[SOLVED] how to debug a CGI from Lazarus
lazarus / 38-Networking and Web Programming

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nomorelogic · 2023-12-07 17:40

Hi all

I'd like to simulate the invocation of a cgi from Lazarus IDE
this to be able to use the integrated debugger

I already know that a cgi must read from environment variables
this is valid for GET method and here all goes fine
but the content of the POST request (parameter -d in curl) is passed
to the cgi using standard input

in Lazarus IDE there is already the possibility to set environment
variables (i am referring to the menu: run -> run parameters ->
environment)

but I have no idea how to set in the run parameters something
equivalent to:
mycgi.pas < input

is there any workaround?

thanks
nomorelogic

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Martin_fr · 2023-12-07 19:23

Unfortunately that is currently not possible. There is already an
issue about it:
https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/40458

Well, you could probably us the "GDB Gnu remote debugger (gdbserver)"
backend.
Then you have to start your exe outside the IDE, inside the gdbserver
tool. And there you probably (not tested) can apply input
redirection).
Then start the debugger and it should connect to the gdbserver.
(gdbserver will pause your app on start, until the IDE connects)
I am not sure of the exact steps. It is ages ago since I even looked
at that.

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toby · 2023-12-07 21:56

what about ?

pgm "`cat cx.txt`" 

deal with what is in file cx.txt in the pgm as paramstr 1

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Martin_fr · 2023-12-07 22:29

Quote from: toby on December 07, 2023, 10:56:02 pmwhat about ?

pgm "`cat cx.txt`" 

deal with what is in file cx.txt in the pgm as paramstr 1

That will work in a shell. But if the IDE (the debugger) starts the
exe, then shell stuff doesn't happen.

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nomorelogic · 2023-12-12 12:27

Quote from: Martin_fr on December 07, 2023, 11:29:31 pmQuote from:
toby on December 07, 2023, 10:56:02 pmwhat about ?

pgm "`cat cx.txt`" 

deal with what is in file cx.txt in the pgm as paramstr 1

That will work in a shell. But if the IDE (the debugger) starts the
exe, then shell stuff doesn't happen.

question:
is it for the same reason that if I use the REQUEST_METHOD environment
variable set to GET, the debugger works correctly
whereas if I set it to POST it crashes on the Run statement?

follow example code

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
#!/usr/bin/instantfpcprogram TestCgi;{$mode objfpc}{$H+} uses 
Classes,  SysUtils,  httpDefs,  fpweb,  custweb,  custcgi, 
webutil; type  TMyCGIHandler = class(TCgiHandler)  public    procedure
HandleRequest(ARequest: Trequest; AResponse: TResponse); override; 
end;    TMyCGIApp = class(TCustomCGIApplication)  protected   
function InitializeWebHandler: TWebHandler; override;  end;   
procedure TMyCGIHandler.HandleRequest(ARequest: Trequest; AResponse:
TResponse);     procedure AddNV(const N, V: string);    begin     
AResponse.Contents.Add('<TR><TD>' + N + '</TD><TD>' + V +
'</TD></TR>');    end;   var    I, P: integer;    N, V: string; 
begin    with AResponse.Contents do    begin      BeginUpdate;     
try        Add('<HTML><TITLE>FPC CGI Test page</TITLE><BODY>');      
Add('<H1>Hello world</H1>');        DumpRequest(ARequest,
AResponse.Contents);        Add('<H1>CGI environment:</H1>');       
Add('<TABLE BORDER="1">');       
Add('<TR><TD>Name</TD><TD>Value</TD></TR>');        for I := 1 to
GetEnvironmentVariableCount do        begin          V :=
GetEnvironmentString(i);          P := Pos('=', V);          N :=
Copy(V, 1, P - 1);          system.Delete(V, 1, P);          AddNV(N,
V);        end;        Add('</TABLE>');        Add('</BODY></HTML>'); 
    finally        EndUpdate;      end;    end;  end;    function
TMyCGIApp.InitializeWebHandler: TWebHandler;  begin    Result :=
TMyCgiHandler.Create(self);  end;  begin  with TMyCGIApp.Create(nil)
do  try    Initialize;    Run;  finally    Free;  end;end.

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Martin_fr · 2023-12-12 12:49

Quote from: nomorelogic on December 12, 2023, 01:27:17 pmQuote from:
Martin_fr on December 07, 2023, 11:29:31 pmThat will work in a shell.
But if the IDE (the debugger) starts the exe, then shell stuff doesn't
happen.

question:
is it for the same reason that if I use the REQUEST_METHOD environment
variable set to GET, the debugger works correctly
whereas if I set it to POST it crashes on the Run statement?

Not sure about your question.
First of all, what crashes, the debugger or your app in the debugger?

But anyway, about the differences between running outside or inside
the IDE (or inside an http server)

If you give a shell the command-line
Code: Text  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i ./myapp
--data=~/data.txt >/tmp/log.txt
The shell will translate this. The shell will replace ~ with your home
dir.
The shell will open the file /tmp/log.txt and set stdout to it.

Your app gets executed with the param "--data=/home/username/data.txt"
and it gets a handle for stdout.

