Refactor the detailed error messages

Cherry-picked and resolved from c74f2ee

src/ocrmypdf/__main__.py

@@ -599,6 +599,13 @@ def do_ruffus_exception(ruffus_five_tuple, options, log):
         base_exc_name = exc_name.replace('ocrmypdf.exceptions.', '')
         exc_class = getattr(ocrmypdf_exceptions, base_exc_name)
         exit_code = getattr(exc_class, 'exit_code', ExitCode.other_error)
+        try:
+            if isinstance(exc_value, exc_class):
+                exc_msg = str(exc_value)
+            else:
+                exc_msg = str(exc_class())
+        except Exception:
+            exc_msg = "Unknown"
 
     if exc_name in ('builtins.SystemExit', 'SystemExit'):
         match = re.search(r"\.(.+?)\)", exc_value)
@@ -622,34 +629,9 @@ def do_ruffus_exception(ruffus_five_tuple, options, log):
         msg = "Error occurred while running this command:"
         log.error(msg + '\n' + exc_value)
         exit_code = ExitCode.child_process_error
-    elif (exc_name == 'PyPDF2.utils.PdfReadError' and \
-            'not been decrypted' in exc_value) or \
-            (exc_name == 'ocrmypdf.exceptions.EncryptedPdfError'):
-        log.error(textwrap.dedent("""\
-            Input PDF is encrypted. The encryption must be removed to
-            perform OCR.
-
-            For information about this PDF's security use
-                qpdf --show-encryption infilename
-
-            You can remove the encryption using
-                qpdf --decrypt [--password=[password]] infilename
-
-            """))
-    elif exc_name == 'ocrmypdf.exceptions.PdfMergeFailedError':
-        log.error(textwrap.dedent("""\
-            Failed to merge PDF image layer with OCR layer
-
-            Usually this happens because the input PDF file is mal-formed and
-            ocrmypdf cannot automatically correct the problem on its own.
-
-            Try using
-                ocrmypdf --pdf-renderer tesseract  [..other args..]
-            """))
-    elif exc_name == 'ocrmypdf.exceptions.TesseractConfigError':
-        log.error(textwrap.dedent("""\
-            Error occurred while parsing a tesseract configuration file
-            """))
+    elif exc_name.startswith('ocrmypdf.exceptions.'):
+        if exc_msg:
+            log.error(exc_msg)
     elif exc_name == 'PIL.Image.DecompressionBombError':
         msg = cleanup_ruffus_error_message(exc_value)
         msg += ("\nUse the --max-image-mpixels argument to set increase the "

src/ocrmypdf/exceptions.py

@@ -17,6 +17,7 @@
 
 
 from enum import IntEnum
+from textwrap import dedent
 
 class ExitCode(IntEnum):
     ok = 0
@@ -35,6 +36,13 @@ class ExitCode(IntEnum):
 
 class ExitCodeException(Exception):
     exit_code = ExitCode.other_error
+    message = ""
+
+    def __str__(self):
+        super_msg = super().__str__()  # Don't do str(super())
+        if self.message:
+            return self.message.format(super_msg)
+        return super_msg
 
 
 class BadArgsError(ExitCodeException):
@@ -43,7 +51,15 @@ class BadArgsError(ExitCodeException):
 
 class PdfMergeFailedError(ExitCodeException):
     exit_code = ExitCode.input_file
+    message = dedent('''\
+        Failed to merge PDF image layer with OCR layer
 
+        Usually this happens because the input PDF file is malformed and
+        ocrmypdf cannot automatically correct the problem on its own.
+
+        Try using
+            ocrmypdf --pdf-renderer sandwich  [..other args..]
+        ''')
 
 class MissingDependencyError(ExitCodeException):
     exit_code = ExitCode.missing_dependency
@@ -75,7 +91,18 @@ class SubprocessOutputError(ExitCodeException):
 
 class EncryptedPdfError(ExitCodeException):
     exit_code = ExitCode.encrypted_pdf
+    message = dedent('''\
+        Input PDF is encrypted. The encryption must be removed to
+        perform OCR.
+
+        For information about this PDF's security use
+            qpdf --show-encryption infilename
+
+        You can remove the encryption using
+            qpdf --decrypt [--password=[password]] infilename
+        ''')
 
 
 class TesseractConfigError(ExitCodeException):
     exit_code = ExitCode.invalid_config
+    message = "Error occurred while parsing a Tesseract configuration file"