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

@@ -8,21 +8,11 @@ MAX_PAGE_WIDTH = 10000
 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"""
 
-    def __init__(self, proc: subprocess.Popen) -> None:
-        self.proc = proc
-        super().__init__()
+    def __init__(self) -> None:
+        super().__init__("The process spawned for the conversion has exited early")
 
 
 class ConversionException(Exception):

dangerzone/isolation_provider/base.py

@@ -27,7 +27,7 @@ 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
 
 
@@ -35,7 +35,7 @@ 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)
 
 
@@ -80,7 +80,7 @@ class IsolationProvider(ABC):
             if document.archive_after_conversion:
                 document.archive()
         except errors.ConverterProcException as e:
-            exception = self.get_proc_exception(e.proc)
+            exception = self.get_proc_exception(conversion_proc)
             self.print_progress(document, True, str(exception), 0)
             document.mark_as_failed()
         except errors.ConversionException as e:
@@ -103,7 +103,7 @@ class IsolationProvider(ABC):
                 p.stdin.write(f.read())
                 p.stdin.close()
             except BrokenPipeError as e:
-                raise errors.ConverterProcException(p)
+                raise errors.ConverterProcException()
 
             assert p.stdout
             n_pages = read_int(p.stdout)

tests/isolation_provider/base.py

@@ -48,7 +48,7 @@ class IsolationProviderTest:
         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 @@ class TestQubes(IsolationProviderTest):
             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]