fix: use bracketed paste mode for chat terminal tool to avoid macOS PTY corruption by jcansdale · Pull Request #301133 · microsoft/vscode

jcansdale · 2026-03-12T15:38:24Z

Summary

Use bracketed paste mode when the chat terminal tool forwards multiline commands to the live terminal. This mitigates the macOS PTY canonical-mode buffer corruption that occurs with multiline input exceeding ~1024 bytes.

The Problem

On macOS, the kernel's PTY line discipline has a MAX_INPUT buffer of ~1024 bytes in canonical mode. When VS Code's chat terminal tool sends large multiline commands (e.g., long echo statements, inline scripts), the data corrupts at the 1024-byte boundary — characters repeat, lines get mangled, or the shell hangs.

This affects all shells on macOS, though the severity varies. See #296955 for details.

The Fix

One-line change in chatTerminalToolProgressPart.ts:

// Before
liveTerminalInstance.sendText(data, false);

// After
liveTerminalInstance.sendText(data, false, true);

The third parameter (bracketedPasteMode: true) tells sendText to wrap the input in \x1b[200~...\x1b[201~ escape sequThe third parameter (bracketedPasteraThe thirdsteThe third parameter (bracketedPasteMode: true) tells sendTextto wrap the input in\x1b[200~...\x1b[201~ escape sequThe third parameter (bracketedPasteraThe thirdsteThe third parameter (bracketedPasteMode: truee vThe third parmodes.bracketedPasteMode`

sendText() already supports wrapping input in bracketed paste sequences
The wrapping only happens when the shell has opted in — safe for all shells

Coverage

Shell	Bracketed Paste	Fixed?
zsh 5.x	Yes (default on)	Yes
bash 5.1+		bash 5.1+
ks	ks	ks

zsh: passes (runs in raw mode by default)
bash (Homebrew 5.x): passes
bash (/bin/bash 3.2): fails — confirms the bug
sh (= bash 3.2 on macOS): fails — confirms the bug
ksh: passes (but would fail with larger payloads)

Refs #296955, #298993, #300762

Copilot

Pull request overview

Adds a new node-based terminal integration test suite intended to exercise TerminalProcess.input() with multiline payloads across a small shell/size matrix, aiming to catch regressions related to PTY multiline writes (notably on macOS).

Changes:

Introduces a new TerminalProcess - multiline write test suite that spawns real PTY shells (skipped on Windows).
Builds and sends a multiline printf command to write deterministic output to a temp file, then asserts the written file matches expected lines.
Runs the same scenario across multiple shells (bash, zsh, sh, etc.) and payload sizes (10, 20 lines).

Copilot · 2026-03-12T15:43:59Z

+		await new Promise<void>(resolve => {
+			const timer = setTimeout(() => {
+				listener.dispose();
+				resolve();
+			}, 10000);
+			const listener = terminalProcess.onProcessData(() => {
+				clearTimeout(timer);
+				listener.dispose();
+				resolve();
+			});


This promise references listener inside the setTimeout callback before listener is declared. TypeScript will error with "Block-scoped variable 'listener' used before its declaration". Declare let listener first (or create the listener before the timer) so both callbacks can dispose it safely.

Copilot · 2026-03-12T15:44:00Z

+					this.skip();
+				}
+
+				this.timeout(10000);


this.timeout(10000) is likely too low given the test can wait up to 10s for initial output plus up to 4s for the output file (and then still needs to shut down/await exit). This can cause frequent Mocha timeouts on slower CI. Increase the test timeout (or reduce the internal waits) so the overall upper bound fits within this.timeout(...).

Suggested change

this.timeout(10000);

this.timeout(20000);

Copilot · 2026-03-12T15:44:00Z

+			{ ...process.env } as Record<string, string>,
+			{ ...process.env } as Record<string, string>,


The environment is being forced to Record<string, string> via a cast, but process.env (and IProcessEnvironment) allows string | undefined values. This cast hides missing env vars and removes type safety in the test. Prefer passing process.env directly (it matches IProcessEnvironment) or explicitly filtering/normalizing undefined values if a strict Record<string, string> is required.

Suggested change

{ ...process.env } as Record<string, string>,

{ ...process.env } as Record<string, string>,

process.env,

process.env,

Copilot · 2026-03-12T15:44:00Z

+	teardown(() => {
+		fs.rmSync(outputDir, { recursive: true, force: true });
+	});


ensureNoDisposablesAreLeakedInTestSuite() registers its own teardown that disposes the DisposableStore. In Mocha, teardown hooks run in reverse registration order, so this fs.rmSync(outputDir, ...) teardown will likely run before the TerminalProcess in the store is disposed (especially when a test fails early), which can cause flaky cleanup. Consider registering the directory cleanup with the disposable store (eg via store.add(toDisposable(...))) or otherwise ensure the terminal process is disposed before deleting outputDir.

