Repository: chanzuckerberg/fogg
Pull request #322 (2019-07-19 17:06:33)

[feature] Cache fogg setup -- custom plugins and providers
### Summary
This will cache `fogg setup` -- custom plugins and providers to the fogg cache (currently at `~/.fogg/cache/custom_plugins`)

### Test Plan
unittests

### References




Patch:
diff --git a/Makefile b/Makefile
index 9b74e7db..49756d26 100644
--- a/Makefile
+++ b/Makefile
@@ -44,6 +44,11 @@ release-snapshot: ## run a release
 build: packr ## build the binary
 	go build ${LDFLAGS} .
 
+deps:
+	go get .
+	go mod tidy
+	go mod vendor
+
 coverage: ## run the go coverage tool, reading file coverage.out
 	go tool cover -html=coverage.out
 
diff --git a/go.mod b/go.mod
index 85c9f6ca..b5ddfec2 100644
--- a/go.mod
+++ b/go.mod
@@ -27,6 +27,7 @@ require (
 	github.com/kr/pretty v0.1.0
 	github.com/leodido/go-urn v1.1.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0
+	github.com/peterbourgon/diskv v2.0.1+incompatible
 	github.com/pkg/errors v0.8.1
 	github.com/segmentio/go-prompt v1.2.1-0.20161017233205-f0d19b6901ad
 	github.com/sirupsen/logrus v1.4.2
diff --git a/go.sum b/go.sum
index 3c1c6d23..78bc5190 100644
--- a/go.sum
+++ b/go.sum
@@ -123,6 +123,7 @@ github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5y
 github.com/golang/protobuf v1.3.0 h1:kbxbvI4Un1LUWKxufD+BiE6AEExYYgkQLQmLFqA1LFk=
 github.com/golang/protobuf v1.3.0/go.mod h1:Qd/q+1AKNOZr9uGQzbzCmRO6sUih6GTPZv6a1/R87v0=
 github.com/golang/snappy v0.0.0-20180518054509-2e65f85255db/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
+github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c h1:964Od4U6p2jUkFxvCydnIczKteheJEzHRToSGK3Bnlw=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
@@ -290,6 +291,8 @@ github.com/openzipkin/zipkin-go v0.1.1/go.mod h1:NtoC/o8u3JlF1lSlyPNswIbeQH9bJTm
 github.com/packer-community/winrmcp v0.0.0-20180102160824-81144009af58/go.mod h1:f6Izs6JvFTdnRbziASagjZ2vmf55NSIkC/weStxCHqk=
 github.com/pascaldekloe/goe v0.0.0-20180627143212-57f6aae5913c/go.mod h1:lzWF7FIEvWOWxwDKqyGYQf6ZUaNfKdP144TG7ZOy1lc=
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
+github.com/peterbourgon/diskv v2.0.1+incompatible h1:UBdAOUP5p4RWqPBg048CAvpKN+vxiaj6gdUUzhl4XmI=
+github.com/peterbourgon/diskv v2.0.1+incompatible/go.mod h1:uqqh8zWWbv1HBMNONnaR/tNboyR3/BZd58JJSHlUSCU=
 github.com/pkg/errors v0.0.0-20170505043639-c605e284fe17/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
diff --git a/plugins/custom_plugin.go b/plugins/custom_plugin.go
index 29bf57ac..a41c21f9 100644
--- a/plugins/custom_plugin.go
+++ b/plugins/custom_plugin.go
@@ -5,9 +5,9 @@ import (
 	"archive/zip"
 	"bytes"
 	"compress/gzip"
-	"fmt"
+	"crypto/sha256"
+	"encoding/base64"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path"
@@ -17,6 +17,8 @@ import (
 	"text/template"
 
 	"github.com/chanzuckerberg/fogg/errs"
+	"github.com/chanzuckerberg/fogg/util"
+	"github.com/peterbourgon/diskv"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/afero"
 )
@@ -39,6 +41,8 @@ type CustomPlugin struct {
 	Format    TypePluginFormat `json:"format" yaml:"format" validate:"required"`
 	TarConfig *TarConfig       `json:"tar_config,omitempty" yaml:"tar_config,omitempty"`
 	TargetDir string           `json:"target_dir,omitempty" yaml:"target_dir,omitempty"`
+
+	cache *diskv.Diskv
 }
 
 // TarConfig configures the tar unpacking
@@ -55,6 +59,9 @@ func (tc *TarConfig) getStripComponents() int {
 
 // Install installs the custom plugin
 func (cp *CustomPlugin) Install(fs afero.Fs, pluginName string) error {
+	if cp.cache == nil {
+		return errs.NewInternal("download cache not configured")
+	}
 	return cp.install(fs, pluginName, cp.URL, runtime.GOOS, runtime.GOARCH)
 }
 
@@ -73,18 +80,19 @@ func (cp *CustomPlugin) install(
 		return errs.NewUser("nil fs")
 	}
 
-	fullUrl, err := Template(url, pluginOS, pluginArch)
+	fullURL, err := Template(url, pluginOS, pluginArch)
 	if err != nil {
 		return err
 	}
-	tmpPath, err := cp.fetch(pluginName, fullUrl)
-	defer os.Remove(tmpPath)
+	file, err := cp.fetch(pluginName, fullURL)
 	if err != nil {
 		return err
 	}
-	return cp.process(fs, pluginName, tmpPath, cp.TargetDir)
+	defer file.Close()
+	return cp.process(fs, pluginName, file, cp.TargetDir)
 }
 
+// Template templatizes a url with os and arch information
 func Template(url, os, arch string) (string, error) {
 	data := struct {
 		OS   string
@@ -104,42 +112,59 @@ func Template(url, os, arch string) (string, error) {
 	return out, nil
 }
 
-// SetTargetPath sets the target path for this plugin
-func (cp *CustomPlugin) SetTargetPath(path string) {
+// WithTargetPath sets the target path for this plugin
+func (cp *CustomPlugin) WithTargetPath(path string) *CustomPlugin {
 	cp.TargetDir = path
+	return cp
+}
+
+// WithCache adds a cache to plugins
+func (cp *CustomPlugin) WithCache(cache *diskv.Diskv) *CustomPlugin {
+	cp.cache = cache
+	return cp
 }
 
 // fetch fetches the custom plugin at URL
-func (cp *CustomPlugin) fetch(pluginName string, url string) (string, error) {
-	tmpFile, err := ioutil.TempFile("", fmt.Sprintf("%s-*.tmp", pluginName))
+func (cp *CustomPlugin) fetch(pluginName string, url string) (io.ReadCloser, error) {
+	h := sha256.New()
+	_, err := h.Write([]byte(url))
 	if err != nil {
-		return "", errs.WrapUser(err, "could not create temporary directory") //FIXME
+		return nil, errs.WrapUser(err, "error hashing url")
 	}
-	logrus.Debugf("downloading %s to tempfile", url)
-	resp, err := http.Get(url)
-	if err != nil {
-		return "", errs.WrapUserf(err, "could not get %s", url) // FIXME
+	cacheKey := base64.URLEncoding.EncodeToString(h.Sum(nil))
+
+	if !cp.cache.Has(cacheKey) {
+		logrus.Debugf("downloading %s to cache", url)
+		resp, err := http.Get(url)
+		if err != nil {
+			return nil, errs.WrapUserf(err, "could not get %s", url) // FIXME
+		}
+		defer resp.Body.Close()
+		err = cp.cache.WriteStream(cacheKey, resp.Body, true)
+		if err != nil {
+			return nil, errs.WrapUser(err, "could not write file to cache")
+		}
 	}
-	defer resp.Body.Close()
-	_, err = io.Copy(tmpFile, resp.Body)
-	return tmpFile.Name(), errs.WrapUser(err, "could not download file") //FIXME
+
+	f, err := cp.cache.ReadStream(cacheKey, false)
+	return f, errs.WrapUserf(err, "could not read %s from cache", url)
 }
 
 // process the custom plugin
-func (cp *CustomPlugin) process(fs afero.Fs, pluginName string, path string, targetDir string) error {
+func (cp *CustomPlugin) process(fs afero.Fs, pluginName string, file io.Reader, targetDir string) error {
 	switch cp.Format {
 	case TypePluginFormatTar:
-		return cp.processTar(fs, path, targetDir)
+		return cp.processTar(fs, file, targetDir)
 	case TypePluginFormatZip:
-		return cp.processZip(fs, path, targetDir)
+		return cp.processZip(fs, file, targetDir)
 	case TypePluginFormatBin:
-		return cp.processBin(fs, pluginName, path, targetDir)
+		return cp.processBin(fs, pluginName, file, targetDir)
 	default:
 		return errs.NewUserf("Unknown plugin format %s", cp.Format)
 	}
 }
 
-func (cp *CustomPlugin) processBin(fs afero.Fs, name string, downloadPath string, targetDir string) error {
+func (cp *CustomPlugin) processBin(fs afero.Fs, name string, file io.Reader, targetDir string) error {
 	target, err := Template(targetDir, runtime.GOOS, runtime.GOARCH)
 	if err != nil {
 		return errs.WrapUser(err, "unable to template url")
@@ -151,19 +176,14 @@ func (cp *CustomPlugin) processBin(fs afero.Fs, name string, downloadPath string
 	}
 
 	targetPath := path.Join(target, name)
-	src, err := os.Open(downloadPath)
-	if err != nil {
-		return errs.WrapUserf(err, "Could not open downloaded file at %s", downloadPath)
-	}
-
 	dst, err := fs.Create(targetPath)
 	if err != nil {
 		return errs.WrapUserf(err, "Could not open target file at %s", targetPath)
 	}
 
-	_, err = io.Copy(dst, src)
+	_, err = io.Copy(dst, file)
 	if err != nil {
-		return errs.WrapUserf(err, "Could not move %s to %s", downloadPath, targetPath)
+		return errs.WrapUserf(err, "Could not move plugin to %s", targetPath)
 	}
 
 	err = fs.Chmod(targetPath, os.FileMode(0755))
@@ -171,23 +191,17 @@ func (cp *CustomPlugin) processBin(fs afero.Fs, name string, downloadPath string
 }
 
 // https://medium.com/@skdomino/taring-untaring-files-in-go-6b07cf56bc07
-func (cp *CustomPlugin) processTar(fs afero.Fs, path string, targetDir string) error {
+func (cp *CustomPlugin) processTar(fs afero.Fs, reader io.Reader, targetDir string) error {
 	targetDir, err := Template(targetDir, runtime.GOOS, runtime.GOARCH)
 	if err != nil {
 		return errs.WrapUser(err, "unable to template url for custom plugin")
 	}
-	logrus.Debugf("untarring from %s to %s", path, targetDir)
 
 	err = fs.MkdirAll(targetDir, 0755)
 	if err != nil {
 		return errs.WrapUserf(err, "Could not create directory %s", targetDir)
 	}
-	f, err := os.Open(path)
-	if err != nil {
-		return errs.WrapUser(err, "could not read staged custom plugin")
-	}
-	defer f.Close()
-	gzr, err := gzip.NewReader(f)
+	gzr, err := gzip.NewReader(reader)
 	if err != nil {
 		return errs.WrapUser(err, "could not create gzip reader")
 	}
@@ -241,22 +255,22 @@ func (cp *CustomPlugin) processTar(fs afero.Fs, path string, targetDir string) e
 }
 
