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feat(v2): add runtime.ResetSignalHandlers() for Linux panic recovery (#4921)
* feat(v2): add runtime.ResetSignalHandlers() for Linux panic recovery Add a new runtime function that allows users to reset signal handlers before code that might panic from nil pointer dereferences. On Linux, WebKit installs signal handlers without the SA_ONSTACK flag, which prevents Go from properly recovering from panics caused by SIGSEGV and other signals. This function adds SA_ONSTACK to the relevant signal handlers (SIGSEGV, SIGBUS, SIGFPE, SIGABRT). Usage: ```go go func() { defer func() { if err := recover(); err != nil { log.Printf("Recovered: %v", err) } }() runtime.ResetSignalHandlers() // Code that might panic... }() ``` The function is a no-op on macOS and Windows. Fixes #3965 Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> * test(v2): add panic-recovery-test example Add an example that demonstrates the Linux signal handler issue (#3965) and verifies the fix using runtime.ResetSignalHandlers(). The example includes: - A Greet function that triggers a nil pointer dereference after a delay - Auto-call from frontend after 5 seconds - README with reproduction steps Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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‎v2/examples/panic-recovery-test/README.md‎

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# Panic Recovery Test
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This example demonstrates the Linux signal handler issue (#3965) and verifies the fix using `runtime.ResetSignalHandlers()`.
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## The Problem
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On Linux, WebKit installs signal handlers without the `SA_ONSTACK` flag, which prevents Go from recovering panics caused by nil pointer dereferences (SIGSEGV). Without the fix, the application crashes with:
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```
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signal 11 received but handler not on signal stack
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fatal error: non-Go code set up signal handler without SA_ONSTACK flag
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```
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## The Solution
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Call `runtime.ResetSignalHandlers()` immediately before code that might panic:
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```go
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import "github.com/wailsapp/wails/v2/pkg/runtime"
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go func() {
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defer func() {
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if err := recover(); err != nil {
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log.Printf("Recovered: %v", err)
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}
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}()
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runtime.ResetSignalHandlers()
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// Code that might panic...
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}()
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```
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## How to Reproduce
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### Prerequisites
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- Linux with WebKit2GTK 4.1 installed
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- Go 1.21+
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- Wails CLI
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### Steps
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1. Build the example:
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```bash
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cd v2/examples/panic-recovery-test
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wails build -tags webkit2_41
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```
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2. Run the application:
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```bash
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./build/bin/panic-recovery-test
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```
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3. Wait ~10 seconds (the app auto-calls `Greet` after 5s, then waits another 5s before the nil pointer dereference)
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### Expected Result (with fix)
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The panic is recovered and you see:
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```
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------------------------------"invalid memory address or nil pointer dereference"
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```
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The application continues running.
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### Without the fix
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Comment out the `runtime.ResetSignalHandlers()` call in `app.go` and rebuild. The application will crash with a fatal signal 11 error.
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## Files
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- `app.go` - Contains the `Greet` function that demonstrates panic recovery
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- `frontend/src/main.js` - Auto-calls `Greet` after 5 seconds to trigger the test
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## Related
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- Issue: https://github.com/wailsapp/wails/issues/3965
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- Original fix PR: https://github.com/wailsapp/wails/pull/2152

‎v2/examples/panic-recovery-test/app.go‎

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package main
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import (
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"context"
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"fmt"
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"time"
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"github.com/wailsapp/wails/v2/pkg/runtime"
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)
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// App struct
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type App struct {
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ctx context.Context
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}
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// NewApp creates a new App application struct
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func NewApp() *App {
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return &App{}
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}
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// startup is called when the app starts. The context is saved
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// so we can call the runtime methods
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func (a *App) startup(ctx context.Context) {
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a.ctx = ctx
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}
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// Greet returns a greeting for the given name
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func (a *App) Greet(name string) string {
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go func() {
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defer func() {
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if err := recover(); err != nil {
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fmt.Printf("------------------------------%#v\n", err)
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}
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}()
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time.Sleep(5 * time.Second)
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// Fix signal handlers right before potential panic using the Wails runtime
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runtime.ResetSignalHandlers()
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// Nil pointer dereference - causes SIGSEGV
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var t *time.Time
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fmt.Println(t.Unix())
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}()
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return fmt.Sprintf("Hello %s, It's show time!", name)
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}

