From 3be3441feb33c4cce72a855f14d0abdd1aa8bbe0 Mon Sep 17 00:00:00 2001
From: Nikita Velat <nvelat@palantir.com>
Date: Thu, 29 Jun 2023 16:18:24 +0100
Subject: [PATCH] add a caching implementation for InstallationsService (#268)

* add caching installation service

* add license header

* typo in sprintf

* switch to time based cache
---
 githubapp/installations_caching.go | 78 ++++++++++++++++++++++++++++++
 go.mod                             |  1 +
 go.sum                             |  2 +
 3 files changed, 81 insertions(+)
 create mode 100644 githubapp/installations_caching.go

diff --git a/githubapp/installations_caching.go b/githubapp/installations_caching.go
new file mode 100644
index 000000000..d32d4d328
--- /dev/null
+++ b/githubapp/installations_caching.go
@@ -0,0 +1,78 @@
+// Copyright 2023 Palantir Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package githubapp
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	ttlcache "github.com/patrickmn/go-cache"
+)
+
+// NewCachingInstallationsService returns an InstallationsService that always queries GitHub. It should be created with
+// a client that authenticates as the target.
+// It uses a time based cache of the provided expiry/cleanup time to store app installation info for repositories
+// or owners and returns the cached installation info when a cache hit exists.
+func NewCachingInstallationsService(delegate InstallationsService, expiry, cleanup time.Duration) InstallationsService {
+	return &cachingInstallationsService{
+		cache:    ttlcache.New(expiry, cleanup),
+		delegate: delegate,
+	}
+}
+
+type cachingInstallationsService struct {
+	cache    *ttlcache.Cache
+	delegate InstallationsService
+}
+
+func (c *cachingInstallationsService) ListAll(ctx context.Context) ([]Installation, error) {
+	// ListAll is not cached due to a lack of keys to retrieve from the cache. Returning all values in the cache is not
+	// always desirable
+	return c.delegate.ListAll(ctx)
+}
+
+func (c *cachingInstallationsService) GetByOwner(ctx context.Context, owner string) (Installation, error) {
+	// if installation is in cache, return it
+	val, ok := c.cache.Get(owner)
+	if ok {
+		return val.(Installation), nil
+	}
+
+	// otherwise, get installation info, save to cache, and return
+	install, err := c.delegate.GetByOwner(ctx, owner)
+	if err != nil {
+		return Installation{}, err
+	}
+	c.cache.Set(owner, install, ttlcache.DefaultExpiration)
+	return install, nil
+}
+
+func (c *cachingInstallationsService) GetByRepository(ctx context.Context, owner, name string) (Installation, error) {
+	// if installation is in cache, return it
+	key := fmt.Sprintf("%s/%s", owner, name)
+	val, ok := c.cache.Get(key)
+	if ok {
+		return val.(Installation), nil
+	}
+
+	// otherwise, get installation info, save to cache, and return
+	install, err := c.delegate.GetByRepository(ctx, owner, name)
+	if err != nil {
+		return Installation{}, err
+	}
+	c.cache.Set(key, install, ttlcache.DefaultExpiration)
+	return install, nil
+}
diff --git a/go.mod b/go.mod
index fc7fc463c..1db079e62 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/google/go-github/v53 v53.2.0
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79
 	github.com/hashicorp/golang-lru v0.6.0
+	github.com/patrickmn/go-cache v2.1.0+incompatible
 	github.com/pkg/errors v0.9.1
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475
 	github.com/rs/zerolog v1.29.1
diff --git a/go.sum b/go.sum
index 5bca6f311..6d9f744fe 100644
--- a/go.sum
+++ b/go.sum
@@ -45,6 +45,8 @@ github.com/mattn/go-colorable v0.1.12 h1:jF+Du6AlPIjs2BiUiQlKOX0rt3SujHxPnksPKZb
 github.com/mattn/go-colorable v0.1.12/go.mod h1:u5H1YNBxpqRaxsYJYSkiCWKzEfiAb1Gb520KVy5xxl4=
 github.com/mattn/go-isatty v0.0.14 h1:yVuAays6BHfxijgZPzw+3Zlu5yQgKGP2/hcQbHb7S9Y=
 github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94=
+github.com/patrickmn/go-cache v2.1.0+incompatible h1:HRMgzkcYKYpi3C8ajMPV8OFXaaRUnok+kx1WdO15EQc=
+github.com/patrickmn/go-cache v2.1.0+incompatible/go.mod h1:3Qf8kWWT7OJRJbdiICTKqZju1ZixQ/KpMGzzAfe6+WQ=
 github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=