 // based on https://golangcode.com/create-zip-files-in-go/
-func (cp *CustomPlugin) processZip(fs afero.Fs, downloadPath string, targetDir string) error {
-	targetDir, err := Template(targetDir, runtime.GOOS, runtime.GOARCH)
+func (cp *CustomPlugin) processZip(fs afero.Fs, reader io.Reader, targetDir string) error {
+	buff := bytes.NewBuffer(nil)
+	size, err := io.Copy(buff, reader)
 	if err != nil {
-		return errs.WrapUserf(err, "could not template targetDir")
+		return errs.WrapUser(err, "could not read plugin contents")
 	}
-
+	zipBytes := bytes.NewReader(buff.Bytes())
 	err = fs.MkdirAll(targetDir, 0755)
 	if err != nil {
 		return errs.WrapUserf(err, "Could not create directory %s", targetDir)
 	}
 
-	r, err := zip.OpenReader(downloadPath)
+	r, err := zip.NewReader(zipBytes, size)
 	if err != nil {
 		return errs.WrapUser(err, "could not read staged custom plugin")
 	}
-	defer r.Close()
 
 	for _, f := range r.File {
 		// We run this in a closure to invoke the `defer`s after each iteration
@@ -297,3 +311,12 @@ func (cp *CustomPlugin) processZip(fs afero.Fs, downloadPath string, targetDir s
 	}
 	return nil
 }
+
+// GetPluginCache returns the cache used for plugins
+func GetPluginCache(cacheDir string) *diskv.Diskv {
+	return diskv.New(diskv.Options{
+		BasePath:    cacheDir,
+		Transform:   func(k string) []string { return []string{"custom_plugins", util.VersionCacheKey(), k} },
+		Compression: diskv.NewGzipCompression(),
+	})
+}
diff --git a/setup/setup.go b/setup/setup.go
index c25296f7..020bfce2 100644
--- a/setup/setup.go
+++ b/setup/setup.go
@@ -4,19 +4,27 @@ import (
 	v2 "github.com/chanzuckerberg/fogg/config/v2"
 	"github.com/chanzuckerberg/fogg/errs"
 	"github.com/chanzuckerberg/fogg/plugins"
+	"github.com/chanzuckerberg/fogg/util"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/afero"
 )
 
+// Setup will download custom plugins and providers
 func Setup(fs afero.Fs, conf *v2.Config) error {
 	logrus.Debug("setting up plugins")
+	cacheDir, err := util.GetFoggCachePath()
+	if err != nil {
+		return err
+	}
+
 	apply := func(name string, plugin *plugins.CustomPlugin) error {
 		logrus.Infof("Setting up plugin %s", name)
 		return errs.WrapUserf(plugin.Install(fs, name), "Error applying plugin %s", name)
 	}
 
+	cache := plugins.GetPluginCache(cacheDir)
 	for pluginName, plugin := range conf.Plugins.CustomPlugins {
-		plugin.SetTargetPath(plugins.CustomPluginDir)
+		plugin.WithTargetPath(plugins.CustomPluginDir).WithCache(cache)
 		err := apply(pluginName, plugin)
 		if err != nil {
 			return err
@@ -24,7 +32,7 @@ func Setup(fs afero.Fs, conf *v2.Config) error {
 	}
 
 	for providerName, provider := range conf.Plugins.TerraformProviders {
-		provider.SetTargetPath(plugins.TerraformCustomPluginCacheDir)
+		provider.WithTargetPath(plugins.TerraformCustomPluginCacheDir).WithCache(cache)
 		err := apply(providerName, provider)
 		if err != nil {
 			return err
diff --git a/util/module_storage.go b/util/module_storage.go
index 82982697..a9018f04 100644
--- a/util/module_storage.go
+++ b/util/module_storage.go
@@ -17,57 +17,63 @@ func DownloadModule(fs afero.Fs, cacheDir, source string) (string, error) {
 	// We want to do these operations from the root of our working repository.
 	// In the case where we have a BaseFs we pull out its root. Otherwise use `pwd`.
 	var pwd string
+	var err error
 	if baseFs, ok := fs.(*afero.BasePathFs); ok {
 		pwd = afero.FullBaseFsPath(baseFs, ".")
 	} else {
-		var e error
-		pwd, e = os.Getwd()
-		if e != nil {
-			return "", errs.WrapUser(e, "could not get pwd")
+		pwd, err = os.Getwd()
+		if err != nil {
+			return "", errs.WrapUser(err, "could not get pwd")
 		}
 	}
 
-	s, e := getter.Detect(source, pwd, getter.Detectors)
-	if e != nil {
-		return "", errs.WrapUser(e, "could not detect module type")
+	s, err := getter.Detect(source, pwd, getter.Detectors)
+	if err != nil {
+		return "", errs.WrapUser(err, "could not detect module type")
 	}
 
 	storage := &getter.FolderStorage{
 		StorageDir: cacheDir,
 	}
 	h := sha256.New()
-	_, e = h.Write([]byte(VersionCacheKey()))
-	if e != nil {
-		return "", errs.WrapUser(e, "could not hash")
+	_, err = h.Write([]byte(VersionCacheKey()))
+	if err != nil {
+		return "", errs.WrapUser(err, "could not hash")
 	}
-	_, e = h.Write([]byte(source))
-	if e != nil {
-		return "", errs.WrapUser(e, "could not hash")
+	_, err = h.Write([]byte(source))
+	if err != nil {
+		return "", errs.WrapUser(err, "could not hash")
 	}
 	hash := string(h.Sum(nil))
 
-	e = storage.Get(hash, s, false)
-	if e != nil {
-		return "", errs.WrapUser(e, "unable to read module from local storage")
+	err = storage.Get(hash, s, false)
+	if err != nil {
+		return "", errs.WrapUser(err, "unable to read module from local storage")
 	}
-	d, _, e := storage.Dir(hash)
-	if e != nil {
-		return "", errs.WrapUser(e, "could not get module storage dir")
+	d, _, err := storage.Dir(hash)
+	if err != nil {
+		return "", errs.WrapUser(err, "could not get module storage dir")
 	}
 	return d, nil
 }
 
-func DownloadAndParseModule(fs afero.Fs, mod string) (*config.Config, error) {
-	homedir, e := homedir.Dir()
-	if e != nil {
-		return nil, errs.WrapUser(e, "unable to find homedir")
+func GetFoggCachePath() (string, error) {
+	homedir, err := homedir.Dir()
+	if err != nil {
+		return "", errs.WrapUser(err, "unable to find homedir")
 	}
-
 	dir := filepath.Join(homedir, ".fogg", "cache")
+	return dir, nil
+}
 
