Implementation of a file-backed persistence store. (#160)

This is a rather large change. It consists of the following changes:

+ Direct access to the keycache has been removed from the core
  package. This forces all interaction with the cache to go
  through the Cryptor, which is required for persistence. The
  Cryptor needs to know when the cache has changed, and the only
  way to do this effectively is to make the Cryptor responsible
  for managing the keycache.

+ A new persist package has been added. This provides a Store
  interface, for which two implementations are provided. The
  first is a null persister: this is used when no persistence
  is configured. The second is a file-backed persistence store.

+ The Cryptor now persists the cache every time it changes.

Additionally, a number of missing returns in a function in the core
package have been added.

core/core.go

@@ -18,12 +18,12 @@ import (
 	"github.com/cloudflare/redoctober/keycache"
 	"github.com/cloudflare/redoctober/order"
 	"github.com/cloudflare/redoctober/passvault"
+	"github.com/cloudflare/redoctober/persist"
 )
 
 var (
-	crypt   cryptor.Cryptor
+	crypt   *cryptor.Cryptor
 	records passvault.Records
-	cache   keycache.Cache
 	orders  order.Orderer
 )
 
@@ -177,14 +177,6 @@ type StatusData struct {
 	Status string
 }
 
-// Delegation restoration and persistance configuration follows.
-
-const (
-	PDStateNeverPersist  = "disabled"
-	PDStateNotPersisting = "inactive"
-	PDStateNowPersisting = "active"
-)
-
 var restore struct {
 	Config *config.Delegations
 	State  string
@@ -199,7 +191,7 @@ func jsonStatusError(err error) ([]byte, error) {
 	return json.Marshal(ResponseData{Status: err.Error()})
 }
 func jsonSummary() ([]byte, error) {
-	return json.Marshal(SummaryData{Status: "ok", Live: cache.GetSummary(), All: records.GetSummary()})
+	return json.Marshal(SummaryData{Status: "ok", Live: crypt.LiveSummary(), All: records.GetSummary()})
 }
 func jsonResponse(resp []byte) ([]byte, error) {
 	return json.Marshal(ResponseData{Status: "ok", Response: resp})
@@ -273,11 +265,10 @@ func Init(path string, config *config.Config) error {
 	}
 
 	restore.Config = config.Delegations
-	restore.State = PDStateNeverPersist
+	restore.State = persist.Disabled
 
 	orders = order.NewOrderer(hipchatClient)
-	cache = keycache.Cache{UserKeys: make(map[keycache.DelegateIndex]keycache.ActiveUser)}
-	crypt = cryptor.New(&records, &cache)
+	crypt, err = cryptor.New(&records, nil, config)
 
 	return err
 }
@@ -320,7 +311,6 @@ func Create(jsonIn []byte) ([]byte, error) {
 func Summary(jsonIn []byte) ([]byte, error) {
 	var s SummaryRequest
 	var err error
-	cache.Refresh()
 
 	defer func() {
 		if err != nil {
@@ -330,6 +320,11 @@ func Summary(jsonIn []byte) ([]byte, error) {
 		}
 	}()
 
+	err = crypt.Refresh()
+	if err != nil {
+		return jsonStatusError(err)
+	}
+
 	if err := json.Unmarshal(jsonIn, &s); err != nil {
 		return jsonStatusError(err)
 	}
@@ -373,7 +368,11 @@ func Purge(jsonIn []byte) ([]byte, error) {
 		return jsonStatusError(err)
 	}
 
-	cache.FlushCache()
+	err = crypt.Flush()
+	if err != nil {
+		return jsonStatusError(err)
+	}
+
 	return jsonStatusOk()
 }
 
@@ -426,7 +425,7 @@ func Delegate(jsonIn []byte) ([]byte, error) {
 	}
 
 	// add signed-in record to active set
-	if err = cache.AddKeyFromRecord(pr, s.Name, s.Password, s.Users, s.Labels, s.Uses, s.Slot, s.Time); err != nil {
+	if err = crypt.Delegate(pr, s.Name, s.Password, s.Users, s.Labels, s.Uses, s.Slot, s.Time); err != nil {
 		return jsonStatusError(err)
 	}
 
@@ -798,27 +797,32 @@ func Order(jsonIn []byte) (out []byte, err error) {
 	// Get the owners of the ciphertext.
 	owners, _, err := crypt.GetOwners(o.EncryptedData)
 	if err != nil {
-		jsonStatusError(err)
+		return jsonStatusError(err)
 	}
 	if o.Duration == "" {
 		err = errors.New("Duration required when placing an order.")
-		jsonStatusError(err)
+		return jsonStatusError(err)
 	}
 	if o.Uses == 0 {
 		err = errors.New("Number of required uses necessary when placing an order.")
-		jsonStatusError(err)
+		return jsonStatusError(err)
 	}
-	cache.Refresh()
+
+	err = crypt.Refresh()
+	if err != nil {
+		return jsonStatusError(err)
+	}
+
 	orderNum := order.GenerateNum()
 
 	if len(o.Users) == 0 {
 		err = errors.New("Must specify at least one user per order.")
-		jsonStatusError(err)
+		return jsonStatusError(err)
 	}
-	adminsDelegated, numDelegated := cache.DelegateStatus(o.Users[0], o.Labels, owners)
+	adminsDelegated, numDelegated := crypt.DelegateStatus(o.Users[0], o.Labels, owners)
 	duration, err := time.ParseDuration(o.Duration)
 	if err != nil {
-		jsonStatusError(err)
+		return jsonStatusError(err)
 	}
 	currentTime := time.Now()
 	ord := order.CreateOrder(o.Name,