[fpc-pascal] Redirecting input to a child process

[Michael Van Canneyt]

On Thu, 19 May 2011, Anton Shepelev wrote:

> Ludo Brands:
>
>> You can file a bug at http://bugs.freepascal.org/.
>
> This is bug #0019325.
>
> ...
> I thought about writing a patch, but it seems that it is not
> enough to modify the implementation of the  Windows-specific
> pipes.inc.
>
> The correct way to create pipes for the three channels (out,
> in and err) on Windows is to create non-inheritable  handles
> and  duplicate  only  the  child process's ends of them into
> inheritable ones, which  means  that  the  CreatePipeHandles
> function  must accept a third parameter indicating which end
> should be inherited: for OUT and ERR channels it will be the
> write-end and for IN -- the read-end.
>
> Here is a possible implementation:
>
> {--------------- changes to pipes.inc -----------------}
> Interface
>   {...}
>   type
>      TDupOpt  = (dupIn, dupOut);
>      TDupOpts = Set of TDupOpt;
>
> Implemenation
>   {...}
>   function DuplicateHandleFP(var handle: THandle): Boolean;
>   var
>      oldHandle: THandle;
>   begin
>      oldHandle := handle;
>      Result := DuplicateHandle
>      (  GetCurrentProcess(),
>         oldHandle,
>         GetCurrentProcess(),
>         @handle,
>         0,
>         true,
>         DUPLICATE_SAME_ACCESS
>      );
>      if Result then
>         Result := CloseHandle(oldHandle);
>   end;
>
>   Function CreatePipeHandles
>   (Var Inhandle,OutHandle : THandle; DupOpts: TDupOpts) : Boolean;
>   begin
>      Result := CreatePipe (Inhandle,OutHandle, at piNonInheritablePipe,0);
>      if Result and (dupIn in DupOpts) then
>         Result := DuplicateHandleFP(Inhandle);
>      if Result and (dupOut in DupOpts) then
>         Result := DuplicateHandleFP(OutHandle);
>   end;
>
>   {----------- process.inc -------------------------}
>   {CreatePipes will have these calls:}
>   begin
>     CreatePipeHandles(SI.hStdInput ,HI, [dupIn ]);
>     CreatePipeHandles(HO,Si.hStdOutput, [dupOut]);
>     if CE then
>       CreatePipeHandles(HE,SI.hStdError, [dupOut])
>   {...}
>
> Unfortunately,  the third parameter will have to be added to
> this  function  in  all  other  platform-specific  pipes.inc
> files, but these will just ignore it and work as before.
>
> If  it is preferable to keep the interface of the pipes unit
> unchanged, the windows-specific part could just be chaged to
> create  non-inheritable  pipes, and the duplication could be
> moved into the windows-specific process.inc.
>
> Will you accept one of such patches?

Yes.

The interface of the pipes unit can be changed with a parameter with 
a default value, so existing code continues to work.

Michael.