Flash messages mechanism, closes #790

datasette/app.py

@@ -2,6 +2,7 @@ import asyncio
 import collections
 import datetime
 import hashlib
+from http.cookies import SimpleCookie
 import itertools
 import json
 import os
@@ -30,6 +31,7 @@ from .views.special import (
     PatternPortfolioView,
     AuthTokenView,
     PermissionsDebugView,
+    MessagesDebugView,
 )
 from .views.table import RowView, TableView
 from .renderer import json_renderer
@@ -156,6 +158,11 @@ async def favicon(scope, receive, send):
 
 
 class Datasette:
+    # Message constants:
+    INFO = 1
+    WARNING = 2
+    ERROR = 3
+
     def __init__(
         self,
         files,
@@ -423,6 +430,38 @@ class Datasette:
         # pylint: disable=no-member
         pm.hook.prepare_connection(conn=conn, database=database, datasette=self)
 
+    def add_message(self, request, message, type=INFO):
+        if not hasattr(request, "_messages"):
+            request._messages = []
+            request._messages_should_clear = False
+        request._messages.append((message, type))
+
+    def _write_messages_to_response(self, request, response):
+        if getattr(request, "_messages", None):
+            # Set those messages
+            cookie = SimpleCookie()
+            cookie["ds_messages"] = self.sign(request._messages, "messages")
+            cookie["ds_messages"]["path"] = "/"
+            # TODO: Co-exist with existing set-cookie headers
+            assert "set-cookie" not in response.headers
+            response.headers["set-cookie"] = cookie.output(header="").lstrip()
+        elif getattr(request, "_messages_should_clear", False):
+            cookie = SimpleCookie()
+            cookie["ds_messages"] = ""
+            cookie["ds_messages"]["path"] = "/"
+            # TODO: Co-exist with existing set-cookie headers
+            assert "set-cookie" not in response.headers
+            response.headers["set-cookie"] = cookie.output(header="").lstrip()
+
+    def _show_messages(self, request):
+        if getattr(request, "_messages", None):
+            request._messages_should_clear = True
+            messages = request._messages
+            request._messages = []
+            return messages
+        else:
+            return []
+
     async def permission_allowed(
         self, actor, action, resource_type=None, resource_identifier=None, default=False
     ):
@@ -808,6 +847,9 @@ class Datasette:
         add_route(
             PermissionsDebugView.as_asgi(self), r"/-/permissions$",
         )
+        add_route(
+            MessagesDebugView.as_asgi(self), r"/-/messages$",
+        )
         add_route(
             PatternPortfolioView.as_asgi(self), r"/-/patterns$",
         )

datasette/static/app.css

@@ -351,3 +351,19 @@ p.zero-results {
 .type-float, .type-int {
     color: #666;
 }
+
+.message-info {
+    padding: 1em;
+    border: 1px solid green;
+    background-color: #c7fbc7;
+}
+.message-warning {
+    padding: 1em;
+    border: 1px solid #ae7100;
+    background-color: #fbdda5;
+}
+.message-error {
+    padding: 1em;
+    border: 1px solid red;
+    background-color: pink;
+}

datasette/templates/base.html

@@ -17,6 +17,14 @@
 <nav class="hd">{% block nav %}{% endblock %}</nav>
 
 <div class="bd">
+{% block messages %}
+{% if show_messages %}
+    {% for message, message_type in show_messages() %}
+        <p class="message-{% if message_type == 1 %}info{% elif message_type == 2 %}warning{% elif message_type == 3 %}error{% endif %}">{{ message }}</p>
+    {% endfor %}
+{% endif %}
+{% endblock %}
+
 {% block content %}
 {% endblock %}
 </div>

datasette/templates/messages_debug.html

@@ -0,0 +1,26 @@
+{% extends "base.html" %}
+
+{% block title %}Debug messages{% endblock %}
+
+{% block content %}
+
+<h1>Debug messages</h1>
+
+<p>Set a message:</p>
+
+<form action="/-/messages" method="POST">
+    <div>
+        <input type="text" name="message" style="width: 40%">
+        <div class="select-wrapper">
+            <select name="message_type">
+                <option>INFO</option>
+                <option>WARNING</option>
+                <option>ERROR</option>
+                <option>all</option>
+            </select>
+        </div>
+        <input type="submit" value="Add message">
+    </div>
+</form>
+
+{% endblock %}

datasette/utils/asgi.py

@@ -180,9 +180,9 @@ class AsgiLifespan:
 
 
 class AsgiView:
-    def dispatch_request(self, request, *args, **kwargs):
+    async def dispatch_request(self, request, *args, **kwargs):
         handler = getattr(self, request.method.lower(), None)
-        return handler(request, *args, **kwargs)
+        return await handler(request, *args, **kwargs)
 
     @classmethod
     def as_asgi(cls, *class_args, **class_kwargs):

datasette/views/base.py

@@ -1,6 +1,7 @@
 import asyncio
 import csv
 import itertools
+from itsdangerous import BadSignature
 import json
 import re
 import time
@@ -73,6 +74,20 @@ class BaseView(AsgiView):
     def database_color(self, database):
         return "ff0000"
 
+    async def dispatch_request(self, request, *args, **kwargs):
+        # Populate request_messages if ds_messages cookie is present
+        if self.ds:
+            try:
+                request._messages = self.ds.unsign(
+                    request.cookies.get("ds_messages", ""), "messages"
+                )
+            except BadSignature:
+                pass
+        response = await super().dispatch_request(request, *args, **kwargs)
+        if self.ds:
+            self.ds._write_messages_to_response(request, response)
+        return response
+
     async def render(self, templates, request, context=None):
         context = context or {}
         template = self.ds.jinja_env.select_template(templates)
@@ -81,6 +96,7 @@ class BaseView(AsgiView):
             **{
                 "database_url": self.database_url,
                 "database_color": self.database_color,
+                "show_messages": lambda: self.ds._show_messages(request),
                 "select_templates": [
                     "{}{}".format(
                         "*" if template_name == template.name else "", template_name

datasette/views/special.py

@@ -94,3 +94,27 @@ class PermissionsDebugView(BaseView):
             request,
             {"permission_checks": reversed(self.ds._permission_checks)},
         )
+
+
+class MessagesDebugView(BaseView):
+    name = "messages_debug"
+
+    def __init__(self, datasette):
+        self.ds = datasette
+
+    async def get(self, request):
+        return await self.render(["messages_debug.html"], request)
+
+    async def post(self, request):
+        post = await request.post_vars()
+        message = post.get("message", "")
+        message_type = post.get("message_type") or "INFO"
+        assert message_type in ("INFO", "WARNING", "ERROR", "all")
+        datasette = self.ds
+        if message_type == "all":
+            datasette.add_message(request, message, datasette.INFO)
+            datasette.add_message(request, message, datasette.WARNING)
+            datasette.add_message(request, message, datasette.ERROR)
+        else:
+            datasette.add_message(request, message, getattr(datasette, message_type))
+        return Response.redirect("/")