How I Fixed: ACF REST API cant_update_item

OK, hopefully this one is as easy to fix for you as it was for me. Easy being the typical (seemingly?) undocumented “one liner” that makes everything work.

In my example, I had just set up WordPress with ACF, added in ACF to REST API, and JWT Authentication for WP-API.

Essentially that gives a combo of admin UI to create and manage the custom fields, and then a REST API endpoint to GET, PUT, POST, etc.

The docs for getting the JWT Authentication plugin set up are good enough. Just a couple of additional define statements required in wp-config.php. Hopefully you have that sorted, and can log in:

curl -X POST \ \
  -d '{
	"username": "my_wp_user",
	"password": "my_wp_users_password"

// should return response, e.g. 

    "token": "aVeryLongStringHere",
    "user_email": "",
    "user_nicename": "my_wp_user",
    "user_display_name": "Admin Person Name"

Sweet. So far, so good.

Next, you need to add in at least one ACF custom field via your admin UI.

I’ve gone with a simple text field.

Even without authenticating, you should be able to hit your WP REST API and see the extra stuff added in by ACF:

curl -X GET \

  "id": 9,
  "date": "2020-06-17T18:41:01",
  "date_gmt": "2020-06-17T17:41:01",
  "guid": {
  "modified": "2020-06-25T09:13:20",
  "modified_gmt": "2020-06-25T09:15:44",
  "slug": "my-post-slug",
  "status": "publish",
  "type": "page",
  "link": "",
  "title": {
  "content": {
  "excerpt": {
  "author": 1,
  "featured_media": 0,
  "parent": 8,
  "menu_order": 0,
  "comment_status": "closed",
  "ping_status": "closed",
  "template": "page-templates/my-page-template.php",
  "meta": [],
  "acf": {
    "example_field": ""
  "_links": {


I’ve trimmed this right down. The interesting bit is the acf key / value. Make sure you see it.

The Problem

Things start to get interesting from here on in.

In order to update the post / page / whatever, we will need to be authenticated. We authenticated earlier, and got back a token. We need to pass that token as a Header on any requests that want to add / update data.

This is really easy – just add the header key of Authorization, and the value of Bearer your_token_from_earlier_goes_here. An example follows below.

But more importantly, as best I can tell, we need to use a special endpoint to update ACF fields.

For regular WP data, you might POST or PUT into e.g. to update data. Technically, PUT is more accurate when updating, and POST is for initial creation, but either seem to work.

curl -X POST \ \
  -H 'authorization: Bearer aVeryLongStringHere' \
  -d '{
    "slug": "my-updated-slug"

// which should return a full JSON response with the all the data, and the updated slug.

But if you try to update ACF this way, it just silently ignores your change:

curl -X POST \ \
  -H 'authorization: Bearer aVeryLongStringHere' \
  -d '{
	"acf": {
	    "example_field": "some interesting update"

// it should 'work' - you get a 200 status code, and a full JSON response, but 'example_field' will not have updated.

My intuition says that seeing as we followed the response structure, this should have worked. But clearly, it doesn’t.

But it turns out that we need to use a separate endpoint for ACF REST API updates:

curl -X GET \

// note again, no auth needed for this GET request

	"acf": {
	    "example_field": ""

So this works, too. This only returns the acf field subset. But still, confusingly, the top level key is acf. And that’s what threw me.

See, if we try to make a POST or PUT following this shape:

curl -X POST \ \
  -H 'authorization: Bearer aVeryLongStringHere' \
  -d '{
	"acf": {
	    "example_field": "some interesting update"

// fails, 500 error

    "code": "cant_update_item",
    "message": "Cannot update item",
    "data": {
        "status": 500

And the same goes for if we drop the acf top level key:

curl -X POST \ \
  -H 'authorization: Bearer aVeryLongStringHere' \
  -d '{ example_field": "some interesting update" }'

// fails, 500 error

    "code": "cant_update_item",
    "message": "Cannot update item",
    "data": {
        "status": 500

The Solution

As I said at the start, this is a one liner. And as far as I could see, it’s not *clearly* documented. Maybe it’s in there somewhere. Maybe if you use WP day in, day out, you already know this. I don’t. And so I didn’t.

Hopefully this saves you some time:

curl -X POST \ \
  -H 'authorization: Bearer aVeryLongStringHere' \
  -d '{
	"fields": {
            "example_field": "some interesting update"

// works, 200, response:

	"acf": {
	    "example_field": "some interesting update"

And lo-and-behold, that works.

