Update app.py

app.py

@@ -7,8 +7,11 @@ Run with:
 from __future__ import annotations
 
 import asyncio
+from html import escape
 import json
+import os
 import re
+import shutil
 import tempfile
 from pathlib import Path
 from typing import Final
@@ -18,6 +21,7 @@ from uuid import uuid4
 from fastapi import FastAPI, Form
 from fastapi.responses import FileResponse, HTMLResponse
 from starlette.background import BackgroundTask
+from playwright.async_api import Error as PlaywrightError
 from playwright.async_api import async_playwright
 
 SAVE_TT_HOME: Final = "https://savett.cc/en1/"
@@ -31,10 +35,54 @@ app = FastAPI(title="TikTok MP4 Downloader", docs_url=None, redoc_url=None)
 download_lock = asyncio.Lock()
 
 
+class BrowserRuntimeError(RuntimeError):
+    """Raised when Chromium is unavailable in the process running FastAPI."""
+
+
+def chromium_launch_options() -> dict[str, object]:
+    """Prefer an explicit Chromium path, then common system browser locations."""
+    configured_path = os.environ.get("PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH")
+    if configured_path:
+        browser_path = Path(configured_path)
+        if not browser_path.is_file():
+            raise BrowserRuntimeError(
+                "PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH is set, but its file does not exist. "
+                "Set it to a valid Chromium executable or remove the variable."
+            )
+        executable_path = str(browser_path)
+    else:
+        executable_path = next(
+            (
+                path
+                for name in ("chromium", "chromium-browser", "google-chrome", "google-chrome-stable")
+                if (path := shutil.which(name))
+            ),
+            None,
+        )
+
+    options: dict[str, object] = {"headless": True}
+    if executable_path:
+        options["executable_path"] = executable_path
+
+    # System Chromium generally refuses to start as root unless this flag is used.
+    # Prefer running the service as an unprivileged user in production.
+    if os.name != "nt" and hasattr(os, "geteuid") and os.geteuid() == 0:
+        options["args"] = ["--no-sandbox", "--disable-dev-shm-usage"]
+    return options
+
+
+def browser_install_message() -> str:
+    return (
+        "Chromium is not available to the FastAPI process. Install it during deployment with "
+        "`python -m playwright install chromium`, or set "
+        "PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH to a valid system Chromium binary."
+    )
+
+
 def render_home(error: str | None = None) -> str:
     error_markup = ""
     if error:
-        error_markup = f'<div class="notice error" role="alert">{error}</div>'
+        error_markup = f'<div class="notice error" role="alert">{escape(error)}</div>'
 
     return f"""<!doctype html>
 <html lang="en">
@@ -151,7 +199,12 @@ async def fetch_mp4(tiktok_url: str) -> tuple[Path, str]:
     output_path = TMP_DIR / f"tiktok_{video_id}_{uuid4().hex[:8]}.mp4"
 
     async with async_playwright() as playwright:
-        browser = await playwright.chromium.launch(headless=True)
+        try:
+            browser = await playwright.chromium.launch(**chromium_launch_options())
+        except PlaywrightError as exc:
+            if "Executable doesn't exist" in str(exc):
+                raise BrowserRuntimeError(browser_install_message()) from exc
+            raise
         context = await browser.new_context(
             user_agent=(
                 "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 "
@@ -238,6 +291,8 @@ async def download(tiktok_url: str = Form(...)):
     try:
         async with download_lock:
             file_path, download_name = await fetch_mp4(validated_url)
+    except BrowserRuntimeError as exc:
+        return HTMLResponse(render_home(str(exc)), status_code=503)
     except Exception as exc:
         return HTMLResponse(render_home(f"Download failed: {exc}"), status_code=502)