implement new service start style

config/config.go

@@ -50,6 +50,7 @@ type Config struct {
 
 		Database struct {
 			ServiceRelativePath   string
+			InstanceRelativePath  string
 			ExecutionRelativePath string
 		}
 	}
@@ -81,6 +82,7 @@ func New() (*Config, error) {
 	c.Core.Name = "engine"
 	c.Core.Path = filepath.Join(home, ".mesg")
 	c.Core.Database.ServiceRelativePath = filepath.Join("database", "services", serviceDBVersion)
+	c.Core.Database.InstanceRelativePath = filepath.Join("database", "instances", serviceDBVersion)
 	c.Core.Database.ExecutionRelativePath = filepath.Join("database", "executions", executionDBVersion)
 	c.Docker.Core.Path = "/mesg"
 	c.Docker.Socket = "/var/run/docker.sock"

core/main.go

@@ -38,6 +38,12 @@ func initDependencies() (*dependencies, error) {
 		return nil, err
 	}
 
+	// init instance db.
+	instanceDB, err := database.NewInstanceDB(filepath.Join(config.Core.Path, config.Core.Database.InstanceRelativePath))
+	if err != nil {
+		return nil, err
+	}
+
 	// init execution db.
 	executionDB, err := database.NewExecutionDB(filepath.Join(config.Core.Path, config.Core.Database.ExecutionRelativePath))
 	if err != nil {
@@ -54,7 +60,7 @@ func initDependencies() (*dependencies, error) {
 	m := dockermanager.New(c)
 
 	// init sdk.
-	sdk := sdk.New(m, c, serviceDB, executionDB)
+	sdk := sdk.New(m, c, serviceDB, instanceDB, executionDB)
 
 	return &dependencies{
 		config:      config,

database/instance_db.go

@@ -0,0 +1,104 @@
+package database
+
+import (
+	"encoding/json"
+
+	"github.com/mesg-foundation/core/service"
+	"github.com/syndtr/goleveldb/leveldb"
+)
+
+// InstanceDB describes the API of Instance database.
+type InstanceDB interface {
+	// Get retrives instance by instance hash.
+	Get(hash string) (*service.Instance, error)
+
+	// Save saves instance to database.
+	Save(i *service.Instance) error
+
+	// Close closes underlying database connection.
+	Close() error
+}
+
+// LevelDBInstanceDB is a database for storing services' instances.
+type LevelDBInstanceDB struct {
+	db *leveldb.DB
+}
+
+// NewInstanceDB returns the database which is located under given path.
+func NewInstanceDB(path string) (*LevelDBInstanceDB, error) {
+	db, err := leveldb.OpenFile(path, nil)
+	if err != nil {
+		return nil, err
+	}
+	return &LevelDBInstanceDB{db: db}, nil
+}
+
+// marshal returns the byte slice from service.
+func (d *LevelDBInstanceDB) marshal(i *service.Instance) ([]byte, error) {
+	return json.Marshal(i)
+}
+
+// unmarshal returns the service from byte slice.
+func (d *LevelDBInstanceDB) unmarshal(id string, value []byte) (*service.Instance, error) {
+	var s service.Instance
+	if err := json.Unmarshal(value, &s); err != nil {
+		return nil, &DecodeError{ID: id}
+	}
+	return &s, nil
+}
+
+// Get retrives instance by instance hash.
+func (d *LevelDBInstanceDB) Get(hash string) (*service.Instance, error) {
+	tx, err := d.db.OpenTransaction()
+	if err != nil {
+		return nil, err
+	}
+	b, err := tx.Get([]byte(hash), nil)
+	if err != nil {
+		tx.Discard()
+		if err == leveldb.ErrNotFound {
+			return nil, &ErrNotFound{ID: hash}
+		}
+		return nil, err
+	}
+	i, err := d.unmarshal(hash, b)
+	if err != nil {
+		tx.Discard()
+		return nil, err
+	}
+	return i, tx.Commit()
+}
+
+// Save saves instance to database.
+func (d *LevelDBInstanceDB) Save(i *service.Instance) error {
+	// check service
+	if i.Hash == "" {
+		return errCannotSaveWithoutHash
+	}
+
+	// open database transaction
+	tx, err := d.db.OpenTransaction()
+	if err != nil {
+		return err
+	}
+
+	// encode service
+	b, err := d.marshal(i)
+	if err != nil {
+		tx.Discard()
+		return err
+	}
+
+	// save instance with hash.
+	if err := tx.Put([]byte(i.Hash), b, nil); err != nil {
+		tx.Discard()
+		return err
+	}
+
+	return tx.Commit()
+}
+
+// Close closes database.
+func (d *LevelDBInstanceDB) Close() error {
+	return d.db.Close()
+}

protobuf/api/instance.proto

@@ -0,0 +1,18 @@
+syntax = "proto3";
+
+package api;
+
+service Instance {
+  rpc Create (CreateInstanceRequest) returns (CreateInstanceResponse) {}
+}
+
+message CreateInstanceRequest {
+  string id = 1;               // Service's sid or hash.
+  repeated string env = 2;     // Env vars to apply to service's instance on runtime.
+}
+
+message CreateInstanceResponse {
+  string sid = 1;         // Service's id.
+  string hash = 2;        // Service's instance hash.
+  string serviceHash = 3; // Service's bare hash.
+}