ing

service/service-registry.go

@@ -0,0 +1,241 @@
+package service
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"sync"
+	"unicode"
+	"unicode/utf8"
+)
+
+var (
+	// Precompute the reflect.Type of error and http.Request
+	typeOfError = reflect.TypeOf((*error)(nil)).Elem()
+)
+
+// ----------------------------------------------------------------------------
+// service
+// ----------------------------------------------------------------------------
+
+type ServiceMeta struct {
+	name    string                 // name of service
+	rcvrV   reflect.Value          // receiver of methods for the service
+	rcvrT   reflect.Type           // type of the receiver
+	methods map[string]*MethodMeta // registered methods
+}
+
+func (sm *ServiceMeta) ReceiverType() reflect.Type {
+	return sm.rcvrT
+}
+
+func (sm *ServiceMeta) ReceiverValue() reflect.Value {
+	return sm.rcvrV
+}
+
+type MethodMeta struct {
+	method     reflect.Method // receiver method
+	paramTypes []reflect.Type // type of the request argument
+	returnType reflect.Type   // type of the response argument
+}
+
+func (mm *MethodMeta) Call(in []reflect.Value) []reflect.Value {
+	return mm.method.Func.Call(in)
+}
+
+func (mm *MethodMeta) ParamValues() (values []reflect.Value, instances []interface{}) {
+	if nil == mm.paramTypes || 0 == len(mm.paramTypes) {
+		return nil, nil
+	}
+
+	pCount := len(mm.paramTypes)
+	values = make([]reflect.Value, pCount)
+	instances = make([]interface{}, pCount)
+
+	for indexI := 0; indexI < pCount; indexI++ {
+		values[indexI] = getValue(mm.paramTypes[indexI])
+		instances[indexI] = values[indexI].Interface()
+	}
+
+	return
+}
+
+func getValue(t reflect.Type) reflect.Value {
+	rt := t
+	if rt.Kind() == reflect.Ptr {
+		rt = rt.Elem()
+	}
+
+	// rv := reflect.New(rt)
+	// if rt.Kind() != reflect.Struct {
+	// 	rv = reflect.Indirect(rv)
+	// }
+
+	// var rv reflect.Value
+
+	// 	switch rt.Kind() {
+	// 	case reflect.Slice:
+	// 		rv = reflect.New(reflect.SliceOf(rt.Elem()))
+	// 	default:
+	// 		rv = reflect.New(rt)
+	// 	}
+
+	return reflect.New(rt)
+}
+
+// ----------------------------------------------------------------------------
+// ServiceRegistry
+// ----------------------------------------------------------------------------
+
+// ServiceRegistry is a registry for services.
+type ServiceRegistry struct {
+	mutex    sync.RWMutex
+	services map[string]*ServiceMeta
+}
+
+func (sm *ServiceRegistry) GetService(name string) interface{} {
+	sm.mutex.RLock()
+	defer sm.mutex.RUnlock()
+	if sm.services == nil {
+		return nil
+	}
+	return sm.services[name]
+}
+
+// register adds a new service using reflection to extract its methods.
+func (sm *ServiceRegistry) Register(rcvr interface{}, name string) error {
+	// Setup service.
+	s := &ServiceMeta{
+		name:    name,
+		rcvrV:   reflect.ValueOf(rcvr),
+		rcvrT:   reflect.TypeOf(rcvr),
+		methods: make(map[string]*MethodMeta),
+	}
+	if name == "" {
+		s.name = reflect.Indirect(s.rcvrV).Type().Name()
+		if !isExported(s.name) {
+			return fmt.Errorf("ServiceRegistry: type %q is not exported", s.name)
+		}
+	}
+	if s.name == "" {
+		return fmt.Errorf("ServiceRegistry: no service name for type %q",
+			s.rcvrT.String())
+	}
+
+	var err error
+	// Setup methods.
+Loop:
+	for i := 0; i < s.rcvrT.NumMethod(); i++ {
+		m := s.rcvrT.Method(i)
+		mt := m.Type
+		// Method must be exported.
+		if m.PkgPath != "" {
+			continue
+		}
+
+		var paramTypes []reflect.Type
+		var returnType reflect.Type
+
+		pCount := mt.NumIn() - 1
+
+		if 0 < pCount {
+			paramTypes = make([]reflect.Type, pCount)
+
+			for indexI := 0; indexI < pCount; indexI++ {
+				pt := mt.In(indexI + 1)
+				if err = validateType(mt.In(indexI + 1)); nil != err {
+					return err
+				}
+				paramTypes[indexI] = pt
+			}
+		}
+
+		switch mt.NumOut() {
+		case 1:
+			if t := mt.Out(0); t != typeOfError {
+				continue Loop
+			}
+		case 2:
+			if t := mt.Out(0); !isExportedOrBuiltin(t) {
+				continue Loop
+			}
+
+			if t := mt.Out(1); t != typeOfError {
+				continue Loop
+			}
+			rt := mt.Out(0)
+			if err = validateType(rt); nil != err {
+				return err
+			}
+			returnType = rt
+		default:
+			continue
+		}
+
+		s.methods[m.Name] = &MethodMeta{
+			method:     m,
+			paramTypes: paramTypes,
+			returnType: returnType,
+		}
+	}
+	if len(s.methods) == 0 {
+		return fmt.Errorf("ServiceRegistry: %q has no exported methods of suitable type", s.name)
+	}
+	// Add to the map.
+	sm.mutex.Lock()
+	defer sm.mutex.Unlock()
+	if sm.services == nil {
+		sm.services = make(map[string]*ServiceMeta)
+	} else if _, ok := sm.services[s.name]; ok {
+		return fmt.Errorf("ServiceRegistry: service already defined: %q", s.name)
+	}
+	sm.services[s.name] = s
+	return nil
+}
+
+func validateType(t reflect.Type) error {
+	if t.Kind() == reflect.Struct {
+		return fmt.Errorf("Type is Struct. Pass by reference, i.e. *%s", t)
+	}
+	return nil
+}
+
+// get returns a registered service given a method name.
+//
+// The method name uses a dotted notation as in "Service.Method".
+func (sm *ServiceRegistry) Get(method string) (*ServiceMeta, *MethodMeta, error) {
+	parts := strings.Split(method, ".")
+	if len(parts) != 2 {
+		err := fmt.Errorf("ServiceRegistry: service/method request ill-formed: %q", method)
+		return nil, nil, err
+	}
+	sm.mutex.Lock()
+	service := sm.services[parts[0]]
+	sm.mutex.Unlock()
+	if service == nil {
+		err := fmt.Errorf("ServiceRegistry: can't find service %q", method)
+		return nil, nil, err
+	}
+	MethodMeta := service.methods[parts[1]]
+	if MethodMeta == nil {
+		err := fmt.Errorf("ServiceRegistry: can't find method %q", method)
+		return nil, nil, err
+	}
+	return service, MethodMeta, nil
+}
+
+// isExported returns true of a string is an exported (upper case) name.
+func isExported(name string) bool {
+	rune, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(rune)
+}
+
+// isExportedOrBuiltin returns true if a type is exported or a builtin.
+func isExportedOrBuiltin(t reflect.Type) bool {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	// PkgPath will be non-empty even for an exported type,
+	// so we need to check the type name as well.
+	return isExported(t.Name()) || t.PkgPath() == ""
+}