Init stage produces unwanted terminal output when run via expect spawn

[lonnywong]

Describe the bug
The init() function calls _ = lipgloss.HasDarkBackground(), which accesses the terminal and produces OSC/DSR sequences (e.g., ^[]11;rgb:0000/0000/0000^[\^[[78;1R) before main().
This output appears when the program is run via spawn in an expect script.

Setup

• OS: macOS
• Shell: bash
• Terminal Emulator: iTerm2
• Terminal Multiplexer: no

To Reproduce

1. Write an expect script that uses spawn to run a Bubble Tea program.
2. Observe that terminal sequences are printed before main() executes.

Source Code

#!/usr/bin/env expect
spawn ./program
expect "Hello"
interact

package main

import (
        "flag"
        "fmt"

        tea "github.com/charmbracelet/bubbletea"
)

func main() {
        useTea := flag.Bool("tea", false, "use Bubble Tea")
        flag.Parse()

        if *useTea {
                tea.Println("Hello, Tea.")
                return
        }

        fmt.Println("Hello, World.")
}

Expected behavior
The init() function should not produce unwanted terminal output when the program is run via spawn in an expect script.

Screenshots

$ ./expect.sh
spawn ./program
^[]11;rgb:0000/0000/0000^[\^[[78;1RHello, World.
^[]11;rgb:0000/0000/0000^[\^[[78;1R

Additional context
Consider performing terminal detection lazily, e.g., with sync.Once when it is actually needed in the program.

[lonnywong]

@aymanbagabas @aymanbagabas

Would it make sense to guard the call to lipgloss.HasDarkBackground() with a sync.Once, and defer it to NewProgram() or (*Program).Run() instead?
This would avoid performing terminal detection during package initialization.

bubbletea/tea_init.go

Line 21 in f9233d5

_ = lipgloss.HasDarkBackground()

[aymanbagabas]

Hi @lonnywong, thank you for reporting this issue. It's a known limitation of the underlying libraries that we use and we solve this in the new v2 packages. Could you try switching to charm.land/bubbletea/v2, charm.land/lipgloss/v2, and others?

You can do so with:

go get charm.land/bubbletea/v2@v2-exp 
go get charm.land/lipgloss/v2@v2-exp 
go get charm.land/bubbles/v2@v2-exp
# Other libraries like glamour, wish, etc...

[lonnywong]

@aymanbagabas Thanks for your reply. I'll give v2 a try - I actually thought v2 wasn't ready for use yet.

[lonnywong]

@aymanbagabas
After switching to v2, all the Views are misaligned and I’m not sure how to fix it. Could we first make some improvements on the previous version before moving to v2?

[lonnywong]

@aymanbagabas I’ve pushed the code upgrading to v2 to the tea_v2 branch. If you’re interested, you could take a look at how to fix the View misalignment issue.

You can install and test it directly with:

go install github.com/trzsz/trzsz-ssh/cmd/tssh@tea_v2
~/go/bin/tssh --enc-secret

If you want to check the code implementation, it’s here:
https://github.com/trzsz/trzsz-ssh/blob/e548941c4e5ca2db366656879a6903f4eb0bc68a/tssh/tools.go#L376-L400

[aymanbagabas]

Hi @lonnywong, thank you for pointing me to your implementation.

TL;DR: You can use the patch below for a quick workaround. I recommend leaving the program input as is since Bubble Tea uses cancelreader already.

The new v2 Bubble Tea renderer is a cell based renderer compared to the older line based renderer. This means that changing the output of your program outside of Bubble Tea can affect and misalign the output of the program.

I noticed that trzsz-ssh uses a custom input reader that wraps cancelreader. The custom reader doesn't implement the term.File interface, which is really important to tell Bubble Tea the TTY file descriptor. Without that, Bubble Tea assumes it's not writing to a terminal, and it omits writing carriage when moving the cursor. This fixes an issue on Wish when the handler accepts PTY requests but doesn't use an actual PTY underneath and the default PTY settings are preserved, which makes the terminal map newlines to newline + carriage return.