-	d, e := DownloadModule(fs, dir, mod)
-	if e != nil {
-		return nil, errs.WrapUser(e, "unable to download module")
+func DownloadAndParseModule(fs afero.Fs, mod string) (*config.Config, error) {
+	dir, err := GetFoggCachePath()
+	if err != nil {
+		return nil, err
+	}
+	d, err := DownloadModule(fs, dir, mod)
+	if err != nil {
+		return nil, errs.WrapUser(err, "unable to download module")
 	}
 	return config.LoadDir(d)
 }
diff --git a/vendor/github.com/google/btree/.travis.yml b/vendor/github.com/google/btree/.travis.yml
new file mode 100644
index 00000000..4f2ee4d9
--- /dev/null
+++ b/vendor/github.com/google/btree/.travis.yml
@@ -0,0 +1,1 @@
+language: go
diff --git a/vendor/github.com/google/btree/LICENSE b/vendor/github.com/google/btree/LICENSE
new file mode 100644
index 00000000..d6456956
--- /dev/null
+++ b/vendor/github.com/google/btree/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
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+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
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+          stating that You changed the files; and
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+          that You distribute, all copyright, patent, trademark, and
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+
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+          notices within Derivative Works that You distribute, alongside
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+          that such additional attribution notices cannot be construed
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+
+      You may add Your own copyright statement to Your modifications and
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+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
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+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
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+      Contributor provides its Contributions) on an "AS IS" BASIS,
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+      appropriateness of using or redistributing the Work and assume any
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+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+
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+
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+
+      To apply the Apache License to your work, attach the following
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+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
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+
+       http://www.apache.org/licenses/LICENSE-2.0
+
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+   distributed under the License is distributed on an "AS IS" BASIS,
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+   limitations under the License.
diff --git a/vendor/github.com/google/btree/README.md b/vendor/github.com/google/btree/README.md
new file mode 100644
index 00000000..6062a4da
--- /dev/null
+++ b/vendor/github.com/google/btree/README.md
@@ -0,0 +1,12 @@
+# BTree implementation for Go
+
+![Travis CI Build Status](https://api.travis-ci.org/google/btree.svg?branch=master)
+
+This package provides an in-memory B-Tree implementation for Go, useful as
+an ordered, mutable data structure.
+
+The API is based off of the wonderful
+http://godoc.org/github.com/petar/GoLLRB/llrb, and is meant to allow btree to
+act as a drop-in replacement for gollrb trees.
+
+See http://godoc.org/github.com/google/btree for documentation.
diff --git a/vendor/github.com/google/btree/btree.go b/vendor/github.com/google/btree/btree.go
new file mode 100644
index 00000000..6ff062f9
--- /dev/null
+++ b/vendor/github.com/google/btree/btree.go
@@ -0,0 +1,890 @@
+// Copyright 2014 Google 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 btree implements in-memory B-Trees of arbitrary degree.
+//
+// btree implements an in-memory B-Tree for use as an ordered data structure.
+// It is not meant for persistent storage solutions.
+//
+// It has a flatter structure than an equivalent red-black or other binary tree,
+// which in some cases yields better memory usage and/or performance.
+// See some discussion on the matter here:
+//   http://google-opensource.blogspot.com/2013/01/c-containers-that-save-memory-and-time.html
+// Note, though, that this project is in no way related to the C++ B-Tree
+// implementation written about there.
+//
+// Within this tree, each node contains a slice of items and a (possibly nil)
+// slice of children.  For basic numeric values or raw structs, this can cause
+// efficiency differences when compared to equivalent C++ template code that
+// stores values in arrays within the node:
+//   * Due to the overhead of storing values as interfaces (each
+//     value needs to be stored as the value itself, then 2 words for the
+//     interface pointing to that value and its type), resulting in higher
+//     memory use.
+//   * Since interfaces can point to values anywhere in memory, values are
+//     most likely not stored in contiguous blocks, resulting in a higher
+//     number of cache misses.
+// These issues don't tend to matter, though, when working with strings or other
+// heap-allocated structures, since C++-equivalent structures also must store
+// pointers and also distribute their values across the heap.
+//
+// This implementation is designed to be a drop-in replacement to gollrb.LLRB
+// trees, (http://github.com/petar/gollrb), an excellent and probably the most
+// widely used ordered tree implementation in the Go ecosystem currently.
+// Its functions, therefore, exactly mirror those of
+// llrb.LLRB where possible.  Unlike gollrb, though, we currently don't
+// support storing multiple equivalent values.
+package btree
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+	"sync"
+)
+
+// Item represents a single object in the tree.
+type Item interface {
+	// Less tests whether the current item is less than the given argument.
+	//
+	// This must provide a strict weak ordering.
+	// If !a.Less(b) && !b.Less(a), we treat this to mean a == b (i.e. we can only
+	// hold one of either a or b in the tree).
+	Less(than Item) bool
+}
+
+const (
+	DefaultFreeListSize = 32
+)
+
+var (
+	nilItems    = make(items, 16)
+	nilChildren = make(children, 16)
+)
+
+// FreeList represents a free list of btree nodes. By default each
+// BTree has its own FreeList, but multiple BTrees can share the same
+// FreeList.
+// Two Btrees using the same freelist are safe for concurrent write access.
+type FreeList struct {
+	mu       sync.Mutex
+	freelist []*node
+}
+
+// NewFreeList creates a new free list.
+// size is the maximum size of the returned free list.
+func NewFreeList(size int) *FreeList {
+	return &FreeList{freelist: make([]*node, 0, size)}
+}
+
+func (f *FreeList) newNode() (n *node) {
+	f.mu.Lock()
+	index := len(f.freelist) - 1
+	if index < 0 {
+		f.mu.Unlock()
+		return new(node)
+	}
+	n = f.freelist[index]
+	f.freelist[index] = nil
+	f.freelist = f.freelist[:index]
+	f.mu.Unlock()
+	return
+}
+
+// freeNode adds the given node to the list, returning true if it was added
+// and false if it was discarded.
+func (f *FreeList) freeNode(n *node) (out bool) {
+	f.mu.Lock()
+	if len(f.freelist) < cap(f.freelist) {
+		f.freelist = append(f.freelist, n)
+		out = true
+	}
+	f.mu.Unlock()
+	return
+}
+
+// ItemIterator allows callers of Ascend* to iterate in-order over portions of
+// the tree.  When this function returns false, iteration will stop and the
+// associated Ascend* function will immediately return.
+type ItemIterator func(i Item) bool
+
+// New creates a new B-Tree with the given degree.
+//
+// New(2), for example, will create a 2-3-4 tree (each node contains 1-3 items
+// and 2-4 children).
+func New(degree int) *BTree {
+	return NewWithFreeList(degree, NewFreeList(DefaultFreeListSize))
+}
+
+// NewWithFreeList creates a new B-Tree that uses the given node free list.
+func NewWithFreeList(degree int, f *FreeList) *BTree {
+	if degree <= 1 {
+		panic("bad degree")
+	}
+	return &BTree{
+		degree: degree,
+		cow:    &copyOnWriteContext{freelist: f},
+	}
+}
+
+// items stores items in a node.
+type items []Item
+
+// insertAt inserts a value into the given index, pushing all subsequent values
+// forward.
+func (s *items) insertAt(index int, item Item) {
+	*s = append(*s, nil)
+	if index < len(*s) {
+		copy((*s)[index+1:], (*s)[index:])
+	}
+	(*s)[index] = item
+}
+
+// removeAt removes a value at a given index, pulling all subsequent values
+// back.
+func (s *items) removeAt(index int) Item {
+	item := (*s)[index]
+	copy((*s)[index:], (*s)[index+1:])
+	(*s)[len(*s)-1] = nil
+	*s = (*s)[:len(*s)-1]
+	return item
+}
+
+// pop removes and returns the last element in the list.
+func (s *items) pop() (out Item) {
+	index := len(*s) - 1
+	out = (*s)[index]
+	(*s)[index] = nil
+	*s = (*s)[:index]
+	return
+}
+
+// truncate truncates this instance at index so that it contains only the
+// first index items. index must be less than or equal to length.
+func (s *items) truncate(index int) {
+	var toClear items
+	*s, toClear = (*s)[:index], (*s)[index:]
+	for len(toClear) > 0 {
+		toClear = toClear[copy(toClear, nilItems):]
+	}
+}
+
+// find returns the index where the given item should be inserted into this
+// list.  'found' is true if the item already exists in the list at the given
+// index.
+func (s items) find(item Item) (index int, found bool) {
+	i := sort.Search(len(s), func(i int) bool {
+		return item.Less(s[i])
+	})
+	if i > 0 && !s[i-1].Less(item) {
+		return i - 1, true
+	}
+	return i, false
+}
+
+// children stores child nodes in a node.
+type children []*node
+
+// insertAt inserts a value into the given index, pushing all subsequent values
+// forward.
+func (s *children) insertAt(index int, n *node) {
+	*s = append(*s, nil)
+	if index < len(*s) {
+		copy((*s)[index+1:], (*s)[index:])
+	}
+	(*s)[index] = n
+}
+
+// removeAt removes a value at a given index, pulling all subsequent values
+// back.
+func (s *children) removeAt(index int) *node {
+	n := (*s)[index]
+	copy((*s)[index:], (*s)[index+1:])
+	(*s)[len(*s)-1] = nil
+	*s = (*s)[:len(*s)-1]
+	return n
+}
+
+// pop removes and returns the last element in the list.
+func (s *children) pop() (out *node) {
+	index := len(*s) - 1
+	out = (*s)[index]
+	(*s)[index] = nil
+	*s = (*s)[:index]
+	return
+}
+
+// truncate truncates this instance at index so that it contains only the
+// first index children. index must be less than or equal to length.
+func (s *children) truncate(index int) {
+	var toClear children
+	*s, toClear = (*s)[:index], (*s)[index:]
+	for len(toClear) > 0 {
+		toClear = toClear[copy(toClear, nilChildren):]
+	}
+}
+
+// node is an internal node in a tree.
+//
+// It must at all times maintain the invariant that either
+//   * len(children) == 0, len(items) unconstrained
+//   * len(children) == len(items) + 1
+type node struct {
+	items    items
+	children children
+	cow      *copyOnWriteContext
+}
+
+func (n *node) mutableFor(cow *copyOnWriteContext) *node {
+	if n.cow == cow {
+		return n
+	}
+	out := cow.newNode()
+	if cap(out.items) >= len(n.items) {
+		out.items = out.items[:len(n.items)]
+	} else {
+		out.items = make(items, len(n.items), cap(n.items))
+	}
+	copy(out.items, n.items)
+	// Copy children
+	if cap(out.children) >= len(n.children) {
+		out.children = out.children[:len(n.children)]
+	} else {
+		out.children = make(children, len(n.children), cap(n.children))
+	}
+	copy(out.children, n.children)
+	return out
+}
+
+func (n *node) mutableChild(i int) *node {
+	c := n.children[i].mutableFor(n.cow)
+	n.children[i] = c
+	return c
+}
+
+// split splits the given node at the given index.  The current node shrinks,
+// and this function returns the item that existed at that index and a new node
+// containing all items/children after it.
+func (n *node) split(i int) (Item, *node) {
+	item := n.items[i]
+	next := n.cow.newNode()
+	next.items = append(next.items, n.items[i+1:]...)
+	n.items.truncate(i)
+	if len(n.children) > 0 {
+		next.children = append(next.children, n.children[i+1:]...)
+		n.children.truncate(i + 1)
+	}
+	return item, next
+}
+
+// maybeSplitChild checks if a child should be split, and if so splits it.
+// Returns whether or not a split occurred.
+func (n *node) maybeSplitChild(i, maxItems int) bool {
+	if len(n.children[i].items) < maxItems {
+		return false
+	}
+	first := n.mutableChild(i)
+	item, second := first.split(maxItems / 2)
+	n.items.insertAt(i, item)
+	n.children.insertAt(i+1, second)
+	return true
+}
+
+// insert inserts an item into the subtree rooted at this node, making sure
+// no nodes in the subtree exceed maxItems items.  Should an equivalent item be
+// be found/replaced by insert, it will be returned.
+func (n *node) insert(item Item, maxItems int) Item {
+	i, found := n.items.find(item)
+	if found {
+		out := n.items[i]
+		n.items[i] = item
+		return out
+	}
+	if len(n.children) == 0 {
+		n.items.insertAt(i, item)
+		return nil
+	}
+	if n.maybeSplitChild(i, maxItems) {
+		inTree := n.items[i]
+		switch {
+		case item.Less(inTree):
+			// no change, we want first split node
+		case inTree.Less(item):
+			i++ // we want second split node
+		default:
+			out := n.items[i]
+			n.items[i] = item
+			return out
+		}
+	}
+	return n.mutableChild(i).insert(item, maxItems)
+}
+
+// get finds the given key in the subtree and returns it.
+func (n *node) get(key Item) Item {
+	i, found := n.items.find(key)
+	if found {
+		return n.items[i]
+	} else if len(n.children) > 0 {
+		return n.children[i].get(key)
+	}
+	return nil
+}
+
+// min returns the first item in the subtree.
+func min(n *node) Item {
+	if n == nil {
+		return nil
+	}
+	for len(n.children) > 0 {
+		n = n.children[0]
+	}
+	if len(n.items) == 0 {
+		return nil
+	}
+	return n.items[0]
+}
+
+// max returns the last item in the subtree.
+func max(n *node) Item {
+	if n == nil {
+		return nil
+	}
+	for len(n.children) > 0 {
+		n = n.children[len(n.children)-1]
+	}
+	if len(n.items) == 0 {
+		return nil
+	}
+	return n.items[len(n.items)-1]
+}
+
+// toRemove details what item to remove in a node.remove call.
+type toRemove int
+
+const (
+	removeItem toRemove = iota // removes the given item
+	removeMin                  // removes smallest item in the subtree
+	removeMax                  // removes largest item in the subtree
+)
+
+// remove removes an item from the subtree rooted at this node.
+func (n *node) remove(item Item, minItems int, typ toRemove) Item {
+	var i int
+	var found bool
+	switch typ {
+	case removeMax:
+		if len(n.children) == 0 {
+			return n.items.pop()
+		}
+		i = len(n.items)
+	case removeMin:
+		if len(n.children) == 0 {
+			return n.items.removeAt(0)
+		}
+		i = 0
+	case removeItem:
+		i, found = n.items.find(item)
+		if len(n.children) == 0 {
+			if found {
+				return n.items.removeAt(i)
+			}
+			return nil
+		}
+	default:
+		panic("invalid type")
+	}
+	// If we get to here, we have children.
+	if len(n.children[i].items) <= minItems {
+		return n.growChildAndRemove(i, item, minItems, typ)
+	}
+	child := n.mutableChild(i)
+	// Either we had enough items to begin with, or we've done some
+	// merging/stealing, because we've got enough now and we're ready to return
+	// stuff.
+	if found {
+		// The item exists at index 'i', and the child we've selected can give us a
+		// predecessor, since if we've gotten here it's got > minItems items in it.
