[danbooru] add 'external' option (closes #1747)

docs/configuration.rst

@@ -806,17 +806,15 @@ Description
     Download embedded videos hosted on https://www.blogger.com/
 
 
-extractor.danbooru.ugoira
--------------------------
+extractor.danbooru.external
+---------------------------
 Type
     ``bool``
 Default
     ``false``
 Description
-    Controls the download target for Ugoira posts.
-
-    * ``true``: Original ZIP archives
-    * ``false``: Converted video files
+    For unavailable or restricted posts,
+    follow the ``source`` and download from there if possible.
 
 
 extractor.danbooru.metadata
@@ -831,6 +829,19 @@ Description
     Note: This requires 1 additional HTTP request for each post.
 
 
+extractor.danbooru.ugoira
+-------------------------
+Type
+    ``bool``
+Default
+    ``false``
+Description
+    Controls the download target for Ugoira posts.
+
+    * ``true``: Original ZIP archives
+    * ``false``: Converted video files
+
+
 extractor.derpibooru.api-key
 ----------------------------
 Type

docs/gallery-dl.conf

@@ -52,8 +52,9 @@
         {
             "username": null,
             "password": null,
-            "ugoira": false,
-            "metadata": false
+            "external": false,
+            "metadata": false,
+            "ugoira": false
         },
         "derpibooru":
         {

gallery_dl/extractor/danbooru.py

@@ -32,6 +32,7 @@ class DanbooruExtractor(Extractor):
         super().__init__(match)
         self.root = "https://{}.donmai.us".format(match.group(1))
         self.ugoira = self.config("ugoira", False)
+        self.external = self.config("external", False)
         self.extended_metadata = self.config("metadata", False)
 
         username, api_key = self._get_auth_info()
@@ -52,6 +53,10 @@ class DanbooruExtractor(Extractor):
             try:
                 url = post["file_url"]
             except KeyError:
+                if self.external and post["source"]:
+                    post.update(data)
+                    yield Message.Directory, post
+                    yield Message.Queue, post["source"], post
                 continue
 
             text.nameext_from_url(url, post)
@@ -126,6 +131,11 @@ class DanbooruTagExtractor(DanbooruExtractor):
         ("https://danbooru.donmai.us/posts?tags=mushishi", {
             "count": ">= 300",
         }),
+        # 'external' option (#1747)
+        ("https://danbooru.donmai.us/posts?tags=pixiv_id%3A1476533", {
+            "options": (("external", True),),
+            "pattern": r"http://img16.pixiv.net/img/takaraakihito/1476533.jpg",
+        }),
         ("https://hijiribe.donmai.us/posts?tags=bonocho"),
         ("https://sonohara.donmai.us/posts?tags=bonocho"),
         ("https://safebooru.donmai.us/posts?tags=bonocho"),