I was able to patch that easily by simply implementing an Fd() uintptr function on the custom input reader and everything worked as expected. However, I would remove the custom input reader implementation when using tea.Program since Bubble Tea uses a cancelreader internally for TTYs.

You can also now use a real cursor in your text inputs instead of the virtual one. A real cursor makes the terminal and the OS track input. You can enable that via textInput.SetVirtualCursor(false) and control the cursor position and style via tea.View.Cursor.

I hope this helps 🙂

diff --git i/tssh/tools.go w/tssh/tools.go
index 9c7141ffd07c..00ca4bbdef43 100644
--- i/tssh/tools.go
+++ w/tssh/tools.go
@@ -66,6 +66,10 @@ type teaStdinReader struct {
 	cancelled  atomic.Bool
 }
 
+func (r *teaStdinReader) Fd() uintptr {
+	return os.Stdin.Fd()
+}
+
 func (r *teaStdinReader) Read(p []byte) (int, error) {
 	stdinFallbackMu.Lock()
 	defer stdinFallbackMu.Unlock()

[lonnywong]

@aymanbagabas Thanks for your help.

I'm using a custom input reader because I don't want TEA to change stdin to raw mode - I prefer to set stdin to raw mode myself. This is mainly for compatibility when running in Cygwin on Windows 7, where TEA would throw an error if it tried to set raw mode. Instead, I can call Cygwin's stty raw to set stdin to raw mode.

Additionally, lipgloss.SetColorProfile(termenv.ANSI256) no longer exists in v2. I set this specifically for Cygwin compatibility, otherwise lipgloss would use colorless output in Cygwin on Windows 7.

Would it be possible to:

• Add an API to inform TEA that stdin is already in raw mode, so it won't throw errors when raw mode setup fails?
• Add an API to inform TEA that stdout supports colors, preventing fallback to colorless output when color detection fails?

[aymanbagabas]

I'm using a custom input reader because I don't want TEA to change stdin to raw mode - I prefer to set stdin to raw mode myself. This is mainly for compatibility when running in Cygwin on Windows 7, where TEA would throw an error if it tried to set raw mode. Instead, I can call Cygwin's stty raw to set stdin to raw mode.

Bubble Tea v2 should handle that out of the box. Could you test using the default input running v2 on Cygwin?

Additionally, lipgloss.SetColorProfile(termenv.ANSI256) no longer exists in v2. I set this specifically for Cygwin compatibility, otherwise lipgloss would use colorless output in Cygwin on Windows 7.

You can now use tea.WithColorProfile(colorprofile.ANSI256) option to force set the color preferences even when the program is not running on a TTY.

Would it be possible to:

• Add an API to inform TEA that stdin is already in raw mode, so it won't throw errors when raw mode setup fails?

You can do that before running your program via term.GetState(stdin.Fd()) and term.IsTerminal(stdin.Fd())

• Add an API to inform TEA that stdout supports colors, preventing fallback to colorless output when color detection fails?

Bubble Tea would fail to detect colors if the input/output are not a file, and there are no environment variables that indicate a terminal with color support like TERM=... and COLORTERM=.... This gets detected by the colorprofile package and expects input/output to have a Fd() uintptr function that returns the underlying file descriptor. You need the actual FD on all platforms to detect if the program is running on a TTY (Unix) or a Console (Windows). That's the first step to detect color support because you don't want to generate colors when you redirect the output to a file for example.

[lonnywong]

Bubble Tea v2 should handle that out of the box. Could you test using the default input running v2 on Cygwin?

Got an error in Cygwin on Windows 7:

input error: bubbletea: could not create cancelable reader: prepare console: set console mode: The parameter is incorrect.

Additionally, lipgloss.SetColorProfile(termenv.ANSI256) no longer exists in v2.

It looks like lipgloss.SetColorProfile(termenv.ANSI256) is no longer necessary.
In my testing, lipgloss in Cygwin on Windows 7 does not strip colors anymore, unlike the behavior in v1.

Add an API to inform TEA that stdin is already in raw mode, so it won't throw errors when raw mode setup fails?
Add an API to inform TEA that stdout supports colors, preventing fallback to colorless output when color detection fails?

