Add length deferrer support to composer

composer.go

@@ -16,6 +16,8 @@ type StoreComposer struct {
 	GetReader          GetReaderDataStore
 	UsesConcater       bool
 	Concater           ConcaterDataStore
+	UsesLengthDeferrer bool
+	LengthDeferrer     LengthDeferrerDataStore
 }
 
 // NewStoreComposer creates a new and empty store composer.
@@ -45,6 +47,9 @@ func newStoreComposerFromDataStore(store DataStore) *StoreComposer {
 	if mod, ok := store.(ConcaterDataStore); ok {
 		composer.UseConcater(mod)
 	}
+	if mod, ok := store.(LengthDeferrerDataStore); ok {
+		composer.UseLengthDeferrer(mod)
+	}
 
 	return composer
 }
@@ -90,6 +95,12 @@ func (store *StoreComposer) Capabilities() string {
 	} else {
 		str += "✗"
 	}
+	str += ` LengthDeferrer: `
+	if store.UsesLengthDeferrer {
+		str += "✓"
+	} else {
+		str += "✗"
+	}
 
 	return str
 }
@@ -120,3 +131,8 @@ func (store *StoreComposer) UseConcater(ext ConcaterDataStore) {
 	store.UsesConcater = ext != nil
 	store.Concater = ext
 }
+
+func (store *StoreComposer) UseLengthDeferrer(ext LengthDeferrerDataStore) {
+	store.UsesLengthDeferrer = ext != nil
+	store.LengthDeferrer = ext
+}

composer.mgo

@@ -31,6 +31,7 @@ type StoreComposer struct {
   USE_FIELD(Locker)
   USE_FIELD(GetReader)
   USE_FIELD(Concater)
+  USE_FIELD(LengthDeferrer)
 }
 
 // NewStoreComposer creates a new and empty store composer.
@@ -50,6 +51,7 @@ func newStoreComposerFromDataStore(store DataStore) *StoreComposer {
   USE_FROM(Locker)
   USE_FROM(GetReader)
   USE_FROM(Concater)
+  USE_FROM(LengthDeferrer)
 
   return composer
 }
@@ -70,6 +72,7 @@ func (store *StoreComposer) Capabilities() string {
   USE_CAP(Locker)
   USE_CAP(GetReader)
   USE_CAP(Concater)
+  USE_CAP(LengthDeferrer)
 
   return str
 }
@@ -85,3 +88,4 @@ USE_FUNC(Finisher)
 USE_FUNC(Locker)
 USE_FUNC(GetReader)
 USE_FUNC(Concater)
+USE_FUNC(LengthDeferrer)