Detect running 7zip on a currupted iso as well as the lack of 7z

executable.
Remove repeated call to _7zip.list_iso(iso_link)
Adjusted line breaking to fit within 80 columns.

scripts/_7zip.py

@@ -61,7 +61,7 @@ def extract_iso(src, dst, pattern=None, suppress_out=True):
         subprocess.call(_cmd, stdin=devnull, stdout=devnull, stderr=devnull, shell=True)
 
 
-def list_iso(iso_link, suppress_out=True):
+def list_iso(iso_link, suppress_out=True, expose_exception=False):
     """
     List the content of ISO files. It does'nt work with non 'utf' characters (simply ignores them).
     :param iso_link:Path to ISO link
@@ -85,6 +85,8 @@ def list_iso(iso_link, suppress_out=True):
                                                shell=True).decode('utf-8', 'ignore').splitlines()
         except Exception as e:
             gen.log(e)
+            if expose_exception:
+                raise
             _cmd_out = ''
         for line in _cmd_out:
             if '...' in line:

scripts/distro.py

@@ -15,7 +15,7 @@ from .gen import *
 from . import _7zip
 
 
-def distro(iso_cfg_ext_dir, iso_link):
+def distro(iso_cfg_ext_dir, iso_link, expose_exception=False):
     """
     Detect if distro is supported by multibootusb.
     :param iso_cfg_ext_dir: Directory where *.cfg files are extracted.
@@ -23,7 +23,7 @@ def distro(iso_cfg_ext_dir, iso_link):
     """
 #     iso9660fs = ISO9660(iso_link)
 #     iso_file_list = iso9660fs.readDir("/")
-    iso_file_list = _7zip.list_iso(iso_link)
+    iso_file_list = _7zip.list_iso(iso_link, expose_exception=expose_exception)
     if platform.system() == "Linux" or platform.system() == "Windows":
         for path, subdirs, files in os.walk(iso_cfg_ext_dir):
             for name in files:
@@ -146,7 +146,7 @@ def distro(iso_cfg_ext_dir, iso_link):
                         elif re.search(r'BOOT_IMAGE=insert', string, re.I):
                             return 'insert'
 
-        distro = detect_iso_from_file_list(iso_link)
+        distro = detect_iso_from_file_list(iso_link, iso_file_list)
 
         if distro:
             return distro
@@ -166,13 +166,12 @@ def distro(iso_cfg_ext_dir, iso_link):
             return None
 
 
-def detect_iso_from_file_list(iso_link):
+def detect_iso_from_file_list(iso_link, iso_file_list):
     """
     Fallback detection script from the content of an ISO.
     :return: supported distro as string
     """
     if os.path.exists(iso_link):
-        iso_file_list = _7zip.list_iso(iso_link)
         if any("sources" in s.lower() for s in iso_file_list) and any("boot.wim" in s.lower() for s in iso_file_list):
             return "Windows"
         elif any("config.isoclient" in s.lower() for s in iso_file_list):

scripts/mbusb_gui.py

@@ -208,14 +208,16 @@ Are you SURE you want to enable it?",
     def browse_iso(self):
         if str(self.ui.image_path.text()):
             self.ui.image_path.clear()
-        preference_file_path = os.path.join(multibootusb_host_dir(), "preference", "iso_dir.txt")
+        preference_file_path = os.path.join(multibootusb_host_dir(),
+                                            "preference", "iso_dir.txt")
         dir_path = ''
         if os.path.exists(preference_file_path):
             dir_path = open(preference_file_path, 'r').read()
 
-        config.image_path = QtWidgets.QFileDialog.getOpenFileName(self, 'Select an iso...', dir_path,
+        config.image_path = QtWidgets.QFileDialog.getOpenFileName(
-                                                                  'ISO Files (*.iso);; Zip Files(*.zip);; '
+            self, 'Select an iso...', dir_path,
-                                                                  'Img Files(*.img);; All Files(*.*)')[0]
+            'ISO Files (*.iso);; Zip Files(*.zip);; '
+            'Img Files(*.img);; All Files(*.*)')[0]
 
         if config.image_path:
             # sanity checks
@@ -223,20 +225,38 @@ Are you SURE you want to enable it?",
                 QtWidgets.QMessageBox.critical(
                     self,
                     "ISO Not readable",
-                    "Sorry, the file \"{0}\" is not readable.".format(config.image_path)
+                    "Sorry, the file \"{0}\" is not readable.".format(
+                        config.image_path)
                 )
                 return
             if iso_size(config.image_path) == 0:
                 QtWidgets.QMessageBox.critical(
                     self,
                     "ISO is an empty file",
-                    "Sorry, the file \"{0}\" contains no data.".format(config.image_path)
+                    "Sorry, the file \"{0}\" contains no data.".format(
+                        config.image_path)
                 )
                 return
-
             default_dir_path = os.path.dirname(config.image_path)
             gen.write_to_file(preference_file_path, default_dir_path)
 
+            # Detect supported distro
+            try:
+                clean_iso_cfg_ext_dir(   # Need to be cleaned.
+                    os.path.join(multibootusb_host_dir(), "iso_cfg_ext_dir"))
+                extract_cfg_file(config.image_path)
+                config.distro = distro(iso_cfg_ext_dir(), config.image_path,
+                                       expose_exception=True)
+            except Exception as exc:
+                QtWidgets.QMessageBox.critical(
+                    self,
+                    "Failure to detect distro type",
+                    'Sorry, failed in examining "{0}" to detect distro type '
+                    'due to the following reason.\n\n"{1}".'
+                    .format(config.image_path, exc)
+                )
+                return
+
             if platform.system() == "Windows":
                 if "/" in config.image_path:
                     config.image_path = config.image_path.strip().replace("/", "\\")
@@ -248,9 +268,6 @@ Are you SURE you want to enable it?",
             self.ui.label_image_bootable_value.setVisible(True)
 
             if os.path.exists(config.image_path):
-                clean_iso_cfg_ext_dir(os.path.join(multibootusb_host_dir(), "iso_cfg_ext_dir"))  # Need to be cleaned.
-                extract_cfg_file(config.image_path)
-                config.distro = distro(iso_cfg_ext_dir(), config.image_path)  # Detect supported distro
                 self.ui.label_image_type_value.setText(str(config.distro))
                 self.ui.label_image_type_value.setVisible(True)
                 if config.distro: