Web UI: File browser does not validate PNG images for Application Covers

[eduardomozart]

Is there an existing issue for this?

• I have searched the existing issues

Is your issue described in the documentation?

• I have read the documentation

Is your issue present in the latest beta/pre-release?

This issue is present in the latest pre-release

Describe the Bug

The "Select File" file browser modal in the Web UI does not validate if the selected file is a PNG image when choosing an Application's Cover Image.

Gravacao.de.Tela.2026-08-18.as.16.12.07.mov

Reproduction Steps:

1. Open the Sunshine Web UI and navigate to the Applications tab.
2. Click Add New or edit an existing application.
3. Scroll down to the Image input field and click the folder icon ("Select File").
4. In the file browser, select a non-PNG file (e.g., a .md file) and click Select.
5. The file browser accepts the file and updates the path, providing no feedback to the user that the file is invalid.

Expected Behavior

The file browser modal should either filter out non-PNG files or display an error message if the user selects an unsupported file type.

Additional Context

Because the Web UI lacks validation, users can mistakenly configure their apps with unsupported images. They won't realize it failed until they notice their game cover is missing on Moonlight, leading to a confusing user experience.

Host Operating System

macOS

Operating System Version

26.5.2

Architecture

arm64/aarch64

Package

macOS - Homebrew

GPU Type

Apple Silicon

GPU Model

n/a

GPU Driver/Mesa Version

n/a

Capture Method

AVCaptureScreen (macOS)

Apps

{
    "apps": [
        {
            "image-path": "desktop.png",
            "name": "Desktop"
        },
        {
            "detached": [
                "open steam://open/bigpicture"
            ],
            "image-path": "steam.png",
            "name": "Steam Big Picture",
            "prep-cmd": [
                {
                    "do": "",
                    "undo": "open steam://close/bigpicture"
                }
            ]
        }
    ],
    "env": {
        "PATH": "$(PATH):$(HOME)/.local/bin"
    }
}

Log output

Online logs

No response

[ReenigneArcher]

FYI - You don't have to create an issue for every PR you're going to make. I know some projects require that, but we do not.