 1*time.Minute)
+	assert.NoError(t, err)
+
+	v, err := cache.Get("foo")
+	assert.NoError(t, err)
+	assert.Equal(t, "bar", v)
+
+	v, err = cache.Get("not-found")
+	assert.NoError(t, err)
+	assert.Equal(t, "", v)
+}
+
+func TestMapCacheExpired(t *testing.T) {
+	cache := NewMapCache()
+	now := time.Date(2023, 1, 1, 0, 0, 0, 0, time.UTC)
+
+	cache.now = func() time.Time {
+		return now
+	}
+
+	err := cache.Set("foo", "bar", 1*time.Minute)
+	assert.NoError(t, err)
+
+	cache.now = func() time.Time {
+		return now.Add(2 * time.Minute)
+	}
+
+	v, err := cache.Get("foo")
+	assert.NoError(t, err)
+	assert.Equal(t, "", v)
+}

xload/providers/cached/doc.go

@@ -0,0 +1,6 @@
+// Package cached provides a cached provider for xload.
+// This loader can be used to cache the results of any loader.
+//
+// Useful for loaders that have a high latency, or loaders that are
+// called frequently.
+package cached

xload/providers/cached/example_test.go

@@ -0,0 +1,113 @@
+package cached_test
+
+import (
+	"context"
+	"time"
+
+	"github.com/gojekfarm/xtools/xload"
+	"github.com/gojekfarm/xtools/xload/providers/cached"
+)
+
+func Example() {
+	// This example shows how to use the cached loader
+	// with a remote loader.
+
+	ctx := context.Background()
+	cfg := struct {
+		Title       string `env:"TITLE"`
+		Link        string `env:"LINK"`
+		ButtonLabel string `env:"BUTTON_LABEL"`
+	}{}
+
+	remoteLoader := xload.LoaderFunc(func(ctx context.Context, key string) (string, error) {
+		// Load the value from a remote source.
+
+		return "", nil
+	})
+
+	err := xload.Load(
+		ctx, &cfg,
+		cached.NewLoader(
+			remoteLoader,
+			cached.TTL(5*60*time.Minute),
+		),
+	)
+	if err != nil {
+		panic(err)
+	}
+}
+
+type CustomCache struct{}
+
+func NewCustomCache() *CustomCache {
+	return &CustomCache{}
+}
+
+func (c *CustomCache) Get(key string) (string, error) {
+	return "", nil
+}
+
+func (c *CustomCache) Set(key, value string, ttl time.Duration) error {
+	return nil
+}
+
+func Example_customCache() {
+	// This example shows how to use a custom cache
+	// with the cached loader.
+
+	ctx := context.Background()
+	cfg := struct {
+		Title       string `env:"TITLE"`
+		Link        string `env:"LINK"`
+		ButtonLabel string `env:"BUTTON_LABEL"`
+	}{}
+
+	remoteLoader := xload.LoaderFunc(func(ctx context.Context, key string) (string, error) {
+		// Load the value from a remote source.
+
+		return "", nil
+	})
+
+	err := xload.Load(
+		ctx, &cfg,
+		cached.NewLoader(
+			remoteLoader,
+			cached.TTL(5*60*time.Minute),
+			cached.Cache(NewCustomCache()),
+		),
+	)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func Example_disableEmptyValueHit() {
+	// By default, the cached loader caches empty values.
+	// This example shows how to disable caching of empty values
+	// with the cached loader.
+
+	ctx := context.Background()
+	cfg := struct {
+		Title       string `env:"TITLE"`
+		Link        string `env:"LINK"`
+		ButtonLabel string `env:"BUTTON_LABEL"`
+	}{}
+
+	remoteLoader := xload.LoaderFunc(func(ctx context.Context, key string) (string, error) {
+		// Load the value from a remote source.
+
+		return "", nil
+	})
+
+	err := xload.Load(
+		ctx, &cfg,
+		cached.NewLoader(
+			remoteLoader,
+			cached.TTL(5*60*time.Minute),
+			cached.DisableEmptyValueHit,
+		),
+	)
+	if err != nil {
+		panic(err)
+	}
+}

xload/providers/cached/go.mod

@@ -0,0 +1,21 @@
+module github.com/gojekfarm/xtools/xload/providers/cached
+
+go 1.20
+
+replace github.com/gojekfarm/xtools/xload => ../..
+
+require (
+	github.com/gojekfarm/xtools/xload v0.0.0-00010101000000-000000000000
+	github.com/stretchr/testify v1.8.4
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/sourcegraph/conc v0.3.0 // indirect
+	github.com/spf13/cast v1.5.1 // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
+	go.uber.org/atomic v1.7.0 // indirect
+	go.uber.org/multierr v1.9.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

xload/providers/cached/go.sum

@@ -0,0 +1,33 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/frankban/quicktest v1.14.4 h1:g2rn0vABPOOXmZUj+vbmUp0lPoXEMuhTpIluN0XL9UY=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/gotidy/ptr v1.4.0 h1:7++suUs+HNHMnyz6/AW3SE+4EnBhupPSQTSI7QNijVc=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
+github.com/sourcegraph/conc v0.3.0 h1:OQTbbt6P72L20UqAkXXuLOj79LfEanQ+YQFNpLA9ySo=
+github.com/sourcegraph/conc v0.3.0/go.mod h1:Sdozi7LEKbFPqYX2/J+iBAM6HpqSLTASQIKqDmF7Mt0=
+github.com/spf13/cast v1.5.1 h1:R+kOtfhWQE6TVQzY+4D7wJLBgkdVasCEFxSUBYBYIlA=
+github.com/spf13/cast v1.5.1/go.mod h1:b9PdjNptOpzXr7Rq1q9gJML/2cdGQAo69NKzQ10KN48=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+go.uber.org/atomic v1.7.0 h1:ADUqmZGgLDDfbSL9ZmPxKTybcoEYHgpYfELNoN+7hsw=
+go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
+go.uber.org/multierr v1.9.0 h1:7fIwc/ZtS0q++VgcfqFDxSBZVv/Xo49/SYnDFupUwlI=
+go.uber.org/multierr v1.9.0/go.mod h1:X2jQV1h+kxSjClGpnseKVIxpmcjrj7MNnI0bnlfKTVQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

xload/providers/cached/loader.go

@@ -0,0 +1,43 @@
+package cached
+
+import (
+	"context"
+
+	"github.com/gojekfarm/xtools/xload"
+)
+
+// NewLoader returns a new cached loader.
+//
+// The cached loader uses these defaults:
+// - TTL: 5 minutes. Configurable via `TTL` option.
+// - Cache: A simple unbounded map cache. Configurable via `Cache` option.
+// - Empty value hit: Enabled. Configurable via `DisableEmptyValueHit` option.
+func NewLoader(l xload.Loader, opts ...Option) xload.LoaderFunc {
+	o := defaultOptions()
+
+	o.apply(opts...)
+
+	return xload.LoaderFunc(func(ctx context.Context, key string) (string, error) {
+		v, err := o.cache.Get(key)
+		if err != nil {
+			return "", err
+		}
+
+		if v != "" {
+			return v, nil
+		}
+
+		loaded, err := l.Load(ctx, key)
+		if err != nil {
+			return "", err
+		}
+
+		if loaded == "" && !o.emptyHit {
+			return "", nil
+		}
+
+		err = o.cache.Set(key, loaded, o.ttl)
+
+		return loaded, err
+	})
+}