‎v2/examples/panic-recovery-test/frontend/index.html‎

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8"/>
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<meta content="width=device-width, initial-scale=1.0" name="viewport"/>
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<title>panic-test</title>
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</head>
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<body>
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<div id="app"></div>
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<script src="./src/main.js" type="module"></script>
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</body>
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</html>

‎v2/examples/panic-recovery-test/frontend/package.json‎

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{
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"name": "frontend",
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"private": true,
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"version": "0.0.0",
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"scripts": {
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"dev": "vite",
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"build": "vite build",
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"preview": "vite preview"
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},
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"devDependencies": {
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"vite": "^3.0.7"
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}
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}

‎v2/examples/panic-recovery-test/frontend/src/app.css‎

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#logo {
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display: block;
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width: 50%;
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height: 50%;
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margin: auto;
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padding: 10% 0 0;
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background-position: center;
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background-repeat: no-repeat;
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background-size: 100% 100%;
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background-origin: content-box;
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}
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.result {
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height: 20px;
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line-height: 20px;
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margin: 1.5rem auto;
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}
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.input-box .btn {
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width: 60px;
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height: 30px;
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line-height: 30px;
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border-radius: 3px;
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border: none;
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margin: 0 0 0 20px;
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padding: 0 8px;
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cursor: pointer;
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}
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.input-box .btn:hover {
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background-image: linear-gradient(to top, #cfd9df 0%, #e2ebf0 100%);
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color: #333333;
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}
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.input-box .input {
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border: none;
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border-radius: 3px;
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outline: none;
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height: 30px;
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line-height: 30px;
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padding: 0 10px;
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background-color: rgba(240, 240, 240, 1);
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-webkit-font-smoothing: antialiased;
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}
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.input-box .input:hover {
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border: none;
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background-color: rgba(255, 255, 255, 1);
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}
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.input-box .input:focus {
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border: none;
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background-color: rgba(255, 255, 255, 1);
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}

