[Bug]: iOS with golang static lib webview load failure

[betamos]

Capacitor Version

💊 Capacitor Doctor 💊

Latest Dependencies:

@capacitor/cli: 7.0.1
@capacitor/core: 7.0.1
@capacitor/android: 7.0.1
@capacitor/ios: 7.0.1

Installed Dependencies:

@capacitor/android: not installed
@capacitor/cli: 7.0.1
@capacitor/core: 7.0.1
@capacitor/ios: 7.0.1

[success] iOS looking great! 👌

Other API Details

➜  mobile git:(cap) ✗ npm --version 
11.0.0
➜  mobile git:(cap) ✗ node --version
v23.6.0
➜  mobile git:(cap) ✗ pod --version
1.16.2
➜  mobile git:(cap) ✗ go version
go version go1.23.4 darwin/arm64

Platforms Affected

• iOS
• Android
• Web

Current Behavior

I have custom native code to add a gomobile static lib as a framework. When I switched to use my bundled site in public for prod, it failed with:

⚡️  WebView failed provisional navigation
⚡️  Error: The file “public” couldn’t be opened.

This happens in both simulator and physical iPhone (both iOS 18.2).

This error returns exactly one search result: #6974 . It's closed, but nevertheless:

• It's suggested there's a workaround, but not how? I share mine below.
• The Go team blames Apple (Foundation Framework) and proceeds to stick head into sand
• Tim Apple isn't even informed, afaik
• In development with HMR, I didn't notice this because if there's a serverUrl it's not triggered

The gomobile command used was: gomobile bind -ldflags="-s" -target ios -tags ios -o ./ios/App/Pld.xcframework

Expected Behavior

Webview should load normally & peacefully.

Project Reproduction

it's not easy to do atm...

Additional Information

I managed to find a workaround through MyViewController (see docs for how to set it up). The actual fix is a one-liner, but to set it up is quite tedious, especially if you're not already using a custom view controller.

import UIKit
import Capacitor

public struct CustomRouter: Router {
    public init() {}
    public var basePath: String = ""
    public func route(for path: String) -> String {
        // FIX: Never pass an empty string here
        let pathUrl = URL(fileURLWithPath: path.isEmpty ? "/" : path)

        // If there's no path extension it also means the path is empty or a SPA route
        if pathUrl.pathExtension.isEmpty {
            return basePath + "/index.html"
        }

        return basePath + path
    }
}

class MyViewController: CAPBridgeViewController {
    
    // CRITICAL: Must pass our own router otherwise *no bueno* 
    override open func router() -> any Router {
        CustomRouter()
    }
    override open func capacitorDidLoad() {
        // Here I register my plugin, but the failure occurs even if I don't register it.
        bridge?.registerPluginInstance(PldPlugin())
    }
}

My understanding is that the non-deterministic behavior of URL(fileURLWithPath:) occurs when the path is empty. Normally an empty path translates to file:/// which is equivalent to passing /.

God knows what combination of things causes this to happen, but if Capacitor can avoid this non-determinism perhaps that's an improvement? It certainly is for me (and clearly, whoever posted that other issue). Happy to send a PR if so.

(Obligatory thanks for a great framework. I'm new to mobile dev and I can't thank the contributors enough.)

[ionitron-bot]

This issue needs more information before it can be addressed. In particular, the reporter needs to provide a minimal sample app that demonstrates the issue. If no sample app is provided within 15 days, the issue will be closed.
Please see the Contributing Guide for how to create a Sample App.
Thanks! Ionitron 💙

[markemer]

As for a reproduction - however you're loading this Go code would be really helpful.

[betamos]

Yay, a human! If there's an intent to solve it I am happy to spend some labor. The Go library is using the gomobile -bind (see above) command to generate an xcframework which is loaded into XCode as a framework (on Android it's an .aar)

I believe the Go runtime initialization causes this bug, because it occurred if I only loaded the framework without even invoking a single method from it (unsure if I left the import statements or not - may be a factor as well). But as far as Go code goes, a hello-world dummy should reproduce it.

I'm suspecting the empty URL is confusing Foundation to use the wrong code path, even though technically it's allowed. The NSURL sibling API says:

path should be a valid system path, and must not be an empty path

My thinking was the safest option is to simply be more specific when using the URL API, in the case the path is otherwise empty. But, to be fair I don't know if my workaround works in every single case/setup.

If it helps, I can pack up a hello-world xcframework and send it your way, in case you don't wanna get dirty with the go toolchain?

[theproducer]

I use Go, and I've used gomobile before in the past. If you want to create a reproduction of a Capacitor app with your framework along with a minimal go project that created the framework I can check it out as well.

[jcesarmobile]

There is a reproduction in #7899, but it uses a very old Capacitor version, so should be updated to Capacitor 7

[predatorx7]

Is this known that golang/go#58225 causes this issue?