Playground fails with a `403` error when wanting to execute Go code with comments

[joseluisq]

Describe the bug
When attempting to execute the code below, the Playground returned a 403 error then shown in the Output panel.
The funny part is that it seems a simple comment in the snippet breaks the playground, and attempting to click on Share also fails.

To Reproduce
Steps to reproduce the behavior:

1. Go to the playground and enter this snippet

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	doneChan := make(chan struct{})
	var wg sync.WaitGroup

	wg.Add(1)
	go func() {
		defer wg.Done()
		time.Sleep(2 * time.Second)
		fmt.Println("Task from WaitGroup done")
	}()

	go func() {
		time.Sleep(1 * time.Second)
		fmt.Println("Task from channel done")
		doneChan <- struct{}{}
	}()
	// This simple comment breaks the playground (remove it and it will work)
	wgDoneChan := make(chan struct{})
	go func() {
		wg.Wait()
		close(wgDoneChan)
	}()

	select {
	case <-doneChan:
		fmt.Println("Received done signal from channel")
	case <-wgDoneChan:
		fmt.Println("All WaitGroup tasks done")
	}
}

2. Click on 'Run'
3. Then you will get an Error 403 ... in the Output panel.

Expected behavior

Code executed without backend issues.

Screenshots

Run

Share

Desktop (please complete the following information):

• OS: macos
• Browser Chrome 138.0.7204.101
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[x1unix]

Thanks, I'll take a look

Probably Infra related

[x1unix]

@joseluisq for some reason, Cloudflare blocks a particular request to format:

I'll try to check what's happening on Cloudflare side and if this can be addressed.

[abulka]

Another example

package main

import (
	"fmt"
)

type Task struct {
	ID   int
	Name string
}

// tasksSlice is a global slice of Task structs for demonstration.  <--- this comment causes 403
var tasksSlice = []Task{{ID: 1, Name: "A"}, {ID: 2, Name: "B"}, {ID: 3, Name: "C"}, {ID: 4, Name: "D"}}

func DeleteTaskFromSliceByIndex(s []Task, index int) []Task {
	if index < 0 || index >= len(s) {
		return s
	}
	return append(s[:index], s[index+1:]...)
}

func main() {
	fmt.Println("Original tasksSlice:", tasksSlice)
	tasksSlice = DeleteTaskFromSliceByIndex(tasksSlice, 1)
	fmt.Println("tasksSlice after deleting index 1:", tasksSlice)
}

[hclihn]

Even without comments, the 403 error can occur in different codes. It's unclear what triggers it. For example, the following example code from the golang.org/x/net/html package runs well in Go playground, but triggers the 403 error here:

package main

import (
	"fmt"
	"log"
	"strings"

	"golang.org/x/net/html"
	"golang.org/x/net/html/atom"
)

func main() {
	s := `<p>Links:</p><ul><li><a href="foo">Foo</a><li><a href="/bar/baz">BarBaz</a></ul>`
	doc, err := html.Parse(strings.NewReader(s))
	if err != nil {
		log.Fatal(err)
	}
	for n := range doc.Descendants() {
		if n.Type == html.ElementNode && n.DataAtom == atom.A {
			for _, a := range n.Attr {
				if a.Key == "href" {
					fmt.Println(a.Val)
					break
				}
			}
		}
	}

}

[x1unix]

@hclihn the issue is that AJAX requests for some reason blocked by Cloudflare. I'm now trying to add Cloudflare Turnstile to mitigate the issue.

[x1unix]

@hclihn @joseluisq @abulka

Seems like the issue was caused by CloudFlare OWASP rules. I tweaked paranoia level as a temporary measure.

Can you please check now if the issue persists?