ContentType specified in AttachmentItem during CreateUploadSession is not preserved; defaults to application/octet-stream

[GregoryJord]

Describe the bug

When creating an upload session using the Microsoft Graph SDK to upload large file attachments, the ContentType set in the AttachmentItem is ignored. After the upload completes, fetching the attachment metadata always shows "application/octet-stream" as the content type, regardless of the originally specified MIME type (e.g., "image/png").

Expected behavior

The MIME type specified in the AttachmentItem.ContentType should be preserved and reflected correctly in the attachment metadata after upload. This would allow proper content type handling when serving the file to users.

How to reproduce

Create an upload session with an AttachmentItem specifying a ContentType (e.g., "image/png").

Upload the file using the session.

Fetch the uploaded attachment metadata using the Microsoft Graph SDK.

Observe that the contentType returned is "application/octet-stream" instead of the specified MIME type.

SDK Version

No response

Latest version known to work for scenario above?

No response

Known Workarounds

No response

Debug output

Click to expand log

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### Configuration

_No response_

### Other information

_No response_

[MIchaelMainer]

Thank you for opening this issue. We need more information to understand whether this is a client library or a service issue. Please provide us with the following information:

1. Full code reproduction.
   • initializing the client
   • how you form objects for requests
   • building the URL
   • adding query parameters
   • any changes made to object state
   • how you handled the response, did you include any custom middleware
2. Environment
   • is this a delegated or application permission scenario
   • what type of application is this: server, web, client, etc
   • what operating system are you on
3. Specific client library version as the latest version is always being updated.
4. Have you been able to form a workaround? If so, what did you do?

[microsoft-github-policy-service]

This issue has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 4 days. It will be closed if no further activity occurs within 3 days of this comment.