add middleware for signposts

django_signposting/middleware.py

@@ -0,0 +1,40 @@
+from typing import Callable
+from django.http import HttpRequest, HttpResponse
+
+
+class SignpostingMiddleware:
+
+    def __init__(self, get_response: Callable[[HttpRequest], HttpResponse]):
+        self.get_response = get_response
+
+    def __call__(self, request: HttpRequest) -> HttpResponse:
+        response = self.get_response(request)
+
+        # no signposts on errors
+        if response.status_code >= 400:
+            return response
+
+        if not hasattr(response, "_signposts"):
+            return response
+
+        self._add_signposts(response, response._signposts)
+
+        return response
+
+    def _add_signposts(self, response: HttpResponse, typed_links: dict[str, list[str|tuple[str, str]]]):
+        """ Adds signposting headers to the respones.
+        params:
+          response - the response object
+          typed_links - a map of relation types to a list of corresponding links. Each link can be a link or a tuple of link and media type.
+        """
+        link_snippets = []
+        for relation_type in typed_links.keys():
+            links = typed_links.get(relation_type, [])
+            for link in links:
+                if isinstance(link, tuple) and len(link) > 1:
+                    link_snippets.append(f'<{link[0]}> ; rel="{relation_type}" ; type="{link[1]}"')
+                else:
+                    link_snippets.append(f'<{link}> ; rel="{relation_type}"')
+
+        response["Link"] = " , ".join(link_snippets)
+