Alexander Gromnitsky's Blog

ESLint's flat config and Emacs

Air Date: 2024-09-07
Latest update: 2024-09-07 11:28:14

I expected to use this "new" eslint as follows:

1. have a user-wide eslint installation with a personal default configuration;
2. given #1, to be able to run eslint in any project (mine or not) to check it against my personal rules;
3. if a project has node_modules/.bin/eslint script (implying there is a config file in the project's root directory), running node_modules/.bin/eslint should ignore the global config and use the local one;
4. Flycheck in Emacs should automatically execute either node_modules/.bin/eslint (if it exists) or the global version otherwise.

Naïvely installing eslint via 'npm i -g' won't do much good since any plugins must still be installed locally.

Hence, I created a directory ~/lib/dotfiles/eslint solely for a "global", user-wide installation & configuration:

|-- eslint*
|-- eslint.config.mjs
|-- node_modules/
|   |-- .bin/
|   |   `-- eslint -> ../eslint/bin/eslint.js*
|   `-- eslint/
`-- package.json

where eslint is a shell script, symlinked from a directory in PATH:

$ stat -c%N `which eslint`
'/home/alex/bin/eslint' -> '/home/alex/lib/dotfiles/eslint/eslint'
$ cat eslint
#!/bin/sh

__dir__=$(dirname "$(readlink -f "$0")")
"$__dir__"/node_modules/.bin/eslint -c "$__dir__"/eslint.config.mjs "$@"

and eslint.config.mjs has common rules for .js files and files without extensions:

import globals from 'globals'
import js from '@eslint/js'
import react from 'eslint-plugin-react'

export default [
  js.configs.recommended,
  {
    rules: {
      "no-unused-vars": [ "warn", { "argsIgnorePattern": "^_" } ],
      …
    },
    languageOptions: {
      globals: {
        ...globals.browser,
        ...globals.node,
        …
      }
    }
  },
  {
    files: ["**/!(*.*)"],
    ignores: ["**/{Makefile,Rakefile,Gemfile,LICENSE,README}"],
  },
  …
]

If you don't care about any custom configurations that arrive with almost any JS project, you may stop here. Otherwise, we need to instruct Emacs where to search for eslint executable.

(defun my--npm-exec-path()
  (let ((npm-root (string-trim
                   (shell-command-to-string "npm root 2>/dev/null"))))
    (when (not (string= "" npm-root))
      (make-local-variable 'exec-path)
      (add-to-list 'exec-path (file-name-concat npm-root ".bin"))
      )))
(add-hook 'js-mode-hook 'my--npm-exec-path)
(add-hook 'js-mode-hook 'flycheck-mode)

This tells the editor to invoke my--npm-exec-path function every time Emacs opens a .js file. The function runs npm root to guess the proper path for node_modules directory and prepends Emacs' internal exec-path list with the path where the eslint script might be installed. Iff such a script is found by Flycheck, our global ~/lib/dotfiles/eslint/eslint.config.mjs is ignored.

Visualising curl downloads

Air Date: 2024-07-11
Latest update: 2024-07-14 21:45:57

If downloading from a server is slow, how would you prove to a devops guy that you're experiencing a slowdown? There are a couple of possibilities, the worst of which would be sending a video. What if you send a speed graph using data from curl?

Every second curl prints to stderr the following:

fprintf(tool_stderr,
        "\r"
        "%-3s " /* percent downloaded */
        "%-3s " /* percent uploaded */
        "%s " /* Dled */
        "%s " /* Uled */
        "%5" CURL_FORMAT_CURL_OFF_T " " /* Xfers */
        "%5" CURL_FORMAT_CURL_OFF_T " " /* Live */
        " %s "  /* Total time */
        "%s "  /* Current time */
        "%s "  /* Time left */
        "%s "  /* Speed */
        "%5s" /* final newline */,
        …

Therefore, by replacing \r with \n we can send a download log:

$ curl http://example.com/1.zip -o 1.zip 2>&1 | tr \\r \\n

To draw a graph with gnuplot, we can use Current time and Speed columns. Gnuplot understands time as input data, but I don't know how to persuade it to interpret values like 100k or 200M, thus we need to convert them into 'bytes'. This is a cute little problem for code golf, but amusingly, it was already solved in coreutils > 12 years ago via numfmt(1).

$ echo 1M and 10M | numfmt --from iec --field 3
1M and 10485760

(macOS & FreeBSD both have coreutils package, where the utility executable is prefixed with 'g'.)

#!/usr/bin/env -S stdbuf -o0 bash

set -e -o pipefail
numfmt=`type -p gnumfmt numfmt;:`; test "${numfmt:?}"

cat <<E
set xdata time
set timefmt "%H:%M:%S"
set xlabel "Time, MM:SS or HH:MM:SS"
set format y "%.0s%cB"
set ylabel "Speed, Unit/second" offset -1,0
set grid
plot "-" using 1:2 with lines title ""
E

curl "$@" -fL -o /dev/null 2>&1 | tr \\r \\n | awk '
/[0-9.][kMGTP]?$/ {
  time = index($10, ":") == 0 ? $11 : $10
  if (time != "--:--:--") print time, $NF
}' | tr k K | $numfmt --from iec --field 2

Usage:

$ ./curlbench http://example.com/1.zip | gnuplot -p

The cheapest NAS

Air Date: 2024-07-01
Latest update: 2024-07-03 19:09:11

I wanted to replace my old trusty 'router' (with an attached HDD)--that was not working as a router, but as a network drive after flashing OpenWRT onto it--I wanter to replace it with an SBC+HDD combo.

