TProcess EOF - CloseInput
lazarus / 66-Unix

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Snify · 2022-02-23 14:37

Hello together

I have the following function to "read" a regular string from stdin:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetStdIn: string;var   tmp: string;begin  result := '';  while not EOF
do begin    readln (tmp);    if EOF then begin      result:= result +
tmp;    end else begin      result:= result + tmp + LineEnding;   
end;  end;end;   
The full test program looks like this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i begin 
writeln (StdErr, 'FIRST ERROR LINE');  writeln ('This line and the
following stdin detection is on stdout');  writeln ('Stdin was:',
LineEnding, GetStdIn);  writeln (StdErr, 'This is on stderror'); 
writeln ('Regular stdout again');  // end of programend.             
                
I am not sure if my function is correct.
This works like a charm if I use the above function in a shell like
this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i printf
"row1\nrow2\n..." | ./project1

However when I use the TProcess Class with the WriteInput Method, the
process locks.

This is what I use to execute my program and try to read and write to
the pipes:
(some of the code is taken from
https://wiki.freepascal.org/Executing_External_Programs)


Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i MyProcess 
            := TProcess.Create(NIL);    MyProcess.Executable    :=
'project1'; // the program with the "GetStdIn"
functionMyProcess.Options               := MyProcess.Options +
[poPassInput, poUsePipes];MyProcess.Execute;mystring                 
             := 'Hello Lazarus';MyProcess.Input.Write(mystring[1],
Length(mystring));MyProcess.CloseInput; // does not trigger EOF?! //
NumBytesAvailable is always 0 for output and stderrwhile
MyProcess.Running or (MyProcess.Output.NumBytesAvailable > 0)
or(MyProcess.Stderr.NumBytesAvailable > 0) dobegin    while
MyProcess.Output.NumBytesAvailable > 0 do    begin        ReadCount :=
Min(512, MyProcess.Output.NumBytesAvailable); //Read up to buffer, not
more        MyProcess.Output.Read(CharBuffer, ReadCount);    end;    
                                while
MyProcess.Stderr.NumBytesAvailable > 0 do    begin        ReadCount :=
Min(512, MyProcess.Stderr.NumBytesAvailable); //Read up to buffer, not
more        MyProcess.Stderr.Read(CharBuffer, ReadCount);   
end;end;MyProcess.Free;                                              
                                
The binary path etc. is simplified here and executes just as it should
be.
If I remove the whole stdin stuff, it works just fine.

Can someone spot my error?

Thank you in advance

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Snify · 2022-02-23 14:54

I just figured out the problem.
Thank you.

I needed to avoid "poPassInput".
This causes to use the stdin from the "parent" process instead of it's
own stdin.