[fpc-devel] TProcess and redirection of StdIn/Out (e.g. from/to files)

[Martin Frb]

On 14/12/2023 20:54, Marco van de Voort via fpc-devel wrote:
>
> Op 14-12-2023 om 20:29 schreef Martin Frb via fpc-devel:
>>  Op 14-12-2023 om 17:30 schreef Martin Frb via fpc-devel:
>>>> If I am right the TProcess currently does not allow redirection of 
>>>> StdOut/In to/from a file (or other handle provided).
>>>
>>> It does, if you need a runcommandloop like routine that writes to 
>>> file. Partially this can be even simplified by inheriting TProcess 
>>> and overriding readinputstream
>> But that means the parent process has to read the data (from the 
>> file) and forward it.
>
> Without a shell that always needs to happen. How else ? Keep in mind 
> that TProcess is a kernel and not a shell level concept.

At least on Windows you can give a handle that is to be used as StdIn.

And on Linux that handle is currently setup after the fork event, in the 
new process => and currently it either is a pipe or (I think) a copy of 
the parent stdin. But nothing stops it to be a filehandle.
But afaik StdIn is just a handle. This handle can be a tty (usually if 
there is a shell), but it can be /dev/nil or a file or ...

I am actually pretty sure, on Linux, I can get what I want by doing it 
in the "OnFork" event of TProcess.
But on Windows it is well hidden away in the "Execute" method, nothing 
virtual that could be intercepted.



>
>> Also not sure how to simulate an EOF in that case....
>>
> Probably close the pipe.
>
> Anyway the full project is here: 
> http://www.stack.nl/~marcov/files/processmemodemo.zip
>
> It is slightly different, a TProcess based application that tries to 
> instrument a secondary binary.
>

Thanks, but I consider that a worst case work around.

I'd rather copy the entire TProcess, so I can make a few tiny changes in 
TProcess.Execute.
I already done a proof of concept on win:
- get the handle to the file
- pass it to the WinAPI for creating the process
=> works.

Haven't yet looked at Linux. But should be even easier.

-----

The reason I ask is, that if there is a chance of a future solution in 
FPC, then I like to avoid my own solution now until I can at least do my 
own solution in a compatible manner.
For that I would have to know enough details on that future solution.

Well depending on the amount of changes, I may still do my own 
incompatible....