Isolate STEPControl_Reader ReadFile

[lorenzncode]

Interface to OCCT Message

[codecov[bot]]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (153ed3f) 94.48% compared to head (4853b7b) 94.37%.

Files	Patch %	Lines
cadquery/occ_impl/message.py	76.92%	5 Missing and 1 partial :warning:
cadquery/occ_impl/importers/__init__.py	80.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1525 +/- ## ========================================== - Coverage 94.48% 94.37% -0.11% ========================================== Files 28 29 +1 Lines 5780 5813 +33 Branches 1071 1077 +6 ========================================== + Hits 5461 5486 +25 - Misses 193 199 +6 - Partials 126 128 +2 ```

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[lorenzncode]

This would allow to process the STEPControl_Reader object without continuing to import the STEP file for example to extract header info. Another use case might be to abort STEP import if certain alerts or messages are issued on read. There may be other more general purpose OCCT message reporting uses.

import cadquery as cq

report = cq.message.Message.add_report()
reader = cq.importers.readStep("BROKEN_FILE.STEP")
alerts = report.GetAlerts(cq.message.Level.info.value)

if alerts:
    raise ValueError("STEP file read resulted in alerts, skip importStep")
else:
    res = cq.importers.importStep(reader)

import cadquery as cq

def import_step_abort_on_alert(filename, report=None):
    """
    Import STEP
    Abort in case of OCCT alert info messages

    This is NOT guaranteed to eliminate all crashes.
    It is an example based a known corrupted STEP file.  See issue #1521.

    It *might* help filter some problematic STEP files.
    In other cases perhaps trace level messages must be inspected or there 
    may not be any way to know up front whether a STEP file is problematic.
    """

    if report is None:
        report = cq.message.Message.add_report()

    report.Clear(cq.message.Level.info.value)
    reader = cq.importers.readStep(filename)
    alerts = report.GetAlerts(cq.message.Level.info.value)

    if alerts:
        raise ValueError("abort STEP import")
    else:
        res = cq.importers.importStep(reader)

    return res

step_files = ("BROKEN_FILE.STEP", "good.step", "BROKEN_FILE.STEP", "good.step")

report = cq.message.Message.add_report()
for f in step_files:
    try:
        res = import_step_abort_on_alert(f, report)
    except ValueError:
        res = None