feat: enhance media file delivery with range support and inline display

- Added support for HTTP Range requests to enable partial downloads for media files, improving streaming capabilities.
- Implemented a new response function to handle binary media responses, including content disposition for inline display.
- Updated the media file download endpoint to utilize the new response handling, ensuring secure and efficient file delivery.
- Enhanced type hints and imports for better code clarity and maintainability.

backend/routers/exercises.py

@@ -8,11 +8,13 @@ import hashlib
 import json
 import logging
 import os
+import re
 from pathlib import Path
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, Iterator, List, Optional, Tuple
+from urllib.parse import quote
 
-from fastapi import APIRouter, HTTPException, Depends, Query, UploadFile, File, Form
-from fastapi.responses import FileResponse
+from fastapi import APIRouter, HTTPException, Depends, Query, Request, UploadFile, File, Form
+from fastapi.responses import FileResponse, Response, StreamingResponse
 from pydantic import BaseModel, Field, model_validator
 
 from db import get_db, get_cursor, r2d
@@ -1818,6 +1820,120 @@ def delete_exercise_variant(
     return {"ok": True}
 
 
+def _content_disposition_inline(filename: Optional[str]) -> str:
+    """Inline-Darstellung im Browser (<video>/<img>), keine attachment-Download-Leiste."""
+    if not filename:
+        return "inline"
+    fn = str(filename).strip()
+    quoted = quote(fn, safe="")
+    escaped = fn.replace('"', "\\")
+    if quoted != fn:
+        return f"inline; filename*=utf-8''{quoted}"
+    return f'inline; filename="{escaped}"'
+
+
+def _parse_bytes_range_single(range_header: str, file_size: int) -> Optional[Tuple[int, int]]:
+    """
+    Aus Range-Header einen inklusiven (start, end)-Bereich; None = gesamte Datei.
+    Nur ein bytes=-Segment (erstes Segment bei mehreren, durch Komma getrennt).
+    """
+    if not range_header:
+        return None
+    hdr = range_header.strip()
+    if "," in hdr:
+        hdr = hdr.split(",", 1)[0].strip()
+    m = re.match(r"^bytes=(\d*)-(\d*)$", hdr)
+    if not m:
+        return None
+    start_s, end_s = m.group(1), m.group(2)
+    if not start_s and not end_s:
+        return None
+    if file_size <= 0:
+        return None
+    last_idx = file_size - 1
+    if start_s == "" and end_s != "":
+        suffix = int(end_s)
+        if suffix <= 0:
+            return None
+        start = max(0, file_size - suffix)
+        end = last_idx
+    elif start_s != "" and end_s == "":
+        start = int(start_s)
+        end = last_idx
+    else:
+        start = int(start_s)
+        end = int(end_s)
+    end = min(end, last_idx)
+    if start > last_idx or start > end:
+        return None
+    return start, end
+
+
+def _iter_file_chunks(path_str: str, start: int, length: int) -> Iterator[bytes]:
+    chunk_size = 64 * 1024
+    remaining = length
+    with open(path_str, "rb") as f:
+        f.seek(start)
+        while remaining > 0:
+            blob = f.read(min(chunk_size, remaining))
+            if not blob:
+                break
+            remaining -= len(blob)
+            yield blob
+
+
+def _binary_media_response(
+    path_arg: Path, mime_type: str, download_name: Optional[str], request: Request
+):
+    """Vollständige oder Range-Download-Antwort; MP4/streaming brauchen oft 206 + Content-Range."""
+    path_str = str(path_arg.resolve())
+    stat_r = os.stat(path_str)
+    file_size = int(stat_r.st_size)
+    cd_val = _content_disposition_inline(download_name)
+    base_h = {"accept-ranges": "bytes", "content-disposition": cd_val}
+
+    if request.method.upper() == "HEAD":
+        return Response(
+            status_code=200,
+            headers={**base_h, "content-type": mime_type or "application/octet-stream", "content-length": str(file_size)},
+        )
+
+    rng = request.headers.get("range")
+    if rng and request.method.upper() != "HEAD":
+        rstrip = rng.strip()
+        if re.match(r"^bytes=(\d*)-(\d*)$", rstrip):
+            parsed = _parse_bytes_range_single(rng, file_size)
+            if parsed is None:
+                return Response(
+                    status_code=416,
+                    headers={
+                        "accept-ranges": "bytes",
+                        "content-range": f"bytes */{file_size}",
+                    },
+                )
+            start, end_incl = parsed
+            content_length = end_incl - start + 1
+            hdrs = {
+                **base_h,
+                "content-type": mime_type or "application/octet-stream",
+                "content-range": f"bytes {start}-{end_incl}/{file_size}",
+                "content-length": str(content_length),
+            }
+            return StreamingResponse(
+                _iter_file_chunks(path_str, start, content_length),
+                status_code=206,
+                headers=hdrs,
+                media_type=mime_type or "application/octet-stream",
+            )
+
+    return FileResponse(
+        path_str,
+        media_type=mime_type or "application/octet-stream",
+        stat_result=stat_r,
+        headers=base_h,
+    )
+
+
 # --- Medien (MEDIA_UPLOAD_SPEC.md / EXERCISES_API_SPEC.md) ---
 
 
@@ -1832,15 +1948,16 @@ def _fetch_media_row(cur, exercise_id: int, media_id: int) -> Optional[dict]:
     return r2d(row) if row else None
 
 
-@router.get("/exercises/{exercise_id}/media/{media_id}/file")
+@router.api_route("/exercises/{exercise_id}/media/{media_id}/file", methods=["GET", "HEAD"])
 def download_exercise_media_file(
+    request: Request,
     exercise_id: int,
     media_id: int,
     tenant: TenantContext = Depends(get_tenant_context_flexible),
 ):
     """
     Dateiauslieferung mit Governance wie GET Übung — Auth via X-Auth-Token oder ?ssetoken (für <img>/<video>).
-    Direktes /media/... ohne Token ist nicht vorgesehen (kein anonymes Hosting).
+    Unterstützt HTTP Range (206) für MP4-Streaming und Content-Disposition: inline (kein attachment).
     """
     with get_db() as conn:
         cur = get_cursor(conn)
@@ -1858,11 +1975,7 @@ def download_exercise_media_file(
 
         mime = media.get("mime_type") or "application/octet-stream"
         fname = media.get("original_filename") or abs_p.name
-        return FileResponse(
-            path=str(abs_p.resolve()),
-            media_type=mime,
-            filename=str(fname),
-        )
+        return _binary_media_response(abs_p, mime, str(fname) if fname else None, request)
 
 
 @router.post("/exercises/{exercise_id}/media", status_code=201)