I think it’s super confusing that the field key is used on create / update, but the acf key is returned on read. Admittedly I have done this myself on API’s before – but as a consumer I now realise how unintuitive and frustrating that is.

How I Fixed: docker: invalid reference format With Makefile

I’m a big fan of makeshift Makefiles. Largely because I don’t seem to have the brain capacity to remember long winded commands. Or maybe, I just don’t like typing out long winded commands. One of the two reasons, for sure.

In using a Makefile to set up a local DNS server to help resolve an issue with multiple different related, but separated Docker projects being able to talk to one another, I ended up coming across this Stack Overflow post which was very helpful.

The solution from the post calls for running a Docker command to spin up a local DNS server, which then allows all the disparate services to talk to one another via hostname, rather than IP address.

I dutifully created a new Makefile entry:

	@docker run \
		--rm \ 
		--hostname=dns.mageddo \
		-p 5380:5380 \
		-v /var/run/docker.sock:/var/run/docker.sock \
		-v /etc/resolv.conf:/etc/resolv.conf \

It’s hard to spot the fault here. That command looks right to me.

I copy / pasted the command direct from the Stack Overflow post, added in the --rm flag to ensure the resulting container gets removed when I kill it, and then tried to run the command:

 ➜ myproject.whatever make start_dev_dns
docker: invalid reference format.
See 'docker run --help'.
make: *** [Makefile:8: start_dev_dns] Error 125


Anyway, after a bit of head scratching, it turns out the issue was an extra space after the line continuation slash.

Really hard to display this one on a blog post. But essentially if you see this and you’re in a similar situation, check you don’t have any rogue spaces after the \‘s at the end of each line.

How To Get Variables From package.json In Your JS / TS Code

Let’s say you have a bit of information inside package.json that you’d like to use somewhere in your code. An example of this in my case is the version string which I have to set for Electron to then generate the new file name for the “built” version of my app.

I figured if I’m specifying the version in package.json, I could display that value in the app footer. This would then, hopefully, help with a variety of first step debugging processes / help / support requests. It’s a quick visual check to ensure the user is on the latest version.

Anyway, this is one of them things that doesn’t come up for me that often, and when it does, I tend to forget how to do it.

import { version as appVersion } from '../package.json';

const Footer = () => {
  return (
        v{appVersion} © 2019 -{' '}
        {new Date().getFullYear()} A6 Software Ltd. All rights reserved.

(Ugh, seems WordPress code formatting has some … issues, shall we say, at present)

Pretty straightforward.

package.json is not a special case here, even though it might seem like it would be. This is how you can get a value from any JSON file.

This may not work immediately, it really depends on how your project is set up.

2020 Macbook Pro Screen “Washed Out” on Wake / Resume

I have no idea how to explain this one, but I’ll do my best.

Infrequently when I open the lid on my 2020 Macbook Pro, the laptop wakes up, but the screen is “washed out” / has this weird very white overlay going on.

Nothing I have done seems to resolve this.

It started almost immediately after purchasing, and subsequent OS updates haven’t solved it. I have no external monitors plugged in, or in fact, anything external at all. The one thing that may be a commonality is having the power cable plugged in.

Annoyingly, when I go to shut down / restart (which fixes it, btw), the screen comes back to normal just as I’m shutting down. How frustrating.

So a cunning fix I’ve found – that solves a crappy problem with a three grand laptop – is to open an app like iTerm, then go to shutdown.

iTerm will then prompt saying “hey, do you really want to shut down?” And this allows me to stop the shutdown process and my screen goes back to normal.

Should I need a bodge workaround for a top of the line Apple product? Apparently: yes.

I should add, btw, that this is not the only problem I have with this laptop. I also suffer from:

  • intermittent key repeat / sticking;
  • headphone jack doesn’t work on wake from sleep;
  • my fat fingers keep accidentally touching the “touch bar” when typing.

Admittedly the last one is my fault… I guess.


Docker Ate My Harddisk – No space left on device

I’ve recently been forced to migrate from Rancher v1.x to using docker-compose to manage my production Docker containers.

In many ways its actually a blessing in disguise. Rancher was a nice GUI, but under the hood it was a total black box. Also, fairly recently they migrated to v2, and no true transition path was provided – other than “LOL, reinstall?”