+		out := n.items[i]
+		// We use our special-case 'remove' call with typ=maxItem to pull the
+		// predecessor of item i (the rightmost leaf of our immediate left child)
+		// and set it into where we pulled the item from.
+		n.items[i] = child.remove(nil, minItems, removeMax)
+		return out
+	}
+	// Final recursive call.  Once we're here, we know that the item isn't in this
+	// node and that the child is big enough to remove from.
+	return child.remove(item, minItems, typ)
+}
+
+// growChildAndRemove grows child 'i' to make sure it's possible to remove an
+// item from it while keeping it at minItems, then calls remove to actually
+// remove it.
+//
+// Most documentation says we have to do two sets of special casing:
+//   1) item is in this node
+//   2) item is in child
+// In both cases, we need to handle the two subcases:
+//   A) node has enough values that it can spare one
+//   B) node doesn't have enough values
+// For the latter, we have to check:
+//   a) left sibling has node to spare
+//   b) right sibling has node to spare
+//   c) we must merge
+// To simplify our code here, we handle cases #1 and #2 the same:
+// If a node doesn't have enough items, we make sure it does (using a,b,c).
+// We then simply redo our remove call, and the second time (regardless of
+// whether we're in case 1 or 2), we'll have enough items and can guarantee
+// that we hit case A.
+func (n *node) growChildAndRemove(i int, item Item, minItems int, typ toRemove) Item {
+	if i > 0 && len(n.children[i-1].items) > minItems {
+		// Steal from left child
+		child := n.mutableChild(i)
+		stealFrom := n.mutableChild(i - 1)
+		stolenItem := stealFrom.items.pop()
+		child.items.insertAt(0, n.items[i-1])
+		n.items[i-1] = stolenItem
+		if len(stealFrom.children) > 0 {
+			child.children.insertAt(0, stealFrom.children.pop())
+		}
+	} else if i < len(n.items) && len(n.children[i+1].items) > minItems {
+		// steal from right child
+		child := n.mutableChild(i)
+		stealFrom := n.mutableChild(i + 1)
+		stolenItem := stealFrom.items.removeAt(0)
+		child.items = append(child.items, n.items[i])
+		n.items[i] = stolenItem
+		if len(stealFrom.children) > 0 {
+			child.children = append(child.children, stealFrom.children.removeAt(0))
+		}
+	} else {
+		if i >= len(n.items) {
+			i--
+		}
+		child := n.mutableChild(i)
+		// merge with right child
+		mergeItem := n.items.removeAt(i)
+		mergeChild := n.children.removeAt(i + 1)
+		child.items = append(child.items, mergeItem)
+		child.items = append(child.items, mergeChild.items...)
+		child.children = append(child.children, mergeChild.children...)
+		n.cow.freeNode(mergeChild)
+	}
+	return n.remove(item, minItems, typ)
+}
+
+type direction int
+
+const (
+	descend = direction(-1)
+	ascend  = direction(+1)
+)
+
+// iterate provides a simple method for iterating over elements in the tree.
+//
+// When ascending, the 'start' should be less than 'stop' and when descending,
+// the 'start' should be greater than 'stop'. Setting 'includeStart' to true
+// will force the iterator to include the first item when it equals 'start',
+// thus creating a "greaterOrEqual" or "lessThanEqual" rather than just a
+// "greaterThan" or "lessThan" queries.
+func (n *node) iterate(dir direction, start, stop Item, includeStart bool, hit bool, iter ItemIterator) (bool, bool) {
+	var ok, found bool
+	var index int
+	switch dir {
+	case ascend:
+		if start != nil {
+			index, _ = n.items.find(start)
+		}
+		for i := index; i < len(n.items); i++ {
+			if len(n.children) > 0 {
+				if hit, ok = n.children[i].iterate(dir, start, stop, includeStart, hit, iter); !ok {
+					return hit, false
+				}
+			}
+			if !includeStart && !hit && start != nil && !start.Less(n.items[i]) {
+				hit = true
+				continue
+			}
+			hit = true
+			if stop != nil && !n.items[i].Less(stop) {
+				return hit, false
+			}
+			if !iter(n.items[i]) {
+				return hit, false
+			}
+		}
+		if len(n.children) > 0 {
+			if hit, ok = n.children[len(n.children)-1].iterate(dir, start, stop, includeStart, hit, iter); !ok {
+				return hit, false
+			}
+		}
+	case descend:
+		if start != nil {
+			index, found = n.items.find(start)
+			if !found {
+				index = index - 1
+			}
+		} else {
+			index = len(n.items) - 1
+		}
+		for i := index; i >= 0; i-- {
+			if start != nil && !n.items[i].Less(start) {
+				if !includeStart || hit || start.Less(n.items[i]) {
+					continue
+				}
+			}
+			if len(n.children) > 0 {
+				if hit, ok = n.children[i+1].iterate(dir, start, stop, includeStart, hit, iter); !ok {
+					return hit, false
+				}
+			}
+			if stop != nil && !stop.Less(n.items[i]) {
+				return hit, false //	continue
+			}
+			hit = true
+			if !iter(n.items[i]) {
+				return hit, false
+			}
+		}
+		if len(n.children) > 0 {
+			if hit, ok = n.children[0].iterate(dir, start, stop, includeStart, hit, iter); !ok {
+				return hit, false
+			}
+		}
+	}
+	return hit, true
+}
+
+// Used for testing/debugging purposes.
+func (n *node) print(w io.Writer, level int) {
+	fmt.Fprintf(w, "%sNODE:%v\n", strings.Repeat("  ", level), n.items)
+	for _, c := range n.children {
+		c.print(w, level+1)
+	}
+}
+
+// BTree is an implementation of a B-Tree.
+//
+// BTree stores Item instances in an ordered structure, allowing easy insertion,
+// removal, and iteration.
+//
+// Write operations are not safe for concurrent mutation by multiple
+// goroutines, but Read operations are.
+type BTree struct {
+	degree int
+	length int
+	root   *node
+	cow    *copyOnWriteContext
+}
+
+// copyOnWriteContext pointers determine node ownership... a tree with a write
+// context equivalent to a node's write context is allowed to modify that node.
+// A tree whose write context does not match a node's is not allowed to modify
+// it, and must create a new, writable copy (IE: it's a Clone).
+//
+// When doing any write operation, we maintain the invariant that the current
+// node's context is equal to the context of the tree that requested the write.
+// We do this by, before we descend into any node, creating a copy with the
+// correct context if the contexts don't match.
+//
+// Since the node we're currently visiting on any write has the requesting
+// tree's context, that node is modifiable in place.  Children of that node may
+// not share context, but before we descend into them, we'll make a mutable
+// copy.
+type copyOnWriteContext struct {
+	freelist *FreeList
+}
+
+// Clone clones the btree, lazily.  Clone should not be called concurrently,
+// but the original tree (t) and the new tree (t2) can be used concurrently
+// once the Clone call completes.
+//
+// The internal tree structure of b is marked read-only and shared between t and
+// t2.  Writes to both t and t2 use copy-on-write logic, creating new nodes
+// whenever one of b's original nodes would have been modified.  Read operations
+// should have no performance degredation.  Write operations for both t and t2
+// will initially experience minor slow-downs caused by additional allocs and
+// copies due to the aforementioned copy-on-write logic, but should converge to
+// the original performance characteristics of the original tree.
+func (t *BTree) Clone() (t2 *BTree) {
+	// Create two entirely new copy-on-write contexts.
+	// This operation effectively creates three trees:
+	//   the original, shared nodes (old b.cow)
+	//   the new b.cow nodes
+	//   the new out.cow nodes
+	cow1, cow2 := *t.cow, *t.cow
+	out := *t
+	t.cow = &cow1
+	out.cow = &cow2
+	return &out
+}
+
+// maxItems returns the max number of items to allow per node.
+func (t *BTree) maxItems() int {
+	return t.degree*2 - 1
+}
+
+// minItems returns the min number of items to allow per node (ignored for the
+// root node).
+func (t *BTree) minItems() int {
+	return t.degree - 1
+}
+
+func (c *copyOnWriteContext) newNode() (n *node) {
+	n = c.freelist.newNode()
+	n.cow = c
+	return
+}
+
+type freeType int
+
+const (
+	ftFreelistFull freeType = iota // node was freed (available for GC, not stored in freelist)
+	ftStored                       // node was stored in the freelist for later use
+	ftNotOwned                     // node was ignored by COW, since it's owned by another one
+)
+
+// freeNode frees a node within a given COW context, if it's owned by that
+// context.  It returns what happened to the node (see freeType const
+// documentation).
+func (c *copyOnWriteContext) freeNode(n *node) freeType {
+	if n.cow == c {
+		// clear to allow GC
+		n.items.truncate(0)
+		n.children.truncate(0)
+		n.cow = nil
+		if c.freelist.freeNode(n) {
+			return ftStored
+		} else {
+			return ftFreelistFull
+		}
+	} else {
+		return ftNotOwned
+	}
+}
+
+// ReplaceOrInsert adds the given item to the tree.  If an item in the tree
+// already equals the given one, it is removed from the tree and returned.
+// Otherwise, nil is returned.
+//
+// nil cannot be added to the tree (will panic).
+func (t *BTree) ReplaceOrInsert(item Item) Item {
+	if item == nil {
+		panic("nil item being added to BTree")
+	}
+	if t.root == nil {
+		t.root = t.cow.newNode()
+		t.root.items = append(t.root.items, item)
+		t.length++
+		return nil
+	} else {
+		t.root = t.root.mutableFor(t.cow)
+		if len(t.root.items) >= t.maxItems() {
+			item2, second := t.root.split(t.maxItems() / 2)
+			oldroot := t.root
+			t.root = t.cow.newNode()
+			t.root.items = append(t.root.items, item2)
+			t.root.children = append(t.root.children, oldroot, second)
+		}
+	}
+	out := t.root.insert(item, t.maxItems())
+	if out == nil {
+		t.length++
+	}
+	return out
+}
+
+// Delete removes an item equal to the passed in item from the tree, returning
+// it.  If no such item exists, returns nil.
+func (t *BTree) Delete(item Item) Item {
+	return t.deleteItem(item, removeItem)
+}
+
+// DeleteMin removes the smallest item in the tree and returns it.
+// If no such item exists, returns nil.
+func (t *BTree) DeleteMin() Item {
+	return t.deleteItem(nil, removeMin)
+}
+
+// DeleteMax removes the largest item in the tree and returns it.
+// If no such item exists, returns nil.
+func (t *BTree) DeleteMax() Item {
+	return t.deleteItem(nil, removeMax)
+}
+
+func (t *BTree) deleteItem(item Item, typ toRemove) Item {
+	if t.root == nil || len(t.root.items) == 0 {
+		return nil
+	}
+	t.root = t.root.mutableFor(t.cow)
+	out := t.root.remove(item, t.minItems(), typ)
+	if len(t.root.items) == 0 && len(t.root.children) > 0 {
+		oldroot := t.root
+		t.root = t.root.children[0]
+		t.cow.freeNode(oldroot)
+	}
+	if out != nil {
+		t.length--
+	}
+	return out
+}
+
+// AscendRange calls the iterator for every value in the tree within the range
+// [greaterOrEqual, lessThan), until iterator returns false.
+func (t *BTree) AscendRange(greaterOrEqual, lessThan Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(ascend, greaterOrEqual, lessThan, true, false, iterator)
+}
+
+// AscendLessThan calls the iterator for every value in the tree within the range
+// [first, pivot), until iterator returns false.
+func (t *BTree) AscendLessThan(pivot Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(ascend, nil, pivot, false, false, iterator)
+}
+
+// AscendGreaterOrEqual calls the iterator for every value in the tree within
+// the range [pivot, last], until iterator returns false.
+func (t *BTree) AscendGreaterOrEqual(pivot Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(ascend, pivot, nil, true, false, iterator)
+}
+
+// Ascend calls the iterator for every value in the tree within the range
+// [first, last], until iterator returns false.
+func (t *BTree) Ascend(iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(ascend, nil, nil, false, false, iterator)
+}
+
+// DescendRange calls the iterator for every value in the tree within the range
+// [lessOrEqual, greaterThan), until iterator returns false.
+func (t *BTree) DescendRange(lessOrEqual, greaterThan Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(descend, lessOrEqual, greaterThan, true, false, iterator)
+}
+
+// DescendLessOrEqual calls the iterator for every value in the tree within the range
+// [pivot, first], until iterator returns false.
+func (t *BTree) DescendLessOrEqual(pivot Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(descend, pivot, nil, true, false, iterator)
+}
+
+// DescendGreaterThan calls the iterator for every value in the tree within
+// the range (pivot, last], until iterator returns false.
+func (t *BTree) DescendGreaterThan(pivot Item, iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(descend, nil, pivot, false, false, iterator)
+}
+
+// Descend calls the iterator for every value in the tree within the range
+// [last, first], until iterator returns false.
+func (t *BTree) Descend(iterator ItemIterator) {
+	if t.root == nil {
+		return
+	}
+	t.root.iterate(descend, nil, nil, false, false, iterator)
+}
+
+// Get looks for the key item in the tree, returning it.  It returns nil if
+// unable to find that item.
+func (t *BTree) Get(key Item) Item {
+	if t.root == nil {
+		return nil
+	}
+	return t.root.get(key)
+}
+
+// Min returns the smallest item in the tree, or nil if the tree is empty.
+func (t *BTree) Min() Item {
+	return min(t.root)
+}
+
+// Max returns the largest item in the tree, or nil if the tree is empty.
+func (t *BTree) Max() Item {
+	return max(t.root)
+}
+
+// Has returns true if the given key is in the tree.
+func (t *BTree) Has(key Item) bool {
+	return t.Get(key) != nil
+}
+
+// Len returns the number of items currently in the tree.
+func (t *BTree) Len() int {
+	return t.length
+}
+
+// Clear removes all items from the btree.  If addNodesToFreelist is true,
+// t's nodes are added to its freelist as part of this call, until the freelist
+// is full.  Otherwise, the root node is simply dereferenced and the subtree
+// left to Go's normal GC processes.
+//
+// This can be much faster
+// than calling Delete on all elements, because that requires finding/removing
+// each element in the tree and updating the tree accordingly.  It also is
+// somewhat faster than creating a new tree to replace the old one, because
+// nodes from the old tree are reclaimed into the freelist for use by the new
+// one, instead of being lost to the garbage collector.
+//
+// This call takes:
+//   O(1): when addNodesToFreelist is false, this is a single operation.
+//   O(1): when the freelist is already full, it breaks out immediately
+//   O(freelist size):  when the freelist is empty and the nodes are all owned
+//       by this tree, nodes are added to the freelist until full.
+//   O(tree size):  when all nodes are owned by another tree, all nodes are
+//       iterated over looking for nodes to add to the freelist, and due to
+//       ownership, none are.
+func (t *BTree) Clear(addNodesToFreelist bool) {
+	if t.root != nil && addNodesToFreelist {
+		t.root.reset(t.cow)
+	}
+	t.root, t.length = nil, 0
+}
+
+// reset returns a subtree to the freelist.  It breaks out immediately if the
+// freelist is full, since the only benefit of iterating is to fill that
+// freelist up.  Returns true if parent reset call should continue.
+func (n *node) reset(c *copyOnWriteContext) bool {
+	for _, child := range n.children {
+		if !child.reset(c) {
+			return false
+		}
+	}
+	return c.freeNode(n) != ftFreelistFull
+}
+
+// Int implements the Item interface for integers.
+type Int int
+
+// Less returns true if int(a) < int(b).
+func (a Int) Less(b Item) bool {
+	return a < b.(Int)
+}
diff --git a/vendor/github.com/google/btree/btree_mem.go b/vendor/github.com/google/btree/btree_mem.go
