NetShareEnum not displaying shares correctly - delphi

Question

I'm developing a project to help me managing my remote network, as I need some very specific features I decided to code it.
I connect to the remote computers using WNetAddConnection2 and this part is working. But now I try to list all the shares (ADMIN$, C$, IPC$, and any shared folders) using the NetShareEnum function. I relied on this function and not on WNetEnumResource because I found more examples working with NetShareEnum, and it's working better for me. The problem is that my implementation of NetShareEnum is listing only some type of folders (looks like only folders that are shared but I have no access). It doesn't list normal folders (where I have access), ADMIN$, C$, IPC$, or anything else. Only shared folders that I'm without rights to access.
I still not sure if the behavior is the same on all servers, but the ones I tested it was. So far what I have is:
unit Unit1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm1 = class(TForm)
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
HostFile: TStringList;
iHost: integer;
type
SharesThread = class(TThread)
strict private
IPAddress: String;
function Authenticate: bool;
procedure EnumShares(RemoteName: PWChar);
protected
constructor Create(const IPv4: string);
procedure Execute; override;
end;
type
_SHARE_INFO_502 = packed record
shi502_netname: PWideChar;
shi502_type: DWORD;
shi502_remark: PWideChar;
shi502_permissions: DWORD;
shi502_max_uses: DWORD;
shi502_current_uses: DWORD;
shi502_path: LPWSTR;
shi502_passwd: LPWSTR;
shi502_reserved: DWORD;
shi502_security_dsc: PSECURITY_DESCRIPTOR;
end;
SHARE_INFO_502 = _SHARE_INFO_502;
PSHARE_INFO_502 = ^SHARE_INFO_502;
LPSHARE_INFO_502 = PSHARE_INFO_502;
TShareInfo502 = SHARE_INFO_502;
PShareInfo502 = PSHARE_INFO_502;
type
TShareInfo502Array = Array [0..MaxWord] of TShareInfo502;
PShareInfo502Array = ^TShareInfo502Array;
function NetApiBufferFree(buffer: Pointer): DWORD; stdcall; external 'netapi32.dll';
function NetShareEnum(servername: PWideChar;
level: DWORD;
bufptr: PByteArray;
prefmaxlen: DWORD;
entriesread: PDWORD;
totalentries: PDWORD;
resume_handle: PDWORD): DWORD; stdcall; external 'netapi32.dll';
implementation
const
NERR_Success = 0;
MAX_PREFERRED_LENGTH = DWORD( -1 );
procedure StartThreads;
var
CurrentIP: string;
begin
if (iHost < HostFile.Count) then
begin
CurrentIP:= HostFile.Strings[iHost];
inc(iHost);
SharesThread.Create(CurrentIP);
end
else
Form1.Memo1.Lines.Add('finished');
end;
constructor SharesThread.Create(const IPv4: string);
begin
inherited Create(false);
FreeOnTerminate:= true;
IPAddress:= IPv4;
end;
function SharesThread.Authenticate;
var
lpNetResource: TNetResource;
myres: cardinal;
begin
with lpNetResource do
begin
dwType := RESOURCETYPE_ANY;
lpLocalName := nil;
lpProvider := nil;
lpRemoteName:= PChar('\\'+IPAddress);
end;
myres := WNetAddConnection2(lpNetResource, PChar('123456'), PChar('BlackNote'), 0);
if ( myres = NO_ERROR ) then
begin
Result:= true;
EnumShares(lpNetResource.lpRemoteName);
end
else
begin
Result:= false;
end;
end;
procedure SharesThread.EnumShares(RemoteName: PWChar);
var
p: PShareInfo502Array;
res, er, tr, resume, i: DWORD;
begin
repeat
res:=NetShareEnum(RemoteName, 502, #p, MAX_PREFERRED_LENGTH, #er, #tr, #resume);
if (res = ERROR_SUCCESS) or (res = ERROR_MORE_DATA) then
begin
for i:=1 to Pred(er) do
begin
Form1.Memo1.Lines.Add(String(p^[i].shi502_netname));
end;
NetApiBufferFree(p);
end;
until (res <> ERROR_MORE_DATA);
end;
procedure SharesThread.Execute;
begin
if Authenticate then
Form1.Memo1.Lines.Add(IPAddress + '=' + 'Listed shares above')
end;
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
HostFile:= TStringList.Create;
HostFile.LoadFromFile('Hosts.txt');
iHost:= 0;
StartThreads;
end;
end.
I can post my IP address here to you try this project, but not sure if this is under the rules. Anyway, is something wrong with this code?

