chelsealong
9c013eaaf8
pty_ws already fell back to the per-channel active-session file when a /chat WS connects with no ?resume= param, replaying the whole session into the PTY, but the frontend only pinned xterm's viewport to the bottom when resumeParam came from the URL (#59591). The implicit path had no way to learn a replay was happening, so the viewport stayed at the top of the scrollback. pty_ws now sends a one-off JSON control frame naming the session id it resolved from the active-session file, before any PTY bytes; PTY output itself always arrives as binary frames, so this is unambiguous on the wire. ChatPage tracks an `effectiveResume` value seeded from resumeParam and updated when this control frame arrives, and the existing follow-scroll/sanitizer/hydration logic keys off it instead of the URL param alone. Fixes #93518.
79 lines
3.0 KiB
TypeScript
79 lines
3.0 KiB
TypeScript
/**
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* Dashboard chat resume-scroll helpers.
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*
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* When a chat session is resumed (`/chat?resume=<id>`) the PTY backend replays
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* the entire scrollback over the WebSocket the instant it opens. xterm.js writes
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* those bytes into its buffer but leaves the viewport wherever it was (e.g. the
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* top of a fresh terminal), so the transcript looks truncated until something
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* else forces a re-render. See #59591.
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*
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* The fix pins the viewport to the bottom *as each replayed chunk commits* (via
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* xterm's `write` callback) instead of guessing with a fixed double-rAF delay,
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* and releases that pin the moment the user scrolls up so their manual review of
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* the backlog is never yanked back down.
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*
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* These two decisions are pulled out here as pure functions so they can be
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* unit-tested without a live terminal; `ChatPage` wires them to the real xterm
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* instance (see `term.onScroll` and `ws.onmessage`).
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*/
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/** The subset of xterm's active `IBuffer` these helpers need. */
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export interface TerminalViewportPosition {
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/** Row index of the top of the current viewport. */
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viewportY: number;
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/** Row index of the viewport top when scrolled fully to the bottom. */
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baseY: number;
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}
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/**
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* True when the viewport is scrolled to (or past) the bottom, i.e. the latest
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* output is on screen. xterm reports `viewportY === baseY` at the bottom; the
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* `>=` also covers the transient overshoot while scrollback rows are trimmed.
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*/
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export function isViewportPinnedToBottom(
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buffer: TerminalViewportPosition,
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): boolean {
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return buffer.viewportY >= buffer.baseY;
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}
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/**
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* Whether a freshly written PTY output chunk should scroll the terminal to the
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* bottom afterwards. We only auto-follow while resuming a session (the replay
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* case) and only while the user hasn't scrolled up to read the backlog. A fresh
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* (non-resume) session returns `false` so normal cursor output is never fought.
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*/
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export function shouldFollowPtyOutput(
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resumeParam: string | null,
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stickToBottom: boolean,
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): boolean {
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return Boolean(resumeParam) && stickToBottom;
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}
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/**
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* When `pty_ws` falls back to the per-channel active-session file (no
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* `?resume=` on the URL), the server sends a one-off JSON text frame naming
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* the session it resolved before any PTY replay bytes arrive, since the
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* frontend has no other way to learn a replay is happening (#93518). PTY
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* output itself always arrives as binary frames, so any text frame is a
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* candidate; this returns the resume id on a match and `null` for anything
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* else (including the plain ANSI error banners `pty_ws` still sends as text
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* on failure, which must keep rendering into the terminal as before).
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*/
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export function parseResumeControlMessage(data: string): string | null {
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try {
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const parsed = JSON.parse(data);
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if (
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parsed &&
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typeof parsed === "object" &&
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parsed.type === "resume" &&
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typeof parsed.id === "string" &&
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parsed.id
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) {
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return parsed.id;
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}
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} catch {
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/* not JSON — an ANSI banner or other plain-text frame */
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}
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return null;
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}
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