integrity: refine Accept header handling

tests/unit/api/test_integrity.py

@@ -16,13 +16,53 @@
 from warehouse.api import integrity
 
 
-def test_select_content_type(db_request):
-    db_request.accept = "application/json"
+@pytest.mark.parametrize(
+    ("accept", "expected"),
+    [
+        # Simple cases
+        (
+            "application/vnd.pypi.integrity.v1+json",
+            integrity.MIME_PYPI_INTEGRITY_V1_JSON,
+        ),
+        ("application/json", integrity.MIME_APPLICATION_JSON),
+        # No accept header means we give the user our first offer
+        (None, integrity.MIME_PYPI_INTEGRITY_V1_JSON),
+        # Accept header contains only things we don't offer
+        ("text/xml", None),
+        ("application/octet-stream", None),
+        ("text/xml, application/octet-stream", None),
+        # Accept header contains both things we offer and things we don't;
+        # we pick our matching offer even if the q-value is lower
+        (
+            "text/xml, application/vnd.pypi.integrity.v1+json",
+            integrity.MIME_PYPI_INTEGRITY_V1_JSON,
+        ),
+        (
+            "application/vnd.pypi.integrity.v1+json; q=0.1, text/xml",
+            integrity.MIME_PYPI_INTEGRITY_V1_JSON,
+        ),
+        # Accept header contains multiple things we offer with the same q-value;
+        # we pick our preferred offer
+        (
+            "application/json, application/vnd.pypi.integrity.v1+json",
+            integrity.MIME_PYPI_INTEGRITY_V1_JSON,
+        ),
+        (
+            "application/vnd.pypi.integrity.v1+json; q=0.5, application/json; q=0.5",
+            integrity.MIME_PYPI_INTEGRITY_V1_JSON,
+        ),
+        # Accept header contains multiple things we offer; we pick our
+        # offer based on the q-value
+        (
+            "application/vnd.pypi.integrity.v1+json; q=0.1, application/json",
+            integrity.MIME_APPLICATION_JSON,
+        ),
+    ],
+)
+def test_select_content_type(db_request, accept, expected):
+    db_request.accept = accept
 
-    assert (
-        integrity._select_content_type(db_request)
-        == integrity.MIME_PYPI_INTEGRITY_V1_JSON
-    )
+    assert integrity._select_content_type(db_request) == expected
 
 
 # Backstop; can be removed/changed once this view supports HTML.
@@ -37,6 +77,15 @@ def test_provenance_for_file_bad_accept(db_request, content_type):
     assert response.json == {"message": "Request not acceptable"}
 
 
+def test_provenance_for_file_accept_multiple(db_request, monkeypatch):
+    db_request.accept = "text/html, application/vnd.pypi.integrity.v1+json; q=0.9"
+    file = pretend.stub(provenance=None, filename="fake-1.2.3.tar.gz")
+
+    response = integrity.provenance_for_file(file, db_request)
+    assert response.status_code == 404
+    assert response.json == {"message": "No provenance available for fake-1.2.3.tar.gz"}
+
+
 def test_provenance_for_file_not_enabled(db_request, monkeypatch):
     monkeypatch.setattr(db_request, "flags", pretend.stub(enabled=lambda *a: True))
 

warehouse/api/integrity.py

@@ -21,23 +21,26 @@
 from warehouse.utils.cors import _CORS_HEADERS
 
 MIME_TEXT_HTML = "text/html"
+MIME_APPLICATION_JSON = "application/json"
 MIME_PYPI_INTEGRITY_V1_HTML = "application/vnd.pypi.integrity.v1+html"
 MIME_PYPI_INTEGRITY_V1_JSON = "application/vnd.pypi.integrity.v1+json"
 
 
-def _select_content_type(request: Request) -> str:
+def _select_content_type(request: Request) -> str | None:
     offers = request.accept.acceptable_offers(
         [
             # JSON currently has the highest priority.
             MIME_PYPI_INTEGRITY_V1_JSON,
-            MIME_TEXT_HTML,
-            MIME_PYPI_INTEGRITY_V1_HTML,
+            MIME_APPLICATION_JSON,
+            # Ensures that we fall back to the first offer if
+            # the client does not provide an Accept header.
+            "identity",
         ]
     )
 
-    # Default case: JSON.
+    # Client provided an Accept header, but none of the offers matched.
     if not offers:
-        return MIME_PYPI_INTEGRITY_V1_JSON
+        return None
     else:
         return offers[0][0]
 
@@ -63,7 +66,7 @@ def provenance_for_file(file: File, request: Request):
     # Determine our response content-type. For the time being, only the JSON
     # type is accepted.
     request.response.content_type = _select_content_type(request)
-    if request.response.content_type != MIME_PYPI_INTEGRITY_V1_JSON:
+    if not request.response.content_type:
         return HTTPNotAcceptable(json={"message": "Request not acceptable"})
 
     if request.flags.enabled(AdminFlagValue.DISABLE_PEP740):

warehouse/api/simple.py

@@ -50,7 +50,7 @@ def _select_content_type(request: Request) -> str:
         ]
     )
 
-    # Default case, we want to return whatevr we want to return
+    # Default case, we want to return whatever we want to return
     # by default when there is no Accept header.
     if not offers:
         return MIME_TEXT_HTML