Graceful exit on broke step file

[qbamca]

We run Flask app that converts step files to stl for further processing. When we were testing the app we noticed that when supplied with manually broken step file, the cadquery library crash gracefully our Flask app. No Error is raised. We tried catching SystemExit with no avail. The app just stops.
I've traced cadquery inner works up to this point:

at which the reader.TransferRoot(i + 1) closes our app.
I don't know how to trace it further inside OCP, so I can't investigate further.

The problem is that, such files can close our service, we have no means to prevent it and results in service downtimes while it's being restarted.
We need to find a way to prevent it from closing the app.

To Reproduce

repro repo
It's a flask app. Run main.py and post file BROKE_FILE.STEP

Backtrace

no backtrace

Environment

OS:
Ubuntu 22.04.2 LTS
python 3.10.12
cadquery v2.3.1
cadquery is installed using pip.

Using: Python interpreter

[adam-urbanczyk]

I tried loading your step directly via CQ and nothing crashes, but I do get an infinite loop it seems. You'll have to raise an issue with OCCT I'm afraid. Is the STEP actually malicious?

[lorenzncode]

Strange, OCCT Draw shows "Could not read file BROKEN_FILE.step , abandon" this corresponds to readstat != IFSelect_RetDone. I also tried with C++ and again ReadFile returns IFSelect_RetError (tested on OCCT 7.7.2, 7.8.0).

Edit: Ignore this comment. My mistake in testing (typo). Actually I do get the same IFSelect_RetDone status.

[adam-urbanczyk]

Interesting, on win I get an infinite loop with 7.7.1 and a silent crash with 7.7.2.

[lorenzncode]

I can reproduce the crash on linux with CQ and 7.7.2.

OCCT Draw does not crash; it does report ERR messages in the output (7.7.2):

Reduced model for translation without additional info will be used 
**** ERR StepFile : Incorrect Syntax : Fails Count : 1 ****
*** ERR StepReaderData : Unresolved Reference : Fails Count : 15 ***

The same ERR messages are printed with CQ with:

from OCP.Message import Message, Message_Gravity
for printer in Message.DefaultMessenger_s().Printers():
    printer.SetTraceLevel(Message_Gravity.Message_Info)

[qbamca]

I wouldn't call STEP file malicious. We did remove a line or two by hand to simulate the broken file, though.
The errors @lorenzncode mentioned, we've seen them already with files that were uploaded by users but it was in different environment where silent crashes were not a problem and we didn't notice the problem then. My point is, we suspect we might have to deal with such files in production and files broken in any way, should not result in silent crash.

[adam-urbanczyk]

@lorenzncode interesting. I checked with draw from 7.5 I do get an infinite loop of sorts. Draw from 7.8 works fine (I don't have 7.7.2 at hand). Looking quickly at the code of OCCT I was not able to tell how to extract the errors programmatically. Would you know?

[lorenzncode]

@adam-urbanczyk I found the messages can be extracted using Message_PrinterToReport.

import io
from OCP.Message import Message, Message_Gravity, Message_PrinterToReport
from OCP.STEPControl import STEPControl_Reader

msger = Message.DefaultMessenger_s()
newprinter = Message_PrinterToReport()
report = newprinter.Report()
msger.AddPrinter(newprinter)

reader = STEPControl_Reader()
reader.ReadFile("BROKEN_FILE.STEP")

f = io.BytesIO()
alerts = report.GetAlerts(Message_Gravity.Message_Info)
for alert in alerts:
    alert.Attribute().DumpJson(f)

print(f.getvalue())
f.close()

[lorenzncode]

I get the same stacktrace in C++ and Draw with

OSD::SetSignal(OSD_SignalMode_Unset, Standard_False);

No crash with OSD::SetSignal();

In Draw, default is set here:
https://github.com/Open-Cascade-SAS/OCCT/blob/cec1ecd0c9f3b3d2572c47035d11949e8dfa85e2/src/Draw/Draw_BasicCommands.cxx#L1004

[lorenzncode]

I opened an OCCT issue https://tracker.dev.opencascade.org/view.php?id=33603

@qbamca Can you also share the unmodified STEP file? Probably not useful but could see the diff.

[adam-urbanczyk]

@lorenzncode what is the current conclusion regarding CQ? I.e. can we change some settings to mitigate the issue?

[lorenzncode]

@adam-urbanczyk Pending a fix in OCCT itself, yes it would be possible to mitigate the issue in CQ by conditionally aborting importStep based on monitoring the Message_Info level alerts.

The simplest way might be to provide an option to abort on any alert (ignoring the contents of the messages). If we find it results in false positives then it might be required to check for specific messages.

In C++ the issue can be mitigated with OSD::SetSignal(). I don't know if that is possible in OCP?

[dpasukhi]

Thank you for the report.

[dpasukhi]

This kind of issue is not stable. The result is undefined if you will disable catching signals.
And there is no specific message information for that kind of access problem.
If you have any kind of crash, we fix that fast. But for a long time, it happened rarely.
And only on non-correct STEP files.

[lorenzncode]

@dpasukhi Thank you for your inputs!

@adam-urbanczyk Since crashes are expected to be rare perhaps CQ can separate the STEPControl_Reader().ReadFile() part of importStep and let the user implement a safer mode if they need it. This would provide the user the opportunity to monitor messages and decide to proceed with reading the step file. I'll share an example.