Q250461: BUG: WSALookupServiceNext Returns Incomplete Data

Article: Q250461
Product(s): Microsoft Windows NT
Version(s): WINDOWS:
Operating System(s): 
Keyword(s): kbnetwork kbAPI kbOSWin2000 kbOSWin2000bug kbSDKPlatform kbSDKWin32 kbWinsock kbDSuppor
Last Modified: 24-OCT-2000

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The information in this article applies to:

- Microsoft Windows 2000 Advanced Server 
- Microsoft Windows 2000 Server 
- Microsoft Windows 2000 Professional 
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SYMPTOMS
========

When you are doing a namespace query for the SVCID_HOSTNAME globally unique
identifier (GUID) and use the WSALookupServiceNext Winsock API to dynamically
determine the buffer size required for the WSAQUERYSET, the subsequent call to
WSALookupServiceNext with the allocated buffer returns incomplete data and
should not be relied upon.

RESOLUTION
==========

To work around this problem, you can allocate an appropriately sized buffer
before you make the first call to WSALookupServiceNext.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

MORE INFORMATION
================

The following code exhibits the bug on Windows 2000, whereas on Windows NT 4.0
this code works as expected.

If you uncomment the lines noted in the code, the call works because the buffer
is allocated beforehand.

  #include <stdio.h>      // Standard I/O
  #include <winsock2.h>   // winsock 2.0
  #include <svcguid.h>    // guids

  int main(int argc, char * argv[])
  {
    WSADATA wsaData;
    DWORD dwResult;
    HANDLE hLookup = 0;
    WSAQUERYSET lpRestrictions;
    GUID guid = SVCID_HOSTNAME;

    dwResult = WSAStartup(MAKEWORD(2,2), &wsaData);

    if (dwResult != 0)
      {
      printf("Cannot startup Winsock: %d\n", dwResult);
      exit(1);
      }

    ZeroMemory(&lpRestrictions, sizeof(WSAQUERYSET));
    lpRestrictions.dwSize = sizeof(WSAQUERYSET);
    lpRestrictions.lpServiceClassId = &guid;

    dwResult = WSALookupServiceBegin(&lpRestrictions, LUP_RETURN_NAME, &hLookup);
    if (dwResult != SOCKET_ERROR)
      {
      DWORD dwLength = 0;
      WSAQUERYSET * pqs = NULL;
      
      // 
      // picking an arbitrary value works fine 
      // 
      // UNCOMMENT below for success on Windows 2000
      // 
      // pqs = (WSAQUERYSET *) malloc(sizeof(WSAQUERYSET) + 100);
      // dwLength = sizeof(WSAQUERYSET) + 100;
      // 

      do
        {
        if (WSALookupServiceNext(hLookup, 0, &dwLength, pqs) != 0)
          dwResult = WSAGetLastError();
        else
          dwResult = 0;

        if (dwResult == WSAEFAULT)
          {
          if (pqs) 
            free(pqs);
          pqs = (WSAQUERYSET *) malloc(dwLength);
          if (!pqs)
            {
            printf("Could not allocate memory: %d\n", GetLastError());
            exit(2);
            }
          else          
            continue;
          }
        
        // output it since we have it now        
        if ((dwResult == 0) && (pqs))
          printf("%s\n", pqs->lpszServiceInstanceName);

        }
        while ((dwResult != WSA_E_NO_MORE) && (dwResult != WSAENOMORE));      
      
      // clean-up
      free(pqs);
      WSALookupServiceEnd(hLookup);
      }
    else
      {
      printf("Error on WSALookupServiceBegin: %d\n", WSAGetLastError());
      exit(3);
      }
    

    WSACleanup();

    return 0;
  }

Additional query words:

======================================================================
Keywords          : kbnetwork kbAPI kbOSWin2000 kbOSWin2000bug kbSDKPlatform kbSDKWin32 kbWinsock kbDSupport kbGrpDSNet 
Technology        : kbwin2000AdvServ kbwin2000AdvServSearch kbwin2000Serv kbwin2000ServSearch kbwin2000Search kbwin2000ProSearch kbwin2000Pro kbWinAdvServSearch
Version           : WINDOWS:
Issue type        : kbbug

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