fix: resolve empty attachment MIME types from filename

apps/api/plane/api/views/asset.py

@@ -18,6 +18,7 @@
 from plane.bgtasks.storage_metadata_task import get_asset_object_metadata
 from plane.settings.storage import S3Storage
 from plane.utils.path_validator import sanitize_filename
+from plane.utils.attachment import resolve_attachment_content_type
 from plane.db.models import FileAsset, User, Workspace
 from plane.app.permissions import WorkspaceUserPermission
 from plane.api.views.base import BaseAPIView
@@ -516,7 +517,7 @@ def post(self, request, slug):
         Supports various file types and includes external source tracking for integrations.
         """
         name = sanitize_filename(request.data.get("name"))
-        type = request.data.get("type")
+        type = resolve_attachment_content_type(name, request.data.get("type"))
         size = int(request.data.get("size", settings.FILE_SIZE_LIMIT))
         project_id = request.data.get("project_id")
         external_id = request.data.get("external_id")

apps/api/plane/api/views/issue.py

@@ -80,6 +80,7 @@
 )
 from plane.settings.storage import S3Storage
 from plane.utils.path_validator import sanitize_filename
+from plane.utils.attachment import resolve_attachment_content_type
 from plane.utils.order_queryset import (
     ACTIVITY_ORDER_BY_ALLOWLIST,
     ISSUE_ORDER_BY_ALLOWLIST,
@@ -1884,7 +1885,7 @@ def post(self, request, slug, project_id, issue_id):
             )
 
         name = sanitize_filename(request.data.get("name"))
-        type = request.data.get("type", False)
+        type = resolve_attachment_content_type(name, request.data.get("type", False))
         size = request.data.get("size")
         external_id = request.data.get("external_id")
         external_source = request.data.get("external_source")

apps/api/plane/app/views/issue/attachment.py

@@ -27,6 +27,7 @@
 from plane.utils.path_validator import sanitize_filename
 from plane.bgtasks.storage_metadata_task import get_asset_object_metadata
 from plane.utils.host import base_host
+from plane.utils.attachment import resolve_attachment_content_type
 
 
 class IssueAttachmentEndpoint(BaseAPIView):
@@ -99,7 +100,7 @@ class IssueAttachmentV2Endpoint(BaseAPIView):
     @allow_permission([ROLE.ADMIN, ROLE.MEMBER, ROLE.GUEST])
     def post(self, request, slug, project_id, issue_id):
         name = sanitize_filename(request.data.get("name")) or "unnamed"
-        type = request.data.get("type", False)
+        type = resolve_attachment_content_type(name, request.data.get("type", False))
         size = int(request.data.get("size", settings.FILE_SIZE_LIMIT))
 
         if not type or type not in settings.ATTACHMENT_MIME_TYPES:

apps/api/plane/settings/common.py

@@ -473,6 +473,8 @@ def _retention_days(env_var, default):
     "application/vnd.openxmlformats-officedocument.presentationml.presentation",
     "text/plain",
     "text/markdown",
+    "text/csv",
+    "text/tab-separated-values",
     "application/rtf",
     "application/vnd.oasis.opendocument.spreadsheet",
     "application/vnd.oasis.opendocument.text",

apps/api/plane/tests/unit/utils/test_attachment.py

@@ -0,0 +1,33 @@
+# Copyright (c) 2023-present Plane Software, Inc. and contributors
+# SPDX-License-Identifier: AGPL-3.0-only
+# See the LICENSE file for details.
+
+"""Unit tests for attachment MIME resolution helpers."""
+
+import pytest
+
+from plane.utils.attachment import resolve_attachment_content_type
+
+
+@pytest.mark.unit
+class TestResolveAttachmentContentType:
+    def test_prefers_provided_content_type(self):
+        assert resolve_attachment_content_type("note.md", "text/plain") == "text/plain"
+        assert resolve_attachment_content_type("note.md", "  text/markdown  ") == "text/markdown"
+
+    def test_falls_back_for_empty_type_on_markdown(self):
+        assert resolve_attachment_content_type("readme.md", "") == "text/markdown"
+        assert resolve_attachment_content_type("readme.md", None) == "text/markdown"
+        assert resolve_attachment_content_type("readme.md", False) == "text/markdown"
+
+    def test_falls_back_for_empty_type_on_txt(self):
+        assert resolve_attachment_content_type("notes.txt", "") == "text/plain"
+
+    def test_falls_back_for_empty_type_on_csv(self):
+        # Platform mimetypes may return text/csv or application/vnd.ms-excel
+        resolved = resolve_attachment_content_type("data.csv", "")
+        assert resolved in {"text/csv", "application/vnd.ms-excel"}
+
+    def test_returns_none_without_name_or_type(self):
+        assert resolve_attachment_content_type(None, "") is None
+        assert resolve_attachment_content_type("", None) is None

