Is there a way to execute only code from a unit from a big exe placed on shared drive?

Question

I admit i am in the dirty tricks area in this question.

PROBLEM: exe is deployed on shared folder(I call it ShaExe from now on), without changing deployment rules somehow I want to cache the file locally (I call it LocExe fromnow on) and while launching ShaExe i finally end up running LocExe. LocExe must be updated (copied from ShaExe) everytime ShaExe is modified (=updated).

Somehow what I am researching is setting up something like this:

Prerequisite: LocExe path is an user\AppData\Local\MyApp harcoded path so ShaExe knows where LocExe is.

1. ShaExe is launched

2. ShaExe compares its size with the size of LocExe, if different it copies ShaExe over LocExe

3. ShaExe executes LocExe with the -skiplauncher command line parameter

4. ShaExe terminates itself

when -skiplauncher is used points 2 3 4 of the above list are not executed (this is to avoid an endless loop of executing LocExe and terminating the applcation)

Now this approach works, but the bottleneck is (1) because ShaExe size is 110MB so somehow launching an exe from shared path takes time (Even if I do not use the flag {$SetPEFlags IMAGE_FILE_NET_RUN_FROM_SWAP}).

I tried to prepare a very small version of ShaExe (basically built without units but only with the launcher logic in it ending up in 6MB of exe).

WIth this "light but useless ShaExe" the whole process is faster.

I would like that (2) (3) and (4) are executed immediately, is this possible or not with Windows?

I am perfectly aware the best practice would be either to copy manually the file locally and run it or create a simple launcher exe that does the job of running LocExe doing the cache when necessary, but I have a very big customer that requires me to do this without changing the deployment procedure.

THis is why I ask for expert advice here.

This is my code (of course simplified, instead of Unit1 imagine 100 units):

//this is the dpr
program MYProgram;

uses
  Vcl.Forms,
  execache in 'execache.pas',
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  RunCachedExe;
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

//this is the execache unit
unit execache;

interface

uses
  Vcl.Forms,
  Windows,
  ShellAPi,
  sysutils,
  dialogs,
  system.IOUtils;

  procedure RunCachedExe;

implementation

procedure RunCachedExe;

function GetFileSize(const aFilename: String): Int64;
  var
    info: TWin32FileAttributeData;
  begin
    result := -1;
    if NOT GetFileAttributesEx(PWideChar(aFileName), GetFileExInfoStandard, @info) then
      EXIT;
    result := Int64(info.nFileSizeLow) or Int64(info.nFileSizeHigh shl 32);
  end;

var
  CurrentInstanceSize, CachedFileSize, i: integer;
  CachedFilePath, Outs: string;
  SkipLauncher: Boolean;
begin
  SkipLauncher := False;
  for i := 0 to paramcount -1 do
    begin
      if Paramstr(i) = '-SkipLauncher' then
        SkipLauncher := True;
    end;
  if not SkipLauncher then
  begin
    // in this code path is hardcoded, in real life I use a function that calls:
    // SHGetSpecialFolderPath with CSIDL_LOCAL_APPDATA
     CachedFilePath := 'C:\Users\myuser\AppData\Local\MyProject\bincache\MyProject.exe';
     CurrentInstanceSize := GetFileSize(Application.ExeName);
     // this will return -1 if file not found
     CachedFileSize := GetFileSize (CachedFilePath);
     if CachedFileSize <> CurrentInstanceSize then
     begin
       ForceDirectories('C:\Users\myuser\AppData\Local\MyProject\bincache\');
       CopyFile(PChar(Application.ExeName), PCHar(CachedFilePath), False);
     end;
     // launch local exe and close this one
     ShellExecute (0, 'open', PWideChar( CachedFilePath ), PWideChar('-SkipLauncher'), nil, SW_SHOWNORMAL);
     Application.Terminate;
  end;
end;

This code uses some functions from other units but I could move all in the execache unit, if this could help to speed up the execution of the exe.

Somehow I would like to run only an initialization part, containing the logic described here and then terminate the app (when ShaExe is in place, that basically means when -skipLauncher is not used).

So, is it possible to run only an initialization logic of a big exe file?

I hope I expressed myself, thanks.

Answer 1

Regardless of the code you have, what you are essentially asking is if partially loading an executable is possible, to have it conditionally execute only a portion of the code it contains. Or a streaming executable perhaps? These are not possible, the OS will have to fetch the entire runtime from the remote location, together with any static dependencies, to the local computer. Even if the executable is to exit immediately.

You can have the behavior you want by separating the conditional part to a different executable though: a launcher. Without any VCL dependency you can have it really small. Even then, the better alternative is to run the executable locally to have it check if a remote location contains an updated version, since networked access is more prone to performance and security issues.