rpc: allow the argument (first arg of method) to be a value rather than a pointer.

Can make the API nicer in some cases.

R=rsc, rog, r2
CC=golang-dev
https://golang.org/cl/4428064

src/pkg/rpc/server.go

@@ -13,8 +13,11 @@
 	Only methods that satisfy these criteria will be made available for remote access;
 	other methods will be ignored:
 
-		- the method receiver and name are exported, that is, begin with an upper case letter.
+		- the method name is exported, that is, begins with an upper case letter.
-		- the method has two arguments, both pointers to exported types.
+		- the method receiver is exported or local (defined in the package
+		  registering the service).
+		- the method has two arguments, both exported or local types.
+		- the method's second argument is a pointer.
 		- the method has return type os.Error.
 
 	The method's first argument represents the arguments provided by the caller; the
@@ -193,6 +196,14 @@ func isExported(name string) bool {
 	return unicode.IsUpper(rune)
 }
 
+// Is this type exported or local to this package?
+func isExportedOrLocalType(t reflect.Type) bool {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	return t.PkgPath() == "" || isExported(t.Name())
+}
+
 // Register publishes in the server the set of methods of the
 // receiver value that satisfy the following conditions:
 //	- exported method
@@ -252,23 +263,20 @@ func (server *Server) register(rcvr interface{}, name string, useName bool) os.E
 			log.Println("method", mname, "has wrong number of ins:", mtype.NumIn())
 			continue
 		}
+		// First arg need not be a pointer.
 		argType := mtype.In(1)
-		ok := argType.Kind() == reflect.Ptr
+		if !isExportedOrLocalType(argType) {
-		if !ok {
+			log.Println(mname, "argument type not exported or local:", argType)
-			log.Println(mname, "arg type not a pointer:", mtype.In(1))
 			continue
 		}
+		// Second arg must be a pointer.
 		replyType := mtype.In(2)
 		if replyType.Kind() != reflect.Ptr {
-			log.Println(mname, "reply type not a pointer:", mtype.In(2))
+			log.Println("method", mname, "reply type not a pointer:", replyType)
 			continue
 		}
-		if argType.Elem().PkgPath() != "" && !isExported(argType.Elem().Name()) {
+		if !isExportedOrLocalType(replyType) {
-			log.Println(mname, "argument type not exported:", argType)
+			log.Println("method", mname, "reply type not exported or local:", replyType)
-			continue
-		}
-		if replyType.Elem().PkgPath() != "" && !isExported(replyType.Elem().Name()) {
-			log.Println(mname, "reply type not exported:", replyType)
 			continue
 		}
 		// Method needs one out: os.Error.
@@ -405,7 +413,15 @@ func (server *Server) ServeCodec(codec ServerCodec) {
 		}
 
 		// Decode the argument value.
-		argv := reflect.New(mtype.ArgType.Elem())
+		var argv reflect.Value
+		argIsValue := false // if true, need to indirect before calling.
+		if mtype.ArgType.Kind() == reflect.Ptr {
+			argv = reflect.New(mtype.ArgType.Elem())
+		} else {
+			argv = reflect.New(mtype.ArgType)
+			argIsValue = true
+		}
+		// argv guaranteed to be a pointer now.
 		replyv := reflect.New(mtype.ReplyType.Elem())
 		err = codec.ReadRequestBody(argv.Interface())
 		if err != nil {
@@ -418,6 +434,9 @@ func (server *Server) ServeCodec(codec ServerCodec) {
 			server.sendResponse(sending, req, replyv.Interface(), codec, err.String())
 			continue
 		}
+		if argIsValue {
+			argv = argv.Elem()
+		}
 		go service.call(server, sending, mtype, req, argv, replyv, codec)
 	}
 	codec.Close()

src/pkg/rpc/server_test.go

@@ -38,7 +38,9 @@ type Reply struct {
 
 type Arith int
 
-func (t *Arith) Add(args *Args, reply *Reply) os.Error {
+// Some of Arith's methods have value args, some have pointer args. That's deliberate.
+
+func (t *Arith) Add(args Args, reply *Reply) os.Error {
 	reply.C = args.A + args.B
 	return nil
 }
@@ -48,7 +50,7 @@ func (t *Arith) Mul(args *Args, reply *Reply) os.Error {
 	return nil
 }
 
-func (t *Arith) Div(args *Args, reply *Reply) os.Error {
+func (t *Arith) Div(args Args, reply *Reply) os.Error {
 	if args.B == 0 {
 		return os.ErrorString("divide by zero")
 	}
@@ -61,8 +63,8 @@ func (t *Arith) String(args *Args, reply *string) os.Error {
 	return nil
 }
 
-func (t *Arith) Scan(args *string, reply *Reply) (err os.Error) {
+func (t *Arith) Scan(args string, reply *Reply) (err os.Error) {
-	_, err = fmt.Sscan(*args, &reply.C)
+	_, err = fmt.Sscan(args, &reply.C)
 	return
 }
 
@@ -262,16 +264,11 @@ func testHTTPRPC(t *testing.T, path string) {
 	}
 }
 
-type ArgNotPointer int
 type ReplyNotPointer int
 type ArgNotPublic int
 type ReplyNotPublic int
 type local struct{}
 
-func (t *ArgNotPointer) ArgNotPointer(args Args, reply *Reply) os.Error {
-	return nil
-}
-
 func (t *ReplyNotPointer) ReplyNotPointer(args *Args, reply Reply) os.Error {
 	return nil
 }
@@ -286,11 +283,7 @@ func (t *ReplyNotPublic) ReplyNotPublic(args *Args, reply *local) os.Error {
 
 // Check that registration handles lots of bad methods and a type with no suitable methods.
 func TestRegistrationError(t *testing.T) {
-	err := Register(new(ArgNotPointer))
+	err := Register(new(ReplyNotPointer))
-	if err == nil {
-		t.Errorf("expected error registering ArgNotPointer")
-	}
-	err = Register(new(ReplyNotPointer))
 	if err == nil {
 		t.Errorf("expected error registering ReplyNotPointer")
 	}