GetAdaptersInfo not working on Delphi XE6

Question

I finally bit the bullet and bought XE6 and as expected, the Unicode conversion is turning into a bit of a nightmare. So if anyone can enlighten me on why this simple Windows API call fails, it would be most appreciated. The function does not return an error, the first call gets the correct buffer length, the second call fills the record with garbage.

This works fine under Delphi 2007 but fails on XE6 with unicode garbage in the pAdapterinfo return record even though it is explicitly declared with AnsiString in IpTypes.pas

System is Win7(64) but compiling for 32 bits.

uses iphlpapi, IpTypes;

function GetFirstAdapterMacAddress:AnsiString;
var pAdapterInfo:PIP_ADAPTER_INFO;
    BufLen,Status:cardinal; i:Integer;
begin
  result:='';
  BufLen:= sizeof(IP_ADAPTER_INFO);
  GetAdaptersInfo(nil, BufLen);
  pAdapterInfo:= AllocMem(BufLen);
  try
    Status:= GetAdaptersInfo(pAdapterInfo,BufLen);
    if (Status <> ERROR_SUCCESS) then
    begin
      case Status of
        ERROR_NOT_SUPPORTED: raise exception.create('GetAdaptersInfo is not supported by the operating ' +
                                     'system running on the local computer.');
        ERROR_NO_DATA: raise exception.create('No network adapter on the local computer.');
      else
        raiselastOSerror;
      end;
      Exit;
    end;
    while (pAdapterInfo^.AddressLength=0) and (pAdapterInfo^.next<>nil) do
     pAdapterInfo:=pAdapterInfo.next;
    if pAdapterInfo^.AddressLength>0 then
    for i := 0 to pAdapterInfo^.AddressLength - 1 do
      result := result + IntToHex(pAdapterInfo^.Address[I], 2);
  finally
    Freemem(pAdapterInfo);
  end;
end;

UPDATE:

I did some more checking. I created a new simple application with one form and a button and called the routine when the button was pressed and it worked.

The differences are...in the working form the size of IP_ADAPTER_INFO is 640 bytes.

When this routine is used in a more complex application it fails and the size of IP_ADAPTER_INFO displays as 1192 bytes.

At this point, it seems the complier is unilaterally deciding to change the type of the ansi chars in the structures to unicode chars. The debugger is showing AdapterName and description fields in unicode form. I did a grep of the system source code, there are no other versions of this data type declared in the library code apart from in the Indy library and that is just a duplicate.

Here is the data structure definition in IPtypes

  PIP_ADAPTER_INFO = ^IP_ADAPTER_INFO;
  {$EXTERNALSYM PIP_ADAPTER_INFO}
  _IP_ADAPTER_INFO = record
    Next: PIP_ADAPTER_INFO;
    ComboIndex: DWORD;
    AdapterName: array [0..MAX_ADAPTER_NAME_LENGTH + 3] of AnsiChar;
    Description: array [0..MAX_ADAPTER_DESCRIPTION_LENGTH + 3] of AnsiChar;
    AddressLength: UINT;
    Address: array [0..MAX_ADAPTER_ADDRESS_LENGTH - 1] of BYTE;
    Index: DWORD;
    Type_: UINT;
    DhcpEnabled: UINT;
    CurrentIpAddress: PIP_ADDR_STRING;
    IpAddressList: IP_ADDR_STRING;
    GatewayList: IP_ADDR_STRING;
    DhcpServer: IP_ADDR_STRING;
    HaveWins: BOOL;
    PrimaryWinsServer: IP_ADDR_STRING;
    SecondaryWinsServer: IP_ADDR_STRING;
    LeaseObtained: time_t;
    LeaseExpires: time_t;
  end;

Looks like a compiler bug.

Answer 1

There are several problems with your code:

1. You are not doing any error handling at all on the first call that calculates the buffer length. You don't even need that call, so get rid of it.

2. You are not doing adequate error handling on subsequent calls, in particular you are not handling the ERROR_BUFFER_OVERFLOW condition when GetAdaptersInfo() needs you to allocate more memory than you already have. Your are allocating only enough memory for one adapter, but GetAdaptersInfo() returns info for all adapters and thus needs a sufficient buffer to hold all of them at one time.

3. GetAdaptersInfo() does not use GetLastError(), so you need to call SetLastError() before you call RaiseLastOSError().

4. You are looping through the adapter list using the original pointer that you used to allocate the list, so you are causing a memory leak if the first adapter does not have a MAC address. You need to use a separate variable as the loop iterator so the original pointer is preserved so it can be freed correctly.

5. You are not taking into account the possibility that none of the adapters has a MAC address, so you will end up accessing a nil pointer after your while loop exits.

6. You appear to have multiple versions of the IpTypes unit on your machine, and the compiler is finding one that happens to use Char instead of AnsiChar in the IP_ADAPTER_INFO record so its size and field offsets are wrong.

With that said, try this instead:

uses
  Winapi.iphlpapi, Winapi.IpTypes;

function GetFirstAdapterMacAddress: String;
var
  pAdapterList, pAdapter: PIP_ADAPTER_INFO;
  BufLen, Status: DWORD;
  I: Integer;
begin
  Result := '';
  BufLen := 1024*15;
  GetMem(pAdapterList, BufLen);
  try
    repeat
      Status := GetAdaptersInfo(pAdapterList, BufLen);
      case Status of
        ERROR_SUCCESS:
        begin
          // some versions of Windows return ERROR_SUCCESS with
          // BufLen=0 instead of returning ERROR_NO_DATA as documented...
          if BufLen = 0 then begin
            raise Exception.Create('No network adapter on the local computer.');
          end;
          Break;
        end;
        ERROR_NOT_SUPPORTED:
        begin
          raise Exception.Create('GetAdaptersInfo is not supported by the operating system running on the local computer.');
        end;
        ERROR_NO_DATA:
        begin
          raise Exception.Create('No network adapter on the local computer.');
        end;
        ERROR_BUFFER_OVERFLOW:
        begin
          ReallocMem(pAdapterList, BufLen);
        end;
      else
        SetLastError(Status);
        RaiseLastOSError;
      end;
    until False;

    pAdapter := pAdapterList;
    while pAdapter <> nil do
    begin
      if pAdapter^.AddressLength > 0 then
      begin
        for I := 0 to pAdapter^.AddressLength - 1 do begin
          Result := Result + IntToHex(pAdapter^.Address[I], 2);
        end;
        Exit;
      end;
      pAdapter := pAdapter^.next;
    end;
  finally
    FreeMem(pAdapterList);
  end;
end;

Answer 2

The explanation is that the types declared in your third party IpTypes unit use Char. This is an alias to AnsiChar in pre-Unicode Delphi, and an alias to WideChar in Unicode Delphi. That would explain the fact that you see non-ANSI text when you inspect the content of the record.

The solution is to fix IpTypes to use AnsiChar in place of Char where appropriate. The best way to do that is to use the IpTypes shipped with Delphi rather than your third party version.

On top of that, the first call to GetAdaptersInfo is wrong. Not only do you fail to check the return value, but you pass nil for the buffer and yet also pass a non-zero length. I think it should go like this:

BufLen := 0;
if GetAdaptersInfo(nil, BufLen) <> ERROR_BUFFER_OVERFLOW then
  raise ....

Of course, you way will work, but I'm just being a little pedantic here. Always check for errors when you call an API function.

Answer 3

Just to conclude this topic.

Changing IPtypes to winapi.IPtypes fixed the problem for me.

I think a third party component is doing something to confuse the compiler and giving the full link fixes it.