add audit/admin trace support for browser requests (#10947)

To support this functionality we had to fork
the gorilla/rpc package with relevant changes

pkg/rpc/map.go

@@ -0,0 +1,169 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Copyright 2020 MinIO, Inc. All rights reserved.
+// forked from https://github.com/gorilla/rpc/v2
+// modified to be used with MinIO under Apache
+// 2.0 license that can be found in the LICENSE file.
+
+package rpc
+
+import (
+	"fmt"
+	"net/http"
+	"reflect"
+	"strings"
+	"sync"
+	"unicode"
+	"unicode/utf8"
+)
+
+var (
+	// Precompute the reflect.Type of error and http.Request
+	typeOfError   = reflect.TypeOf((*error)(nil)).Elem()
+	typeOfRequest = reflect.TypeOf((*http.Request)(nil)).Elem()
+)
+
+// ----------------------------------------------------------------------------
+// service
+// ----------------------------------------------------------------------------
+
+type service struct {
+	name     string                    // name of service
+	rcvr     reflect.Value             // receiver of methods for the service
+	rcvrType reflect.Type              // type of the receiver
+	methods  map[string]*serviceMethod // registered methods
+}
+
+type serviceMethod struct {
+	method    reflect.Method // receiver method
+	argsType  reflect.Type   // type of the request argument
+	replyType reflect.Type   // type of the response argument
+}
+
+// ----------------------------------------------------------------------------
+// serviceMap
+// ----------------------------------------------------------------------------
+
+// serviceMap is a registry for services.
+type serviceMap struct {
+	mutex    sync.Mutex
+	services map[string]*service
+}
+
+// register adds a new service using reflection to extract its methods.
+func (m *serviceMap) register(rcvr interface{}, name string) error {
+	// Setup service.
+	s := &service{
+		name:     name,
+		rcvr:     reflect.ValueOf(rcvr),
+		rcvrType: reflect.TypeOf(rcvr),
+		methods:  make(map[string]*serviceMethod),
+	}
+	if name == "" {
+		s.name = reflect.Indirect(s.rcvr).Type().Name()
+		if !isExported(s.name) {
+			return fmt.Errorf("rpc: type %q is not exported", s.name)
+		}
+	}
+	if s.name == "" {
+		return fmt.Errorf("rpc: no service name for type %q",
+			s.rcvrType.String())
+	}
+	// Setup methods.
+	for i := 0; i < s.rcvrType.NumMethod(); i++ {
+		method := s.rcvrType.Method(i)
+		mtype := method.Type
+		// Method must be exported.
+		if method.PkgPath != "" {
+			continue
+		}
+		// Method needs four ins: receiver, *http.Request, *args, *reply.
+		if mtype.NumIn() != 4 {
+			continue
+		}
+		// First argument must be a pointer and must be http.Request.
+		reqType := mtype.In(1)
+		if reqType.Kind() != reflect.Ptr || reqType.Elem() != typeOfRequest {
+			continue
+		}
+		// Second argument must be a pointer and must be exported.
+		args := mtype.In(2)
+		if args.Kind() != reflect.Ptr || !isExportedOrBuiltin(args) {
+			continue
+		}
+		// Third argument must be a pointer and must be exported.
+		reply := mtype.In(3)
+		if reply.Kind() != reflect.Ptr || !isExportedOrBuiltin(reply) {
+			continue
+		}
+		// Method needs one out: error.
+		if mtype.NumOut() != 1 {
+			continue
+		}
+		if returnType := mtype.Out(0); returnType != typeOfError {
+			continue
+		}
+		s.methods[method.Name] = &serviceMethod{
+			method:    method,
+			argsType:  args.Elem(),
+			replyType: reply.Elem(),
+		}
+	}
+	if len(s.methods) == 0 {
+		return fmt.Errorf("rpc: %q has no exported methods of suitable type",
+			s.name)
+	}
+	// Add to the map.
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+	if m.services == nil {
+		m.services = make(map[string]*service)
+	} else if _, ok := m.services[s.name]; ok {
+		return fmt.Errorf("rpc: service already defined: %q", s.name)
+	}
+	m.services[s.name] = s
+	return nil
+}
+
+// get returns a registered service given a method name.
+//
+// The method name uses a dotted notation as in "Service.Method".
+func (m *serviceMap) get(method string) (*service, *serviceMethod, error) {
+	parts := strings.Split(method, ".")
+	if len(parts) != 2 {
+		err := fmt.Errorf("rpc: service/method request ill-formed: %q", method)
+		return nil, nil, err
+	}
+	m.mutex.Lock()
+	service := m.services[parts[0]]
+	m.mutex.Unlock()
+	if service == nil {
+		err := fmt.Errorf("rpc: can't find service %q", method)
+		return nil, nil, err
+	}
+	serviceMethod := service.methods[parts[1]]
+	if serviceMethod == nil {
+		err := fmt.Errorf("rpc: can't find method %q", method)
+		return nil, nil, err
+	}
+	return service, serviceMethod, 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() == ""
+}