vienalatina/apps/board/app.py

"""Application factory for the members area.

Served at /comunidad/ on the main domain, behind Caddy, alongside the static
Hugo output and Decap. It is the only part of vienalatina.com that runs code to
answer a request; everything else is a file on disk.
"""

from __future__ import annotations

import os
from datetime import datetime, timezone

from flask import Flask, render_template
from werkzeug.middleware.proxy_fix import ProxyFix

from .db import close_db, init_db
from .security import check_csrf, csrf_token

URL_PREFIX = "/comunidad"


def _env_flag(name: str, default: bool) -> bool:
    raw = os.environ.get(name)
    if raw is None:
        return default
    return raw.strip().lower() in ("1", "true", "yes", "on")


def create_app(overrides: dict | None = None) -> Flask:
    # Static files have to live under the prefix too: Caddy only forwards
    # /comunidad/*, so a default /static/… would fall through to the Hugo
    # file_server and 404.
    app = Flask(__name__, static_url_path=f"{URL_PREFIX}/static")

    # Caddy terminates TLS and forwards plain HTTP, so without this the app
    # believes every request arrived unencrypted and sends its redirects to
    # http:// — an extra hop, and a moment where the session cookie could
    # travel in the clear.
    #
    # Trusting these headers is only safe because the container binds to
    # 127.0.0.1 and nothing but Caddy can reach it. Expose the port and a
    # client can forge its own address and scheme.
    app.wsgi_app = ProxyFix(app.wsgi_app, x_for=1, x_proto=1, x_host=1)
    app.config.update(
        SECRET_KEY=os.environ.get("BOARD_SECRET_KEY", ""),
        DB_PATH=os.environ.get("BOARD_DB", "/data/board.db"),
        GITEA_URL=os.environ.get("GITEA_URL", "https://git.vienalatina.com"),
        OAUTH_CLIENT_ID=os.environ.get("BOARD_OAUTH_CLIENT_ID", ""),
        OAUTH_CLIENT_SECRET=os.environ.get("BOARD_OAUTH_CLIENT_SECRET", ""),
        ADMIN_TOKEN=os.environ.get("GITEA_ADMIN_TOKEN", ""),
        OWNER_LOGIN=os.environ.get("BOARD_OWNER", ""),
        BASE_URL=os.environ.get("BOARD_BASE_URL", "https://vienalatina.com"),
        URL_PREFIX=URL_PREFIX,
        COOLDOWN_SECONDS=int(os.environ.get("BOARD_COOLDOWN_SECONDS", "20")),
        SESSION_COOKIE_HTTPONLY=True,
        SESSION_COOKIE_SAMESITE="Lax",
        # Off only for tests and local http; on the server this must stay true
        # or the session cookie travels in cleartext the first time someone
        # types the address without https.
        SESSION_COOKIE_SECURE=_env_flag("BOARD_COOKIE_SECURE", True),
        SESSION_COOKIE_NAME="vl_board",
        MAX_CONTENT_LENGTH=256 * 1024,
    )
    if overrides:
        app.config.update(overrides)

    if not app.config["SECRET_KEY"]:
        # A generated key would "work" and silently log everyone out on every
        # restart, which is a confusing way to find out the variable is unset.
        raise RuntimeError("BOARD_SECRET_KEY is required (generate one with `openssl rand -hex 32`).")

    from . import auth, board, members
    app.register_blueprint(auth.bp, url_prefix=URL_PREFIX)
    app.register_blueprint(members.bp, url_prefix=URL_PREFIX)
    app.register_blueprint(board.bp, url_prefix=URL_PREFIX)

    app.teardown_appcontext(close_db)
    app.jinja_env.globals["csrf_token"] = csrf_token
    app.jinja_env.globals["url_prefix"] = URL_PREFIX

    @app.context_processor
    def _year():
        return {"current_year": datetime.now(timezone.utc).year}

    @app.before_request
    def _before():
        # Order matters: reject forged writes before any handler can act on
        # them, but after the member is known so errors can render the chrome.
        auth.load_member()
        check_csrf()

    @app.after_request
    def _harden(response):
        # The members area must never appear in a search result. Both halves
        # are needed: robots.txt asks crawlers not to fetch, this tells the
        # ones that fetched anyway not to index.
        response.headers["X-Robots-Tag"] = "noindex, nofollow"
        response.headers["X-Content-Type-Options"] = "nosniff"
        response.headers["Referrer-Policy"] = "same-origin"
        # No 'unsafe-inline'. Two consequences worth knowing rather than
        # rediscovering: an onsubmit="" or onclick="" attribute in a template
        # is silently ignored (see static/board.js), and a markdown image
        # pointing at another site will not load — which for a private board is
        # the right answer anyway, since an external image is a request that
        # tells someone else who read the thread and when.
        response.headers["Content-Security-Policy"] = (
            "default-src 'self'; img-src 'self' data:; frame-ancestors 'none'"
        )
        return response

    @app.errorhandler(400)
    def _bad_request(error):
        return render_template("error.html", code=400,
                               message=getattr(error, "description", "Solicitud inválida.")), 400

    @app.errorhandler(403)
    def _forbidden(_error):
        return render_template("error.html", code=403,
                               message="No tienes permiso para hacer esto."), 403

    @app.errorhandler(404)
    def _not_found(_error):
        return render_template("error.html", code=404,
                               message="No encontramos esa página."), 404

    @app.errorhandler(413)
    def _too_large(_error):
        return render_template("error.html", code=413,
                               message="El mensaje es demasiado largo."), 413

    init_db(app)
    return app