Converting Delphi code to list all network adapters on a Windows
system to FPC
lazarus / 38-Networking and Web Programming

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vfclists · 2014-05-06 12:06

I am trying out some Delphi code to obtain the list of network
adapters on a system, based on code in this stackoverflow question:
http://stackoverflow.com/questions/18378630/get-information-about-the-
installed-network-adapters.

The code uses the Windows and Winsock unit and when I try to run the
solution offered by the guy with the approved answer -  JRL - it seems
to cause some kind of buffer overrun or stack overflow which causes it
to use a lot of CPU and it gets terminated.

Can someone look into it and explain the crash? It makes a lot of
Windows system calls and I suspect there may be some mismatch between
the API calls, the data structures and FreePascal.

I have added the code below and have attached a project for testing
it.  The last answer in that question offers another solution, but I
will discuss that in a separate question.

Code: [Select]Unit USock;

Interface

Uses Windows, Winsock;


{ Unit to identify the network interfaces
  This code requires at least Win98/ME/2K, 95 OSR 2 or NT service pack
#3
  as WinSock 2 is used (WS2_32.DLL) }


// Constants found in manual on non-officially documented M$ Winsock
functions
Const SIO_GET_INTERFACE_LIST = $4004747F;
      IFF_UP                 = $00000001;
      IFF_BROADCAST          = $00000002;
      IFF_LOOPBACK           = $00000004;
      IFF_POINTTOPOINT       = $00000008;
      IFF_MULTICAST          = $00000010;


Type SockAddr_Gen          = Packed Record
                               AddressIn             : SockAddr_In;
                               Padding               : Packed Array
[0..7] of Byte;
                             end;

     Interface_Info        = Record
                               iiFlags               : u_Long;
                               iiAddress             : SockAddr_Gen;
                               iiBroadcastAddress    : SockAddr_Gen;
                               iiNetmask             : SockAddr_Gen;
                             end;

     tNetworkInterface     = Record
                               ComputerName          : String;
                               AddrIP                : String;
                               SubnetMask            : String;
                               AddrNet               : String;
                               AddrLimitedBroadcast  : String;
                               AddrDirectedBroadcast : String;
                               IsInterfaceUp         : Boolean;
                               BroadcastSupport      : Boolean;
                               IsLoopback            : Boolean;
                             end;

     tNetworkInterfaceList = Array of tNetworkInterface;


Function WSAIoctl (aSocket              : TSocket;
                   aCommand             : DWord;
                   lpInBuffer           : Pointer;
                   dwInBufferLen        : DWord;
                   lpOutBuffer          : Pointer;
                   dwOutBufferLen       : DWord;
                   lpdwOutBytesReturned : LPDWord;
                   lpOverLapped         : Pointer;
                   lpOverLappedRoutine  : Pointer) : Integer; stdcall;
external 'WS2_32.DLL';

Function GetNetworkInterfaces (Var aNetworkInterfaceList :
tNetworkInterfaceList): Boolean;


implementation


Function GetNetworkInterfaces (Var aNetworkInterfaceList :
tNetworkInterfaceList): Boolean;
// Returns a complete list the of available network interfaces on a
system (IPv4)
// Copyright by Dr. Jan Schulz, 23-26th March 2007
// This version can be used for free and non-profit projects. In any
other case get in contact
// Written with information retrieved from MSDN
// www.code10.net
Var aSocket             : TSocket;
    aWSADataRecord      : WSAData;
    NoOfInterfaces      : Integer;
    NoOfBytesReturned   : u_Long;
    InterfaceFlags      : u_Long;
    NameLength          : DWord;
    pAddrIP             : SockAddr_In;
    pAddrSubnetMask     : SockAddr_In;
    pAddrBroadcast      : Sockaddr_In;
    DirBroadcastDummy   : In_Addr;
    NetAddrDummy        : In_Addr;
    Buffer              : Array [0..30] of Interface_Info;
    i                   : Integer;
Begin
  Result := False;
  SetLength (aNetworkInterfaceList, 0);

