CSOM is url encoding filenames

[sch-alib]

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

SharePoint CSOM

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

No response

Describe the bug / error

A file created in SPO library using CSOM with FileCreationInformation object is using url-encoded format for character that are not letters, in the file name.

For example "(" is getting replaced with "%28"

The issue was observed only on Mar/11 and Mar/12 2025 ... before and after these dates its working fine , non-letter characters in filename are not getting url-encoded

Steps to reproduce

// Define new file creation information
FileCreationInformation newFile = new FileCreationInformation
{
Url = "filename(1).txt", // Only the name of the file
Content = System.Text.Encoding.UTF8.GetBytes("This is the content of the file."), // File content as byte array
Overwrite = true // Set overwrite to true or false as needed
};

Expected behavior

The filename for the newly created file in SPO library should not url-encode non-letter characters

[Amey-MSFT]

Hello @sch-alib ,
Thank you for bringing this issue to our attention. We will look into it and get back to you shortly.

[Ashlesha-MSFT]

@sch-alib,

1. I was not able to repro as I was not able to authenticate using code. Could you please share the code you are using for authentication? This will help us verify if there is any difference in the authentication approach that might be affecting the filename behavior.

2. I tested the same scenario using PowerShell, and the expected behavior was observed—the file was created with the correct name, without URL encoding non-letter characters. It seems that the issue might be specific to CSOM in C#.

thanks!

[sch-alib]

@Ashlesha-MSFT

2. I tested the same scenario using PowerShell, and the expected behavior was observed—the file was created with the correct name, without URL encoding non-letter characters. It seems that the issue might be specific to CSOM in C#.

The issue was observed only on Mar/11 and Mar/12 2025 ... before and after these dates its working fine , non-letter characters in filename are not getting url (percent) encoded

Are there any new API changes coming that we should be aware of ?
Or was there an unintentional API change that was reverted back ?

[sch-alib]

@Ashlesha-MSFT
For auth, its a client credential flow using PnP AuthenticationManager's GetACSAppOnlyContext function

https://pnp.github.io/pnpframework/api/PnP.Framework.AuthenticationManager.html#PnP_Framework_AuthenticationManager_GetACSAppOnlyContext_System_String_System_String_System_String_

The code then uses the client context returned from the function.

[Ashlesha-MSFT]

@sch-alib,
we have already escalated this question to the engineering team, and they will respond back with further details
Thanks!.