Yaowei Zheng
42 lines
1.7 KiB
TypeScript
42 lines
1.7 KiB
TypeScript
/**
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* Bounded Trace-head reads (shared by the Session index's session_meta backfill and the
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* Trace listing's first-prompt title fallback): parse only the head window of a shard
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* instead of pulling a whole multi-MB file into memory.
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*/
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import { open } from "node:fs/promises";
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import { parseTraceLines, readTraceTolerant } from "@prismshadow/penguin-core";
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import type { OmniMessage } from "@prismshadow/penguin-core";
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/** Head window for Trace head reads: generous for a long system prompt, far below a whole multi-MB shard. */
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export const TRACE_HEAD_BYTES = 256 * 1024;
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/**
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* Parse a Trace file's head window only. session_meta is the first line core writes to
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* every shard (and the first user prompt follows right behind it in the earliest shard),
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* so a bounded read finds them without pulling the whole file into memory.
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* The window is cut at its last newline (the tail fragment is incomplete); a first line
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* larger than the whole window falls back to the full tolerant read.
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*/
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export async function readTraceHead(filePath: string): Promise<OmniMessage[]> {
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const fh = await open(filePath, "r");
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let text: string;
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let truncated: boolean;
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try {
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// allocUnsafe: only subarray(0, bytesRead) is ever read, so the uninitialized tail never leaks.
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const { buffer, bytesRead } = await fh.read(
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Buffer.allocUnsafe(TRACE_HEAD_BYTES),
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0,
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TRACE_HEAD_BYTES,
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0,
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);
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text = buffer.subarray(0, bytesRead).toString("utf8");
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truncated = bytesRead === TRACE_HEAD_BYTES;
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} finally {
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await fh.close();
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}
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if (!truncated) return parseTraceLines(text);
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const nl = text.lastIndexOf("\n");
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if (nl === -1) return readTraceTolerant(filePath);
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return parseTraceLines(text.slice(0, nl + 1));
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}
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