fix(attachments): infer MIME type from filename when stored as octet-stream

src/sentry/models/eventattachment.py

@@ -247,7 +247,9 @@ def putfile(cls, project_id: int, attachment: CachedAttachment) -> PutfileResult
 
 def normalize_content_type(content_type: str | None, name: str) -> str:
     if content_type:
-        return content_type.split(";")[0].strip()
+        normalized = content_type.split(";")[0].strip()
+        if normalized.lower() != "application/octet-stream":
+            return normalized
     return mimetypes.guess_type(name)[0] or "application/octet-stream"
 
 

tests/sentry/ingest/ingest_consumer/test_ingest_consumer_processing.py

@@ -523,15 +523,15 @@ def test_process_stored_attachment(
 @pytest.mark.parametrize(
     "attachment",
     [
-        ([b"Hello ", b"World!"], "event.attachment", "application/octet-stream"),
-        ([b""], "event.attachment", "application/octet-stream"),
-        ([], "event.attachment", "application/octet-stream"),
+        ([b"Hello ", b"World!"], "event.attachment", "text/plain"),
+        ([b""], "event.attachment", "text/plain"),
+        ([], "event.attachment", "text/plain"),
         (
             [b'{"rendering_system":"flutter","windows":[]}'],
             "event.view_hierarchy",
             "application/json",
         ),
-        (b"inline attachment", "event.attachment", "application/octet-stream"),
+        (b"inline attachment", "event.attachment", "text/plain"),
     ],
     ids=["basic", "zerolen", "nochunks", "view_hierarchy", "inline"],
 )

tests/sentry/models/test_eventattachment.py

@@ -4,7 +4,7 @@
 from unittest import mock
 from uuid import uuid4
 
-from sentry.models.eventattachment import EventAttachment
+from sentry.models.eventattachment import EventAttachment, normalize_content_type
 from sentry.testutils.cases import TestCase
 
 
@@ -48,3 +48,29 @@ def test_v2_delete_skips_objectstore_during_cleanup(
 
         mock_get_session.return_value.delete.assert_not_called()
         assert not EventAttachment.objects.filter(id=attachment.id).exists()
+
+
+class NormalizeContentTypeTest(TestCase):
+    def test_returns_explicit_content_type(self):
+        assert normalize_content_type("image/png", "file.png") == "image/png"
+
+    def test_strips_charset_from_content_type(self):
+        assert normalize_content_type("text/plain; charset=utf-8", "file.txt") == "text/plain"
+
+    def test_infers_from_filename_when_none(self):
+        assert normalize_content_type(None, "screenshot.png") == "image/png"
+
+    def test_infers_from_filename_when_octet_stream(self):
+        assert normalize_content_type("application/octet-stream", "screenshot.png") == "image/png"
+
+    def test_falls_back_to_octet_stream_when_unrecognized(self):
+        assert normalize_content_type(None, "data.bin") == "application/octet-stream"
+
+    def test_octet_stream_with_unrecognized_name(self):
+        assert (
+            normalize_content_type("application/octet-stream", "noext")
+            == "application/octet-stream"
+        )
+
+    def test_octet_stream_case_insensitive(self):
+        assert normalize_content_type("Application/Octet-Stream", "screenshot.png") == "image/png"