[Issue] Getting "Error in data loop! System.IO.EndOfStreamException: Attempted to read past the end of the stream." on Mac M3 Max.

[nattb8]

What platform are you experiencing this issue on?

Windows x64

What version of UWB are you using?

2.2.5

What Unity version are you running?

2021.3.26f1

Describe what the issue you are experiencing is.

Unable to use UWB on Mac. I'm getting "Error in data loop! System.IO.EndOfStreamException: Attempted to read past the end of the stream." on my Mac M3 Max.

Provide reproducible steps for this issue.

1. Add Web Browser Full to my scene
2. Set "Popup action" to "Open External Window".
3. Set initial URL to https://javascript.info/popup-windows
4. UWB successfully loads the page
5. Under the "Example: a minimalistic window" section, there's play button in the example code. Click on the play button which then launches a pop-up.
6. Close the pop-up

[UWB]: Error in data loop! System.IO.EndOfStreamException: Attempted to read past the end of the stream.

[UWB]: An error occured while executing task SendMouseMoveEvent! System.IO.EndOfStreamException: Attempted to read past the end of the stream.

[UWB]: It appears that the engine process has quit!

Any additional info you like to provide?

This works fine on Windows. You can test it with this link.

[debadri-naskar]

I am having the exact same issue. Following are the details:

• System Info: Mac M2 Pro with Mac OS version 15.2
• Unity Version: 2021.3.45f1 (Intel)
• UWB Version: 2.2.5

Please provide a solution for this. I'm currently stuck.
Thanks in advance.

[Voltstro]

I've taken a look at this issue and have replicated it in a MacOS vm. The engine process is crashing, the crash seems to come from CEF, and is probably something to do with UWB's plist config, but not too sure. Need someone with better MacOS know-how to look.

[CodeSchwert]

I ran into this on Mac M1 Pro but managed to fix it by running CEF with the single process flag:

//  dev.voltstro.unitywebbrowser@2.2.5/Runtime/Core/WebBrowserArgsBuilder.cs
/// <summary>
///     Adds a flag-only argument (without parameters)
/// </summary>
/// <param name="arg"></param>
public void AppendFlag(string arg)
{
    arguments.Add($"-{arg}");
}

// dev.voltstro.unitywebbrowser@2.2.5/Runtime/Core/WebBrowserClient.cs
argsBuilder.AppendFlag("single-process");

[taranasus]

@Voltstro @nattb8

I've done extensive investigation into this issue for my game Vecter to get it ported to MacOS and have it play youtube videos in-game, and found the root cause. It's not a UWB plist configuration issue - it's a macOS Sequoia code signing/notarization requirement that affects CEF subprocesses.

Root Cause Analysis: macOS Sequoia CEF Subprocess Validation

After extensive debugging of this issue, I've identified the root cause. This is not a UWB bug - it's a macOS Sequoia platform requirement.

The Problem

macOS Sequoia (15.x+) has significantly stricter subprocess signature validation. When CEF launches its helper processes (GPU, Network, Renderer, Plugin), macOS validates their signatures before allowing execution. The error -67030 (errSecCSInfoPlistFailed) indicates signature validation failure.

What We Tried

1. Single-process mode (--single-process) - Crashes immediately, CEF doesn't support this properly

2. Ad-hoc signing (codesign --sign -) - Insufficient, no Team ID for subprocess validation

3. Developer ID signing - Works for signature validation but...

4. Hardened runtime with entitlements - Including all the entitlements from jcefbuild:

   • com.apple.security.cs.allow-jit
   • com.apple.security.cs.allow-unsigned-executable-memory
   • com.apple.security.cs.disable-library-validation
   • com.apple.security.cs.allow-dyld-environment-variables
   • com.apple.security.cs.disable-executable-page-protection
   • com.apple.security.inherit

5. Hierarchical inside-out signing - Signing from innermost frameworks outward to main app

The Actual Requirement

Even with proper Developer ID signing and all entitlements, spctl -a -vvv shows:

source=Unnotarized Developer ID

macOS Sequoia requires full Apple Notarization for subprocess validation to work. This means:

• Apple Developer Program membership ($99/year)
• Developer ID Application certificate
• Submitting the app to Apple's notarization service
• Apple scanning and approving the binaries
• Stapling the notarization ticket to the app

Why This Is Problematic for UWB

The CEF engine binaries ship as part of UWB packages. For notarization to work:

1. Either UWB maintainers would need to notarize the CEF engine packages (significant ongoing cost and maintenance)
2. Or every developer using UWB on macOS would need to notarize their entire build including the CEF engine - This is more fesable for production, for-profit games since they would be able to build up a relationship with apple and have interest in distribution they game.

My Workaround

For my case (a free game on Steam), I've simply disabled the feature in-game and will just inform my mac player-base (all 0.2 of them) that the feature doesn't work thanks to apple's insanity. There's nothing more that really can be done in my situation.

Recommendations

1. Document this limitation - macOS Sequoia users should be aware that UWB/CEF requires notarization to function in a production environment (when distributing the app / game to users)
2. Consider alternative approaches for macOS:
   • Native WebView (WKWebView) integration for macOS builds
   • Disabling the feature on macOS (our approach)
   • Full notarization pipeline for commercial products

This isn't something that can be "fixed" in UWB - it's an Apple platform policy. The only solutions are compliance (notarization) or avoidance (disable on macOS).

---

Environment:

• macOS Sequoia 15.x / Darwin 25.1.0
• Unity 6000.2.x
• UWB with CEF 137
• Apple Silicon (M2 Max)

[taranasus]

Update: Found a Working Solution!

After more investigation, I discovered why CEF works in the Unity Editor but fails in builds - and found a fix that doesn't require notarization. The Key Insight In the Unity Editor, CEF runs as a standalone app on the filesystem. In builds, CEF was being placed inside the main app bundle (Vecter.app/Contents/Frameworks/). The problem is that Vecter.app has the hardened runtime flag enabled, and macOS Sequoia's stricter validation doesn't like ad-hoc signed nested bundles inside hardened runtime apps. The Solution: Place CEF Outside the App Bundle Instead of nesting CEF inside the app bundle, place it as a sibling folder:

builds/
├── Vecter.app/
└── UWBEngine/
├── arm64/
│ └── UnityWebBrowser.Engine.Cef.app/
└── x64/
└── UnityWebBrowser.Engine.Cef.app/

Implementation
Update CEFEngineConfig.asset to use a relative path outside the bundle:

For ARM64

engineRuntimeLocation: ../../UWBEngine/arm64/

For x64

engineRuntimeLocation: ../../UWBEngine/x64/

Modify your build post-processor to copy CEF to the sibling folder instead of inside Contents/Frameworks/.

Important: Kill stale CEF processes on game startup and quit to avoid port conflicts (TCP 5555/5556). CEF doesn't always clean up properly, especially if the game crashes.

Result: YouTube playback now works reliably on macOS Sequoia without notarization. The -67030 signature validation error no longer occurs because CEF runs as an independent app bundle rather than a nested subprocess inside a hardened runtime app.

Caveats

Distribution is slightly more complex (need to ship the UWBEngine folder alongside the .app)
For Steam, you'll need to include the UWBEngine folder in your depot
You may want to add process cleanup logic to handle stale CEF processes between sessions

Happy to share more details on the implementation if anyone needs it.