apps/api/plane/utils/attachment.py

@@ -0,0 +1,46 @@
+# Copyright (c) 2023-present Plane Software, Inc. and contributors
+# SPDX-License-Identifier: AGPL-3.0-only
+# See the LICENSE file for details.
+
+"""Helpers for work item / generic attachment uploads."""
+
+from __future__ import annotations
+
+import mimetypes
+import os
+
+# System mimetypes databases often omit or mis-map common text extensions
+# (e.g. .md → None, .csv → text/csv vs application/vnd.ms-excel). Prefer an
+# allowlisted type when guessing from the filename alone.
+_EXTENSION_MIME_FALLBACKS: dict[str, str] = {
+    ".md": "text/markdown",
+    ".markdown": "text/markdown",
+    ".mdown": "text/markdown",
+    ".mkd": "text/markdown",
+    ".txt": "text/plain",
+    ".text": "text/plain",
+    ".log": "text/plain",
+    ".csv": "text/csv",
+    ".tsv": "text/tab-separated-values",
+}
+
+
+def resolve_attachment_content_type(name: str | None, content_type: str | None | bool) -> str | None:
+    """Return a usable MIME type for an attachment upload.
+
+    Browsers (notably on macOS) often send an empty ``File.type`` for text
+    extensions such as ``.md``, ``.csv``, and ``.txt``. Fall back to guessing
+    from the filename so allowlisted types are not rejected incorrectly.
+    """
+    if content_type and isinstance(content_type, str) and content_type.strip():
+        return content_type.strip()
+
+    if not name or not isinstance(name, str):
+        return None
+
+    guessed, _ = mimetypes.guess_type(name)
+    if guessed:
+        return guessed
+
+    extension = os.path.splitext(name)[1].lower()
+    return _EXTENSION_MIME_FALLBACKS.get(extension)

packages/services/src/file/helper.ts

@@ -81,6 +81,34 @@ const detectMimeTypeFromSignature = async (file: File): Promise<string> => {
   }
 };
 
+/**
+ * Extension → MIME map for text-like files that lack a binary signature.
+ * Browsers (especially on macOS) often leave File.type empty for these.
+ */
+const EXTENSION_MIME_FALLBACKS: Record<string, string> = {
+  md: "text/markdown",
+  markdown: "text/markdown",
+  mdown: "text/markdown",
+  mkd: "text/markdown",
+  txt: "text/plain",
+  text: "text/plain",
+  log: "text/plain",
+  csv: "text/csv",
+  tsv: "text/tab-separated-values",
+};
+
+/**
+ * @description Guess MIME type from filename extension when browser/signature detection fails
+ * @param {string} filename
+ * @returns {string} guessed MIME type or empty string
+ */
+const guessMimeTypeFromFilename = (filename: string): string => {
+  const parts = filename.toLowerCase().split(".");
+  if (parts.length < 2) return "";
+  const extension = parts[parts.length - 1] || "";
+  return EXTENSION_MIME_FALLBACKS[extension] || "";
+};
+
 /**
  * @description Validate and detect the MIME type of a file using signature detection
  * Also performs basic security checks on filename
@@ -103,7 +131,17 @@ const validateAndDetectFileType = async (file: File): Promise<string> => {
     console.warn("Error detecting file type from signature:", _error);
   }
 
-  // fallback for unknown files
+  // Browser-provided type (empty for many text files on macOS)
+  if (file.type && file.type.trim()) {
+    return file.type.trim();
+  }
+
+  // Extension fallback for text-like uploads with no magic bytes
+  const extensionType = guessMimeTypeFromFilename(file.name);
+  if (extensionType) {
+    return extensionType;
+  }
+
   return "";
 };