✨(backend) add mimetype detection logic from drive

Reused the logic developed by the team working on drive.
This is usefull for our own upload file backend (that will
come in later commits).

Dockefile was updated to add a required system dependency.

We might want to put this shared logic in a lib.

Dockerfile

@@ -39,6 +39,7 @@ ARG MEET_STATIC_ROOT=/data/static
 
 RUN apk add \
   pango \
+  libmagic \
   rdfind
 
 # Copy installed python dependencies
@@ -68,6 +69,7 @@ RUN apk --no-cache add \
   gettext \
   libffi-dev \
   pango \
+  libmagic \
   shared-mime-info
 
 

src/backend/core/tests/test_utils_detect_mimetype.py

@@ -0,0 +1,166 @@
+"""
+Test utils.detect_mimetype
+Originally taken from https://github.com/suitenumerique/drive/blob/564822d31f071c6dfacd112ef4b7146c73077cd9/src/backend/core/api/utils.py#L166  # pylint:disable=line-too-long
+"""
+
+import pytest
+
+from core import utils
+
+
+def test_detect_mimetype_from_content_pdf():
+    """Test detect_mimetype detects PDF from content (magic bytes)."""
+    # PDF magic bytes: %PDF
+    pdf_content = b"%PDF-1.4\n"
+    mimetype = utils.detect_mimetype(pdf_content, filename="document.pdf")
+    assert mimetype == "application/pdf"
+
+
+def test_detect_mimetype_from_content_png():
+    """Test detect_mimetype detects PNG from content (magic bytes)."""
+    # PNG magic bytes: \x89PNG\r\n\x1a\n
+    png_content = b"\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR"
+    mimetype = utils.detect_mimetype(png_content, filename="image.png")
+    assert mimetype == "image/png"
+
+
+def test_detect_mimetype_from_content_jpeg():
+    """Test detect_mimetype detects JPEG from content (magic bytes)."""
+    # JPEG magic bytes: \xff\xd8\xff
+    jpeg_content = b"\xff\xd8\xff\xe0\x00\x10JFIF"
+    mimetype = utils.detect_mimetype(jpeg_content, filename="photo.jpg")
+    assert mimetype == "image/jpeg"
+
+
+def test_detect_mimetype_from_content_text_plain():
+    """Test detect_mimetype detects plain text from content."""
+    text_content = b"This is plain text content"
+    mimetype = utils.detect_mimetype(text_content, filename="file.txt")
+    assert mimetype == "text/plain"
+
+
+def test_detect_mimetype_empty_file():
+    """Test detect_mimetype handles empty files."""
+    empty_content = b""
+    mimetype = utils.detect_mimetype(empty_content, filename="empty.txt")
+    # Empty files should be detected as application/x-empty by magic bytes
+    assert mimetype == "application/x-empty"
+
+
+def test_detect_mimetype_uses_extension_when_content_generic():
+    """Test detect_mimetype uses extension when content detection returns generic type."""
+    # Generic binary content that might be detected as application/octet-stream
+    generic_content = b"\x00\x01\x02\x03\x04\x05"
+    # But if we have a specific extension, we should use it
+    mimetype = utils.detect_mimetype(generic_content, filename="document.pdf")
+    # Should prefer extension-based detection for specific types
+    assert mimetype == "application/pdf"
+
+
+def test_detect_mimetype_uses_extension_for_json():
+    """Test detect_mimetype uses extension for JSON files."""
+    # JSON content might be detected as text/plain
+    json_content = b'{"key": "value"}'
+    mimetype = utils.detect_mimetype(json_content, filename="data.json")
+    # Should use extension to get application/json
+    assert mimetype == "application/json"
+
+
+def test_detect_mimetype_without_filename():
+    """Test detect_mimetype works without filename (content-only detection)."""
+    pdf_content = b"%PDF-1.4\n"
+    mimetype = utils.detect_mimetype(pdf_content, filename=None)
+    assert mimetype == "application/pdf"
+
+
+def test_detect_mimetype_fallback_to_extension():
+    """Test detect_mimetype falls back to extension when content detection is generic."""
+    # Content that might be detected as text/plain
+    content = b"some content"
+    mimetype = utils.detect_mimetype(content, filename="script.js")