When the chat terminal tool forwards multiline commands to the live terminal, use bracketed paste mode (when the shell supports it) to avoid macOS PTY canonical-mode buffer corruption with input exceeding ~1024 bytes. Shells that support bracketed paste (zsh, bash 5.1+) will receive the input wrapped in ESC[200~ / ESC[201~ sequences, treating it as a single paste operation. For shells that don't support it (bash 3.2, ksh), this is a no-op since sendText only wraps when bracketedPasteMode is enabled. Refs microsoft#296955

Add tests proving that wrapping multiline input in bracketed paste sequences (ESC[200~ / ESC[201~) prevents macOS PTY canonical-mode buffer corruption for shells that support it (zsh). The trailing carriage return must come after the paste end marker, as content inside the markers is treated as literal buffer input.

Run multiple iterations per test in parallel to increase I/O contention, and write input in small chunks (4 bytes) with event loop yields to better simulate xterm.js write patterns. Note: zsh still passes at the PTY level even with these changes. The real-world zsh failure requires the full xterm.js/terminal UI rendering loop (as shown by vscode-extension test-electron tests). The PTY-level tests reliably reproduce the bug for bash 3.2/sh/ksh.

meganrogge · 2026-03-17T21:42:15Z

+		// Use bracketed paste mode when available to avoid macOS PTY canonical-mode
+		// buffer corruption with multiline input exceeding ~1024 bytes.
 		this._register(mirror.onDidInput(data => {
 			if (!liveTerminalInstance.isDisposed) {


shouldn't we restrict this to macOS?

meganrogge

It seems to work based on my testing. One change and incorporating Copilot's comments would be good.

connor4312 · 2026-03-18T17:11:38Z

This seems to work for me as well!

jcansdale · 2026-03-19T16:25:36Z

Closing this in favor of #302526.

jcansdale · 2026-03-19T16:27:47Z

@connor4312 fyi 👉🏻 #302526

test: add multiline PTY shell matrix tests

80d1936

Copilot AI review requested due to automatic review settings March 12, 2026 15:38

Copilot started reviewing on behalf of jcansdale March 12, 2026 15:39 View session

Copilot AI reviewed Mar 12, 2026

View reviewed changes

vs-code-engineering Bot assigned Tyriar and meganrogge Mar 12, 2026

jcansdale added 2 commits March 12, 2026 17:40

Use echo '...' | wc -c shape for PTY multiline tests, drop csh/tcsh

6a23144

jcansdale changed the title ~~test: add multiline PTY shell matrix tests~~ fix: use bracketed paste mode for chat terminal tool to avoid macOS PTY corruption Mar 13, 2026

jcansdale added 3 commits March 13, 2026 00:46

test: expand multiline PTY tests to 30, 40, 50 lines

70595ac

jcansdale force-pushed the jcansdale/pty-multiline-tests branch from 46dbe34 to 26267fb Compare March 13, 2026 10:03

jcansdale mentioned this pull request Mar 13, 2026

Test bracketed paste mode as a workaround jcansdale/macos-pty-multiline-bug#4

Open

Copilot AI mentioned this pull request Mar 13, 2026

Add bracketed paste mode as a before/after mitigation test jcansdale/macos-pty-multiline-bug#5

Draft

jcansdale mentioned this pull request Mar 14, 2026

Add terminal integration test harness and multiline repro jcansdale/terminal-mcp#1

Merged

meganrogge self-requested a review March 17, 2026 21:39

meganrogge reviewed Mar 17, 2026

View reviewed changes

meganrogge requested changes Mar 18, 2026

View reviewed changes

meganrogge requested a review from connor4312 March 18, 2026 16:13

jcansdale closed this Mar 19, 2026

jcansdale deleted the jcansdale/pty-multiline-tests branch March 19, 2026 16:27

vs-code-engineering Bot locked and limited conversation to collaborators May 3, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

fix: use bracketed paste mode for chat terminal tool to avoid macOS PTY corruption#301133

fix: use bracketed paste mode for chat terminal tool to avoid macOS PTY corruption#301133
jcansdale wants to merge 6 commits into
microsoft:mainfrom
jcansdale:jcansdale/pty-multiline-tests

jcansdale commented Mar 12, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

meganrogge Mar 17, 2026

Uh oh!

meganrogge left a comment

Uh oh!

connor4312 commented Mar 18, 2026

Uh oh!

jcansdale commented Mar 19, 2026

Uh oh!

jcansdale commented Mar 19, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

		{ ...process.env } as Record<string, string>,
		{ ...process.env } as Record<string, string>,

Conversation

jcansdale commented Mar 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

The Problem

The Fix

Coverage

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

meganrogge Mar 17, 2026

Choose a reason for hiding this comment

Uh oh!

meganrogge left a comment

Choose a reason for hiding this comment

Uh oh!

connor4312 commented Mar 18, 2026

Uh oh!

jcansdale commented Mar 19, 2026

Uh oh!

jcansdale commented Mar 19, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

jcansdale commented Mar 12, 2026 •

edited

Loading