refactor: #85 T6a extrait lecture fichiers vers backend/routers (comportement inchange)

backend/routers/helpers.py

@@ -0,0 +1,51 @@
+"""Shared helpers for the file routers (ROADMAP #85, tranche 6a).
+
+Petites fonctions pures extraites de :mod:`backend.main` sans changement
+de comportement. Regroupées ici car utilisées par plusieurs routers
+(``files_read`` aujourd'hui, ``files_media`` / mutations ensuite) :
+- :func:`content_disposition` — aussi utilisée par ``_stream_file_with_range``
+  (resté dans ``main`` jusqu'à la tranche media).
+- :func:`media_max_inline_bytes` — aussi utilisée par ``/api/media``.
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+
+def content_disposition(disposition: str, filename: str) -> str:
+    """Build a header-safe Content-Disposition value.
+
+    HTTP header values must be ASCII. Unicode filenames are sent per
+    RFC 5987 via ``filename*`` (percent-encoded UTF-8) with a pure-ASCII
+    ``filename`` fallback. This avoids a UnicodeDecodeError / HTTP 500 when
+    the filename contains accented characters (e.g. 'Bière blonde…pdf').
+    """
+    from urllib.parse import quote
+    ascii_name = "".join(c for c in filename if c.isascii() and (c.isalnum() or c in " _-.")).strip() or "file"
+    ext = Path(filename).suffix
+    if ext and not Path(ascii_name).suffix:
+        ascii_name = ascii_name + ext
+    return f"{disposition}; filename=\"{ascii_name}\"; filename*=UTF-8''{quote(filename)}"
+
+
+def media_max_inline_bytes() -> int:
+    """Maximum size (bytes) for inline audio/video playback (roadmap #109-A3).
+
+    Configurable via ``OBSIGATE_MEDIA_MAX_INLINE_MB`` (default 500 MB). Files
+    above the limit are not streamed in the viewer (the UI falls back to the
+    download button), which keeps a single uvicorn worker from being pinned by
+    multi-gigabyte media. Invalid or non-positive values fall back to default.
+    """
+    default_mb = 500
+    raw = os.environ.get("OBSIGATE_MEDIA_MAX_INLINE_MB", "").strip()
+    if not raw:
+        return default_mb * 1024 * 1024
+    try:
+        mb = float(raw)
+    except ValueError:
+        return default_mb * 1024 * 1024
+    if mb <= 0:
+        return default_mb * 1024 * 1024
+    return int(mb * 1024 * 1024)