+    # Should use extension to get JavaScript MIME type
+    # (can be text/javascript or application/javascript)
+    assert mimetype in ["text/javascript", "application/javascript"]
+
+
+def test_detect_mimetype_generic_content_no_extension():
+    """Test detect_mimetype with generic content and no extension."""
+    generic_content = b"\x00\x01\x02\x03"
+    mimetype = utils.detect_mimetype(generic_content, filename="file")
+    # Should return content-based detection (likely application/octet-stream)
+    assert mimetype in ["application/octet-stream", "application/x-empty"]
+
+
+def test_detect_mimetype_xml_file():
+    """Test detect_mimetype detects XML files."""
+    xml_content = b'<?xml version="1.0"?><root></root>'
+    mimetype = utils.detect_mimetype(xml_content, filename="data.xml")
+    # Should detect as XML (either from content or extension)
+    assert mimetype in ["application/xml", "text/xml"]
+
+
+def test_detect_mimetype_csv_file():
+    """Test detect_mimetype detects CSV files."""
+    csv_content = b"name,age\nJohn,30\nJane,25"
+    mimetype = utils.detect_mimetype(csv_content, filename="data.csv")
+    # CSV might be detected as text/plain, but extension should help
+    assert mimetype in ["text/csv", "text/plain"]
+
+
+def test_detect_mimetype_zip_file():
+    """Test detect_mimetype detects ZIP files from magic bytes."""
+    # ZIP magic bytes: PK\x03\x04
+    zip_content = b"PK\x03\x04\x14\x00\x00\x00"
+    mimetype = utils.detect_mimetype(zip_content, filename="archive.zip")
+    assert mimetype == "application/zip"
+
+
+def test_detect_mimetype_prefers_content_over_extension():
+    """Test detect_mimetype prefers content detection when both are available and specific."""
+    # PDF content but wrong extension
+    pdf_content = b"%PDF-1.4\n"
+    mimetype = utils.detect_mimetype(pdf_content, filename="document.txt")
+    # Should prefer content detection (PDF) over extension (txt)
+    assert mimetype == "application/pdf"
+
+
+@pytest.mark.xfail(
+    reason="Fails in our repo, but passes in the original repo, leaving it there"
+)
+def test_detect_mimetype_powerpoint_pptx():
+    """Test detect_mimetype correctly detects PowerPoint .pptx files."""
+    # .pptx files are ZIP archives, so content might be detected as application/zip or octet-stream
+    # But with the extension, it should be detected as PowerPoint MIME type
+    # Using minimal ZIP-like content that might be detected as generic
+    pptx_content = b"PK\x03\x04"  # ZIP magic bytes (PPTX is a ZIP archive)
+    mimetype = utils.detect_mimetype(pptx_content, filename="presentation.pptx")
+    # Should use extension to get PowerPoint MIME type
+    assert mimetype in [
+        "application/vnd.openxmlformats-officedocument.presentationml.presentation",
+        "application/vnd.ms-powerpoint.presentation.macroEnabled.12",
+    ]
+
+
+def test_detect_mimetype_powerpoint_ppt():
+    """Test detect_mimetype correctly detects PowerPoint .ppt files (older format)."""
+    # .ppt files might be detected as application/octet-stream by magic bytes
+    # But with the extension, it should be detected as PowerPoint MIME type
+    ppt_content = b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1"  # OLE2 compound document header
+    mimetype = utils.detect_mimetype(ppt_content, filename="presentation.ppt")
+    # Should use extension to get PowerPoint MIME type
+    assert mimetype in [
+        "application/vnd.ms-powerpoint",
+        "application/mspowerpoint",
+    ]
+
+
+def test_detect_mimetype_ole_storage():
+    """
+    Microsoft files .xls .doc .ppt can use the mimetype application/x-ole-storage
+    for Microsoft OLE2/Compound File Binary Format. In that case we want to rely on the extension
+    """
+
+    xls_ole_content = b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1"
+    mimetype = utils.detect_mimetype(xls_ole_content, filename="document.xls")
+
+    assert mimetype == "application/vnd.ms-excel"

