From 8d5779acf0041cfd0db7f68f468419f9008b86ec Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Wed, 2 Feb 2022 13:32:47 -0800
Subject: [PATCH] Refactored alternate_url_json mechanism, refs #1620, #1533

---
 datasette/templates/base.html     |  3 +++
 datasette/templates/database.html |  1 -
 datasette/templates/query.html    |  1 -
 datasette/templates/row.html      |  1 -
 datasette/templates/table.html    |  1 -
 datasette/views/base.py           | 17 +++++++++++++---
 datasette/views/database.py       | 32 -------------------------------
 datasette/views/table.py          | 20 -------------------
 docs/json_api.rst                 |  4 ++--
 tests/test_html.py                |  9 ++++++++-
 10 files changed, 27 insertions(+), 62 deletions(-)
diff --git a/datasette/templates/base.html b/datasette/templates/base.html
index 836b7bb7..c3a71acb 100644
--- a/datasette/templates/base.html
+++ b/datasette/templates/base.html
@@ -10,6 +10,9 @@
 {% for url in extra_js_urls %}
     <script {% if url.module %}type="module" {% endif %}src="{{ url.url }}"{% if url.sri %} integrity="{{ url.sri }}" crossorigin="anonymous"{% endif %}></script>
 {% endfor %}
+{%- if alternate_url_json -%}
+    <link rel="alternate" type="application/json+datasette" href="{{ alternate_url_json }}">
+{%- endif -%}
 {%- block extra_head %}{% endblock -%}
 </head>
 <body class="{% block body_class %}{% endblock %}">
diff --git a/datasette/templates/database.html b/datasette/templates/database.html
index 8f0c65d7..e76bc49e 100644
--- a/datasette/templates/database.html
+++ b/datasette/templates/database.html
@@ -4,7 +4,6 @@
 
 {% block extra_head %}
 {{- 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 d0121976..8c920527 100644
--- a/datasette/templates/query.html
+++ b/datasette/templates/query.html
@@ -4,7 +4,6 @@
 
 {% block extra_head %}
 {{- 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/templates/row.html b/datasette/templates/row.html
index 1ac16268..10770ce9 100644
--- a/datasette/templates/row.html
+++ b/datasette/templates/row.html
@@ -4,7 +4,6 @@
 
 {% block extra_head %}
 {{- super() -}}
-<link rel="alternate" type="application/json+datasette" href="{{ alternate_url_json }}">
 <style>
 @media only screen and (max-width: 576px) {
 {% for column in columns %}
diff --git a/datasette/templates/table.html b/datasette/templates/table.html
index 403e1d5b..81bd044a 100644
--- a/datasette/templates/table.html
+++ b/datasette/templates/table.html
@@ -4,7 +4,6 @@
 
 {% block extra_head %}
 {{- super() -}}
-<link rel="alternate" type="application/json+datasette" href="{{ alternate_url_json }}">
 <script src="{{ urls.static('table.js') }}" defer></script>
 <style>
 @media only screen and (max-width: 576px) {
diff --git a/datasette/views/base.py b/datasette/views/base.py
index a414892a..c74d6141 100644
--- a/datasette/views/base.py
+++ b/datasette/views/base.py
@@ -55,6 +55,7 @@ class DatasetteError(Exception):
 
