A guard that redirects

Task: send visitors who are not signed in to the sign-in page with a message, and make sure they cannot post to the page's actions either.

# Recipe: a guard -- a top-level q:if with q:redirect -- protects the page and
# its actions.
paths:
  components: ./components
  migrations: ./migrations

datasources:
  db:
    driver: sqlite
    database: ./data/notes.db

CREATE TABLE notes (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    author TEXT NOT NULL,
    body TEXT NOT NULL
);

A q:if at the top of the page whose branch has a q:redirect is a guard. It runs before the page and before each of its actions, so a post sent straight to add is stopped too:

<q:component name="Notes">
  <!-- The guard: it runs before the page AND before each of its actions. -->
  <q:if condition="not session.authenticated">
    <q:redirect url="/login" flash="Sign in to write notes." />
  </q:if>

  <q:action name="add" method="POST">
    <q:param name="body" required="true" minlength="2" />
    <q:query name="added" datasource="db">
      INSERT INTO notes (author, body) VALUES (:author, :body)
      <q:param name="author" value="{session.userName}" type="string" />
      <q:param name="body" value="{body}" type="string" />
    </q:query>
    <q:redirect url="/" flash="Saved." />
  </q:action>

  <q:query name="notes" datasource="db">
    SELECT author, body FROM notes ORDER BY id DESC
  </q:query>

  <h1>Notes</h1>
  <q:if condition="flash"><p>{flash}</p></q:if>
  <form method="POST"><input name="body" /><button>Add</button></form>
  <q:loop query="notes"><p>{notes.author}: {notes.body}</p></q:loop>
</q:component>

<q:component name="Login">
  <q:if condition="flash"><p>{flash}</p></q:if>
  <h1>Sign in</h1>
</q:component>

The second test posts to the action without a session and checks that no row was written:

<q:test name="the guard sends a visitor to sign in" page="/">
  <test:visit />
  <test:expect status="302" redirect="/login" />
  <test:expect text="Sign in to write notes." />
</q:test>

<q:test name="the guard also stops the action: nothing is written" page="/">
  <test:submit action="add" body="Sneaky note" />
  <test:expect status="302" redirect="/login" />
  <test:expect table="notes" count="0" />
</q:test>

<q:test name="a signed-in user writes a note" page="/">
  <test:as user="ana" role="member" />
  <test:submit action="add" body="Buy coffee" />
  <test:expect redirect="/" flash="Saved." />
  <test:expect table="notes" count="1" where="author = 'ana' AND body = 'Buy coffee'" />
  <test:expect text="ana: Buy coffee" />
</q:test>

tests/guard.test.q
  PASS  the guard sends a visitor to sign in
  PASS  the guard also stops the action: nothing is written
  PASS  a signed-in user writes a note
3 passed, 0 failed

A guard can check anything the session holds. To only ask for a signed-in user or a role, require_auth and require_role say it in one attribute (A page for one role only).