Implementace prevodu HTML na PDF

Sluzba prijme adresu HTML dokumentu nebo HTML v tele requestu a vrati PDF.
Navrzena pro dokumenty o stovkach az tisicich stranek.

Rendering:
- WeasyPrint jako vychozi engine, spravne CSS Paged Media, nizka pametova
  narocnost, bez JavaScriptu
- Chromium pres Playwright pro dokumenty dokreslovane skripty
- rezim auto s detekci skriptu a fallbackem pri selhani WeasyPrintu

Velke dokumenty:
- deleni na casti na strukturalnich hranicich, rez nikdy uvnitr tabulky
  nebo odstavce
- dvoupruchodovy render obsahu se skutecnymi cisly stranek, pozice nadpisu
  se ctou z kotev hlasenych u kazde stranky
- cislovani stranek bud pres CSS countery, nebo pres cislovaci vrstvu
  nastampovanou na hotove PDF, rozmer stranky se cte z vysledneho souboru
- Chromium se restartuje po N jobech, nikdy vsak behem beziciho renderu

API:
- POST /convert synchronne, POST /jobs asynchronne se sledovanim stavu,
  stahovanim vysledku, rusenim a volitelnym callbackem
- GET /health s overenim dostupnosti obou enginu a stavem fronty
- OpenAPI respektuje prefix reverse proxy pres root_path

Bezpecnost a provoz:
- SSRF kontrola po DNS resolvu, na kazdem presmerovani a u vsech pozadavku
  prohlizece
- nedostupne assety render nezastavi, ale hlasi se v odpovedi i v logu
- fronta s omezenym poctem workeru, rozpracovane joby se pri ukonceni
  oznaci jako failed, nezmizi potichu
- strukturovane JSON logovani s job_id
- vsechny limity vypnute ve vychozim stavu

Dockerfile je dvoufazovy, obsahuje zavislosti WeasyPrintu, Chromium
a fonty s ceskou diakritikou.

Autentizace zamerne neni implementovana, zpusob predavani neni domluveny.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/config.py

@@ -0,0 +1,79 @@
+"""Runtime configuration read from environment variables.
+
+AppFactory injects variables through the generated runtime .env file, so every
+option below has a safe default and the service starts without any variable set.
+"""
+
+import os
+from dataclasses import dataclass, field
+from functools import lru_cache
+
+
+def _bool(name: str, default: bool) -> bool:
+    raw = os.getenv(name)
+    if raw is None or raw.strip() == "":
+        return default
+    return raw.strip().lower() in ("1", "true", "yes", "on")
+
+
+def _int(name: str, default: int) -> int:
+    raw = os.getenv(name)
+    if raw is None or raw.strip() == "":
+        return default
+    try:
+        return int(raw)
+    except ValueError:
+        return default
+
+
+def _list(name: str) -> list[str]:
+    raw = os.getenv(name, "")
+    return [item.strip() for item in raw.split(",") if item.strip()]
+
+
+@dataclass(frozen=True)
+class Settings:
+    app_name: str = field(default_factory=lambda: os.getenv("APP_NAME", "html-to-pdf"))
+    app_version: str = field(default_factory=lambda: os.getenv("APP_VERSION", "1.0.0"))
+    root_path: str = field(
+        default_factory=lambda: os.getenv("ROOT_PATH") or os.getenv("BASE_PATH") or ""
+    )
+    log_level: str = field(default_factory=lambda: os.getenv("LOG_LEVEL", "INFO").upper())
+
+    # Job queue
+    workers: int = field(default_factory=lambda: _int("WORKERS", 2))
+    queue_max_size: int = field(default_factory=lambda: _int("QUEUE_MAX_SIZE", 100))
+    sync_timeout_seconds: int = field(default_factory=lambda: _int("SYNC_TIMEOUT_SECONDS", 60))
+    job_result_ttl_seconds: int = field(default_factory=lambda: _int("JOB_RESULT_TTL_SECONDS", 3600))
+    storage_dir: str = field(default_factory=lambda: os.getenv("STORAGE_DIR", "/tmp/html-to-pdf"))
+
+    # Engines
+    default_engine: str = field(default_factory=lambda: os.getenv("DEFAULT_ENGINE", "auto"))
+    chromium_enabled: bool = field(default_factory=lambda: _bool("CHROMIUM_ENABLED", True))
+    chromium_restart_after_jobs: int = field(
+        default_factory=lambda: _int("CHROMIUM_RESTART_AFTER_JOBS", 50)
+    )
+
+    # Network
+    fetch_timeout_seconds: int = field(default_factory=lambda: _int("FETCH_TIMEOUT_SECONDS", 30))
+    asset_timeout_seconds: int = field(default_factory=lambda: _int("ASSET_TIMEOUT_SECONDS", 10))
+    max_redirects: int = field(default_factory=lambda: _int("MAX_REDIRECTS", 5))
+
+    # SSRF protection. Blocking is on by default and can be widened or narrowed.
+    ssrf_block_private: bool = field(default_factory=lambda: _bool("SSRF_BLOCK_PRIVATE", True))
+    ssrf_extra_blocked_cidrs: list[str] = field(default_factory=lambda: _list("SSRF_EXTRA_BLOCKED_CIDRS"))
+    ssrf_allowed_hosts: list[str] = field(default_factory=lambda: _list("SSRF_ALLOWED_HOSTS"))
+
+    # Optional limits. Zero means no limit, which is the default on purpose.
+    max_pages: int = field(default_factory=lambda: _int("MAX_PAGES", 0))
+    max_html_bytes: int = field(default_factory=lambda: _int("MAX_HTML_BYTES", 0))
+    max_render_seconds: int = field(default_factory=lambda: _int("MAX_RENDER_SECONDS", 0))
+
+    # Callback delivery
+    callback_timeout_seconds: int = field(default_factory=lambda: _int("CALLBACK_TIMEOUT_SECONDS", 15))
+    callback_retries: int = field(default_factory=lambda: _int("CALLBACK_RETRIES", 3))
+
+
+@lru_cache(maxsize=1)
+def get_settings() -> Settings:
+    return Settings()