minio/cmd/rpc/server.go

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/*
* Minio Cloud Storage, (C) 2018 Minio, Inc.
*
* 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
*
* http://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 rpc
import (
"bytes"
"encoding/gob"
"errors"
"fmt"
"net/http"
"reflect"
"strings"
"unicode"
"unicode/utf8"
)
// Authenticator - validator of first argument of any RPC call.
type Authenticator interface {
// Method to validate first argument of any RPC call.
Authenticate() error
}
// reflect.Type of error interface.
var errorType = reflect.TypeOf((*error)(nil)).Elem()
// reflect.Type of Authenticator interface.
var authenticatorType = reflect.TypeOf((*Authenticator)(nil)).Elem()
func gobEncode(e interface{}) ([]byte, error) {
var buf bytes.Buffer
if err := gob.NewEncoder(&buf).Encode(e); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func gobDecode(data []byte, e interface{}) error {
return gob.NewDecoder(bytes.NewReader(data)).Decode(e)
}
// Returns whether given type is exported or builin type or not.
func isExportedOrBuiltinType(t reflect.Type) bool {
for t.Kind() == reflect.Ptr {
t = t.Elem()
}
rune, _ := utf8.DecodeRuneInString(t.Name())
return unicode.IsUpper(rune) || t.PkgPath() == ""
}
// Makes method name map from given type.
func getMethodMap(receiverType reflect.Type) map[string]reflect.Method {
methodMap := make(map[string]reflect.Method)
for i := 0; i < receiverType.NumMethod(); i++ {
// Method.PkgPath is empty for this package.
method := receiverType.Method(i)
// Methods must have three arguments (receiver, args, reply)
if method.Type.NumIn() != 3 {
continue
}
// First argument must be exported.
if !isExportedOrBuiltinType(method.Type.In(1)) {
continue
}
// First argument must be Authenticator.
if !method.Type.In(1).Implements(authenticatorType) {
continue
}
// Second argument must be exported or builtin type.
if !isExportedOrBuiltinType(method.Type.In(2)) {
continue
}
// Second argument must be a pointer.
if method.Type.In(2).Kind() != reflect.Ptr {
continue
}
// Method must return one value.
if method.Type.NumOut() != 1 {
continue
}
// The return type of the method must be error.
if method.Type.Out(0) != errorType {
continue
}
methodMap[method.Name] = method
}
return methodMap
}
// Server - HTTP based RPC server.
type Server struct {
serviceName string
receiverValue reflect.Value
methodMap map[string]reflect.Method
}
// RegisterName - registers receiver with given name to handle RPC requests.
func (server *Server) RegisterName(name string, receiver interface{}) error {
server.serviceName = name
server.receiverValue = reflect.ValueOf(receiver)
if !reflect.Indirect(server.receiverValue).IsValid() {
return fmt.Errorf("nil receiver")
}
receiverName := reflect.Indirect(server.receiverValue).Type().Name()
receiverType := reflect.TypeOf(receiver)
server.methodMap = getMethodMap(receiverType)
if len(server.methodMap) == 0 {
str := "rpc.Register: type " + receiverName + " has no exported methods of suitable type"
// To help the user, see if a pointer receiver would work.
if len(getMethodMap(reflect.PtrTo(receiverType))) != 0 {
str += " (hint: pass a pointer to value of that type)"
}
return errors.New(str)
}
return nil
}
// call - call service method in receiver.
func (server *Server) call(serviceMethod string, argBytes []byte) (replyBytes []byte, err error) {
tokens := strings.SplitN(serviceMethod, ".", 2)
if len(tokens) != 2 {
return nil, fmt.Errorf("invalid service/method request ill-formed %v", serviceMethod)
}
serviceName := tokens[0]
if serviceName != server.serviceName {
return nil, fmt.Errorf("can't find service %v", serviceName)
}
methodName := tokens[1]
method, found := server.methodMap[methodName]
if !found {
return nil, fmt.Errorf("can't find method %v", methodName)
}
var argv reflect.Value
// Decode the argument value.
argIsValue := false // if true, need to indirect before calling.
if method.Type.In(1).Kind() == reflect.Ptr {
argv = reflect.New(method.Type.In(1).Elem())
} else {
argv = reflect.New(method.Type.In(1))
argIsValue = true
}
if err = gobDecode(argBytes, argv.Interface()); err != nil {
return nil, err
}
if argIsValue {
argv = argv.Elem()
}
// call Authenticate() method.
authMethod, ok := method.Type.In(1).MethodByName("Authenticate")
if !ok {
panic("Authenticate() method not found. This should not happen.")
}
returnValues := authMethod.Func.Call([]reflect.Value{argv})
errInter := returnValues[0].Interface()
if errInter != nil {
err = errInter.(error)
}
if err != nil {
return nil, err
}
replyv := reflect.New(method.Type.In(2).Elem())
switch method.Type.In(2).Elem().Kind() {
case reflect.Map:
replyv.Elem().Set(reflect.MakeMap(method.Type.In(2).Elem()))
case reflect.Slice:
replyv.Elem().Set(reflect.MakeSlice(method.Type.In(2).Elem(), 0, 0))
}
returnValues = method.Func.Call([]reflect.Value{server.receiverValue, argv, replyv})
errInter = returnValues[0].Interface()
if errInter != nil {
err = errInter.(error)
}
if err != nil {
return nil, err
}
return gobEncode(replyv.Interface())
}
// CallRequest - RPC call request parameters.
type CallRequest struct {
Method string
ArgBytes []byte
}
// CallResponse - RPC call response parameters.
type CallResponse struct {
Error string
ReplyBytes []byte
}
// ServeHTTP - handles RPC on HTTP request.
func (server *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
if req.Method != http.MethodPost {
w.WriteHeader(http.StatusMethodNotAllowed)
return
}
var callRequest CallRequest
if err := gob.NewDecoder(req.Body).Decode(&callRequest); err != nil {
w.WriteHeader(http.StatusBadRequest)
return
}
var callResponse CallResponse
var err error
callResponse.ReplyBytes, err = server.call(callRequest.Method, callRequest.ArgBytes)
if err != nil {
callResponse.Error = err.Error()
}
data, err := gobEncode(callResponse)
if err != nil {
w.WriteHeader(http.StatusInternalServerError)
return
}
w.Write(data)
}
// NewServer - returns new RPC server.
func NewServer() *Server {
return &Server{}
}