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Respond to OSC 10/11/4, DA2, DSR, and XTVERSION terminal queries
Nathan Herald
(Apr 15, 2026, 2:47 PM +0200)
a5b37169
fb4e6d55
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src/server.ts
+61
src/server.ts
···
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return false;
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});
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// ── Terminal query responses ──
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// Programs send queries expecting the terminal to respond on stdin.
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// xterm-headless doesn't answer, so the query leaks to the client's
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// real terminal, whose response comes back as garbage input. We
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// intercept common queries and respond directly to the PTY process.
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// OSC 10: foreground color query (less, vim)
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this.terminal.parser.registerOscHandler(10, (data: string) => {
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if (data === "?") {
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this.ptyProcess.write("\x1b]10;rgb:c0c0/c0c0/c0c0\x1b\\");
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}
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return false;
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});
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// OSC 11: background color query (less, vim)
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this.terminal.parser.registerOscHandler(11, (data: string) => {
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if (data === "?") {
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this.ptyProcess.write("\x1b]11;rgb:0000/0000/0000\x1b\\");
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}
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return false;
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});
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// OSC 4: palette color query (vim, emacs)
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this.terminal.parser.registerOscHandler(4, (data: string) => {
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if (data.includes("?")) {
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// Format: "N;?" — respond with color N's value
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const idx = parseInt(data, 10);
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if (!isNaN(idx)) {
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// Respond with xterm-256color default for this index
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this.ptyProcess.write(`\x1b]4;${idx};rgb:0000/0000/0000\x1b\\`);
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}
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}
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return false;
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});
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// DA2: secondary device attributes (vim, tmux)
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this.terminal.parser.registerCsiHandler(
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{ prefix: ">", final: "c" },
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(_params) => {
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// Respond as xterm version 382
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this.ptyProcess.write("\x1b[>0;382;0c");
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return false;
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}
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);
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// DSR: cursor position query (CSI 6 n, vim, readline)
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this.terminal.parser.registerCsiHandler(
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{ final: "n" },
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(params) => {
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if (params.length === 1 && params[0] === 6) {
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const buf = this.terminal.buffer.active;
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this.ptyProcess.write(`\x1b[${buf.cursorY + 1};${buf.cursorX + 1}R`);
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}
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return false;
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}
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);
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// XTVERSION: terminal version query (CSI > 0 q, vim)
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this.terminal.parser.registerCsiHandler(
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{ prefix: ">", final: "q" },
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(_params) => {
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this.ptyProcess.write("\x1bP>|pty(0.8)\x1b\\");
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return false;
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}
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);
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// Spawn the child process in a PTY via a shell, so that shell scripts,
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// symlinks, and shebangs all work reliably (like tmux/screen do).
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// `exec "$@"` replaces the shell with the actual process.
+76
tests/terminal-queries.test.ts
+76
tests/terminal-queries.test.ts
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import { describe, it, expect, afterAll } from "vitest";
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import * as fs from "node:fs";
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import * as os from "node:os";
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import { Session } from "../src/testing/index.ts";
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// Isolate from real session directory
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const testSessionDir = fs.mkdtempSync(os.tmpdir() + "/pty-queries-");
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process.env.PTY_SESSION_DIR = testSessionDir;
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afterAll(() => {
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return new Promise((resolve) => {
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setTimeout(() => {
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try { fs.rmSync(testSessionDir, { recursive: true, force: true }); } catch {}
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resolve(undefined);
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}, 500);
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});
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});
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describe("terminal query responses", () => {
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it("responds to DA1 (ESC[c)", async () => {
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// Fish uses this — already tested in shells.test.ts, but verify directly
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const session = await Session.server("sh", ["-c", "printf '\\033[c'; cat"], {
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rows: 24,
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cols: 80,
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});
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await session.attach();
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// The response (\x1b[?62;22c) goes to the PTY's stdin, cat echoes it
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await session.waitForText("62;22", 3000);
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await session.close();
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}, 15000);
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it("responds to OSC 11 background color query", async () => {
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// less sends this — the response should appear as echoed output from cat
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const session = await Session.server("sh", ["-c", "printf '\\033]11;?\\033\\\\'; cat"], {
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rows: 24,
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cols: 80,
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});
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await session.attach();
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// The response contains rgb:0000/0000/0000
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await session.waitForText("0000/0000/0000", 3000);
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await session.close();
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}, 15000);
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it("responds to OSC 10 foreground color query", async () => {
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const session = await Session.server("sh", ["-c", "printf '\\033]10;?\\033\\\\'; cat"], {
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rows: 24,
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cols: 80,
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});
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await session.attach();
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await session.waitForText("c0c0/c0c0/c0c0", 3000);
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await session.close();
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}, 15000);
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it("responds to DSR cursor position query (ESC[6n)", async () => {
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const session = await Session.server("sh", ["-c", "printf '\\033[6n'; cat"], {
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rows: 24,
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cols: 80,
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});
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await session.attach();
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// Response: ESC[row;colR — cursor should be at row 1 or 2
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await session.waitForText(";", 3000);
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const ss = session.screenshot();
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expect(ss.text).toMatch(/\d+;\d+R/);
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await session.close();
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}, 15000);
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it("responds to DA2 (ESC[>c)", async () => {
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const session = await Session.server("sh", ["-c", "printf '\\033[>c'; cat"], {
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rows: 24,
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cols: 80,
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});
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await session.attach();
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// Response: ESC[>0;382;0c
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await session.waitForText("382", 3000);
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await session.close();
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}, 15000);
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});