From 370d4d833684821293efe8295635712200a78520 Mon Sep 17 00:00:00 2001
From: Daniel Bauer <daniel.bauer@senckenberg.de>
Date: Thu, 15 Aug 2024 21:44:20 +0200
Subject: [PATCH] add middleware for signposts

---
 django_signposting/middleware.py | 40 +++++++++++++++++
 tests/test_middleware.py         | 75 ++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 django_signposting/middleware.py
 create mode 100644 tests/test_middleware.py

diff --git a/django_signposting/middleware.py b/django_signposting/middleware.py
new file mode 100644
index 0000000..27fed75
--- /dev/null
+++ b/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)
+
diff --git a/tests/test_middleware.py b/tests/test_middleware.py
new file mode 100644
index 0000000..82e896d
--- /dev/null
+++ b/tests/test_middleware.py
@@ -0,0 +1,75 @@
+from django.http import HttpResponse, HttpRequest
+from django.conf import settings
+from django_signposting.middleware import SignpostingMiddleware
+import pytest
+
+
+@pytest.fixture(scope="module", autouse=True)
+def configure_django_settings():
+    settings.configure()
+
+
+def test_middleware_no_signposting():
+    response = HttpResponse()
+    response.status_code = 200
+
+    middleware = SignpostingMiddleware(lambda request: response)
+    response = middleware(None)
+    assert "Link" not in response.headers
+
+
+def test_middleware_signposting():
+    response = HttpResponse()
+    response.status_code = 200
+    response._signposts = {"author": ["http://example.com"]}
+
+    middleware = SignpostingMiddleware(lambda request: response)
+    response = middleware(None)
+    assert response.headers["Link"] == '<http://example.com> ; rel="author"'
+
+
+def test_middleware_multiple_signposts():
+    response = HttpResponse()
+    response.status_code = 200
+    response._signposts = {
+        "author": [
+            "http://example.com",
+            "http://example2.com"
+        ],
+        "cite-as": [
+            "http://example3.com"
+        ]
+    }
+
+    middleware = SignpostingMiddleware(lambda request: response)
+    response = middleware(None)
+    links = [x.strip() for x in response.headers["Link"].split(",")]
+    assert '<http://example.com> ; rel="author"' in links
+    assert '<http://example2.com> ; rel="author"' in links
+    assert '<http://example3.com> ; rel="cite-as"' in links
+
+
+def test_middleware_signpost_with_content_type():
+    response = HttpResponse()
+    response.status_code = 200
+    response._signposts = {
+        "item": [
+            ("http://example.com", "test/json"),
+        ]
+    }
+
+    middleware = SignpostingMiddleware(lambda request: response)
+    response = middleware(None)
+    assert response.headers["Link"] == '<http://example.com> ; rel="item" ; type="test/json"'
+
+
+def test_middleware_ignore_error_responses():
+    response = HttpResponse()
+    response.status_code = 400
+    response._signposts = {
+        "author": ["https://example.com"]
+    }
+
+    middleware = SignpostingMiddleware(lambda request: response)
+    response = middleware(None)
+    assert "Link" not in response.headers