fix: process links w/o the prefix (#70)

There's times when the underlying STAC API might not have a path on its
root URL, but **stac-auth-proxy** has a path on its `upstream_url`; one
such case is if there's an API Gateway in the way. This patch uses
string replacement for link rewriting, rather than slicing, to handle
these cases while preserving previous behavior.

---------

Co-authored-by: Anthony Lukach <[email protected]>

Author: gadomski

src/stac_auth_proxy/middleware/ProcessLinksMiddleware.py

@@ -53,9 +53,12 @@ def transform_json(self, data: dict[str, Any], request: Request) -> dict[str, An
                     continue
 
                 # Remove the upstream_url path from the link if it exists
-                if urlparse(self.upstream_url).path != "/":
+                parsed_upstream_url = urlparse(self.upstream_url)
+                if parsed_upstream_url.path != "/" and parsed_link.path.startswith(
+                    parsed_upstream_url.path
+                ):
                     parsed_link = parsed_link._replace(
-                        path=parsed_link.path[len(urlparse(self.upstream_url).path) :]
+                        path=parsed_link.path[len(parsed_upstream_url.path) :]
                     )
 
                 # Add the root_path to the link if it exists

tests/test_process_links.py

@@ -186,3 +186,19 @@ def test_transform_json_nested_links(middleware, request_scope):
         transformed["collections"][0]["links"][1]["href"]
         == "http://proxy.example.com/proxy/collections/test-collection/items"
     )
+
+
+def test_transform_without_prefix(request_scope):
+    """Sometimes the upstream url will have a path, but the links won't."""
+    middleware = ProcessLinksMiddleware(
+        app=None, upstream_url="http://upstream.example.com/prod/", root_path=""
+    )
+    request = Request(request_scope)
+
+    data = {
+        "links": [
+            {"rel": "data", "href": "http://proxy.example.com/collections"},
+        ]
+    }
+    transformed = middleware.transform_json(data, request)
+    assert transformed["links"][0]["href"] == "http://proxy.example.com/collections"