Anyway, one thing that Rancher was doing for me – at least, I think – was making sure the log files didn’t eat up all my hard disk space.

This one just completely caught me by surprise, as I am yet to get my monitoring setup back up and running on this particular box:

➜ ssh chris@ # obv not real

Welcome to chris server
System information as of Wed May 13 12:28:24 CEST 2020
System load: 3.37

Usage of /: 100.0% of 1.77TB

Memory usage: 13%
Swap usage: 0%
Processes: 321
Users logged in: 0

=> / is using 100.0% of 1.77TB


There’s a pretty handy command to drill down into exactly what is eating up all your disk space – this isn’t specific to Docker either:

chris@chris-server / # du -h --max-depth=1
16G ./export
607M ./lib
60M ./boot
13M ./bin
5.1M ./etc
48K ./tmp
180K ./root
8.0K ./media
2.3T ./var
4.0K ./mnt
0 ./sys
4.0K ./srv
28K ./home
0 ./dev
59G ./docker
1.2G ./usr
13M ./sbin
0 ./proc
8.0K ./snap
4.0K ./lib64
316M ./run
16K ./lost+found
16K ./opt
2.4T .

The culprit here being /var with its 2.3T used… of 1.8T file system? Yeah.. idk.

Anyway you can keep drilling down with the disk usage command until you isolate the culprit. But as this is Docker related, I’ll save you the bother:

chris@chris-server /var/lib/docker/containers # du -h --max-depth=1
270G ./b3ec5a04079d5b3060d5575e011dd5e482950a794d52b4470659823dc5d5a6be
1.9M ./4b1eff96be524bdb20e87448520a30329a5e42bb36f9ba523f458d87cb8b5dc7
44K ./fc7552b499aca543a9bc6d8ef223a09d1ed21c4d054aa150b29c1d4023c151d9
40K ./43ef97d1a135f7404ca4a0330fb0ae6310ef87316358324a05bf6a65cc8d06b0
64K ./a0155805cc59d65b5815352f97939f12a4e87e30662eafa253ae8395eb553e0c
44K ./b4fd3f35324278dc832a5e98fe5a3e5655fecaf61d4de8c5e8080f8af63c22fe
40K ./b37593cd946407872e71c57af6d30b1c85c30fc42a8e075aad542fa820fbdc97
192K ./cb1e3eac9d1c1d997471f915d42fd0f999454fbee772ddc451f28e60ff1a4d22
281G ./3dd2886e627555cd6db45f68e0d1d9e520a6ab4ad443a2e43c70498b51b81fc4
1.9M ./552a0d7a7dd13afa65050381104e86395b2510c6437f650782260664ba195deb
40K ./111da287b97d0eff6b710cd7a9f0d80b7febd03c4ee30db8e2c0519e9a506c8a
40K ./47112f1fd4b0399c506fc1318ba2c0d03502b3ad731169f43a317a09556b2a6d
40K ./afeb8b8c2fbc918caaf199ae0aaca78f68e91412f9a7bc389963c6c15d6e2832
1.9M ./cb3c71ddb7181f9bbd3803cc644f36c05eedd922d4529c62354c68dedfc3bc02
624K ./c7ba5a354cdb2ab6f31fe443c04b72fad2a2e8107bc42a875422c4d80a164144
212K ./5d2b649bdb9eca4f0e14304e4ffad22b7d50d5c099a72072862a1135488105c6
56K ./781635651e0890695e1002639b5167cebf56e78fdeed3e839fc91c0681d9edd2
28M ./65aa3252acc8cf7a7af9301a0df9c117670c602f08bdb0f256eb37382a3eb859
68K ./8c8bf1febde03cf957cae5b695baf70427f6e2dec53d07d3a495ecbf2c9a3ac0
44K ./990279783af4cfacaa2e71c18eba0e6870d472dfd11e261e40a512779783fef5
40K ./37dfd1291842da4debff4c07c58d60b4efcd9e060ebfe29f1508bf418c284ca8
304K ./34c7bfcf01a6ca8e830e6108056eb0df70d4fe88eda699f3e3aa067c1afca2da
40K ./c7be4d913f95ffc040d72374bb77ad37a31846a80f40404c8b82bd5ec725d99f
1.9M ./af173be6ea5d961be308596a28e8039a20e38bc0facf623a65ee0894f28920e2
44K ./3cb4c8b263ca4c802b6df699510374929df50784b25ab8e63802ee8f2054ffc9
328K ./574599803c9143e2f87cabcc211fa3ee47f28f1e765298141f081fa1e457ced6
281G ./6bfcad1f93a7fffa8f0e2b852a401199faf628f5ed7054ad01606f38c24fc568
108K ./e5656136a35ffb242590abf50c203f5478e09bf954a6ca682cb391c11328d251
1.1M ./0150dafffbdbb830dc6ab158913eb8bd4003bf07e280579421aaeb29a7ac5623
271G ./0b5947f687fa47a70b71869468d851e4aeb3857a599a2d7eba8cf58f3b8d6bda
40K ./d014ae83b6314bcad0a159ae3cfad03a8589d4631e7c66a68ad55f1ad722f2fe
52K ./a85b7ab40a097b1548a8dea2826277742815a5e9b0c3c803b065504a2c526bb4
588K ./b5e0a0a4900e1c6fd066f5ae8d534bb832708f0caf917839c578d7debaea3783
52K ./53dd57dcbbca5248456423ebb4f0499b5d15eb5f4be7c0821979a7c880dbaa89
1.1T .

Son of a diddly.

Basically, this wasn’t caused by Docker directly. This was caused by my shonky migration.

The underlying issue here is that some of the Docker containers I run are Workers. They are little Node apps that connect to RabbitMQ, pull a job down, and do something with it.

When the brown stuff hits the twirly thing, they log out a bit of info to help me figure out what went wrong. Fairly standard stuff, I admit.

However, in this new setup, there was no limit to what was getting logged. I guess previously Rancher had enforced some max filesize limits or was helpfully rotating logs periodically.

In this case, the first port of call was to truncate a log. This might not actually be safe, but seeing as it’s my server and it’s not mission critical, I just truncated one of the huge logs:

/var/lib/docker/containers/6bfcad1f93a7fffa8f0e2b852a401199faf628f5ed7054ad01606f38c24fc568 # ls -la
total 294559628
drwx------ 4 root root 4096 May 9 10:26 .
drwx------ 36 root root 12288 May 9 16:50 ..
-rw-r----- 1 root root 301628608512 May 13 12:44 6bfcad1f93a7fffa8f0e2b852a401199faf628f5ed7054ad01606f38c24fc568-json.log
drwx------ 2 root root 4096 May 2 10:14 checkpoints
-rw------- 1 root root 4247 May 9 10:26 config.v2.json
-rw-r--r-- 1 root root 1586 May 9 10:26 hostconfig.json
-rw-r--r-- 1 root root 34 May 9 10:25 hostname
-rw-r--r-- 1 root root 197 May 9 10:25 hosts
drwx------ 3 root root 4096 May 2 10:14 mounts
-rw-r--r-- 1 root root 38 May 9 10:25 resolv.conf
-rw-r--r-- 1 root root 71 May 9 10:25 resolv.conf.hash

truncate --size 0 6bfcad1f93a7fffa8f0e2b852a401199faf628f5ed7054ad01606f38c24fc568-json.log

That freed up about 270gb. Top lols.

Anyway, I had four of these workers running, so that’s where all my disk space had gone.

Not Out Of The Woods Just Yet

There’s two further issues to address though at this point:

Firstly, I needed to update the Docker image to set the proper path to the RabbitMQ instance. This would stop the log file spam. Incidentally, within the space of truncating and then running a further ls -la, the log was already at 70mb. That’s some aggressive connecting.

This would have been nicer as an environment variable – you shouldn’t need to do a rebuild to fix a parameter. But that’s not really the point here. Please excuse my crappy setup.

Secondly, and more importantly, I needed a way to enforce Docker never to misbehave in this way again.

Fortunately, docker-compose has a solution to this problem.

Here’s a small sample from my revised config:

version: '3.7'

    max-size: '12m'
    max-file: '5'
  driver: json-file


        image: someimage:version
          BLAH: 'blah'
        logging: *default-logging

          - rabbitmq
        logging: *default-logging

OK, obviously a bit stripped down, but the gist of this is I borrow the config directly from the Docker Compose docs.

The one thing that I had to do was to put the x-logging declaration above the services declaration. Not sure why the order matters, but it didn’t seem to want to work until I made this change.

Once done, restarting all the Docker containers in this project (with the revised Docker image for the workers) not only resolved the log spam, but helpfully removed all the old containers – and associated huge log files – as part of the restart process.

Another fine disaster averted.