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Handle xterm normal/reset escape sequence #72

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dosisod opened this issue Mar 1, 2023 · 5 comments
Closed

Handle xterm normal/reset escape sequence #72

dosisod opened this issue Mar 1, 2023 · 5 comments

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@dosisod
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dosisod commented Mar 1, 2023

I recently found out that xterm uses a weird escape sequence for the normal/reset sequence (aka sgr0). Most terminals use \e[0m, but xterm uses \e(B\e[m:

$ env TERM=st-256color tput sgr0 | xxd
00000000: 1b5b 306d                                .[0m
$ env TERM=xterm tput sgr0 | xxd
00000000: 1b28 421b 5b6d                           .(B.[m

Here is a small repro:

<html>

<head>
<script src="./ansi_up.js"></script>
</head>

<body>
<pre id="console"></pre>

<script>
const ansi_up = new AnsiUp();

const colors = "\033[1m\033[32mABC";

const xterm = "\033(B\033[mDEF\n";
const notXterm = "\033[0mDEF\n";

const html = ansi_up.ansi_to_html(colors + xterm + colors + notXterm);

document.getElementById("console").innerHTML += html;
</script>
</body>
</html>

And this is what it is displaying:

image

They both reset the color, though the (B bit shouldn't be there in the top line.
@drudru
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drudru commented Mar 1, 2023

I don’t think this is a common sequence.
Most apps have moved away from using the term cap database. They usually conform to a popular, common subset.

I personally use xterm-256 in tmux.

what app is sending this sequence?

still, if it is easy, then I don’t see why not.

@dosisod
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dosisod commented Mar 1, 2023

The program in question is Mypy, specifically this line:

        normal = curses.tigetstr("sgr0")

I might open an issue/PR about replacing the curses calls with hardcoded escapes, but I suspect there are lots of other apps out there that are using curses for their escape sequences. A search with grep.app shows about ~160 open source Python repos are using the curses.tigetstr() function.

And I agree that if it is easy to add then it should be added just for better compatibility/coverage.

@drudru
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drudru commented Mar 9, 2023

Looking at this today…

@drudru
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drudru commented Mar 9, 2023

So, the sequence ESC ( C is actually resetting the character set to USASCII.
ESC ( A - is United Kingdom, C is Finnish.
Interesting.
I think the best strategy is to just ignore it. The data should be UTF8 already.

@dosisod
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dosisod commented Mar 10, 2023

I agree, ignoring it is probably best.

@drudru drudru closed this as completed in 94cc84b Mar 16, 2023
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@drudru @dosisod