Alain Thiffault
Reputation: 608
WlanAPI WlanGetNetworkBssList returning invalid data
I'm stuck in my debugging efforts with a call to WlanGetNetworkBssList and would appreciate some pointers. My end objective is to construct a Wifi scanner/profiler tool to help me troubleshoot networking issues on remote sites.
I am using the Windows Native Wifi API (link) and Delphi/Pascal interface found here using Delphi Berlin 10.1 Update 2 under Windows 10 (VCL).
I started with a simple and crude test app (VCL) to get a feel for the API and ran into a problem calling WlanGetNetworkBssList so I created a small console app focused on that problem. The issue is that it works in a console app running in a command prompt but not in my VCL test app. The functions are pretty much copy-paste equivalent and stepping through the code side-by-side shows that the data is identical except for the return data from WlanGetNetworkBssList call (pWlanBssList)
Question: Since the call is to an external DLL what steps can I do to further debug this and understand the difference between the VCL and the console app.
Note: The WlanGetNetworkBssList has two modes of operation where an SSID can be supplied to get the BSSID (MAC of the access point) for that specific SSID. By passing NULL instead of an SSID the API will return the BSSIDs of all APs. Passing NULL works on both the VLC and console app. What breaks is when a specific SSID is requested. After verification, the SSID data structure is identical in both apps but the data buffer returned is invalid with the VCL app. How can this be?
Console app:
program CWifiScan;
{$APPTYPE CONSOLE}
uses
Windows,
System.SysUtils,
nduWlanAPI,
nduWlanTypes;
const
WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_ADHOC_PROFILES = $00000001;
var
hWlan: THandle;
guid : TGUID;
dwSupportedVersion: DWORD = 0;
dwClientVersion: DWORD = 1;
i,j : integer;
pInterfaceInfo : Pndu_WLAN_INTERFACE_INFO;
pInterfaceList : Pndu_WLAN_INTERFACE_INFO_LIST;
pAvailableNetworkList : Pndu_WLAN_AVAILABLE_NETWORK_LIST;
procedure GetBSSIDList(clientHandle : THandle;
interfaceGUID : TGUID;
pSSID : Pndu_DOT11_SSID = nil;
SSID_Type : Tndu_DOT11_BSS_Type = dot11_BSS_type_any;
SecurityEnabled : BOOL = True);
var
//to check if interface is connected
pData : Pndu_WLAN_INTERFACE_STATE;
pdwDataSize : DWORD;
isConnected : Boolean;
//to get list of BSSids from available APs
pWlanBssList : Pndu_WLAN_BSS_LIST;
items : integer;
itemIndex : integer;
SSID : string;
MAC : string;
begin
//check if interface is connected
isConnected := False;
if WlanQueryInterface(clientHandle,
@interfaceGUID,
wlan_intf_opcode_interface_state,
nil,
@pdwDataSize,
@pData,
nil) = ERROR_SUCCESS then
begin
isConnected := (pData^ = Tndu_WLAN_INTERFACE_STATE.wlan_interface_state_connected);
end;
//get the list of BSSids for the provided interface
if isConnected then
begin
if WlanGetNetworkBssList(clientHandle,
@interfaceGUID,
pSSID,
SSID_Type,
SecurityEnabled,
nil,
@pWlanBssList) = ERROR_SUCCESS then
begin
items := pWlanBssList^.dwNumberOfItems;
for itemIndex := 0 to items - 1 do
begin
SSID := String(PAnsiChar(@pWlanBssList^.wlanBssEntries[itemIndex].dot11Ssid.ucSSID));
MAC := Format('%.2x:%.2x:%.2x:%.2x:%.2x:%.2x', [
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[0],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[1],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[2],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[3],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[4],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[5]]);
Writeln('');
Writeln('SSID: ................ '+SSID);
Writeln('Physical Address: .... '+MAC);
end; {for itemIndex}
Writeln(#10+#13+'Done.');
end; {WlanGetNetworkBssList succeeds}
end; {isConnected}
end;
begin
hWlan := 0;
if WlanOpenHandle(2, nil,@dwSupportedVersion, @hWlan)= ERROR_SUCCESS then
begin
if WlanEnumInterfaces(hWlan, nil, @pInterfaceList) = ERROR_SUCCESS then
begin
try
for i := 0 to pInterfaceList^.dwNumberOfItems-1 do
begin
Writeln('Wifi Adapter - '+GUIDToString( pInterfaceList^.InterfaceInfo[i].InterfaceGuid ) );
Writeln('Scanning: .... '+pInterfaceList^.InterfaceInfo[i].strInterfaceDescription);
guid := pInterfaceList^.InterfaceInfo[i].InterfaceGuid;
//Get all BSSids for this interface
GetBSSIDList(hWlan, guid);
if WlanGetAvailableNetworkList(hWlan,
@guid,
WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_ADHOC_PROFILES,
nil,
pAvailableNetworkList) = ERROR_SUCCESS then
begin
try
for j := 0 to pAvailableNetworkList^.dwNumberOfItems - 1 do
begin
//Get BSSid for this specific SSID
GetBSSIDList(hWlan,
guid,
@pAvailableNetworkList^.Network[j].dot11Ssid,
pAvailableNetworkList^.Network[j].dot11BssType,
pAvailableNetworkList^.Network[j].bSecurityEnabled);
end;
finally
if pAvailableNetworkList<>nil then
WlanFreeMemory(pAvailableNetworkList);
end;
end;
end;
finally
if pInterfaceList<>nil then
WlanFreeMemory(pInterfaceList);
end;
end;
WlanCloseHandle(hWlan, nil);
readln;
end;
end.