The http server also set stdout, and it does set additional
environment.

---
The debugger does not translate "~".
And the debugger does not set stdout/stdin

The only thing the debugger currently does is set environment, if you
specify it.


Quotefollow example code

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
#!/usr/bin/instantfpcprogram TestCgi; 
"instantfpc" doesn't matter to the debugger => you must have compiled
the code, or set up the IDE to have it compiled before the debugger
starts.

Another difference here.

A shell will look into the file, and recognize it starts with #!.
The shell will then call
  /usr/bin/instantfpc  the_file

The debugger will not do that. It expects an executable binary (with
machine code in it).


Actually about stdin/stdout

Go to Tools > Options > Debugger > Backend
and choose "Gdb GNU debugger"
==> I think this should set up your stdin, if in "run parameters" you
specify " <somefile "


What is planned....

* stdin/stdout
There is an open issue, and plans to implement stdin/stdout
redirection to work with FpDebug.

That does not include piping between commands like "echo 123 |
yourapp"


* ~  (and others)
Not planned (Though the ~ would be trivial)

* #!
Not planned
At least not from the debuggers perspective. If someone implements
that on the IDE side, so it would be done before the debugger gets
involved, .... But I have no knowledge that anyone is looking at it.

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nomorelogic · 2023-12-13 08:32

thank you for your attention and answers
really appreciated

regarding what I called "crash" above:
Lazarus debugging works fine with InstantFpc projects: it simply
ignores the initial shebang and then treats the project like any
pascal project.
However, when I set REQUEST_METHOD = POST (or PUT) in the environment
variables and proceed with debugging, when execution is paused on the
'Run' instruction (line 75 of the code above) and I then proceed with
'Step Into' or 'Step Over', the debugger and the IDE freeze and
control will not return until the debugger is stopped manually.
I get the idea that at that moment the debugger waits for input that
will never arrive. Of course, I do not know if this impression is
correct.

On the other hand, when I start the debugger with REQUEST_METHOD =
GET, I don't encounter any problems: everything works perfectly.

As soon as possible I will try "Gdb GNU debugger" as suggested.

Thanks again.

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MarkMLl · 2023-12-13 09:37

Quote from: nomorelogic on December 13, 2023, 09:32:10 amAs soon as
possible I will try "Gdb GNU debugger" as suggested.

Note that Martin specifically suggested the *Remote* debugger. I've
used this in the past for various things, but there's a bit of a
question mark over it now that the IDE is moving to fpDebug.

Alternatively, have you tried starting your program as normal and then
getting the IDE to attach the debugger to it?

What OS etc. are you running? To what extent does the web server
require elevated privilege?

MarkMLl

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Martin_fr · 2023-12-13 09:44

Quote from: MarkMLl on December 13, 2023, 10:37:40 amQuote from:
nomorelogic on December 13, 2023, 09:32:10 amAs soon as possible I
will try "Gdb GNU debugger" as suggested.

Note that Martin specifically suggested the *Remote* debugger. I've
used this in the past for various things, but there's a bit of a
question mark over it now that the IDE is moving to fpDebug.

With regards to setting a redirected stdin => the normal gdb debugger
should be enough. (at least with the gdb version I tested on Windows.

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Martin_fr · 2023-12-13 10:11

As MarkMLI asked: What OS are you using?

Quote from: nomorelogic on December 13, 2023, 09:32:10 amregarding
what I called "crash" above:
Lazarus debugging works fine with InstantFpc projects: it simply
ignores the initial shebang and then treats the project like any
pascal project.
However, when I set REQUEST_METHOD = POST (or PUT) in the environment
variables and proceed with debugging, when execution is paused on the
'Run' instruction (line 75 of the code above) and I then proceed with
'Step Into' or 'Step Over', the debugger and the IDE freeze and
control will not return until the debugger is stopped manually.
I get the idea that at that moment the debugger waits for input that
will never arrive. Of course, I do not know if this impression is
correct.

To me "the IDE freeze" would mean that you can't even move the caret
in the source editor anymore. You can't use any menus, and do nothing
with the IDE?

Because I just tested your project, and my IDE kept working (then
again, I am using the latest version 3.99 / but 3.0 RC should be the
same)

As for the app, yes it waits forever. The CGI will want to read the
STDIN until EOF. But its connected to the "View > Debug Windows >
Console in/output", which delivers keystrokes from the keyboard (if
focused). And which never gets to EOL.
Hence yes, your CGI app will wait forever.

But I also checked: Using "gdb" I could supply a command line ("run
parameters"):  </home/name/somefile.txt
And then your app would process it, and print some html.

Mind that I entered </home/name  and not <~/somefile => because ~ will
not work.

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nomorelogic · 2023-12-13 14:16

@MarkMLl
I am working under Linux Devuan and use Apache as my web server.


@Martin_fr
I expressed myself wrongly, the ide works as you described, it is the
debugging that freezes
in the sense that it is perpetually waiting.

I tried with gdb and putting in the "run parameters" an input file
like: /home/user/testdata.dat
the debugger works even with POST!

I thank everyone!