new file mode 100644
index 00000000..cb95b7fa
--- /dev/null
+++ b/vendor/github.com/google/btree/btree_mem.go
@@ -0,0 +1,76 @@
+// Copyright 2014 Google 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.
+
+// +build ignore
+
+// This binary compares memory usage between btree and gollrb.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math/rand"
+	"runtime"
+	"time"
+
+	"github.com/google/btree"
+	"github.com/petar/GoLLRB/llrb"
+)
+
+var (
+	size   = flag.Int("size", 1000000, "size of the tree to build")
+	degree = flag.Int("degree", 8, "degree of btree")
+	gollrb = flag.Bool("llrb", false, "use llrb instead of btree")
+)
+
+func main() {
+	flag.Parse()
+	vals := rand.Perm(*size)
+	var t, v interface{}
+	v = vals
+	var stats runtime.MemStats
+	for i := 0; i < 10; i++ {
+		runtime.GC()
+	}
+	fmt.Println("-------- BEFORE ----------")
+	runtime.ReadMemStats(&stats)
+	fmt.Printf("%+v\n", stats)
+	start := time.Now()
+	if *gollrb {
+		tr := llrb.New()
+		for _, v := range vals {
+			tr.ReplaceOrInsert(llrb.Int(v))
+		}
+		t = tr // keep it around
+	} else {
+		tr := btree.New(*degree)
+		for _, v := range vals {
+			tr.ReplaceOrInsert(btree.Int(v))
+		}
+		t = tr // keep it around
+	}
+	fmt.Printf("%v inserts in %v\n", *size, time.Since(start))
+	fmt.Println("-------- AFTER ----------")
+	runtime.ReadMemStats(&stats)
+	fmt.Printf("%+v\n", stats)
+	for i := 0; i < 10; i++ {
+		runtime.GC()
+	}
+	fmt.Println("-------- AFTER GC ----------")
+	runtime.ReadMemStats(&stats)
+	fmt.Printf("%+v\n", stats)
+	if t == v {
+		fmt.Println("to make sure vals and tree aren't GC'd")
+	}
+}
diff --git a/vendor/github.com/peterbourgon/diskv/LICENSE b/vendor/github.com/peterbourgon/diskv/LICENSE
new file mode 100644
index 00000000..41ce7f16
--- /dev/null
+++ b/vendor/github.com/peterbourgon/diskv/LICENSE
@@ -0,0 +1,19 @@
+Copyright (c) 2011-2012 Peter Bourgon
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/vendor/github.com/peterbourgon/diskv/README.md b/vendor/github.com/peterbourgon/diskv/README.md
new file mode 100644
index 00000000..3474739e
--- /dev/null
+++ b/vendor/github.com/peterbourgon/diskv/README.md
@@ -0,0 +1,141 @@
+# What is diskv?
+
+Diskv (disk-vee) is a simple, persistent key-value store written in the Go
+language. It starts with an incredibly simple API for storing arbitrary data on
+a filesystem by key, and builds several layers of performance-enhancing
+abstraction on top.  The end result is a conceptually simple, but highly
+performant, disk-backed storage system.
+
+[![Build Status][1]][2]
+
+[1]: https://drone.io/github.com/peterbourgon/diskv/status.png
+[2]: https://drone.io/github.com/peterbourgon/diskv/latest
+
+
+# Installing
+
+Install [Go 1][3], either [from source][4] or [with a prepackaged binary][5].
+Then,
+
+```bash
+$ go get github.com/peterbourgon/diskv
+```
+
+[3]: http://golang.org
+[4]: http://golang.org/doc/install/source
+[5]: http://golang.org/doc/install
+
+
+# Usage
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/peterbourgon/diskv"
+)
+
+func main() {
+	// Simplest transform function: put all the data files into the base dir.
+	flatTransform := func(s string) []string { return []string{} }
+
+	// Initialize a new diskv store, rooted at "my-data-dir", with a 1MB cache.
+	d := diskv.New(diskv.Options{
+		BasePath:     "my-data-dir",
+		Transform:    flatTransform,
+		CacheSizeMax: 1024 * 1024,
+	})
+
+	// Write three bytes to the key "alpha".
+	key := "alpha"
+	d.Write(key, []byte{'1', '2', '3'})
+
+	// Read the value back out of the store.
+	value, _ := d.Read(key)
+	fmt.Printf("%v\n", value)
+
+	// Erase the key+value from the store (and the disk).
+	d.Erase(key)
+}
+```
+
+More complex examples can be found in the "examples" subdirectory.
+
+
+# Theory
+
+## Basic idea
+
+At its core, diskv is a map of a key (`string`) to arbitrary data (`[]byte`).
+The data is written to a single file on disk, with the same name as the key.
+The key determines where that file will be stored, via a user-provided
+`TransformFunc`, which takes a key and returns a slice (`[]string`)
+corresponding to a path list where the key file will be stored. The simplest
+TransformFunc,
+
+```go
+func SimpleTransform (key string) []string {
+    return []string{}
+}
+```
+
+will place all keys in the same, base directory. The design is inspired by
+[Redis diskstore][6]; a TransformFunc which emulates the default diskstore
+behavior is available in the content-addressable-storage example.
+
+[6]: http://groups.google.com/group/redis-db/browse_thread/thread/d444bc786689bde9?pli=1
+
+**Note** that your TransformFunc should ensure that one valid key doesn't
+transform to a subset of another valid key. That is, it shouldn't be possible
+to construct valid keys that resolve to directory names. As a concrete example,
+if your TransformFunc splits on every 3 characters, then
+
+```go
+d.Write("abcabc", val) // OK: written to <base>/abc/abc/abcabc
+d.Write("abc", val)    // Error: attempted write to <base>/abc/abc, but it's a directory
+```
+
+This will be addressed in an upcoming version of diskv.
+
+Probably the most important design principle behind diskv is that your data is
+always flatly available on the disk. diskv will never do anything that would
+prevent you from accessing, copying, backing up, or otherwise interacting with
+your data via common UNIX commandline tools.
+
+## Adding a cache
+
+An in-memory caching layer is provided by combining the BasicStore
+functionality with a simple map structure, and keeping it up-to-date as
+appropriate. Since the map structure in Go is not threadsafe, it's combined
+with a RWMutex to provide safe concurrent access.
+
+## Adding order
+
+diskv is a key-value store and therefore inherently unordered. An ordering
+system can be injected into the store by passing something which satisfies the
+diskv.Index interface. (A default implementation, using Google's
+[btree][7] package, is provided.) Basically, diskv keeps an ordered (by a
+user-provided Less function) index of the keys, which can be queried.
+
+[7]: https://github.com/google/btree
+
+## Adding compression
+
+Something which implements the diskv.Compression interface may be passed
+during store creation, so that all Writes and Reads are filtered through
+a compression/decompression pipeline. Several default implementations,
+using stdlib compression algorithms, are provided. Note that data is cached
+compressed; the cost of decompression is borne with each Read.
+
+## Streaming
+
+diskv also now provides ReadStream and WriteStream methods, to allow very large
+data to be handled efficiently.
+
+
+# Future plans
+
+ * Needs plenty of robust testing: huge datasets, etc...
+ * More thorough benchmarking
+ * Your suggestions for use-cases I haven't thought of
diff --git a/vendor/github.com/peterbourgon/diskv/compression.go b/vendor/github.com/peterbourgon/diskv/compression.go
new file mode 100644
index 00000000..5192b027
--- /dev/null
+++ b/vendor/github.com/peterbourgon/diskv/compression.go
@@ -0,0 +1,64 @@
+package diskv
+
+import (
+	"compress/flate"
+	"compress/gzip"
+	"compress/zlib"
+	"io"
+)
+
+// Compression is an interface that Diskv uses to implement compression of
+// data. Writer takes a destination io.Writer and returns a WriteCloser that
+// compresses all data written through it. Reader takes a source io.Reader and
+// returns a ReadCloser that decompresses all data read through it. You may
+// define these methods on your own type, or use one of the NewCompression
+// helpers.
+type Compression interface {
+	Writer(dst io.Writer) (io.WriteCloser, error)
+	Reader(src io.Reader) (io.ReadCloser, error)
+}
+
+// NewGzipCompression returns a Gzip-based Compression.
+func NewGzipCompression() Compression {
+	return NewGzipCompressionLevel(flate.DefaultCompression)
+}
+
+// NewGzipCompressionLevel returns a Gzip-based Compression with the given level.
+func NewGzipCompressionLevel(level int) Compression {
+	return &genericCompression{
+		wf: func(w io.Writer) (io.WriteCloser, error) { return gzip.NewWriterLevel(w, level) },
+		rf: func(r io.Reader) (io.ReadCloser, error) { return gzip.NewReader(r) },
+	}
+}
+
+// NewZlibCompression returns a Zlib-based Compression.
+func NewZlibCompression() Compression {
+	return NewZlibCompressionLevel(flate.DefaultCompression)
+}
+
+// NewZlibCompressionLevel returns a Zlib-based Compression with the given level.
+func NewZlibCompressionLevel(level int) Compression {
+	return NewZlibCompressionLevelDict(level, nil)
+}
+
+// NewZlibCompressionLevelDict returns a Zlib-based Compression with the given
+// level, based on the given dictionary.
+func NewZlibCompressionLevelDict(level int, dict []byte) Compression {
+	return &genericCompression{
+		func(w io.Writer) (io.WriteCloser, error) { return zlib.NewWriterLevelDict(w, level, dict) },
+		func(r io.Reader) (io.ReadCloser, error) { return zlib.NewReaderDict(r, dict) },
+	}
+}
+
+type genericCompression struct {
+	wf func(w io.Writer) (io.WriteCloser, error)
+	rf func(r io.Reader) (io.ReadCloser, error)
+}
+
+func (g *genericCompression) Writer(dst io.Writer) (io.WriteCloser, error) {
+	return g.wf(dst)
+}
+
+func (g *genericCompression) Reader(src io.Reader) (io.ReadCloser, error) {
+	return g.rf(src)
+}
diff --git a/vendor/github.com/peterbourgon/diskv/diskv.go b/vendor/github.com/peterbourgon/diskv/diskv.go
new file mode 100644
index 00000000..524dc0a6
--- /dev/null
+++ b/vendor/github.com/peterbourgon/diskv/diskv.go
@@ -0,0 +1,624 @@
+// Diskv (disk-vee) is a simple, persistent, key-value store.
+// It stores all data flatly on the filesystem.
+
+package diskv
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+const (
+	defaultBasePath             = "diskv"
+	defaultFilePerm os.FileMode = 0666
+	defaultPathPerm os.FileMode = 0777
+)
+
+var (
+	defaultTransform   = func(s string) []string { return []string{} }
+	errCanceled        = errors.New("canceled")
+	errEmptyKey        = errors.New("empty key")
+	errBadKey          = errors.New("bad key")
+	errImportDirectory = errors.New("can't import a directory")
+)
+
+// TransformFunction transforms a key into a slice of strings, with each
+// element in the slice representing a directory in the file path where the
+// key's entry will eventually be stored.
+//
+// For example, if TransformFunc transforms "abcdef" to ["ab", "cde", "f"],
+// the final location of the data file will be <basedir>/ab/cde/f/abcdef
+type TransformFunction func(s string) []string
+
+// Options define a set of properties that dictate Diskv behavior.
+// All values are optional.
+type Options struct {
+	BasePath     string
+	Transform    TransformFunction
+	CacheSizeMax uint64 // bytes
+	PathPerm     os.FileMode
+	FilePerm     os.FileMode
+	// If TempDir is set, it will enable filesystem atomic writes by
+	// writing temporary files to that location before being moved
+	// to BasePath.
+	// Note that TempDir MUST be on the same device/partition as
+	// BasePath.
+	TempDir string
+
+	Index     Index
+	IndexLess LessFunction
+
+	Compression Compression
+}
+
+// Diskv implements the Diskv interface. You shouldn't construct Diskv
+// structures directly; instead, use the New constructor.
+type Diskv struct {
+	Options
+	mu        sync.RWMutex
+	cache     map[string][]byte
+	cacheSize uint64
+}
+
+// New returns an initialized Diskv structure, ready to use.
+// If the path identified by baseDir already contains data,
+// it will be accessible, but not yet cached.
+func New(o Options) *Diskv {
+	if o.BasePath == "" {
+		o.BasePath = defaultBasePath
+	}
+	if o.Transform == nil {
+		o.Transform = defaultTransform
+	}
+	if o.PathPerm == 0 {
+		o.PathPerm = defaultPathPerm
+	}
+	if o.FilePerm == 0 {
+		o.FilePerm = defaultFilePerm
+	}
+
+	d := &Diskv{
+		Options:   o,
+		cache:     map[string][]byte{},
+		cacheSize: 0,
+	}
+
+	if d.Index != nil && d.IndexLess != nil {
+		d.Index.Initialize(d.IndexLess, d.Keys(nil))
+	}
+
+	return d
+}
+
+// Write synchronously writes the key-value pair to disk, making it immediately
+// available for reads. Write relies on the filesystem to perform an eventual
+// sync to physical media. If you need stronger guarantees, see WriteStream.
+func (d *Diskv) Write(key string, val []byte) error {
+	return d.WriteStream(key, bytes.NewBuffer(val), false)
+}
+
+// WriteStream writes the data represented by the io.Reader to the disk, under
+// the provided key. If sync is true, WriteStream performs an explicit sync on
+// the file as soon as it's written.
+//
+// bytes.Buffer provides io.Reader semantics for basic data types.
+func (d *Diskv) WriteStream(key string, r io.Reader, sync bool) error {
+	if len(key) <= 0 {
+		return errEmptyKey
+	}
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	return d.writeStreamWithLock(key, r, sync)
+}
+
+// createKeyFileWithLock either creates the key file directly, or
+// creates a temporary file in TempDir if it is set.
+func (d *Diskv) createKeyFileWithLock(key string) (*os.File, error) {
+	if d.TempDir != "" {
+		if err := os.MkdirAll(d.TempDir, d.PathPerm); err != nil {
+			return nil, fmt.Errorf("temp mkdir: %s", err)
+		}
+		f, err := ioutil.TempFile(d.TempDir, "")
+		if err != nil {
+			return nil, fmt.Errorf("temp file: %s", err)
+		}
+
+		if err := f.Chmod(d.FilePerm); err != nil {
+			f.Close()           // error deliberately ignored
+			os.Remove(f.Name()) // error deliberately ignored
+			return nil, fmt.Errorf("chmod: %s", err)
+		}
+		return f, nil
+	}
+
+	mode := os.O_WRONLY | os.O_CREATE | os.O_TRUNC // overwrite if exists
+	f, err := os.OpenFile(d.completeFilename(key), mode, d.FilePerm)
+	if err != nil {
+		return nil, fmt.Errorf("open file: %s", err)
+	}
+	return f, nil
+}
+
+// writeStream does no input validation checking.
+func (d *Diskv) writeStreamWithLock(key string, r io.Reader, sync bool) error {
+	if err := d.ensurePathWithLock(key); err != nil {
+		return fmt.Errorf("ensure path: %s", err)
+	}
+
+	f, err := d.createKeyFileWithLock(key)
+	if err != nil {
+		return fmt.Errorf("create key file: %s", err)
+	}
+
+	wc := io.WriteCloser(&nopWriteCloser{f})
+	if d.Compression != nil {
+		wc, err = d.Compression.Writer(f)
+		if err != nil {
+			f.Close()           // error deliberately ignored
+			os.Remove(f.Name()) // error deliberately ignored
+			return fmt.Errorf("compression writer: %s", err)
+		}
+	}
+
+	if _, err := io.Copy(wc, r); err != nil {
+		f.Close()           // error deliberately ignored
+		os.Remove(f.Name()) // error deliberately ignored
+		return fmt.Errorf("i/o copy: %s", err)
+	}
+
+	if err := wc.Close(); err != nil {
+		f.Close()           // error deliberately ignored
+		os.Remove(f.Name()) // error deliberately ignored
+		return fmt.Errorf("compression close: %s", err)
+	}
+
+	if sync {
+		if err := f.Sync(); err != nil {
+			f.Close()           // error deliberately ignored
+			os.Remove(f.Name()) // error deliberately ignored
+			return fmt.Errorf("file sync: %s", err)
+		}
+	}
+
+	if err := f.Close(); err != nil {
+		return fmt.Errorf("file close: %s", err)
+	}
+
+	if f.Name() != d.completeFilename(key) {
+		if err := os.Rename(f.Name(), d.completeFilename(key)); err != nil {
+			os.Remove(f.Name()) // error deliberately ignored
+			return fmt.Errorf("rename: %s", err)
+		}
+	}
+
+	if d.Index != nil {
+		d.Index.Insert(key)
+	}
+
+	d.bustCacheWithLock(key) // cache only on read
+
+	return nil
+}
+
+// Import imports the source file into diskv under the destination key. If the