The relevant parts of the VCL app are:
uses
... nduWlanAPI, nduWlanTypes, nduWinDot11;
function TForm1.GetBSSID(clientHandle: THandle;
interfaceGuid: TGUID;
pSSID: Pndu_DOT11_SSID = nil;
SSID_Type : Tndu_DOT11_BSS_TYPE = dot11_BSS_type_any;
SecurityEnabled: boolean = true): string;
var
//used to determin if the interface is connected
pData : Pndu_WLAN_INTERFACE_STATE;
isConnected : boolean;
//used to extract a list of BSSIDs for a given interface
pWlanBssList : Pndu_WLAN_BSS_LIST;
lastError : DWORD;
pdwDataSize : DWORD;
items,
itemIndex: Integer;
begin
pData := nil;
pdwDataSize := 0;
isConnected := False;
//check if the interface is connected
lastError := WlanQueryInterface(clientHandle,
@interfaceGuid,
wlan_intf_opcode_interface_state,
nil,
@pdwDataSize,
@pData,
nil);
if (lastError = ERROR_SUCCESS) then
begin
//isConnected := (Tndu_WLAN_INTERFACE_STATE(pData^.isState) = Tndu_WLAN_INTERFACE_STATE.wlan_interface_state_connected);
isConnected := (pData^ = Tndu_WLAN_INTERFACE_STATE.wlan_interface_state_connected);
end
else
DisplayError('Error in WlanQueryInterface() function', lastError);
if isConnected then
begin
pWlanBssList := nil;
lastError := WlanGetNetworkBssList(clientHandle,
@interfaceGuid,
pSSID,
SSID_Type,
SecurityEnabled,
nil,
@pWlanBssList);
try
if (lastError = ERROR_SUCCESS) then
begin
items := pWlanBssList^.dwNumberOfItems;
for itemIndex := 0 to items-1 do
begin
Result := (Format('%.2x:%.2x:%.2x:%.2x:%.2x:%.2x', [
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[0],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[1],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[2],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[3],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[4],
pWlanBssList^.wlanBssEntries[itemIndex].dot11Bssid[5]]));
end;
end
else
DisplayError('Error in the WlanGetNetworkBssList() function call', lastError);
finally
if pData<>nil then
WlanFreeMemory(pData);
if pWlanBssList<>nil then
WlanFreeMemory(pWlanBssList);
end;
end;
end;
Which is called as follows:
function TForm1.ScanWifi(): THandle;
const
WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_ADHOC_PROFILES = $00000001;
var
hClient : THandle;
dwVersion : DWORD;
lastError : DWORD;
pInterface : Pndu_WLAN_INTERFACE_INFO_LIST;
i : Integer;
j : Integer;
pAvailableNetworkList: Pndu_WLAN_AVAILABLE_NETWORK_LIST;
interfaceGuid : TGUID;
BSSID : string;
begin
lastError:=WlanOpenHandle(NDU_WLAN_API_VERSION, nil, @dwVersion, @hClient);
if lastError<> ERROR_SUCCESS then
begin
//DisplayError('Error in the WlanOpenHandle() function call', lastError);
Result := 0;
Exit;
end;
//L(Format('Requested WLAN interface version [%d], negotiated version [%d]', [NDU_WLAN_API_VERSION, dwVersion]));
Result := hClient;
try
lastError:=WlanEnumInterfaces(hClient, nil, @pInterface);
try
if lastError<> ERROR_SUCCESS then
begin
//DisplayError('Errorin the WlanEnumInterfaces() function call', lastError);
Exit;
end;
for i := 0 to pInterface^.dwNumberOfItems - 1 do
begin
interfaceGuid:= pInterface^.InterfaceInfo[i].InterfaceGuid;
lastError:=WlanGetAvailableNetworkList(hClient,
@interfaceGuid,
WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_ADHOC_PROFILES,
nil,
pAvailableNetworkList);
try
if lastError<> ERROR_SUCCESS then
begin
//DisplayError('Error WlanGetAvailableNetworkList', lastError);
Exit;
end
else
begin
for j := 0 to pAvailableNetworkList^.dwNumberOfItems - 1 do
Begin
BSSID := GetBssid(hClient,
interfaceGuid,
@pAvailableNetworkList^.Network[j].dot11Ssid,
pAvailableNetworkList^.Network[j].dot11BssType,
pAvailableNetworkList^.Network[j].bSecurityEnabled
);
//FAPList.AddOrSetValue(BSSID,J);
end;
end;
finally
if pAvailableNetworkList <> nil then
WlanFreeMemory(pAvailableNetworkList);
end;
end;
finally
if pInterface <> nil then
WlanFreeMemory(pInterface);
end;
finally
WlanCloseHandle(FhClient, nil);
end;
end;
Comparing the data between the two apps the only difference is the result (pWlanBssList) as seen here (left=console, right=VCL):
Upvotes: 0
Views: 1043
Answers (1)
EugeneK
Reputation: 2214
Looks like compiler bug in boolean conversion, problem is following line in VCL code
SecurityEnabled: boolean = true
you need to change it to
SecurityEnabled: bool = true
Upvotes: 2
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