Fix the static URLs in exercise descriptions

Previously the code fixing relative URLs pointing to static content
assumed that they are located on grader server. These days the
static content is on Gitmanager, so the URLs should be fixed
accordingly.

Closes #974.

Author: PasiSa

lib/remote_page.py

@@ -237,6 +237,16 @@ def _fix_relative_urls(self, url, tag_name, attr_name):
         # URLs /plain, /info, /info/model, /info/template.
         exercise_info = re.compile(r'/((plain)|(info(/model|/template)?))/?(#.+)?$')
 
+        # If Gitmanager is in use, fix relative static URLs to that host
+        if settings.GITMANAGER_URL:
+            gmurl = urlparse(settings.GITMANAGER_URL)
+            if settings.REMOTE_PAGE_HOSTS_MAP:
+                domain = settings.REMOTE_PAGE_HOSTS_MAP.get(gmurl.netloc, gmurl.netloc)
+                gmurl = gmurl._replace(netloc=domain)
+            staticurl = url._replace(scheme=gmurl.scheme, netloc=gmurl.netloc)
+        else:
+            staticurl = url
+
         for element in self.soup.find_all(tag_name, {attr_name:True}):
             value = element[attr_name]
             if not value:
@@ -312,15 +322,16 @@ def _fix_relative_urls(self, url, tag_name, attr_name):
 
                 # url points to the exercise service, e.g., MOOC-Grader.
                 # This fixes links to static files (such as images) in RST chapters.
-                # The image URL must be absolute and refer to the grader server
-                # instead of the A+ server. A relative URL with only path
-                # "/static/course/image.png" would target the A+ server when
-                # it is included in the A+ page. The value should be a relative
+                # The image URL must be absolute and refer to the server with static content
+                # instead of the A+ server. Traditionally this has been the grader server, but
+                # recently gitmanager is used. If GITMANAGER_URL is specified, we assume gitmanager.
+                # A relative URL with only path "/static/course/image.png" would target the A+ server
+                # when it is included in the A+ page. The value should be a relative
                 # path in the course build directory so that it becomes the full
                 # correct URL to the target file.
                 # E.g., urljoin('http://localhost:8080/static/default/module1/chapter.html', "../_images/image.png")
                 # -> 'http://localhost:8080/static/default/_images/image.png'
-                element[attr_name] = urljoin(url.geturl(), value)
+                element[attr_name] = urljoin(staticurl.geturl(), value)
 
     def find_and_replace(self, attr_name, list_of_attributes):
         l = len(list_of_attributes)