+// destination key already exists, it's overwritten. If move is true, the
+// source file is removed after a successful import.
+func (d *Diskv) Import(srcFilename, dstKey string, move bool) (err error) {
+	if dstKey == "" {
+		return errEmptyKey
+	}
+
+	if fi, err := os.Stat(srcFilename); err != nil {
+		return err
+	} else if fi.IsDir() {
+		return errImportDirectory
+	}
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if err := d.ensurePathWithLock(dstKey); err != nil {
+		return fmt.Errorf("ensure path: %s", err)
+	}
+
+	if move {
+		if err := syscall.Rename(srcFilename, d.completeFilename(dstKey)); err == nil {
+			d.bustCacheWithLock(dstKey)
+			return nil
+		} else if err != syscall.EXDEV {
+			// If it failed due to being on a different device, fall back to copying
+			return err
+		}
+	}
+
+	f, err := os.Open(srcFilename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	err = d.writeStreamWithLock(dstKey, f, false)
+	if err == nil && move {
+		err = os.Remove(srcFilename)
+	}
+	return err
+}
+
+// Read reads the key and returns the value.
+// If the key is available in the cache, Read won't touch the disk.
+// If the key is not in the cache, Read will have the side-effect of
+// lazily caching the value.
+func (d *Diskv) Read(key string) ([]byte, error) {
+	rc, err := d.ReadStream(key, false)
+	if err != nil {
+		return []byte{}, err
+	}
+	defer rc.Close()
+	return ioutil.ReadAll(rc)
+}
+
+// ReadStream reads the key and returns the value (data) as an io.ReadCloser.
+// If the value is cached from a previous read, and direct is false,
+// ReadStream will use the cached value. Otherwise, it will return a handle to
+// the file on disk, and cache the data on read.
+//
+// If direct is true, ReadStream will lazily delete any cached value for the
+// key, and return a direct handle to the file on disk.
+//
+// If compression is enabled, ReadStream taps into the io.Reader stream prior
+// to decompression, and caches the compressed data.
+func (d *Diskv) ReadStream(key string, direct bool) (io.ReadCloser, error) {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	if val, ok := d.cache[key]; ok {
+		if !direct {
+			buf := bytes.NewBuffer(val)
+			if d.Compression != nil {
+				return d.Compression.Reader(buf)
+			}
+			return ioutil.NopCloser(buf), nil
+		}
+
+		go func() {
+			d.mu.Lock()
+			defer d.mu.Unlock()
+			d.uncacheWithLock(key, uint64(len(val)))
+		}()
+	}
+
+	return d.readWithRLock(key)
+}
+
+// read ignores the cache, and returns an io.ReadCloser representing the
+// decompressed data for the given key, streamed from the disk. Clients should
+// acquire a read lock on the Diskv and check the cache themselves before
+// calling read.
+func (d *Diskv) readWithRLock(key string) (io.ReadCloser, error) {
+	filename := d.completeFilename(key)
+
+	fi, err := os.Stat(filename)
+	if err != nil {
+		return nil, err
+	}
+	if fi.IsDir() {
+		return nil, os.ErrNotExist
+	}
+
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	var r io.Reader
+	if d.CacheSizeMax > 0 {
+		r = newSiphon(f, d, key)
+	} else {
+		r = &closingReader{f}
+	}
+
+	var rc = io.ReadCloser(ioutil.NopCloser(r))
+	if d.Compression != nil {
+		rc, err = d.Compression.Reader(r)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return rc, nil
+}
+
+// closingReader provides a Reader that automatically closes the
+// embedded ReadCloser when it reaches EOF
+type closingReader struct {
+	rc io.ReadCloser
+}
+
+func (cr closingReader) Read(p []byte) (int, error) {
+	n, err := cr.rc.Read(p)
+	if err == io.EOF {
+		if closeErr := cr.rc.Close(); closeErr != nil {
+			return n, closeErr // close must succeed for Read to succeed
+		}
+	}
+	return n, err
+}
+
+// siphon is like a TeeReader: it copies all data read through it to an
+// internal buffer, and moves that buffer to the cache at EOF.
+type siphon struct {
+	f   *os.File
+	d   *Diskv
+	key string
+	buf *bytes.Buffer
+}
+
+// newSiphon constructs a siphoning reader that represents the passed file.
+// When a successful series of reads ends in an EOF, the siphon will write
+// the buffered data to Diskv's cache under the given key.
+func newSiphon(f *os.File, d *Diskv, key string) io.Reader {
+	return &siphon{
+		f:   f,
+		d:   d,
+		key: key,
+		buf: &bytes.Buffer{},
+	}
+}
+
+// Read implements the io.Reader interface for siphon.
+func (s *siphon) Read(p []byte) (int, error) {
+	n, err := s.f.Read(p)
+
+	if err == nil {
+		return s.buf.Write(p[0:n]) // Write must succeed for Read to succeed
+	}
+
+	if err == io.EOF {
+		s.d.cacheWithoutLock(s.key, s.buf.Bytes()) // cache may fail
+		if closeErr := s.f.Close(); closeErr != nil {
+			return n, closeErr // close must succeed for Read to succeed
+		}
+		return n, err
+	}
+
+	return n, err
+}
+
+// Erase synchronously erases the given key from the disk and the cache.
+func (d *Diskv) Erase(key string) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	d.bustCacheWithLock(key)
+
+	// erase from index
+	if d.Index != nil {
+		d.Index.Delete(key)
+	}
+
+	// erase from disk
+	filename := d.completeFilename(key)
+	if s, err := os.Stat(filename); err == nil {
+		if s.IsDir() {
+			return errBadKey
+		}
+		if err = os.Remove(filename); err != nil {
+			return err
+		}
+	} else {
+		// Return err as-is so caller can do os.IsNotExist(err).
+		return err
+	}
+
+	// clean up and return
+	d.pruneDirsWithLock(key)
+	return nil
+}
+
+// EraseAll will delete all of the data from the store, both in the cache and on
+// the disk. Note that EraseAll doesn't distinguish diskv-related data from non-
+// diskv-related data. Care should be taken to always specify a diskv base
+// directory that is exclusively for diskv data.
+func (d *Diskv) EraseAll() error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.cache = make(map[string][]byte)
+	d.cacheSize = 0
+	if d.TempDir != "" {
+		os.RemoveAll(d.TempDir) // errors ignored
+	}
+	return os.RemoveAll(d.BasePath)
+}
+
+// Has returns true if the given key exists.
+func (d *Diskv) Has(key string) bool {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if _, ok := d.cache[key]; ok {
+		return true
+	}
+
+	filename := d.completeFilename(key)
+	s, err := os.Stat(filename)
+	if err != nil {
+		return false
+	}
+	if s.IsDir() {
+		return false
+	}
+
+	return true
+}
+
+// Keys returns a channel that will yield every key accessible by the store,
+// in undefined order. If a cancel channel is provided, closing it will
+// terminate and close the keys channel.
+func (d *Diskv) Keys(cancel <-chan struct{}) <-chan string {
+	return d.KeysPrefix("", cancel)
+}
+
+// KeysPrefix returns a channel that will yield every key accessible by the
+// store with the given prefix, in undefined order. If a cancel channel is
+// provided, closing it will terminate and close the keys channel. If the
+// provided prefix is the empty string, all keys will be yielded.
+func (d *Diskv) KeysPrefix(prefix string, cancel <-chan struct{}) <-chan string {
+	var prepath string
+	if prefix == "" {
+		prepath = d.BasePath
+	} else {
+		prepath = d.pathFor(prefix)
+	}
+	c := make(chan string)
+	go func() {
+		filepath.Walk(prepath, walker(c, prefix, cancel))
+		close(c)
+	}()
+	return c
+}
+
+// walker returns a function which satisfies the filepath.WalkFunc interface.
+// It sends every non-directory file entry down the channel c.
+func walker(c chan<- string, prefix string, cancel <-chan struct{}) filepath.WalkFunc {
+	return func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if info.IsDir() || !strings.HasPrefix(info.Name(), prefix) {
+			return nil // "pass"
+		}
+
+		select {
+		case c <- info.Name():
+		case <-cancel:
+			return errCanceled
+		}
+
+		return nil
+	}
+}
+
+// pathFor returns the absolute path for location on the filesystem where the
+// data for the given key will be stored.
+func (d *Diskv) pathFor(key string) string {
+	return filepath.Join(d.BasePath, filepath.Join(d.Transform(key)...))
+}
+
+// ensurePathWithLock is a helper function that generates all necessary
+// directories on the filesystem for the given key.
+func (d *Diskv) ensurePathWithLock(key string) error {
+	return os.MkdirAll(d.pathFor(key), d.PathPerm)
+}
+
+// completeFilename returns the absolute path to the file for the given key.
+func (d *Diskv) completeFilename(key string) string {
+	return filepath.Join(d.pathFor(key), key)
+}
+
+// cacheWithLock attempts to cache the given key-value pair in the store's
+// cache. It can fail if the value is larger than the cache's maximum size.
+func (d *Diskv) cacheWithLock(key string, val []byte) error {
+	valueSize := uint64(len(val))
+	if err := d.ensureCacheSpaceWithLock(valueSize); err != nil {
+		return fmt.Errorf("%s; not caching", err)
+	}
+
+	// be very strict about memory guarantees
+	if (d.cacheSize + valueSize) > d.CacheSizeMax {
+		panic(fmt.Sprintf("failed to make room for value (%d/%d)", valueSize, d.CacheSizeMax))
+	}
+
+	d.cache[key] = val
+	d.cacheSize += valueSize
+	return nil
+}
+
+// cacheWithoutLock acquires the store's (write) mutex and calls cacheWithLock.
+func (d *Diskv) cacheWithoutLock(key string, val []byte) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.cacheWithLock(key, val)
+}
+
+func (d *Diskv) bustCacheWithLock(key string) {
+	if val, ok := d.cache[key]; ok {
+		d.uncacheWithLock(key, uint64(len(val)))
+	}
+}
+
+func (d *Diskv) uncacheWithLock(key string, sz uint64) {
+	d.cacheSize -= sz
+	delete(d.cache, key)
+}
+
+// pruneDirsWithLock deletes empty directories in the path walk leading to the
+// key k. Typically this function is called after an Erase is made.
+func (d *Diskv) pruneDirsWithLock(key string) error {
+	pathlist := d.Transform(key)
+	for i := range pathlist {
+		dir := filepath.Join(d.BasePath, filepath.Join(pathlist[:len(pathlist)-i]...))
+
+		// thanks to Steven Blenkinsop for this snippet
+		switch fi, err := os.Stat(dir); true {
+		case err != nil:
+			return err
+		case !fi.IsDir():
+			panic(fmt.Sprintf("corrupt dirstate at %s", dir))
+		}
+
+		nlinks, err := filepath.Glob(filepath.Join(dir, "*"))
+		if err != nil {
+			return err
+		} else if len(nlinks) > 0 {
+			return nil // has subdirs -- do not prune
+		}
+		if err = os.Remove(dir); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// ensureCacheSpaceWithLock deletes entries from the cache in arbitrary order
+// until the cache has at least valueSize bytes available.
+func (d *Diskv) ensureCacheSpaceWithLock(valueSize uint64) error {
+	if valueSize > d.CacheSizeMax {
+		return fmt.Errorf("value size (%d bytes) too large for cache (%d bytes)", valueSize, d.CacheSizeMax)
+	}
+
+	safe := func() bool { return (d.cacheSize + valueSize) <= d.CacheSizeMax }
+
+	for key, val := range d.cache {
+		if safe() {
+			break
+		}
+
+		d.uncacheWithLock(key, uint64(len(val)))
+	}
+
+	if !safe() {
+		panic(fmt.Sprintf("%d bytes still won't fit in the cache! (max %d bytes)", valueSize, d.CacheSizeMax))
+	}
+
+	return nil
+}
+
+// nopWriteCloser wraps an io.Writer and provides a no-op Close method to
+// satisfy the io.WriteCloser interface.
+type nopWriteCloser struct {
+	io.Writer
+}
+
+func (wc *nopWriteCloser) Write(p []byte) (int, error) { return wc.Writer.Write(p) }
+func (wc *nopWriteCloser) Close() error                { return nil }
diff --git a/vendor/github.com/peterbourgon/diskv/index.go b/vendor/github.com/peterbourgon/diskv/index.go
new file mode 100644
index 00000000..96fee515
--- /dev/null
+++ b/vendor/github.com/peterbourgon/diskv/index.go
@@ -0,0 +1,115 @@
+package diskv
+
+import (
+	"sync"
+
+	"github.com/google/btree"
+)
+
+// Index is a generic interface for things that can
+// provide an ordered list of keys.
+type Index interface {
+	Initialize(less LessFunction, keys <-chan string)
+	Insert(key string)
+	Delete(key string)
+	Keys(from string, n int) []string
+}
+
+// LessFunction is used to initialize an Index of keys in a specific order.
+type LessFunction func(string, string) bool
+
+// btreeString is a custom data type that satisfies the BTree Less interface,
+// making the strings it wraps sortable by the BTree package.
+type btreeString struct {
+	s string
+	l LessFunction
+}
+
+// Less satisfies the BTree.Less interface using the btreeString's LessFunction.
+func (s btreeString) Less(i btree.Item) bool {
+	return s.l(s.s, i.(btreeString).s)
+}
+
+// BTreeIndex is an implementation of the Index interface using google/btree.
+type BTreeIndex struct {
+	sync.RWMutex
+	LessFunction
+	*btree.BTree
+}
+
+// Initialize populates the BTree tree with data from the keys channel,
+// according to the passed less function. It's destructive to the BTreeIndex.
+func (i *BTreeIndex) Initialize(less LessFunction, keys <-chan string) {
+	i.Lock()
+	defer i.Unlock()
+	i.LessFunction = less
+	i.BTree = rebuild(less, keys)
+}
+
+// Insert inserts the given key (only) into the BTree tree.
+func (i *BTreeIndex) Insert(key string) {
+	i.Lock()
+	defer i.Unlock()
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+	i.BTree.ReplaceOrInsert(btreeString{s: key, l: i.LessFunction})
+}
+
+// Delete removes the given key (only) from the BTree tree.
+func (i *BTreeIndex) Delete(key string) {
+	i.Lock()
+	defer i.Unlock()
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+	i.BTree.Delete(btreeString{s: key, l: i.LessFunction})
+}
+
+// Keys yields a maximum of n keys in order. If the passed 'from' key is empty,
+// Keys will return the first n keys. If the passed 'from' key is non-empty, the
+// first key in the returned slice will be the key that immediately follows the
+// passed key, in key order.
+func (i *BTreeIndex) Keys(from string, n int) []string {
+	i.RLock()
+	defer i.RUnlock()
+
+	if i.BTree == nil || i.LessFunction == nil {
+		panic("uninitialized index")
+	}
+
+	if i.BTree.Len() <= 0 {
+		return []string{}
+	}
+
+	btreeFrom := btreeString{s: from, l: i.LessFunction}
+	skipFirst := true
+	if len(from) <= 0 || !i.BTree.Has(btreeFrom) {
+		// no such key, so fabricate an always-smallest item
+		btreeFrom = btreeString{s: "", l: func(string, string) bool { return true }}
+		skipFirst = false
+	}
+
+	keys := []string{}
+	iterator := func(i btree.Item) bool {
+		keys = append(keys, i.(btreeString).s)
+		return len(keys) < n
+	}
+	i.BTree.AscendGreaterOrEqual(btreeFrom, iterator)
+
+	if skipFirst && len(keys) > 0 {
+		keys = keys[1:]
+	}
+
+	return keys
+}
+
+// rebuildIndex does the work of regenerating the index
+// with the given keys.
+func rebuild(less LessFunction, keys <-chan string) *btree.BTree {
+	tree := btree.New(2)
+	for key := range keys {
+		tree.ReplaceOrInsert(btreeString{s: key, l: less})
+	}
+	return tree
+}
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 6a8a0e5e..e5166717 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -94,6 +94,8 @@ github.com/golang/protobuf/protoc-gen-go/descriptor
 github.com/golang/protobuf/ptypes/any
 github.com/golang/protobuf/ptypes/duration
 github.com/golang/protobuf/ptypes/timestamp
+# github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c
+github.com/google/btree
 # github.com/google/go-cmp v0.3.0
 github.com/google/go-cmp/cmp
 github.com/google/go-cmp/cmp/internal/diff
@@ -217,6 +219,8 @@ github.com/mitchellh/hashstructure
 github.com/mitchellh/mapstructure
 # github.com/mitchellh/reflectwalk v1.0.0
 github.com/mitchellh/reflectwalk
+# github.com/peterbourgon/diskv v2.0.1+incompatible
+github.com/peterbourgon/diskv
 # github.com/pkg/errors v0.8.1
 github.com/pkg/errors
 # github.com/pmezard/go-difflib v1.0.0


Test patch:
diff --git a/plugins/custom_plugin_test.go b/plugins/custom_plugin_test.go
index 15908a80..7ed4a067 100644
--- a/plugins/custom_plugin_test.go
+++ b/plugins/custom_plugin_test.go
@@ -18,15 +18,21 @@ import (
 	"github.com/chanzuckerberg/fogg/util"
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestCustomPluginTar(t *testing.T) {
-	a := assert.New(t)
+	a := require.New(t)
 	pluginName := "test-provider"
 	fs, d, err := util.TestFs()
 	a.NoError(err)
 	defer os.RemoveAll(d)
 
+	cacheDir, err := ioutil.TempDir("", "")
+	a.NoError(err)
+	defer os.RemoveAll(cacheDir)
+	cache := plugins.GetPluginCache(cacheDir)
+
 	files := []string{"test.txt", "terraform-provider-testing"}
 	tarPath := generateTar(t, files, nil)
 	defer os.Remove(tarPath)
@@ -43,7 +49,7 @@ func TestCustomPluginTar(t *testing.T) {
 		URL:    ts.URL,
 		Format: plugins.TypePluginFormatTar,
 	}
-	customPlugin.SetTargetPath(plugins.CustomPluginDir)
+	customPlugin.WithTargetPath(plugins.CustomPluginDir).WithCache(cache)
 	a.Nil(customPlugin.Install(fs, pluginName))
 
