When shortening filepaths to conform to windows path length limitations, remove text from the middle of each component instead of the ends. Fix #8451 (Error Communicating with Device).

src/calibre/devices/prs505/driver.py

@@ -98,6 +98,9 @@ class PRS505(USBMS):
 
     THUMBNAIL_HEIGHT = 200
 
+    MAX_PATH_LEN = 201 # 250 - (max(len(CACHE_THUMBNAIL), len(MEDIA_THUMBNAIL)) +
+                       # len('main_thumbnail.jpg') + 1)
+
     def windows_filter_pnp_id(self, pnp_id):
         return '_LAUNCHER' in pnp_id
 
@@ -201,10 +204,13 @@ class PRS505(USBMS):
                                 self._card_b_prefix if idx == 2 \
                                     else self._main_prefix
                 for book in bl:
-                    p = os.path.join(prefix, book.lpath)
-                    self._upload_cover(os.path.dirname(p),
-                                      os.path.splitext(os.path.basename(p))[0],
-                                      book, p)
+                    try:
+                        p = os.path.join(prefix, book.lpath)
+                        self._upload_cover(os.path.dirname(p),
+                                          os.path.splitext(os.path.basename(p))[0],
+                                          book, p)
+                    except:
+                        debug_print('FAILED to upload cover', p)
         else:
             debug_print('PRS505: NOT uploading covers in sync_booklists')
 
@@ -232,8 +238,7 @@ class PRS505(USBMS):
         try:
             self._upload_cover(path, filename, metadata, filepath)
         except:
-            import traceback
-            traceback.print_exc()
+            debug_print('FAILED to upload cover', filepath)
 
     def _upload_cover(self, path, filename, metadata, filepath):
         if metadata.thumbnail and metadata.thumbnail[-1]:

src/calibre/devices/usbms/device.py

@@ -98,6 +98,9 @@ class Device(DeviceConfig, DevicePlugin):
     # copy these back to the library
     BACKLOADING_ERROR_MESSAGE = None
 
+    #: The maximum length of paths created on the device
+    MAX_PATH_LEN = 250
+
     def reset(self, key='-1', log_packets=False, report_progress=None,
             detected_device=None):
         self._main_prefix = self._card_a_prefix = self._card_b_prefix = None
@@ -875,7 +878,7 @@ class Device(DeviceConfig, DevicePlugin):
 
     def create_upload_path(self, path, mdata, fname, create_dirs=True):
         path = os.path.abspath(path)
-        extra_components = []
+        maxlen = self.MAX_PATH_LEN
 
         special_tag = None
         if mdata.tags:
@@ -902,7 +905,7 @@ class Device(DeviceConfig, DevicePlugin):
         app_id = str(getattr(mdata, 'application_id', ''))
         # The db id will be in the created filename
         extra_components = get_components(template, mdata, fname,
-                timefmt=opts.send_timefmt, length=250-len(app_id)-1)
+                timefmt=opts.send_timefmt, length=maxlen-len(app_id)-1)
         if not extra_components:
             extra_components.append(sanitize(self.filename_callback(fname,
                 mdata)))
@@ -937,12 +940,11 @@ class Device(DeviceConfig, DevicePlugin):
             return ans
 
         extra_components = list(map(remove_trailing_periods, extra_components))
-        components = shorten_components_to(250 - len(path), extra_components)
+        components = shorten_components_to(maxlen - len(path), extra_components)
         components = self.sanitize_path_components(components)
         filepath = os.path.join(path, *components)
         filedir = os.path.dirname(filepath)
 
-
         if create_dirs and not os.path.exists(filedir):
             os.makedirs(filedir)
 

src/calibre/gui2/custom_column_widgets.py

@@ -599,7 +599,7 @@ class BulkEnumeration(BulkBase, Enumeration):
         value = None
         ret_value = None
         dialog_shown = False
-        for book_id in book_ids:
+        for i,book_id in enumerate(book_ids):
             val = self.db.get_custom(book_id, num=self.col_id, index_is_id=True)
             if val and val not in self.col_metadata['display']['enum_values']:
                 if not dialog_shown:
@@ -610,7 +610,7 @@ class BulkEnumeration(BulkBase, Enumeration):
                             show=True, show_copy_button=False)
                     dialog_shown = True
                 ret_value = ' nochange '
-            elif value is not None and value != val:
+            elif (value is not None and value != val) or (val and i != 0):
                 ret_value = ' nochange '
             value = val
         if ret_value is None:

src/calibre/utils/filenames.py

@@ -42,30 +42,44 @@ def supports_long_names(path):
     else:
         return True
 
-def shorten_components_to(length, components):
+def shorten_component(s, by_what):
+    l = len(s)
+    if l < by_what:
+        return s
+    l = (l - by_what)//2
+    if l <= 0:
+        return s
+    return s[:l] + s[-l:]
+
+def shorten_components_to(length, components, more_to_take=0):
     filepath = os.sep.join(components)
-    extra = len(filepath) - length
+    extra = len(filepath) - (length - more_to_take)
     if extra < 1:
         return components
-    delta = int(ceil(extra/float(len(components))))
-    ans = []
+    deltas = []
     for x in components:
+        pct = len(x)/float(len(filepath))
+        deltas.append(int(ceil(pct*extra)))
+    ans = []
+
+    for i, x in enumerate(components):
+        delta = deltas[i]
         if delta > len(x):
             r = x[0] if x is components[-1] else ''
         else:
             if x is components[-1]:
                 b, e = os.path.splitext(x)
                 if e == '.': e = ''
-                r = b[:-delta]+e
+                r = shorten_component(b, delta)+e
                 if r.startswith('.'): r = x[0]+r
             else:
-                r = x[:-delta]
+                r = shorten_component(x, delta)
             r = r.strip()
             if not r:
                 r = x.strip()[0] if x.strip() else 'x'
         ans.append(r)
     if len(os.sep.join(ans)) > length:
-        return shorten_components_to(length, ans)
+        return shorten_components_to(length, components, more_to_take+2)
     return ans
 
 def find_executable_in_path(name, path=None):