  // Startup of old the WinSock
  // WSAStartup ($0101, aWSADataRecord);

  // Startup of WinSock2
  WSAStartup(MAKEWORD(2, 0), aWSADataRecord);

  // Open a socket
  aSocket := Socket (AF_INET, SOCK_STREAM, 0);

  // If impossible to open a socket, not worthy to go any further
  If (aSocket = INVALID_SOCKET) THen Exit;

  Try
    If WSAIoCtl (aSocket, SIO_GET_INTERFACE_LIST, NIL, 0,
                 @Buffer, 1024, @NoOfBytesReturned, NIL, NIL) <>
SOCKET_ERROR THen
    Begin
      NoOfInterfaces := NoOfBytesReturned  Div SizeOf
(Interface_Info);
      SetLength (aNetworkInterfaceList, NoOfInterfaces);

      // For each of the identified interfaces get:
      For i := 0 to NoOfInterfaces - 1 do
      Begin

        With aNetworkInterfaceList[i] do
        Begin

          // Get the name of the machine
          NameLength := MAX_COMPUTERNAME_LENGTH + 1;
          SetLength (ComputerName, NameLength)  ;
          If Not GetComputerName (PChar (Computername), NameLength)
THen ComputerName := '';

          // Get the IP address
          pAddrIP                  := Buffer[i].iiAddress.AddressIn;
          AddrIP                   := string(inet_ntoa
(pAddrIP.Sin_Addr));

          // Get the subnet mask
          pAddrSubnetMask          := Buffer[i].iiNetMask.AddressIn;
          SubnetMask               := string(inet_ntoa
(pAddrSubnetMask.Sin_Addr));

          // Get the limited broadcast address
          pAddrBroadcast           :=
Buffer[i].iiBroadCastAddress.AddressIn;
          AddrLimitedBroadcast     := string(inet_ntoa
(pAddrBroadcast.Sin_Addr));

          // Calculate the net and the directed broadcast address
          NetAddrDummy.S_addr      :=
Buffer[i].iiAddress.AddressIn.Sin_Addr.S_Addr;
          NetAddrDummy.S_addr      := NetAddrDummy.S_addr And
Buffer[i].iiNetMask.AddressIn.Sin_Addr.S_Addr;
          DirBroadcastDummy.S_addr := NetAddrDummy.S_addr Or Not
Buffer[i].iiNetMask.AddressIn.Sin_Addr.S_Addr;

          AddrNet                  := string(inet_ntoa
((NetAddrDummy)));
          AddrDirectedBroadcast    := string(inet_ntoa
((DirBroadcastDummy)));

          // From the evaluation of the Flags we receive more
information
          InterfaceFlags           := Buffer[i].iiFlags;

          // Is the network interface up or down ?
          If (InterfaceFlags And IFF_UP) = IFF_UP THen IsInterfaceUp
:= True
                                                  Else IsInterfaceUp
:= False;

          // Does the network interface support limited broadcasts ?
          If (InterfaceFlags And IFF_BROADCAST) = IFF_BROADCAST THen
BroadcastSupport := True
                                                                Else
BroadcastSupport := False;

          // Is the network interface a loopback interface ?
          If (InterfaceFlags And IFF_LOOPBACK) = IFF_LOOPBACK THen
IsLoopback := True
                                                              Else
IsLoopback := False;
        end;
      end;
    end;
  Except
    //Result := False;
  end;

  // Cleanup the mess
  CloseSocket (aSocket);
  WSACleanUp;
  Result := True;
end;

end.

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Blaazen · 2014-05-06 13:05

Hi,

I tested attached project under Wine and it seems fine.
I got no crash and output to memo is:
Code: [Select]6.5.2014 15:01:15 :

#                          : 0
Name                       : msi-NB
IP-Address                 : 192.168.2.4
Subnet mask                : 255.255.255.0
Net address                : 192.168.2.0
Limited broadcast address  : 192.168.2.255
Directed Broadcast address : 192.168.2.255
Interface up               : True
Broadcast supported        : True
Loopback interface         : Falsewhich seems correct too.

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vfclists · 2014-05-06 13:09

Quote from: Blaazen on May 06, 2014, 03:05:46 pmHi,

I tested attached project under Wine and it seems fine.
I got no crash and output to memo is:
Code: [Select]6.5.2014 15:01:15 :

#                          : 0
Name                       : msi-NB
IP-Address                 : 192.168.2.4
Subnet mask                : 255.255.255.0
Net address                : 192.168.2.0
Limited broadcast address  : 192.168.2.255
Directed Broadcast address : 192.168.2.255
Interface up               : True
Broadcast supported        : True
Loopback interface         : Falsewhich seems correct too.
Thanks. Can you test it on a proper Windows system and see?

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Blaazen · 2014-05-06 13:13

Unfortunately no. I have no real Windows here, only Wine.

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marcov · 2014-05-06 13:24

Converted to console app, both the .lpr and unit compiled with -Sd (to
avoid trouble with alignment):

D:\src\listWindowsNICs>listwindowsnics
5/6/2014 15:22:52 :
Size of aNetInterfaceList - 1

#                          : 0
Name                       : CANDMARLAPTOP
IP-Address                 : 127.0.0.1
Subnet mask                : 255.0.0.0
Net address                : 127.0.0.0
Limited broadcast address  : 0.0.0.0
Directed Broadcast address : 127.255.255.255
Interface up               : True
Broadcast supported        : False
Loopback interface         : True


#                          : 1
Name                       : CANDMARLAPTOP
IP-Address                 : 192.168.187.110
Subnet mask                : 255.255.255.0
Net address                : 192.168.187.0
Limited broadcast address  : 255.255.255.255
Directed Broadcast address : 192.168.187.255
Interface up               : True
Broadcast supported        : True
Loopback interface         : False


It doesn't seem to detect my wireless card though.

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vfclists · 2014-05-06 14:20

Quote from: marcov on May 06, 2014, 03:24:17 pmConverted to console
app, both the .lpr and unit compiled with -Sd (to avoid trouble with
alignment):

D:\src\listWindowsNICs>listwindowsnics
5/6/2014 15:22:52 :
Size of aNetInterfaceList - 1

#                          : 0
Name                       : CANDMARLAPTOP
IP-Address                 : 127.0.0.1
Subnet mask                : 255.0.0.0
Net address                : 127.0.0.0
Limited broadcast address  : 0.0.0.0
Directed Broadcast address : 127.255.255.255
Interface up               : True
Broadcast supported        : False
Loopback interface         : True


#                          : 1
Name                       : CANDMARLAPTOP
IP-Address                 : 192.168.187.110
Subnet mask                : 255.255.255.0
Net address                : 192.168.187.0
Limited broadcast address  : 255.255.255.255
Directed Broadcast address : 192.168.187.255
Interface up               : True
Broadcast supported        : True
Loopback interface         : False


It doesn't seem to detect my wireless card though.

Thanks. I tested it on 2 other PCs and it worked fine. I suspect the
problem may be on the development system.

Where do you set the -Sd option in Lazarus? What is the proper name
for it?

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Blaazen · 2014-05-06 14:36

AFAIK -Sd is {$mode delphi}

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marcov · 2014-05-06 14:53

Yes. Note that a $mode in the sourcecode overrules anything on the
cmdline. So remove $mode objfpc's if you have them

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vfclists · 2014-05-06 15:25

Do modes apply to the whole project or can they change according to
the unit?

Quote from: marcov on May 06, 2014, 04:53:59 pmYes. Note that a $mode
in the sourcecode overrules anything on the cmdline. So remove $mode
objfpc's if you have them

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Leledumbo · 2014-05-06 15:28

Quote from: vfclists on May 06, 2014, 05:25:21 pmDo modes apply to the
whole project or can they change according to the unit?
http://www.freepascal.org/docs-html/user/userse33.html