Answer 1

I think you have BAD multithreading issues.
First of all, check if the very API you use is thread-safe.
I did not found this particular information, but http://computer-programming-forum.com/82-mfc/8e7756aee43ed65a.htm
Maybe you just can not call that function from different threads at the same time.
Second: all hundreds of your threads do Form1.Memo1.Lines.Add(String(p^[i].shi502_netname)) - that is VERY wrong.
You CAN NOT access GUI objects from threads. CAN NOT. Period.
See Delphi 7 Occasional deadlock changing TLabel.Font.Style from IdHTTPListener event for example.
The very process of loading form from DFM-resource, initializing it, creating Windows and Delphi objects and binding them, together is complex.
When at the same time hundreds of threads are crashing into half-created from and updating half-created MEMO they literally do destroy actions of one another.
Basically you told us that Windows did not returned you all the shares - but what you mean is that half-created TMemo abused by hundreds of threads does not show you all the shares. That is not the same, that might mean Windows work badly, but it also might mean Windows works ok, but you fail to put all the results into VCL GUI. You have to ensure what exactly happened.
Try getting shares
1.1 only in one single thread!
1.2 and that should be MAIN thread, not extra ones.
1.3 and you only should start it after the form is created - for example from some button click event.
And check if there is the difference.
You should not add data by one line to the memo - it is VERY slow.
Make a simple test.
uses Hourglass; // http://www.deltics.co.nz/blog/posts/tag/delticshourglass
const cMax = 10000;
procedure TForm1.Button1Click( Sender: TObject );
var sl: TStrings; i: integer; t: cardinal;
begin
HourglassOn();
t := GetTickCount();
sl := TStringList.Create;
try
for i := 1 to cMax do
sl.Add(IntToStr(i));
Memo1.Lines.Clear;
Memo1.Lines.AddStrings(sl);
finally
sl.Destroy;
end;
t := GetTickCount - t;
ShowMessage('It took ' + IntoToStr(t) + '/1000 seconds');
end;
procedure TForm2.Button1Click( Sender: TObject );
var i: integer; t: cardinal;
begin
HourglassOn();
t := GetTickCount();
Memo1.Lines.Clear;
for i := 1 to cMax do begin
Memo1.Lines.Add(IntToStr(i));
// giving Windows chance to repaint the memo
// simulating access from extra threads
// when main thread is free to repaint forms time and again
Application.ProcessMessages;
end;
t := GetTickCount - t;
ShowMessage('It took ' + IntoToStr(t) + '/1000 seconds');
end;
So a little draft to test your issues might be like this
http://docwiki.embarcadero.com/Libraries/XE2/en/System.IOUtils.TFile.ReadAllLines
http://www.thedelphigeek.com/2010/06/omnithreadlibrary-20-sneak-preview-1.html
http://www.thedelphigeek.com/2010/11/multistage-processes-with.html
http://otl.17slon.com/book/chap04.html#highlevel-pipeline
Just a draft for you to look into generic approach
const WM_EnumEnded = WM_USER + 1;
type TFrom1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
....
public
var Enums: iOmniBlockingCollection;
procedure StartEnum( const SingleThread: boolean );
procedure ShowResults( var m: TMessage); message WM_EnumEnded;
.....
procedure TFrom1.StartEnum( const SingleThread: boolean );
var hosts: TStringDynArray; // TArray<string>, array of string....
Source: IOmniBlockingCollection;
iWorker: IOmniParallelLoop<T>; // variable only needed for if-then-else
begin
hosts := TFile.ReadAllLines('hosts.txt');
Self.Enums := TOmniBlockingCollection.Create; // Results accumulator
Source := TOmniBlockingCollection.Create;
Source.Add( TOmniValue.FromArray<string>(hosts) );
iWorker := Parallel.ForEach<string>( Source ).NoWait().OnStop(
procedure begin PostMessage( Self.Handle, WM_EnumEnded, 0, 0) end
);
if SingleThread then iWorker := iWorker.NumTasks(1);
iWorker.Execute(
procedure(const value: String)
var i: integer;
begin
....
res:=NetShareEnum(RemoteName, 502 { 503 better ?? } ... );
....
Self.Enums.Add( TOmniValue(String(p^[i].shi502_netname)) );
...
end;
);
end;
procedure TFrom1.ShowResults( var m: TMessage );
var sa: TArray<String>;
begin
Self.Enums.CompleteAdding;
sa := TOmniblockingCollection.ToArray<string>( Self.Enums );
Memo1.Clear;
Memo1.Lines.AddStrings( sa );
end;
procedure TFrom1.Button1Click(sender: Tobject);
begin
StartEnum( True );
end;
procedure TFrom1.Button2Click(sender: Tobject);
begin
StartEnum( False );
end;