From b72b2423c79dea4600b2337949db98269d0b6215 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Wed, 2 Feb 2022 13:21:11 -0800
Subject: [PATCH] rel=alternate JSON for queries and database pages, closes
 #1620

---
 datasette/templates/database.html |  3 ++-
 datasette/templates/query.html    |  3 ++-
 datasette/views/database.py       | 32 ++++++++++++++++++++++
 docs/json_api.rst                 |  2 +-
 tests/test_canned_queries.py      |  9 +++++++
 tests/test_html.py                | 45 +++++++++++++++++++++++++++++++
 tests/test_table_html.py          | 28 -------------------
 7 files changed, 91 insertions(+), 31 deletions(-)

diff --git a/datasette/templates/database.html b/datasette/templates/database.html
index c1e39bd1..8f0c65d7 100644
--- a/datasette/templates/database.html
+++ b/datasette/templates/database.html
@@ -3,7 +3,8 @@
 {% block title %}{{ database }}{% endblock %}
 
 {% block extra_head %}
-{{ super() }}
+{{- super() -}}
+<link rel="alternate" type="application/json+datasette" href="{{ alternate_url_json }}">
 {% include "_codemirror.html" %}
 {% endblock %}
 
diff --git a/datasette/templates/query.html b/datasette/templates/query.html
index 75f7f1b1..d0121976 100644
--- a/datasette/templates/query.html
+++ b/datasette/templates/query.html
@@ -3,7 +3,8 @@
 {% block title %}{{ database }}{% if query and query.sql %}: {{ query.sql }}{% endif %}{% endblock %}
 
 {% block extra_head %}
-{{ super() }}
+{{- super() -}}
+<link rel="alternate" type="application/json+datasette" href="{{ alternate_url_json }}">
 {% if columns %}
 <style>
 @media only screen and (max-width: 576px) {
diff --git a/datasette/views/database.py b/datasette/views/database.py
index e26706e7..f3641dc5 100644
--- a/datasette/views/database.py
+++ b/datasette/views/database.py
@@ -123,6 +123,10 @@ class DatabaseView(DataView):
 
         attached_databases = [d.name for d in await db.attached_databases()]
 
+        alternate_url_json = self.ds.absolute_url(
+            request,
+            self.ds.urls.path(path_with_format(request=request, format="json")),
+        )
         return (
             {
                 "database": database,
@@ -140,6 +144,7 @@ class DatabaseView(DataView):
                 ),
             },
             {
+                "alternate_url_json": alternate_url_json,
                 "database_actions": database_actions,
                 "show_hidden": request.args.get("_show_hidden"),
                 "editable": True,
@@ -148,6 +153,11 @@ class DatabaseView(DataView):
                 and not db.is_mutable
                 and not db.is_memory,
                 "attached_databases": attached_databases,
+                "_extra_headers": {
+                    "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
+                        alternate_url_json
+                    )
+                },
             },
             (f"database-{to_css_class(database)}.html", "database.html"),
         )
@@ -308,7 +318,14 @@ class QueryView(DataView):
             else:
 
                 async def extra_template():
+                    alternate_url_json = self.ds.absolute_url(
+                        request,
+                        self.ds.urls.path(
+                            path_with_format(request=request, format="json")
+                        ),
+                    )
                     return {
+                        "alternate_url_json": alternate_url_json,
                         "request": request,
                         "path_with_added_args": path_with_added_args,
                         "path_with_removed_args": path_with_removed_args,
@@ -316,6 +333,11 @@ class QueryView(DataView):
                         "canned_query": canned_query,
                         "success_message": request.args.get("_success") or "",
                         "canned_write": True,
+                        "_extra_headers": {
+                            "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
+                                alternate_url_json
+                            )
+                        },
                     }
 
                 return (
@@ -448,7 +470,12 @@ class QueryView(DataView):
                     show_hide_link = path_with_added_args(request, {"_hide_sql": 1})
                     show_hide_text = "hide"
             hide_sql = show_hide_text == "show"
+            alternate_url_json = self.ds.absolute_url(
+                request,
+                self.ds.urls.path(path_with_format(request=request, format="json")),
+            )
             return {
+                "alternate_url_json": alternate_url_json,
                 "display_rows": display_rows,
                 "custom_sql": True,
                 "named_parameter_values": named_parameter_values,
@@ -462,6 +489,11 @@ class QueryView(DataView):
                 "show_hide_text": show_hide_text,
                 "show_hide_hidden": markupsafe.Markup(show_hide_hidden),
                 "hide_sql": hide_sql,
+                "_extra_headers": {
+                    "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
+                        alternate_url_json
+                    )
+                },
             }
 
         return (
diff --git a/docs/json_api.rst b/docs/json_api.rst
index b5a6744b..4f9eaddb 100644
--- a/docs/json_api.rst
+++ b/docs/json_api.rst
@@ -442,7 +442,7 @@ in ``metadata.json`` - see :ref:`label_columns`.
 Discovering the JSON for a page
 -------------------------------
 
