Start from snapshot.

- This operation is also known as snapshot restore.

frontend/src/host_orchestrator/api/v1/messages.go

@@ -141,3 +141,8 @@ type CreateSnapshotResponse struct {
 type EmptyResponse struct{}
 
 type StopCVDResponse = EmptyResponse
+
+type StartCVDRequest struct {
+	// Start from the relevant snaphost if not empty.
+	SnapshotID string `json:"snapshot_id,omitempty"`
+}

frontend/src/host_orchestrator/orchestrator/controller.go

@@ -71,6 +71,8 @@ func (c *Controller) AddRoutes(router *mux.Router) {
 		httpHandler(newCreateCVDBugReportHandler(c.Config, c.OperationManager))).Methods("POST")
 	router.Handle("/cvds/{group}/{name}",
 		httpHandler(newExecCVDCommandHandler(c.Config, c.OperationManager, "remove"))).Methods("DELETE")
+	router.Handle("/cvds/{group}/{name}/:start",
+		httpHandler(newStartCVDHandler(c.Config, c.OperationManager))).Methods("POST")
 	router.Handle("/cvds/{group}/{name}/:stop",
 		httpHandler(newExecCVDCommandHandler(c.Config, c.OperationManager, "stop"))).Methods("POST")
 	router.Handle("/cvds/{group}/{name}/:powerwash",
@@ -295,6 +297,35 @@ func (h *createSnapshotHandler) Handle(r *http.Request) (interface{}, error) {
 	return NewCreateSnapshotAction(opts).Run()
 }
 
+type startCVDHandler struct {
+	Config Config
+	OM     OperationManager
+}
+
+func newStartCVDHandler(c Config, om OperationManager) *startCVDHandler {
+	return &startCVDHandler{Config: c, OM: om}
+}
+
+func (h *startCVDHandler) Handle(r *http.Request) (interface{}, error) {
+	req := &apiv1.StartCVDRequest{}
+	err := json.NewDecoder(r.Body).Decode(req)
+	if err != nil {
+		return nil, operator.NewBadRequestError("Malformed JSON in request", err)
+	}
+	vars := mux.Vars(r)
+	group := vars["group"]
+	name := vars["name"]
+	opts := StartCVDActionOpts{
+		Request:          req,
+		Selector:         CVDSelector{Group: group, Name: name},
+		Paths:            h.Config.Paths,
+		OperationManager: h.OM,
+		ExecContext:      exec.CommandContext,
+		CVDUser:          h.Config.CVDUser,
+	}
+	return NewStartCVDAction(opts).Run()
+}
+
 type getCVDLogsHandler struct {
 	Config Config
 }

frontend/src/host_orchestrator/orchestrator/startcvdaction.go

@@ -0,0 +1,78 @@
+// Copyright 2023 Google LLC
+//
+// 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
+//
+// https://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 orchestrator
+
+import (
+	"log"
+	"os/user"
+	"path/filepath"
+
+	apiv1 "github.com/google/android-cuttlefish/frontend/src/host_orchestrator/api/v1"
+	"github.com/google/android-cuttlefish/frontend/src/host_orchestrator/orchestrator/cvd"
+	"github.com/google/android-cuttlefish/frontend/src/liboperator/operator"
+)
+
+type StartCVDActionOpts struct {
+	Request          *apiv1.StartCVDRequest
+	Selector         CVDSelector
+	Paths            IMPaths
+	OperationManager OperationManager
+	ExecContext      ExecContext
+	CVDUser          *user.User
+}
+
+type StartCVDAction struct {
+	req         *apiv1.StartCVDRequest
+	selector    CVDSelector
+	paths       IMPaths
+	om          OperationManager
+	execContext cvd.CVDExecContext
+}
+
+func NewStartCVDAction(opts StartCVDActionOpts) *StartCVDAction {
+	return &StartCVDAction{
+		req:         opts.Request,
+		selector:    opts.Selector,
+		paths:       opts.Paths,
+		om:          opts.OperationManager,
+		execContext: newCVDExecContext(opts.ExecContext, opts.CVDUser),
+	}
+}
+
+func (a *StartCVDAction) Run() (apiv1.Operation, error) {
+	op := a.om.New()
+	go func(op apiv1.Operation) {
+		result := &OperationResult{}
+		result.Value, result.Error = a.exec(op)
+		if err := a.om.Complete(op.Name, result); err != nil {
+			log.Printf("error completing operation %q: %v\n", op.Name, err)
+		}
+	}(op)
+	return op, nil
+}
+
+func (a *StartCVDAction) exec(op apiv1.Operation) (*apiv1.EmptyResponse, error) {
+	args := a.selector.ToCVDCLI()
+	args = append(args, "start")
+	if a.req.SnapshotID != "" {
+		dir := filepath.Join(a.paths.SnapshotsRootDir, a.req.SnapshotID)
+		args = append(args, "--snapshot_path", dir)
+	}
+	cmd := cvd.NewCommand(a.execContext, args, cvd.CommandOpts{})
+	if err := cmd.Run(); err != nil {
+		return nil, operator.NewInternalError("cvd start failed", err)
+	}
+	return &apiv1.EmptyResponse{}, nil
+}