75 lines
2.5 KiB
TypeScript
75 lines
2.5 KiB
TypeScript
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/**
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* Watermark-based flow control for terminal output.
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*
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* SSH/PTY output has no back-pressure by default: the source streams as fast as
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* it can, the main process forwards it over IPC, and the renderer queues every
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* chunk into xterm. When output outpaces rendering (e.g. `cat` of a big file, a
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* noisy build, `tail -f`, `yes`), the renderer-side backlog and xterm's internal
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* buffer grow without bound — memory climbs and the whole UI, typing included,
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* janks.
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*
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* This tracks bytes that have been received but not yet acknowledged by xterm's
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* write callback. When the backlog crosses `highWaterMark` it asks the caller to
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* pause the source; once it drains back to `lowWaterMark` it asks to resume. The
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* hysteresis gap avoids rapid pause/resume flapping. During interactive use the
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* backlog hovers near zero, so this never engages.
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*/
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export interface OutputFlowController {
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/** Account bytes handed to xterm (call when a chunk is received). */
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received(bytes: number): void;
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/** Account bytes whose xterm write callback has fired. */
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written(bytes: number): void;
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/** Clear pending state; calls `onResume` if currently paused. */
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reset(options?: { resume?: boolean }): void;
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pendingBytes(): number;
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isPaused(): boolean;
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}
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export interface OutputFlowControllerOptions {
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highWaterMark: number;
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lowWaterMark: number;
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/** Asked to pause the source when the backlog crosses the high watermark. */
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onPause: () => void;
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/** Asked to resume the source when the backlog drains to the low watermark. */
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onResume: () => void;
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}
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export function createOutputFlowController(
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options: OutputFlowControllerOptions,
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): OutputFlowController {
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const { highWaterMark, lowWaterMark, onPause, onResume } = options;
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let pending = 0;
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let paused = false;
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return {
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received(bytes: number): void {
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if (bytes <= 0) return;
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pending += bytes;
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if (!paused && pending >= highWaterMark) {
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paused = true;
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onPause();
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}
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},
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written(bytes: number): void {
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if (bytes <= 0) return;
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pending -= bytes;
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if (pending < 0) pending = 0;
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if (paused && pending <= lowWaterMark) {
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paused = false;
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onResume();
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}
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},
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reset(options?: { resume?: boolean }): void {
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if (paused && options?.resume !== false) onResume();
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pending = 0;
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paused = false;
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},
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pendingBytes(): number {
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return pending;
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},
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isPaused(): boolean {
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return paused;
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},
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};
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}
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