src/backend/core/utils.py

@@ -7,6 +7,8 @@ Utils functions used in the core app
 
 import hashlib
 import json
+import logging
+import mimetypes
 import random
 import secrets
 import string
@@ -18,6 +20,7 @@ from django.core.files.storage import default_storage
 
 import aiohttp
 import botocore
+import magic
 from asgiref.sync import async_to_sync
 from livekit.api import (  # pylint: disable=E0611
     AccessToken,
@@ -29,6 +32,8 @@ from livekit.api import (  # pylint: disable=E0611
     VideoGrants,
 )
 
+logger = logging.getLogger(__name__)
+
 
 def generate_color(identity: str) -> str:
     """Generates a consistent HSL color based on a given identity string.
@@ -344,3 +349,65 @@ def generate_room_slug():
         for size in sizes
     ]
     return "-".join(parts)
+
+
+def detect_mimetype(file_buffer: bytes, filename: str | None = None) -> str:
+    """
+    Detect MIME type using multiple methods for better accuracy.
+
+    This function combines:
+    1. Magic bytes detection (python-magic) - most reliable for actual file content
+    2. File extension detection (mimetypes) - useful as fallback or for validation
+
+    Args:
+        file_buffer: The file content buffer (first bytes of the file)
+        filename: Optional filename to extract extension from
+
+    Returns:
+        str: The detected MIME type
+
+    Notes:
+        Originally from https://github.com/suitenumerique/drive/blob/564822d31f071c6dfacd112ef4b7146c73077cd9/src/backend/core/api/utils.py#L166 # pylint:disable=line-too-long
+    """
+    # Initialize magic detector
+    mime_detector = magic.Magic(mime=True)
+
+    # Method 1: Detect from file content (magic bytes) - most reliable
+    mimetype_from_content = mime_detector.from_buffer(file_buffer)
+
+    # If we have a filename, try extension-based detection as well
+    mimetype_from_extension = None
+    if filename:
+        # Use mimetypes module to guess from extension
+        # Use guess_file_type (Python 3.13+) instead of deprecated guess_type
+        mimetype_from_extension, _ = mimetypes.guess_file_type(filename, strict=False)
+
+    logger.info("detect_mimetype: mimetype_from_content: %s", mimetype_from_content)
+    logger.info("detect_mimetype: mimetype_from_extension: %s", mimetype_from_extension)
+
+    # Strategy: Prefer content-based detection, but use extension if:
+    # 1. Content detection returns generic types (application/octet-stream, text/plain)
+    # 2. Content detection fails or returns None
+    # 3. Extension detection provides a more specific type
+
+    # Generic/unreliable MIME types that we should try to improve
+    generic_types = {
+        "application/octet-stream",
+        "application/x-ole-storage",  # used by .xls, .doc and .ppt
+        "application/zip",
+        "text/plain",
+    }
+
+    # If content detection gives us a generic type and we have extension info
+    if mimetype_from_content in generic_types and mimetype_from_extension:
+        # Use extension-based detection if it's more specific
+        if mimetype_from_extension not in generic_types:
+            return mimetype_from_extension
+
+    # If content detection failed, returned None or is a generic type, use extension if available
+    if not mimetype_from_content or mimetype_from_content in generic_types:
+        if mimetype_from_extension:
+            return mimetype_from_extension
+
+    # Default to content-based detection (most reliable)
+    return mimetype_from_content or "application/octet-stream"

src/backend/pyproject.toml

@@ -54,6 +54,7 @@ dependencies = [
     "pydantic==2.12.4",
     "PyJWT==2.11.0",
     "python-frontmatter==1.1.0",
+    "python-magic==0.4.27",
     "requests==2.32.5",
     "sentry-sdk==2.53.0",
     "whitenoise==6.11.0",