Get underlying error when conversion fails

When we get an early EOF from the converter process, we should
immediately get the exit code of that process, to find out the actual
underlying error. Currently, the exception we raise masks the underlying
error.

Raise a ConverterProcException, that in turns makes our error handling
code read the exit code of the spawned process, and converts it to a
helpful error message.

Fixes #714

dangerzone/conversion/errors.py

@@ -8,15 +8,6 @@
 MAX_PAGE_HEIGHT = 10000
 
 
-class InterruptedConversionException(Exception):
-    """Data received was less than expected"""
-
-    def __init__(self) -> None:
-        super().__init__(
-            "Something interrupted the conversion and it could not be completed."
-        )
-
-
 class ConverterProcException(Exception):
     """Some exception occurred in the converter"""
 

dangerzone/isolation_provider/base.py

@@ -27,15 +27,15 @@ def read_bytes(f: IO[bytes], size: int, exact: bool = True) -> bytes:
     """Read bytes from a file-like object."""
     buf = f.read(size)
     if exact and len(buf) != size:
-        raise errors.InterruptedConversionException()
+        raise errors.ConverterProcException()
     return buf
 
 
 def read_int(f: IO[bytes]) -> int:
     """Read 2 bytes from a file-like object, and decode them as int."""
     untrusted_int = f.read(INT_BYTES)
     if len(untrusted_int) != INT_BYTES:
-        raise errors.InterruptedConversionException()
+        raise errors.ConverterProcException()
     return int.from_bytes(untrusted_int, "big", signed=False)
 
 

tests/isolation_provider/base.py

@@ -48,7 +48,7 @@ def start_doc_to_pixels_proc() -> subprocess.Popen:
         monkeypatch.setattr(
             provider, "start_doc_to_pixels_proc", start_doc_to_pixels_proc
         )
-        with pytest.raises(errors.InterruptedConversionException):
+        with pytest.raises(errors.ConverterProcException):
             provider.doc_to_pixels(doc, tmpdir)
             assert provider.get_proc_exception(proc) == errors.MaxPagesException  # type: ignore [arg-type]
 

tests/isolation_provider/test_qubes.py

@@ -58,7 +58,7 @@ def start_doc_to_pixels_proc() -> subprocess.Popen:
             provider, "start_doc_to_pixels_proc", start_doc_to_pixels_proc
         )
 
-        with pytest.raises(errors.InterruptedConversionException) as e:
+        with pytest.raises(errors.ConverterProcException) as e:
             doc = Document(sample_doc)
             provider.doc_to_pixels(doc, tmpdir)
             assert provider.get_proc_exception(proc) == errors.QubesQrexecFailed  # type: ignore [arg-type]