preview: Use a dataclass for the embed data.

This is significantly cleaner than passing around `Dict[str, Any]` all
of the time.

(cherry picked from commit 327ff9ea0f)

zerver/lib/url_preview/parsers/open_graph.py

@@ -1,37 +1,33 @@
-from typing import Dict
 from urllib.parse import urlparse
 
+from zerver.lib.url_preview.types import UrlEmbedData
+
 from .base import BaseParser
 
 
 class OpenGraphParser(BaseParser):
-    allowed_og_properties = {
-        "og:title",
-        "og:description",
-        "og:image",
-    }
-
-    def extract_data(self) -> Dict[str, str]:
+    def extract_data(self) -> UrlEmbedData:
         meta = self._soup.findAll("meta")
-        result = {}
+
+        data = UrlEmbedData()
+
         for tag in meta:
             if not tag.has_attr("property"):
                 continue
-            if tag["property"] not in self.allowed_og_properties:
-                continue
-
-            og_property_name = tag["property"][len("og:") :]
             if not tag.has_attr("content"):
                 continue
 
-            if og_property_name == "image":
+            if tag["property"] == "og:title":
+                data.title = tag["content"]
+            elif tag["property"] == "og:description":
+                data.description = tag["content"]
+            elif tag["property"] == "og:image":
                 try:
                     # We use urlparse and not URLValidator because we
                     # need to support relative URLs.
                     urlparse(tag["content"])
                 except ValueError:
                     continue
+                data.image = tag["content"]
 
-            result[og_property_name] = tag["content"]
-
-        return result
+        return data