emit log messages on download failure

and when retrying with fallback URLs

gallery_dl/job.py

@@ -155,14 +155,20 @@ class DownloadJob(Job):
     def handle_url(self, url, keywords):
         """Download the resource specified in 'url'"""
         if self._prepare_download(keywords):
-            self.get_downloader(url).download(url, self.pathfmt)
+            dlobj = self.get_downloader(url)
+            if not dlobj.download(url, self.pathfmt):
+                self._report_failure(dlobj)
 
     def handle_urllist(self, urls, keywords):
         """Download the resource specified in 'url'"""
         if self._prepare_download(keywords):
-            for url in urls:
-                if self.get_downloader(url).download(url, self.pathfmt):
+            for num, url in enumerate(urls):
+                dlobj = self.get_downloader(url)
+                if num:
+                    dlobj.log.info("Trying fallback URL #%d", num)
+                if dlobj.download(url, self.pathfmt):
                     return
+            self._report_failure(dlobj)
 
     def handle_directory(self, keywords):
         """Set and create the target directory for downloads"""
@@ -199,6 +205,9 @@ class DownloadJob(Job):
             time.sleep(self.sleep)
         return True
 
+    def _report_failure(self, dlobj):
+        dlobj.log.error("Failed to download %s", self.pathfmt.filename)
+
 
 class KeywordJob(Job):
     """Print available keywords"""

gallery_dl/util.py

@@ -352,6 +352,7 @@ class PathFormat():
 
         self.has_extension = False
         self.keywords = {}
+        self.filename = ""
         self.directory = self.realdirectory = ""
         self.path = self.realpath = self.partpath = ""
 
@@ -419,12 +420,12 @@ class PathFormat():
     def build_path(self):
         """Use filename-keywords and directory to build a full path"""
         try:
-            filename = text.clean_path(
+            self.filename = text.clean_path(
                 self.formatter.vformat(self.filename_fmt, self.keywords))
         except Exception as exc:
             raise exception.FormatError(exc, "filename")
 
-        filename = os.sep + filename
+        filename = os.sep + self.filename
         self.path = self.directory + filename
         self.realpath = self.realdirectory + filename