This new device should not only preserve all the services the old one provided (samba, git, rsyncd, a dnf repo), but also perform faster, for having a potato instead of a CPU, the ex-router struggled with rsync over ssh &, being gravely RAM limited, choked when I did 'git push' commits containing binaries > 15MB.

Searching for a suitable SBC led me to libre.computer, a company I had never heard of before. At first glance, they had the el cheapo AML-S805X-AC board I needed:

• LAN port (but 100 Mb only);
• 2 USB-A (but 2.0 only);
• 4-core ARM Cortex-A53;
• 1 GB RAM;
• booting from an USB;
• up-to-date Debian;
• easy to buy without hunting it down.

100Mb may seem like a joke nowadays, but the main purpose of such a toy NAS for me is to keep a copy of a directory with ~200K small files. Having 1Gb would only marginally improve the syncing speed even if the SBC supported USB 3.0.

But this is just a board. I also needed an hdd enclosure with an external power supply (for the device provides up to 900mA for each USB-A), at least 3A power supply & a micro-USB cable that can handle 3A.

(I didn't include an HDD in the table, for I presume everyone has a couple of them lying around.)

When I bought the HDD enclosure, I didn't read the description carefully & thought it was going to be a small plastic container for 2.5-inch drives, but when the package arrived, it turned out to be a box for 3.5-inch ones. Hence, I decided to shove the SBC into it too.

After connecting the TTL-to-USB dongle to the board's GPIO

& typing

$ sudo screen /dev/ttyUSB0 115200

one of the 1st readouts appeared as:

U-Boot 2023.07+ (Nov 03 2023 - 15:10:36 -0400) Libre Computer AML-S805X-AC

Model: Libre Computer AML-S805X-AC
SoC:   Amlogic Meson GXL (S805X) Revision 21:d (34:2)
DRAM:  512 MiB (effective 1 GiB)

What does the last line mean exactly? After I dd'ed Debian-12 onto a flash drive, free(1) said it saw 1GB. Anyway, libre.computer has an official OS image, based on stock Debian:

$ fdisk debian-12-base-arm64+arm64.img -l
Disk debian-12-base-arm64+arm64.img: 2.25 GiB, 2415919104 bytes, 4718592 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x71f3f7cf

Device                          Boot  Start     End Sectors  Size Id Type
debian-12-base-arm64+arm64.img1 *      2048  524287  522240  255M ef EFI (FAT-12/16/32)
debian-12-base-arm64+arm64.img2      524288 4718591 4194304    2G 83 Linux

Yes, it has an EFI partition with the MBR layout! The 2nd partition is btrfs (supposedly it's faster & more gentle to flash storage than ext4; no idea if both claims are true). You can examine its contents via:

$ sudo mount -o loop,offset=$((524288*512)) debian-12-base-arm64+arm64.img ~/mnt/misc

This partition gets auto-resized on the 1st boot to fill the rest of the free space available on the drive. Doing this on USB dongles proved to be a miserable experience: of the 3 I had available, one permanently got stuck on resizing, and another, despite finishing the operation, became so sluggish afterwards that a 20-year-old PC would've felt snappier.

This is I didn't like at all. There is no repo with from which the OS image gets generated. The explanation is bizarre:

"The distribution builder is a proprietary commercial offering as it involves a lot of customer IP and integrations so it cannot be public."

but with an consolation advice:

"If you want to study them [images], bootstrap and do a diff. We don't make any changes to the standard distros outside of setting a few configs since we're not distro maintainers."

Make of it what you will.

Then I connected the HDD enclosure to the board. This time, the process went much, much faster (though there were still some unexpected delays in random places). Right after logging in, I started getting uas_eh_abort_handler errors from the kernel. It turns out I got one of the worst HDD enclosure innards possible, if you believe reviews from the interwebs:

$ lsusb
Bus 001 Device 002: ID 152d:0578 JMicron Technology Corp. / JMicron USA Technology Corp. JMS578 SATA 6Gb/s
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

The remedy is to turn UAS off via adding usb-storage.quirks=152d:0578:u to the kernel cmdline. It did help, the delays went away, although 'benchmarks' became hardly thrilling:

$ lsusb -t
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/2p, 480M
    |__ Port 2: Dev 2, If 0, Class=Mass Storage, Driver=usb-storage, 480M
$ sync; time sh -c "dd if=/dev/urandom of=1 bs=500k count=1k && sync"; rm 1
1024+0 records in
1024+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 15.1014 s, 34.7 MB/s

real    0m21.876s
user    0m0.001s
sys     0m7.976s

which means $\frac{524}{21.876}=23.95$ MB/s on an ext4 partition.

Would I recommend this setup? I wouldn't. One of the reasons I've chosen the path with an SBC instead of a common micro-ITX route is to save on power consumption. If you don't have similar problems, I see 0 reasons to struggle with such a finicky Chinese device.

Of flags and keyletters

Air Date: 2024-03-07
Latest update: 2024-03-07 16:35:47

Date: Fri, 1 Mar 2024 10:49:42 -0500
From: Douglas McIlroy <douglas.mcilroy@dartmouth.edu>
Newsgroups: gmane.org.unix-heritage.general
Subject: Of flags and keyletters
Message-ID: <CAKH6PiV3ixuwoZ-d31JNXpQpHxAAcfpRKreUcn11msW1yjboLg@mail.gmail.com>

> why did AT&T refer to "flags" as "keyletters" in its SysV documentation?

Bureaucracies beget bureaucratese--polysyllabic obfuscation, witness
APPLICATION USAGE in place of BUGS.

One might argue that replacing "flag" by "option", thus doubling the number
of syllables, was a small step in that direction. In fact it was a
deliberate attempt to discard jargon in favor of normal English usage.