add and implement Queue message

gallery_dl/extractor/message.py

@@ -13,3 +13,4 @@ class Message():
     Url = 3
     Headers = 4
     Cookies = 5
+    Queue = 6

gallery_dl/jobs.py

@@ -20,6 +20,7 @@ class DownloadJob():
             return
         self.directory = self.get_base_directory()
         self.downloaders = {}
+        self.queue = None
         self.filename_fmt = config.get(
             ("extractor", self.extractor.category, "filename"),
             default=self.extractor.filename_fmt
@@ -48,6 +49,9 @@ class DownloadJob():
             elif msg[0] == Message.Directory:
                 self.set_directory(msg)
 
+            elif msg[0] == Message.Queue:
+                self.enqueue(msg[1])
+
             elif msg[0] == Message.Version:
                 if msg[1] != 1:
                     raise "unsupported message-version ({}, {})".format(
@@ -55,6 +59,10 @@ class DownloadJob():
                     )
                 # TODO: support for multiple message versions
 
+        if self.queue:
+            for url in self.queue:
+                DownloadJob(url).run()
+
     def download(self, msg):
         """Download the resource specified in 'msg'"""
         _, url, metadata = msg
@@ -91,6 +99,13 @@ class DownloadJob():
             self.downloaders[scheme] = instance
         return instance
 
+    def enqueue(self, url):
+        """Add url to work-queue"""
+        try:
+            self.queue.append(url)
+        except AttributeError:
+            self.queue = [url]
+
     @staticmethod
     def get_base_directory():
         """Return the base-destination-directory for downloads"""