Interrupts while trying to read from stdin can cause the application to hang

[DanStough]

Describe the bug

Firstly, thanks for the great OSS project!

I'm building a CLI that reads from STDIN, and I'm trying to make sure it's cancelable using SIGINT. I observe that when I'm using Fang, there is a race condition when exiting that causes the application to hang indefinitely, maybe 50% of the time.

Setup

Please complete the following information along with version numbers, if applicable.

• OS: MacOS 15.5
• Shell: zsh
• Terminal Emulator: ghostty
• Terminal Multiplexer: n/a

To Reproduce

Steps to reproduce the behavior:

1. Run the sample code below.
2. Ctrl+C to close
3. Observe that frequently the application doesn't close, or closes slowly.

Source Code

Here is a simplified example of my setup:

package main

import (
	"context"
	"io"
	"os"

	"github.com/charmbracelet/fang"
	"github.com/spf13/cobra"
)

func main() {
	// NewRootCMD creates the root command for the epok CLI application.
	rootCmd := &cobra.Command{
		Use:  "test",
		RunE: handler,
	}

	fang.Execute(context.Background(), rootCmd,
		fang.WithNotifySignal(os.Interrupt, os.Kill))
}

func handler(cmd *cobra.Command, _ []string) error {
	data := make(chan string)

	go func() {
		in := cmd.InOrStdin()
		_, _ = io.ReadAll(in) // Will block
	}()

	ctx := cmd.Context()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-data:
		return nil
	}
}

Expected behavior

I expect the application to consistently exit as it would w/o fang.

Additional context

I traced the problem to this line, which uses STDIN to determine the terminal background. I imagine there is contention reading from the same descriptor.

Assuming it's not user error, one solution that works for me is to pre-compute the styles in Execute before running the cobra command. If you think that's the right change, I'm happy to make a PR.

[ccoVeille]

This reminds what I had to code for a scanner that respects context

https://github.com/CodeWithEmad/gh-fork-cleanup/blob/master/scanner.go

[caarlos0]

You might want to take a look at https://github.com/muesli/cancelreader

The main problem there is that the read is not canceled, and then Fang's error handler tries to figure out colors and etc...

Not sure if/how we can make this better in Fang, btw 🤔

[DanStough]

Thanks all. I can take a look at cancelreader. The scanner solution has the same problems as using io.

This will "fix" fang, in the sense that it works around the issue.