‎v2/examples/panic-recovery-test/frontend/src/assets/fonts/OFL.txt‎

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Copyright 2016 The Nunito Project Authors (contact@sansoxygen.com),
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This Font Software is licensed under the SIL Open Font License, Version 1.1.
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This license is copied below, and is also available with a FAQ at:
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http://scripts.sil.org/OFL
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-----------------------------------------------------------
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SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
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-----------------------------------------------------------
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PREAMBLE
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The goals of the Open Font License (OFL) are to stimulate worldwide
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development of collaborative font projects, to support the font creation
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efforts of academic and linguistic communities, and to provide a free and
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open framework in which fonts may be shared and improved in partnership
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with others.
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The OFL allows the licensed fonts to be used, studied, modified and
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redistributed freely as long as they are not sold by themselves. The
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fonts, including any derivative works, can be bundled, embedded,
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redistributed and/or sold with any software provided that any reserved
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names are not used by derivative works. The fonts and derivatives,
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however, cannot be released under any other type of license. The
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requirement for fonts to remain under this license does not apply
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to any document created using the fonts or their derivatives.
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DEFINITIONS
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"Font Software" refers to the set of files released by the Copyright
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Holder(s) under this license and clearly marked as such. This may
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include source files, build scripts and documentation.
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"Reserved Font Name" refers to any names specified as such after the
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copyright statement(s).
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"Original Version" refers to the collection of Font Software components as
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distributed by the Copyright Holder(s).
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"Modified Version" refers to any derivative made by adding to, deleting,
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or substituting -- in part or in whole -- any of the components of the
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Original Version, by changing formats or by porting the Font Software to a
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new environment.
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"Author" refers to any designer, engineer, programmer, technical
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writer or other person who contributed to the Font Software.
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PERMISSION & CONDITIONS
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of the Font Software, to use, study, copy, merge, embed, modify,
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redistribute, and sell modified and unmodified copies of the Font
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Software, subject to the following conditions:
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1) Neither the Font Software nor any of its individual components,
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in Original or Modified Versions, may be sold by itself.
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2) Original or Modified Versions of the Font Software may be bundled,
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redistributed and/or sold with any software, provided that each copy
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contains the above copyright notice and this license. These can be
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included either as stand-alone text files, human-readable headers or
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in the appropriate machine-readable metadata fields within text or
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binary files as long as those fields can be easily viewed by the user.
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3) No Modified Version of the Font Software may use the Reserved Font
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Name(s) unless explicit written permission is granted by the corresponding
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Copyright Holder. This restriction only applies to the primary font name as
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presented to the users.
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4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
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Software shall not be used to promote, endorse or advertise any
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Modified Version, except to acknowledge the contribution(s) of the
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Copyright Holder(s) and the Author(s) or with their explicit written
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permission.
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5) The Font Software, modified or unmodified, in part or in whole,
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must be distributed entirely under this license, and must not be
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distributed under any other license. The requirement for fonts to
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remain under this license does not apply to any document created
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using the Font Software.
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TERMINATION
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This license becomes null and void if any of the above conditions are
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not met.
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DISCLAIMER
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THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
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OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
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COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
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DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
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OTHER DEALINGS IN THE FONT SOFTWARE.

‎v2/examples/panic-recovery-test/frontend/src/assets/fonts/nunito-v16-latin-regular.woff2‎

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‎v2/examples/panic-recovery-test/frontend/src/assets/images/logo-universal.png‎

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‎v2/examples/panic-recovery-test/frontend/src/main.js‎

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import './style.css';
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import './app.css';
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import logo from './assets/images/logo-universal.png';
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import {Greet} from '../wailsjs/go/main/App';
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document.querySelector('#app').innerHTML = `
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<img id="logo" class="logo">
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<div class="result" id="result">Please enter your name below 👇</div>
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<div class="input-box" id="input">
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<input class="input" id="name" type="text" autocomplete="off" />
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<button class="btn" onclick="greet()">Greet</button>
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</div>
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</div>
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`;
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document.getElementById('logo').src = logo;
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let nameElement = document.getElementById("name");
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nameElement.focus();
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let resultElement = document.getElementById("result");
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// Setup the greet function
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window.greet = function () {
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// Get name
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let name = nameElement.value;
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// Check if the input is empty
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if (name === "") return;
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// Call App.Greet(name)
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try {
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Greet(name)
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.then((result) => {
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// Update result with data back from App.Greet()
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resultElement.innerText = result;
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})
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.catch((err) => {
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console.error(err);
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});
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} catch (err) {
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console.error(err);
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}
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};
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// Auto-call Greet after 5 seconds to trigger the panic test
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setTimeout(() => {
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console.log("Auto-calling Greet to trigger panic test...");
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Greet("PanicTest")
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.then((result) => {
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resultElement.innerText = result + " (auto-called - panic will occur in 5s)";
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})
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.catch((err) => {
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console.error("Error:", err);
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});
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}, 5000);

‎v2/examples/panic-recovery-test/frontend/src/style.css‎

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html {
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background-color: rgba(27, 38, 54, 1);
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text-align: center;
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color: white;
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}
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body {
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margin: 0;
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color: white;
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font-family: "Nunito", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto",
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"Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue",
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sans-serif;
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}
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@font-face {
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font-family: "Nunito";
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font-style: normal;
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font-weight: 400;
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src: local(""),
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url("assets/fonts/nunito-v16-latin-regular.woff2") format("woff2");
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}
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#app {
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height: 100vh;
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text-align: center;
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}

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