 class BaseView:
     ds = None
+    has_json_alternate = True
 
     def __init__(self, datasette):
         self.ds = datasette
@@ -137,10 +138,20 @@ class BaseView:
                 ],
             },
         }
-        # Hacky cheat to add extra headers
         headers = {}
-        if "_extra_headers" in context:
-            headers.update(context["_extra_headers"])
+        if self.has_json_alternate:
+            alternate_url_json = self.ds.absolute_url(
+                request,
+                self.ds.urls.path(path_with_format(request=request, format="json")),
+            )
+            template_context["alternate_url_json"] = alternate_url_json
+            headers.update(
+                {
+                    "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
+                        alternate_url_json
+                    )
+                }
+            )
         return Response.html(
             await self.ds.render_template(
                 template,
diff --git a/datasette/views/database.py b/datasette/views/database.py
index f3641dc5..e26706e7 100644
--- a/datasette/views/database.py
+++ b/datasette/views/database.py
@@ -123,10 +123,6 @@ 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,
@@ -144,7 +140,6 @@ class DatabaseView(DataView):
                 ),
             },
             {
-                "alternate_url_json": alternate_url_json,
                 "database_actions": database_actions,
                 "show_hidden": request.args.get("_show_hidden"),
                 "editable": True,
@@ -153,11 +148,6 @@ 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"),
         )
@@ -318,14 +308,7 @@ 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,
@@ -333,11 +316,6 @@ 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 (
@@ -470,12 +448,7 @@ 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,
@@ -489,11 +462,6 @@ 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/datasette/views/table.py b/datasette/views/table.py
index 6bbee352..be9e9c3b 100644
--- a/datasette/views/table.py
+++ b/datasette/views/table.py
@@ -851,12 +851,7 @@ class TableView(RowTableShared):
                 for table_column in table_columns
                 if table_column not in columns
             ]
-            alternate_url_json = self.ds.absolute_url(
-                request,
-                self.ds.urls.path(path_with_format(request=request, format="json")),
-            )
             d = {
-                "alternate_url_json": alternate_url_json,
                 "table_actions": table_actions,
                 "use_rowid": use_rowid,
                 "filters": filters,
@@ -887,11 +882,6 @@ class TableView(RowTableShared):
                 "metadata": metadata,
                 "view_definition": await db.get_view_definition(table),
                 "table_definition": await db.get_table_definition(table),
-                "_extra_headers": {
-                    "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
-                        alternate_url_json
-                    )
-                },
             }
             d.update(extra_context_from_filters)
             return d
@@ -975,12 +965,7 @@ class RowView(RowTableShared):
             )
             for column in display_columns:
                 column["sortable"] = False
-            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,
                 "foreign_key_tables": await self.foreign_key_tables(
                     database, table, pk_values
                 ),
@@ -995,11 +980,6 @@ class RowView(RowTableShared):
                 .get(database, {})
                 .get("tables", {})
                 .get(table, {}),
-                "_extra_headers": {
-                    "Link": '{}; rel="alternate"; type="application/json+datasette"'.format(
-                        alternate_url_json
-                    )
-                },
             }
 
         data = {
diff --git a/docs/json_api.rst b/docs/json_api.rst
index 4f9eaddb..aa6fcdaa 100644
--- a/docs/json_api.rst
+++ b/docs/json_api.rst
@@ -442,9 +442,9 @@ in ``metadata.json`` - see :ref:`label_columns`.
 Discovering the JSON for a page
 -------------------------------
 
-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.
+Most of the HTML pages served by Datasette 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:
+You can find this near the top of the source code of those pages, looking like this:
 
 .. code-block:: python
 
diff --git a/tests/test_html.py b/tests/test_html.py
index 273e4914..4b6cbd13 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -875,12 +875,14 @@ def test_trace_correctly_escaped(app_client):
 @pytest.mark.parametrize(
     "path,expected",
     (
+        # Instance index page
+        ("/", "http://localhost/.json"),
         # Table page
+        ("/fixtures/facetable", "http://localhost/fixtures/facetable.json"),
         (
             "/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",
@@ -901,6 +903,11 @@ def test_trace_correctly_escaped(app_client):
             "/fixtures/neighborhood_search?text=town",
             "http://localhost/fixtures/neighborhood_search.json?text=town",
         ),
+        # /-/ pages
+        (
+            "/-/plugins",
+            "http://localhost/-/plugins.json",
+        ),
     ),
 )
 def test_alternate_url_json(app_client, path, expected):
