Add inmem remote backend

Add an Inmem remote state backend.

The only config option right now is a lock_id, which will instantiate
the backend in a locked state for testing.

backend/remote-state/inmem/backend.go

@@ -0,0 +1,41 @@
+package inmem
+
+import (
+	"context"
+
+	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/backend/remote-state"
+	"github.com/hashicorp/terraform/helper/schema"
+	"github.com/hashicorp/terraform/state"
+	"github.com/hashicorp/terraform/state/remote"
+)
+
+// New creates a new backend for Inmem remote state.
+func New() backend.Backend {
+	return &remotestate.Backend{
+		ConfigureFunc: configure,
+
+		// Set the schema
+		Backend: &schema.Backend{
+			Schema: map[string]*schema.Schema{
+				"lock_id": &schema.Schema{
+					Type:        schema.TypeString,
+					Optional:    true,
+					Description: "initializes the state in a locked configuration",
+				},
+			},
+		},
+	}
+}
+
+func configure(ctx context.Context) (remote.Client, error) {
+	data := schema.FromContextBackendConfig(ctx)
+	if v, ok := data.GetOk("lock_id"); ok && v.(string) != "" {
+		info := state.NewLockInfo()
+		info.ID = v.(string)
+		info.Operation = "test"
+		info.Info = "test config"
+		return &RemoteClient{LockInfo: info}, nil
+	}
+	return &RemoteClient{}, nil
+}

backend/remote-state/inmem/client.go

@@ -0,0 +1,79 @@
+package inmem
+
+import (
+	"crypto/md5"
+	"errors"
+	"time"
+
+	"github.com/hashicorp/terraform/state"
+	"github.com/hashicorp/terraform/state/remote"
+)
+
+// RemoteClient is a remote client that stores data in memory for testing.
+type RemoteClient struct {
+	Data []byte
+	MD5  []byte
+
+	LockInfo *state.LockInfo
+}
+
+func (c *RemoteClient) Get() (*remote.Payload, error) {
+	if c.Data == nil {
+		return nil, nil
+	}
+
+	return &remote.Payload{
+		Data: c.Data,
+		MD5:  c.MD5,
+	}, nil
+}
+
+func (c *RemoteClient) Put(data []byte) error {
+	md5 := md5.Sum(data)
+
+	c.Data = data
+	c.MD5 = md5[:]
+	return nil
+}
+
+func (c *RemoteClient) Delete() error {
+	c.Data = nil
+	c.MD5 = nil
+	return nil
+}
+
+func (c *RemoteClient) Lock(info *state.LockInfo) (string, error) {
+	lockErr := &state.LockError{
+		Info: &state.LockInfo{},
+	}
+
+	if c.LockInfo != nil {
+		lockErr.Err = errors.New("state locked")
+		// make a copy of the lock info to avoid any testing shenanigans
+		*lockErr.Info = *c.LockInfo
+		return "", lockErr
+	}
+
+	info.Created = time.Now().UTC()
+	c.LockInfo = info
+
+	return c.LockInfo.ID, nil
+}
+
+func (c *RemoteClient) Unlock(id string) error {
+	if c.LockInfo == nil {
+		return errors.New("state not locked")
+	}
+
+	lockErr := &state.LockError{
+		Info: &state.LockInfo{},
+	}
+	if id != c.LockInfo.ID {
+		lockErr.Err = errors.New("invalid lock id")
+		*lockErr.Info = *c.LockInfo
+		return lockErr
+	}
+
+	c.LockInfo = nil
+	return nil
+}

backend/remote-state/inmem/client_test.go

@@ -0,0 +1,28 @@
+package inmem
+
+import (
+	"testing"
+
+	"github.com/hashicorp/terraform/backend"
+	remotestate "github.com/hashicorp/terraform/backend/remote-state"
+	"github.com/hashicorp/terraform/state/remote"
+)
+
+func TestRemoteClient_impl(t *testing.T) {
+	var _ remote.Client = new(RemoteClient)
+	var _ remote.ClientLocker = new(RemoteClient)
+}
+
+func TestRemoteClient(t *testing.T) {
+	b := backend.TestBackendConfig(t, New(), nil)
+	remotestate.TestClient(t, b)
+}
+
+func TestInmemLocks(t *testing.T) {
+	s, err := backend.TestBackendConfig(t, New(), nil).State()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	remote.TestRemoteLocks(t, s.(*remote.State).Client, s.(*remote.State).Client)
+}