Use built in client http caching (#129)

* Use built in client http caching

* Use LRU cache implementation; set some defaults and config

* Use human readable cache sizes

.gitignore

@@ -5,3 +5,4 @@
 *.iws
 
 build/
+config/bulldozer.yml

config/bulldozer.example.yml

@@ -14,6 +14,11 @@ logging:
   # Choose from: debug, info, warn, error
   level: debug
 
+# Options for the HTTP Cache
+cache:
+  # The maximum size of the cache (specified in human readable units)
+  max_size: 50 MB
+
 # Options for connecting to GitHub
 github:
   # The URL of the GitHub homepage

server/config.go

@@ -15,6 +15,7 @@
 package server
 
 import (
+	"github.com/c2h5oh/datasize"
 	"github.com/palantir/go-baseapp/baseapp"
 	"github.com/palantir/go-baseapp/baseapp/datadog"
 	"github.com/palantir/go-githubapp/githubapp"
@@ -35,13 +36,18 @@ type Config struct {
 	Options Options            `yaml:"options"`
 	Logging LoggingConfig      `yaml:"logging"`
 	Datadog datadog.Config     `yaml:"datadog"`
+	Cache   CacheConfig        `yaml:"cache"`
 }
 
 type LoggingConfig struct {
 	Level string `yaml:"level"`
 	Text  bool   `yaml:"text"`
 }
 
+type CacheConfig struct {
+	MaxSize datasize.ByteSize `yaml:"max_size"`
+}
+
 type Options struct {
 	AppName                  string            `yaml:"app_name"`
 	ConfigurationPath        string            `yaml:"configuration_path"`

server/server.go

@@ -17,6 +17,9 @@ package server
 import (
 	"fmt"
 
+	"github.com/c2h5oh/datasize"
+	"github.com/die-net/lrucache"
+	"github.com/gregjones/httpcache"
 	"github.com/palantir/go-baseapp/baseapp"
 	"github.com/palantir/go-baseapp/baseapp/datadog"
 	"github.com/palantir/go-githubapp/githubapp"
@@ -48,10 +51,16 @@ func New(c *Config) (*Server, error) {
 		return nil, errors.Wrap(err, "failed to initialize base server")
 	}
 
+	maxSize := int64(50 * datasize.MB)
+	if c.Cache.MaxSize != 0 {
+		maxSize = int64(c.Cache.MaxSize)
+	}
+
 	userAgent := fmt.Sprintf("%s/%s", c.Options.AppName, version.GetVersion())
 	clientCreator, err := githubapp.NewDefaultCachingClientCreator(
 		c.Github,
 		githubapp.WithClientUserAgent(userAgent),
+		githubapp.WithClientCaching(true, func() httpcache.Cache { return lrucache.New(maxSize, 0) }),
 		githubapp.WithClientMiddleware(
 			githubapp.ClientLogging(zerolog.DebugLevel),
 			githubapp.ClientMetrics(base.Registry()),