 	a.NoError(afero.Walk(fs, "", func(path string, info os.FileInfo, err error) error {
@@ -65,12 +71,17 @@ func TestCustomPluginTar(t *testing.T) {
 }
 
 func TestCustomPluginTarStripComponents(t *testing.T) {
-	a := assert.New(t)
+	a := require.New(t)
 	pluginName := "test-provider"
 	fs, d, err := util.TestFs()
 	a.NoError(err)
 	defer os.RemoveAll(d)
 
+	cacheDir, err := ioutil.TempDir("", "")
+	a.NoError(err)
+	defer os.RemoveAll(cacheDir)
+	cache := plugins.GetPluginCache(cacheDir)
+
 	files := []string{"a/test.txt", "terraform-provider-testing"}
 	expected_files := []string{"test.txt", ""}
 	dirs := []string{"a"}
@@ -92,7 +103,7 @@ func TestCustomPluginTarStripComponents(t *testing.T) {
 			StripComponents: 1,
 		},
 	}
-	customPlugin.SetTargetPath(plugins.CustomPluginDir)
+	customPlugin.WithTargetPath(plugins.CustomPluginDir).WithCache(cache)
 	a.Nil(customPlugin.Install(fs, pluginName))
 
 	a.NoError(afero.Walk(fs, "", func(path string, info os.FileInfo, err error) error {
@@ -127,6 +138,11 @@ func TestCustomPluginZip(t *testing.T) {
 	a.NoError(err)
 	defer os.RemoveAll(d)
 
+	cacheDir, err := ioutil.TempDir("", "")
+	a.NoError(err)
+	defer os.RemoveAll(cacheDir)
+	cache := plugins.GetPluginCache(cacheDir)
+
 	files := []string{"test.txt", "terraform-provider-testing"}
 	zipPath := generateZip(t, files)
 	defer os.Remove(zipPath)
@@ -143,7 +159,7 @@ func TestCustomPluginZip(t *testing.T) {
 		URL:    ts.URL,
 		Format: plugins.TypePluginFormatZip,
 	}
-	customPlugin.SetTargetPath(plugins.CustomPluginDir)
+	customPlugin.WithTargetPath(plugins.CustomPluginDir).WithCache(cache)
 	a.Nil(customPlugin.Install(fs, pluginName))
 
 	a.NoError(afero.Walk(fs, "", func(path string, info os.FileInfo, err error) error {
@@ -172,6 +188,11 @@ func TestCustomPluginBin(t *testing.T) {
 	defer os.RemoveAll(d)
 	fileContents := "some contents"
 
+	cacheDir, err := ioutil.TempDir("", "")
+	a.NoError(err)
+	defer os.RemoveAll(cacheDir)
+	cache := plugins.GetPluginCache(cacheDir)
+
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		_, err := fmt.Fprint(w, fileContents)
 		a.Nil(err)
@@ -183,7 +204,7 @@ func TestCustomPluginBin(t *testing.T) {
 		Format: plugins.TypePluginFormatBin,
 	}
 
-	customPlugin.SetTargetPath(plugins.CustomPluginDir)
+	customPlugin.WithTargetPath(plugins.CustomPluginDir).WithCache(cache)
 	a.Nil(customPlugin.Install(fs, pluginName))
 
 	a.NoError(afero.Walk(fs, "", func(path string, info os.FileInfo, err error) error {
@@ -297,3 +318,18 @@ func TestTemplate(t *testing.T) {
 		})
 	}
 }
+
+func TestInstallErrorsOnNoCache(t *testing.T) {
+	r := require.New(t)
+	fs, d, err := util.TestFs()
+	r.NoError(err)
+	defer os.RemoveAll(d)
+
+	customPlugin := &plugins.CustomPlugin{
+		URL:    "my url",
+		Format: plugins.TypePluginFormatBin,
+	}
+
+	err = customPlugin.Install(fs, "my plugin name")
+	r.Error(err, "download cache not configured")
+}
diff --git a/templates/templates_test.go b/templates/templates_test.go
new file mode 100644
index 00000000..1c33fe62
--- /dev/null
+++ b/templates/templates_test.go
@@ -0,0 +1,43 @@
+package templates
+
+import (
+	"testing"
+
+	"github.com/chanzuckerberg/fogg/util"
+	"github.com/gobuffalo/packr"
+	"github.com/stretchr/testify/require"
+)
+
+func TestOpenTemplate(t *testing.T) {
+	temps := Templates
+
+	type args struct {
+		box  packr.Box
+		path string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		tLen    int
+		wantErr bool
+	}{
+		{"foo", args{temps.Account, "Makefile.tmpl"}, 5, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := require.New(t)
+			f, err := tt.args.box.Open(tt.args.path)
+			r.NoError(err)
+
+			temp, err := util.OpenTemplate(f, &temps.Common)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("OpenTemplate() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			r.NotNil(temp.Templates())
+			r.Len(temp.Templates(), tt.tLen)
+		})
+	}
+}
diff --git a/util/template_test.go b/util/template_test.go
index 5821a658..d720f69a 100644
--- a/util/template_test.go
+++ b/util/template_test.go
@@ -3,9 +3,6 @@ package util
 import (
 	"testing"
 
-	"github.com/chanzuckerberg/fogg/templates"
-	"github.com/gobuffalo/packr"
-	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -13,46 +10,7 @@ func TestDict(t *testing.T) {
 	m := make(map[string]string)
 	m["foo"] = "bar"
 	r := dict(m)
-	assert.NotNil(t, r)
-	assert.IsType(t, map[string]interface{}{}, r)
-	assert.Equal(t, "bar", r["foo"])
-}
-
-func TestOpenTemplate(t *testing.T) {
-	temps := templates.Templates
-
-	type args struct {
-		box  packr.Box
-		path string
-	}
-	tests := []struct {
-		name    string
-		args    args
-		tLen    int
-		wantErr bool
-	}{
-		// TODO: Add test cases.
-		{"foo", args{temps.Account, "Makefile.tmpl"}, 5, false},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			r := require.New(t)
-			f, err := tt.args.box.Open(tt.args.path)
-			r.NoError(err)
-
-			temp, err := OpenTemplate(f, &temps.Common)
-			if (err != nil) != tt.wantErr {
-				t.Errorf("OpenTemplate() error = %v, wantErr %v", err, tt.wantErr)
-				return
-			}
-
-			r.NotNil(temp.Templates())
-			r.Len(temp.Templates(), tt.tLen)
-
-			// if !reflect.DeepEqual(got, tt.want) {
-			// t.Errorf("OpenTemplate() = %v, want %v", got, tt.want)
-			// }
-		})
-	}
+	require.NotNil(t, r)
+	require.IsType(t, map[string]interface{}{}, r)
+	require.Equal(t, "bar", r["foo"])
 }