backend/init: a package for storing the factories for backends

backend/init/init.go

@@ -0,0 +1,55 @@
+// Package init contains the list of backends that can be initialized and
+// basic helper functions for initializing those backends.
+package init
+
+import (
+	"sync"
+
+	"github.com/hashicorp/terraform/backend"
+
+	backendlegacy "github.com/hashicorp/terraform/backend/legacy"
+	backendlocal "github.com/hashicorp/terraform/backend/local"
+	backendconsul "github.com/hashicorp/terraform/backend/remote-state/consul"
+	backendinmem "github.com/hashicorp/terraform/backend/remote-state/inmem"
+)
+
+// backends is the list of available backends. This is a global variable
+// because backends are currently hardcoded into Terraform and can't be
+// modified without recompilation.
+//
+// To read an available backend, use the Backend function. This ensures
+// safe concurrent read access to the list of built-in backends.
+//
+// Backends are hardcoded into Terraform because the API for backends uses
+// complex structures and supporting that over the plugin system is currently
+// prohibitively difficult. For those wanting to implement a custom backend,
+// they can do so with recompilation.
+var backends map[string]func() backend.Backend
+var backendsLock sync.Mutex
+
+func init() {
+	// Our hardcoded backends. We don't need to acquire a lock here
+	// since init() code is serial and can't spawn goroutines.
+	backends = map[string]func() backend.Backend{
+		"local":  func() backend.Backend { return &backendlocal.Local{} },
+		"consul": func() backend.Backend { return backendconsul.New() },
+		"inmem":  func() backend.Backend { return backendinmem.New() },
+	}
+
+	// Add the legacy remote backends that haven't yet been convertd to
+	// the new backend API.
+	backendlegacy.Init(backends)
+}
+
+// Backend returns the initialization factory for the given backend, or
+// nil if none exists.
+func Backend(name string) func() backend.Backend {
+	backendsLock.Lock()
+	defer backendsLock.Unlock()
+	return backends[name]
+}
+
+// NOTE(@mitchellh): At some point I'm sure we'll want Add() to add a backend
+// to the list. Right now we hardcode all backends and there isn't a reasonable
+// use case for this so we're leaving it out. It would be trivial to add in
+// the future.