These two APIs likely aren’t needed either.

However, in Cygwin on Windows 7 the output from Bubble Tea is not visible, so this needs further investigation. Because Bubble Tea fails to create a cancelable reader, I fall back to a custom input reader; The output is not shown, regardless of whether the reader implements Fd() uintptr.

After escaping the output using strconv.QuoteToASCII, I can see that Bubble Tea continuously emits ANSI escape sequences. The output starts with sequences like:

\x1b[?2026$p\x1b[?25l\x1b[?2004h\x1b[=1;1u\x1b[?u\r

And then followed by a large amount of \x1b[J repeated:

\x1b[J\x1b[J\x1b[J\x1b[J\x1b[J\x1b[J\x1b[J\x1b[J...

After pressing Ctrl+C, the final output shows:

\x1b[J\x1b[J\x1b[J\x1b[J\x1b[J\x1b[=0;1u\x1b[A\x1b[J\x1b[?25h\x1b[?2004linput error: program was killed: program was interrupted

No visible UI is rendered in the terminal.

[lonnywong]

@aymanbagabas After I added tea.WithWindowSize(width, height), I was able to see output in Cygwin on Windows 7. And adding tea.WithColorProfile(colorprofile.ANSI256) fixed the color issue as well.

However, even after adding:

func (r *teaStdinReader) Fd() uintptr {
    return os.Stdin.Fd()
}

Tea still considers stdin in Cygwin on Windows 7 to be not a terminal.

I did a quick test in Cygwin on Windows 7 using github.com/charmbracelet/x/term:

• term.IsTerminal(os.Stdin.Fd())returns false.
• term.MakeRaw(os.Stdin.Fd()) fails with The handle is invalid.

Would it make sense to add an option to explicitly override TTY detection and enable terminal-style output (including emitting \r)?

[aymanbagabas]

@aymanbagabas After I added tea.WithWindowSize(width, height), I was able to see output in Cygwin on Windows 7. And adding tea.WithColorProfile(colorprofile.ANSI256) fixed the color issue as well.

I'm glad to hear that.

However, even after adding:

func (r *teaStdinReader) Fd() uintptr {
return os.Stdin.Fd()
}
Tea still considers stdin in Cygwin on Windows 7 to be not a terminal.

I did a quick test in Cygwin on Windows 7 using github.com/charmbracelet/x/term:

• term.IsTerminal(os.Stdin.Fd())returns false.
• term.MakeRaw(os.Stdin.Fd()) fails with The handle is invalid.

Would it make sense to add an option to explicitly override TTY detection and enable terminal-style output (including emitting \r)?

We could, however, I would try to find a solution to this via a more streamlined way and figure out why Cygwin doesn't implement a TTY driver properly. Fwiw, Bubble Tea should work fine on cmd.exe and powerline.exe. It might even be a better experience that Cygwin.

[lonnywong]

Would it make sense to add an option to explicitly override TTY detection and enable terminal-style output (including emitting \r)?

We could, however, I would try to find a solution to this via a more streamlined way and figure out why Cygwin doesn't implement a TTY driver properly. Fwiw, Bubble Tea should work fine on cmd.exe and powerline.exe. It might even be a better experience that Cygwin.

@aymanbagabas Windows 7 is a legacy operating system that's no longer supported by Microsoft or GoLang. Cygwin 3.4.10 was the last Cygwin version supporting Windows 7. I don't think you need to spend too much time supporting it - providing a compatible option would be sufficient.

[aymanbagabas]

@aymanbagabas Windows 7 is a legacy operating system that's no longer supported by Microsoft or GoLang. Cygwin 3.4.10 was the last Cygwin version supporting Windows 7. I don't think you need to spend too much time supporting it - providing a compatible option would be sufficient.

Thanks again @lonnywong for verifying this on Windows 7. I've made a small change in 76f2e6d to always emit \r even when Bubble Tea can't set the terminal to raw.
I believe this should fix your issue on Windows 7 and you won't need to have a custom input for your application. Please let me know if this doesn't solve your issue 🙂

You can get these changes with:

go get charm.land/bubbletea/v2@v2-exp`