Correctly identify offending file in multi-decoding error messages, and use Exception.__cause__

Identify the offending file in ZXing CommandLineRunner output requires
parsing some really fugly Java tracebooks, but it addresses the FIXME from
e7974a9 "re-add add multi-decoding".

Also, we should use Exception.__cause__ rather than rolling our own
BarCodeReaderException.underlying.

Author: dlenski

zxing/__init__.py

@@ -10,16 +10,24 @@
 import pathlib
 import re
 import subprocess as sp
+import urllib.parse
 import zipfile
 from enum import Enum
 
 from .version import __version__  # noqa: F401
 
 
+def file_uri_to_path(s):
+    uri = urllib.parse.urlparse(s)
+    if (uri.scheme, uri.netloc, uri.query, uri.fragment) != ('file', '', '', ''):
+        raise ValueError(uri)
+    return urllib.parse.unquote_plus(uri.path)
+
+
 class BarCodeReaderException(Exception):
-    def __init__(self, message, filename=None, underlying=None):
-        self.message, self.filename, self.underlying = message, filename, underlying
-        super().__init__(message, filename, underlying)
+    def __init__(self, message, filename=None):
+        self.message, self.filename = message, filename
+        super().__init__(message, filename)
 
 
 class BarCodeReader(object):
@@ -65,35 +73,40 @@ def decode(self, filenames, try_harder=False, possible_formats=None, pure_barcod
 
         try:
             p = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.STDOUT, universal_newlines=False)
-        except FileNotFoundError as e:
-            raise BarCodeReaderException("Java binary specified (%s) does not exist" % self.java, self.java, e)
-        except PermissionError as e:
-            raise BarCodeReaderException("Java binary specified (%s) is not executable" % self.java, self.java, e)
+        except OSError as e:
+            raise BarCodeReaderException("Could not execute specified Java binary", self.java) from e
         stdout, stderr = p.communicate()
 
         if stdout.startswith((b'Error: Could not find or load main class com.google.zxing.client.j2se.CommandLineRunner',
                               b'Exception in thread "main" java.lang.NoClassDefFoundError:')):
             raise BarCodeReaderException("Java JARs not found in classpath (%s)" % self.classpath, self.classpath)
         elif stdout.startswith((b'''Exception in thread "main" javax.imageio.IIOException: Can't get input stream from URL!''',
                                 b'''Exception in thread "main" java.util.concurrent.ExecutionException: javax.imageio.IIOException: Can't get input stream from URL!''')):
-            raise BarCodeReaderException("Could not find image path: %s" % filenames, filenames)
+            # Find the line that looks like: "Caused by: java.io.FileNotFoundException: $FILENAME ({No such file or directory,Permission denied,*)"
+            fn, err = next((map(bytes.decode, l[42:].rsplit(b' (', 1)) for l in stdout.splitlines() if l.startswith(b"Caused by: java.io.FileNotFoundException: ")), ('', ''))
+            if err == 'No such file or directory)':
+                err = FileNotFoundError(fn)
+            elif err == 'Permission denied)':
+                err = PermissionError(fn)
+            else:
+                err = OSError(err[:-1])
+            raise BarCodeReaderException("Java library could not read image", fn) from err
         elif stdout.startswith(b'''Exception in thread "main" java.io.IOException: Could not load '''):
-            raise BarCodeReaderException("Java library could not read image; is it in a supported format?", filenames)
+            # First line ends with file:// URI
+            fn = file_uri_to_path(stdout.splitlines()[0][63:].decode())
+            raise BarCodeReaderException("Java library could not read image (is it in a supported format?)", fn)
         elif stdout.startswith(b'''Exception '''):
-            raise BarCodeReaderException("Unknown Java exception: %s" % stdout)
+            raise BarCodeReaderException("Unknown Java exception", self.java) from RuntimeError(stdout)
         elif p.returncode:
-            raise BarCodeReaderException("Unexpected Java subprocess return code %d" % p.returncode, self.java)
-
-        if p.returncode:
-            codes = [None for fn in filenames]
-        else:
-            file_results = []
-            for line in stdout.splitlines(True):
-                if line.startswith((b'file:///', b'Exception')):
-                    file_results.append(line)
-                else:
-                    file_results[-1] += line
-            codes = [BarCode.parse(result) for result in file_results]
+            raise BarCodeReaderException("Unexpected Java subprocess return code", self.java) from sp.CalledProcessError(p.returncode, cmd, stdout)
+
+        file_results = []
+        for line in stdout.splitlines(True):
+            if line.startswith((b'file:///', b'Exception')):
+                file_results.append(line)
+            else:
+                file_results[-1] += line
+        codes = [BarCode.parse(result) for result in file_results]
 
         if one_file:
             return codes[0]

zxing/__main__.py

@@ -26,7 +26,7 @@ def main():
         try:
             bc = bcr.decode(fn, try_harder=args.try_harder)
         except BarCodeReaderException as e:
-            p.error(e.message + (('\n\t' + e.filename) if e.filename else ''))
+            p.error(e.message + ((': ' + e.filename) if e.filename else '') + (('\n\tCaused by: ' + repr(e.__cause__) if e.__cause__ else '')))
         if args.csv:
             wr.writerow((fn, bc.format, bc.type, bc.raw, bc.parsed) if bc else (fn, 'ERROR', None, None, None))
         else: