COM中的UTF-16字符串

Question

谁来解释一下Go指针的魔力我试着调用COM函数

func (p *IServer) Authorize(user, pass string) error {
  UserName := ole.SysAllocString(login.UserName)
  defer ole.SysFreeString(UserName)
  UserPsw := ole.SysAllocString(login.UserPsw)
  defer ole.SysFreeString(UserPsw)  

  // HRESULT IServer::Authorize([in] BSTR UserName, [in] BSTR UserPsw, [out] VARIANT* SID, [out, retval] long* Result)
  hr, _, _ := Call(p.VTable().Authorize,
    uintptr(unsafe.Pointer(p)),
    uintptr(unsafe.Pointer(UserName)),
    uintptr(unsafe.Pointer(UserPsw)),
    uintptr(unsafe.Pointer(sid)),
    uintptr(unsafe.Pointer(&res)))

   ...
}

这段代码运行良好，但当我将转换替换为

UserName := syscall.StringToUTF16Ptr(login.UserName)
UserPsw := syscall.StringToUTF16Ptr(login.UserPsw)

它会导致访问冲突！来源: go-ole

func SysAllocString(v string) (ss *int16) {
  pss, _, _ := procSysAllocString.Call(uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(v))))
  ss = (*int16)(unsafe.Pointer(pss))
  return
}

我做错了什么？

更新:在C/C++ wchar*中，指针在386/amd64中都能正常工作

void Authorize(IServer* p wchar* user, wchar* pass) {
   p.Authorize(user, pass ....
}

Answer 1

SysAllocString返回BSTR类型，即com类型对象。

 typedef struct {
 #ifdef _WIN64
     DWORD pad;
 #endif
     DWORD size;
     union {
         char ptr[1];
         WCHAR str[1];
         DWORD dwptr[1];
     } u; // take it as a starting point of the string 
 } bstr_t;

换句话说，它是相同的utf16编码字符串，但是前缀的形式是它的大小( Unicode字符的长度乘以wchar_t的大小(2-4字节))。出于优化的原因，它也有填充。

由于它的浮动大小，最好使用ole包，而不是重复发明轮子。如果您想自己实现它，并且wchar_t的大小为int16 (2字节)，那么您必须执行以下操作：

(半个伪代码，我没有测试它)

type BSTR *uint16

func SysAllocString(str string) (result BSTR) {
    // DWORD == int32 == rune
    const padf = "\x00" // only for 64 bit system
    const sizef = "\x00"

    // int32 == 4 byte 
    // int16 == 2 byte
    const wordSize = unsafe.Sizeof(int16(0))

    utf16 := utf16.Encode([]rune(padf + sizef + str))

    /* pad is on index 0 and 1 */
    size :=  &utf16[2 /* 0 for 32 bit system */]

    // set "size" field as unicode charachers length multypled by size of wchar_t
    *(*rune)(unsafe.Pointer(size)) = rune((len(utf16)-2) * int(wordSize))


    result = BSTR(&utf16[0])

    return
}

// ...
bstr := SysAllocString(login.UserName)

uintptr(unsafe.Pointer(bstr))