-The :ref:`table <TableView>` and :ref:`row <RowView>` HTML pages both provide a mechanism for discovering their JSON equivalents using the HTML ``link`` mechanism.
+The :ref:`database <DatabaseView>`, :ref:`table <TableView>`, :ref:`custom/canned query <sql>` and :ref:`row <RowView>` HTML pages all provide a mechanism for discovering their JSON equivalents using the HTML ``link`` mechanism.
 
 You can find this near the top of those pages, looking like this:
 
diff --git a/tests/test_canned_queries.py b/tests/test_canned_queries.py
index c5ccaf5c..5abffdcc 100644
--- a/tests/test_canned_queries.py
+++ b/tests/test_canned_queries.py
@@ -364,3 +364,12 @@ def test_canned_write_custom_template(canned_write_client):
         in response.text
     )
     assert "!!!CUSTOM_UPDATE_NAME_TEMPLATE!!!" in response.text
+    # And test for link rel=alternate while we're here:
+    assert (
+        '<link rel="alternate" type="application/json+datasette" href="http://localhost/data/update_name.json">'
+        in response.text
+    )
+    assert (
+        response.headers["link"]
+        == 'http://localhost/data/update_name.json; rel="alternate"; type="application/json+datasette"'
+    )
diff --git a/tests/test_html.py b/tests/test_html.py
index 1bbf335c..273e4914 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -870,3 +870,48 @@ def test_trace_correctly_escaped(app_client):
     response = app_client.get("/fixtures?sql=select+'<h1>Hello'&_trace=1")
     assert "select '<h1>Hello" not in response.text
     assert "select &#39;&lt;h1&gt;Hello" in response.text
+
+
+@pytest.mark.parametrize(
+    "path,expected",
+    (
+        # Table page
+        (
+            "/fixtures/table%2Fwith%2Fslashes.csv",
+            "http://localhost/fixtures/table%2Fwith%2Fslashes.csv?_format=json",
+        ),
+        ("/fixtures/facetable", "http://localhost/fixtures/facetable.json"),
+        # Row page
+        (
+            "/fixtures/no_primary_key/1",
+            "http://localhost/fixtures/no_primary_key/1.json",
+        ),
+        # Database index page
+        (
+            "/fixtures",
+            "http://localhost/fixtures.json",
+        ),
+        # Custom query page
+        (
+            "/fixtures?sql=select+*+from+facetable",
+            "http://localhost/fixtures.json?sql=select+*+from+facetable",
+        ),
+        # Canned query page
+        (
+            "/fixtures/neighborhood_search?text=town",
+            "http://localhost/fixtures/neighborhood_search.json?text=town",
+        ),
+    ),
+)
+def test_alternate_url_json(app_client, path, expected):
+    response = app_client.get(path)
+    link = response.headers["link"]
+    assert link == '{}; rel="alternate"; type="application/json+datasette"'.format(
+        expected
+    )
+    assert (
+        '<link rel="alternate" type="application/json+datasette" href="{}">'.format(
+            expected
+        )
+        in response.text
+    )
diff --git a/tests/test_table_html.py b/tests/test_table_html.py
index 7d08d230..021268c3 100644
--- a/tests/test_table_html.py
+++ b/tests/test_table_html.py
@@ -1069,31 +1069,3 @@ def test_table_page_title(app_client, path, expected):
     response = app_client.get(path)
     title = Soup(response.text, "html.parser").find("title").text
     assert title == expected
-
-
-@pytest.mark.parametrize(
-    "path,expected",
-    (
-        (
-            "/fixtures/table%2Fwith%2Fslashes.csv",
-            "http://localhost/fixtures/table%2Fwith%2Fslashes.csv?_format=json",
-        ),
-        ("/fixtures/facetable", "http://localhost/fixtures/facetable.json"),
-        (
-            "/fixtures/no_primary_key/1",
-            "http://localhost/fixtures/no_primary_key/1.json",
-        ),
-    ),
-)
-def test_alternate_url_json(app_client, path, expected):
-    response = app_client.get(path)
-    link = response.headers["link"]
-    assert link == '{}; rel="alternate"; type="application/json+datasette"'.format(
-        expected
-    )
-    assert (
-        '<link rel="alternate" type="application/json+datasette" href="{}">'.format(
-            expected
-        )
-        in response.text
-    )