base/mac/scoped_objc_class_swizzler.mm

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #import "base/mac/scoped_objc_class_swizzler.h"
   6
   7 #include <string.h>
   8
   9 #include "base/logging.h"
  10
  11 namespace base {
  12 namespace mac {
  13
  14 ScopedObjCClassSwizzler::ScopedObjCClassSwizzler(Class target,
  15                                                  Class source,
  16                                                  SEL selector)
  17     : old_selector_impl_(NULL), new_selector_impl_(NULL) {
  18   Init(target, source, selector, selector);
  19 }
  20
  21 ScopedObjCClassSwizzler::ScopedObjCClassSwizzler(Class target,
  22                                                  SEL original,
  23                                                  SEL alternate)
  24     : old_selector_impl_(NULL), new_selector_impl_(NULL) {
  25   Init(target, target, original, alternate);
  26 }
  27
  28 ScopedObjCClassSwizzler::~ScopedObjCClassSwizzler() {
  29   if (old_selector_impl_ && new_selector_impl_)
  30     method_exchangeImplementations(old_selector_impl_, new_selector_impl_);
  31 }
  32
  33 IMP ScopedObjCClassSwizzler::GetOriginalImplementation() {
  34   // Note that while the swizzle is in effect the "new" method is actually
  35   // pointing to the original implementation, since they have been swapped.
  36   return method_getImplementation(new_selector_impl_);
  37 }
  38
  39 void ScopedObjCClassSwizzler::Init(Class target,
  40                                    Class source,
  41                                    SEL original,
  42                                    SEL alternate) {
  43   old_selector_impl_ = class_getInstanceMethod(target, original);
  44   new_selector_impl_ = class_getInstanceMethod(source, alternate);
  45   if (!old_selector_impl_ && !new_selector_impl_) {
  46     // Try class methods.
  47     old_selector_impl_ = class_getClassMethod(target, original);
  48     new_selector_impl_ = class_getClassMethod(source, alternate);
  49   }
  50
  51   DCHECK(old_selector_impl_);
  52   DCHECK(new_selector_impl_);
  53   if (!old_selector_impl_ || !new_selector_impl_)
  54     return;
  55
  56   // The argument and return types must match exactly.
  57   const char* old_types = method_getTypeEncoding(old_selector_impl_);
  58   const char* new_types = method_getTypeEncoding(new_selector_impl_);
  59   DCHECK(old_types);
  60   DCHECK(new_types);
  61   DCHECK_EQ(0, strcmp(old_types, new_types));
  62   if (!old_types || !new_types || strcmp(old_types, new_types)) {
  63     old_selector_impl_ = new_selector_impl_ = NULL;
  64     return;
  65   }
  66
  67   method_exchangeImplementations(old_selector_impl_, new_selector_impl_);
  68 }
  69
  70 }  // namespace mac
  71 }  // namespace base