Events

1import { type Reader, advance } from "../readers/core.js";
2import { readDateTime } from "../readers/datetime.js";
3import { readUInt64 } from "../readers/integers.js";
4import { readString } from "../readers/strings.js";
5import { readUVarint } from "../readers/varint.js";
6
7/**
8 * Example: a plain events table — the scalar baseline.
9 *
10 * Columns (the trigger — generate this reader when a result has these types):
11 *   id   UInt64
12 *   name String
13 *   ts   DateTime('UTC')
14 *
15 * A wide integer (returned as `bigint`, never a lossy `number`), an arbitrary
16 * `String`, and a `DateTime` rendered to an ISO-8601 string here for a stable,
17 * timezone-independent result (the raw reader returns a JS `Date`). Drive it over
18 * a whole result with `readRows(readEventRow)`.
19 */
20export type EventRow = { id: bigint; name: string; ts: string };
21
22export const readEventRow: Reader<EventRow> = (s) => ({
23  id: readUInt64(s),
24  name: readString(s),
25  ts: readDateTime(s).toISOString(),
26});
27
28/**
29 * Optimized {@link readEventRow}: the same three reads inlined into one function
30 * body — no per-field reader calls, the `String` length + slice and the
31 * `DateTime` math written out in place. All scalars, so there is little for the
32 * monomorphization to remove (the JIT already inlines the leaf readers); see
33 * `events.bench.ts`. Still goes through `advance()`, so it stays streaming-safe.
34 *
35 * MEASURED (Node 24 / V8, `events.bench.ts`): ~1.05x — essentially ON PAR, within
36 * run-to-run noise. A purely scalar row has no per-row closures to remove and V8
37 * already inlines the leaf readers, so there is no real win here: prefer the
38 * clearer API `readEventRow` unless your own profiling says otherwise. (Contrast
39 * the composite examples, where monomorphization removes per-row closures and
40 * wins 1.3x–2.7x.)
41 */
42export const readEventRowFast: Reader<EventRow> = (s) => {
43  const id = s.view.getBigUint64(advance(s, 8), true);
44  const len = readUVarint(s);
45  const start = advance(s, len);
46  const name = s.buf.toString("utf8", start, start + len);
47  const ts = new Date(
48    s.view.getUint32(advance(s, 4), true) * 1000,
49  ).toISOString();
50  return { id, name, ts };
51};