homeio

1import "server-only";
2
3import { readFile } from "node:fs/promises";
4
5// /proc/diskstats counts in 512-byte sectors whatever the disk's own sector size.
6const SECTOR_BYTES = 512;
7// Whole disks only: partitions (sda1, nvme0n1p1, mmcblk0p1) would count the
8// same bytes twice, and loop, RAM, zram and device-mapper devices are not disks.
9const WHOLE_DISK = /^(sd[a-z]+|hd[a-z]+|vd[a-z]+|xvd[a-z]+|nvme\d+n\d+|mmcblk\d+)$/;
10
11export type DiskCounters = { readBytes: number; writeBytes: number };
12export type DiskRate = { readBytesPerSec: number; writeBytesPerSec: number };
13
14/** Bytes read and written per whole disk since boot, from /proc/diskstats. */
15export function parseDiskstats(text: string): Map<string, DiskCounters> {
16  const counters = new Map<string, DiskCounters>();
17  for (const line of text.split("\n")) {
18    const fields = line.trim().split(/\s+/);
19    // major minor name reads merged sectors_read ms writes merged sectors_written ...
20    if (fields.length < 10) continue;
21    const name = fields[2];
22    if (!WHOLE_DISK.test(name)) continue;
23    const sectorsRead = Number(fields[5]);
24    const sectorsWritten = Number(fields[9]);
25    if (!Number.isFinite(sectorsRead) || !Number.isFinite(sectorsWritten)) continue;
26    counters.set(name, {
27      readBytes: sectorsRead * SECTOR_BYTES,
28      writeBytes: sectorsWritten * SECTOR_BYTES,
29    });
30  }
31  return counters;
32}
33
34export async function readDiskCounters(): Promise<Map<string, DiskCounters> | null> {
35  try {
36    return parseDiskstats(await readFile("/proc/diskstats", "utf8"));
37  } catch {
38    // Not Linux: there is no /proc/diskstats.
39    return null;
40  }
41}
42
43/**
44 * Turns successive counter readings into per-disk rates. Each caller keeps its
45 * own tracker, so the history sampler and the Disks tab do not reset each
46 * other's baseline.
47 */
48export function createDiskRateTracker(maxGapMs = 60_000) {
49  let previous: { at: number; counters: Map<string, DiskCounters> } | null = null;
50
51  return function update(counters: Map<string, DiskCounters>, at: number) {
52    const rates = new Map<string, DiskRate>();
53    if (previous && at > previous.at && at - previous.at <= maxGapMs) {
54      const seconds = (at - previous.at) / 1000;
55      for (const [name, now] of counters) {
56        const before = previous.counters.get(name);
57        if (!before) continue;
58        // A counter that went backwards (device re-added) gives no rate this round.
59        const read = now.readBytes - before.readBytes;
60        const write = now.writeBytes - before.writeBytes;
61        if (read < 0 || write < 0) continue;
62        rates.set(name, { readBytesPerSec: read / seconds, writeBytesPerSec: write / seconds });
63      }
64    }
65    previous = { at, counters };
66    return rates;
67  };
68}
69
70/** Sum of all disks, in MB/s, or null when there is no rate yet. */
71export function totalMegabytesPerSecond(rates: Map<string, DiskRate>) {
72  if (rates.size === 0) return { readMBps: null, writeMBps: null };
73  let read = 0;
74  let write = 0;
75  for (const rate of rates.values()) {
76    read += rate.readBytesPerSec;
77    write += rate.writeBytesPerSec;
78  }
79  return { readMBps: read / 1_000_000, writeMBps: write / 1_000_000 };
80}
81