passing string from RPC client to server

[Wolvorine]

Hi,

I need to return the string data from the RPC function that i am calling. String will be very dynamic so i am interested in using stl string inside the idl.


I tried dynamic arrays but i am unable to persist the pointer from heap corruption... e.g. here is my idl code

interface myinterface
{

void RPC_GetGroupStatusEx([out] char ** szXMLString);

}

server implemented code

void RPC_GetGroupStatusEx(unsigned char ** szXMLString)
{
     
   CString strXmlRawData = GetSomeXmlData(); //it return xml string

    unsigned char* dyn = new unsigned char[strXmlRawData.GetLength()];

    sprintf((char*)dyn,"%s", strXmlRawData.GetBuffer());
	
   *szXMLString =dyn;
}

client caller code

unsigned char *ms = NULL; 

//i have tried even initialized pointer by sending it to the server but it also gave me heap corruption , also i have used address of pointer but same result

          RpcTryExcept
	   {
		
		   RPC_GetGroupStatusEx(&ms);

	   }
	   RpcExcept(1)
	   {
		   int a = RpcExceptionCode();
		  
		  std::cerr << "Runtime reported exception " << RpcExceptionCode()
					<< std::endl;
	   }
	   RpcEndExcept

it always crash at the server side code after leaving that function , one more thing is RPC server is on the different machine. Every other functions with data types works fine except string.


Please guide me what i am doing wrong in the code? How can i use stl string inside the idl file ?


Regards

[Igor Vartanov]

Something like this (please refer to IDL documentation)

interface myinterface
{

void RPC_GetGroupStatusEx(UINT nSize, [ out, size_is(nSize)] char ** szXMLString);

}

[Wolvorine]

hi Igor Vartanov,

i have tried this example after your recommendation also from the documentation which is written http://msdn.microsoft.com/en-us/libr...=vs.85%29.aspx



HRESULT Proc7(
[out] long * pSize,
[out, size_is( , *pSize)] my_type ** ppMyType); /* Specifies a pointer
to a sized pointer,
which points to a block
of my_types, whose size is
unknown when the stub
calls the server. */




But at the end of my function inside server i see this error

HEAP CORRUPTION DETECTED: after Normal block (#4165) at 0x0081F710.
CRT detected that the application wrote to memory after end of heap buffer.

my new idl file is now as

interface myinterface
{

void RPC_GetGroupStatusEx(([out] long  * pSize,[out, size_is( , *pSize)] char ** szXMLString););

}

server code

void RPC_GetGroupStatusEx (long *size,unsigned char ** szXMLString)
{
    CString strXmlRawData = GetSomeXmlData(); //it return xml string

    unsigned char* dyn = new unsigned char[strXmlRawData.GetLength()];

    sprintf((char*)dyn,"%s", strXmlRawData.GetBuffer());
	
    *pSize = strXmlRawData.GetLength()
   *szXMLString =dyn;

}

Also i have used another way as below

void RPC_GetGroupStatusEx (long *size,unsigned char ** szXMLString)
{
    CString strXmlRawData = GetSomeXmlData(); //it return xml string

    *size = strXmlRawData.GetLength();
    *szXMLString =new unsigned char[*size];
      sprintf((char*)*szXMLString,"%s",strXmlRawData.GetBuffer());

}

both of the style of server function gives heap error , first one raised right after the end of the function while the second one gives in after the end of function and then in middle of another statement.


any idea? please help

[VictorN]

Is your build ANSI or UNICODE? Your code seems to assume it'd be incorrect in the UNICODE build!

[Wolvorine]

my server and client both are unicode but my interface is non-unicode and i am communicating things with using char instead of wchar. So basically when i call the rpc function i provides non-unicode character pointers.

What do you think???

[VictorN]

I think that the length of CString text in bytes (aka unsigned chars) is GetLength() * sizeof(TCHAR), not just the GetLength()

[Wolvorine]

USES_CONVERSION;
	CStringA strXmlRawData = W2A(objStatusXml.GetRawData().GetBuffer());
	
	*size = strXmlRawData.GetLength();
	
	*szXMLString =new unsigned char[*size];
	
	sprintf((char*)*szXMLString,"%s",strXmlRawData.GetBuffer());

above is my code CStringA is asci version explicitly initialized but still it gives error with both of the styles i previously mentioned...

[Igor Vartanov]

	*size = strXmlRawData.GetLength() + 1;
	
	*szXMLString =new unsigned char[*size];
	
	sprintf((char*)*szXMLString,"%s",strXmlRawData.GetBuffer());

Your buffer allocation seems missing space for a zero terminator. Besides, I'm not sure about the way you allocate that (actually, I'm sure new doesn't belong here). You definitely need some reading about RPC out parameters, what side and how allocates that.