ActiveStorage unable to render attachment URLs across subdomains

[tylerbodway]

I am developing a mutli-subdomain application, and because of that I utilize lvh.me as my host to be able to navigate those subdomains locally.

As of 6fb3ac1 on the ActiveStorage Disk service, the host was defaulted to localhost:3000 which forces me to set the host: setting in my config/storage.yml

local:
  service: Disk
  root: <%= Rails.root.join("storage") %>
  host: http://lvh.me:5000

I would expect that attached images would be able to look at the current environment's server and build the url from there. I would expect that if I upload an image on admin.lvh.me:5000, it would be able to render on lvh.me:5000

Because I have to explicity set the host, the generated image urls are only available on the subdomain I specify in the config/storage.yml

With the configuration as seen above, when I am on the admin subdomain I receive this error when displaying an attached image

Without anyway to dynamically set that ActiveStorage url host, I'm not sure how to get around this issue.

Ruby: 2.4.2
Rails: 5.2.0.rc1

[42he]

This was introduced in the Commit

Provide a sensible default host 6fb3ac1

The problem is, with setting host to "localhost" you don't get relative URLs. But relative URLs for the Disk Storage Adapter are fine.

And there is a second BUG: When you set another host in the yml file, AS will ignore the setting. I'ts always "localhost".

[pixeltrix]

@42he when you say that AS ignores the setting, is that the generated url is using 'localhost' but ActiveStorage::Blob.service.host is configured correctly? Testing locally seems to configure the host correctly on the service.

[42he]

I have the mirror service:

local:
service: Disk
root: <%= Rails.root.join('storage') %>
host: https://example.com
amazon:
service: S3
(...)
mirror:
service: Mirror
primary: local
mirrors: [amazon]

irb(main):001:0> ActiveStorage::Blob.service.host
NoMethodError: undefined method `host' for #ActiveStorage::Service::MirrorService:0x007f861fe988e0
from (irb):1

The links all start with localhost:3000

I don't know if it setted the host correct before your commit, but with no host setting i got "relative" URLS witch worked perfekly fine.

[pixeltrix]

@42he what do you get if you do ActiveStorage::Blob.service.primary.host ?

I think what you may be seeing is the stable url in the view which then gets redirected to the service url by the ActiveStorage::BlobsController#show action.

[stevenharman]

The latest fix for this, ccac681, breaks any non-browser direct upload clients. e.g., an iOS or Android native client as the direct upload url is no longer a url, but a relative path. I mentioned this same case in #32139. But it was OK there because we could still set a host option to something like host: my-machine.local:5000 and things would work. (See: #32139 (comment)).

Is there a reason to not allow the host option? Is there something different that non-browser ActiveStorage clients should be doing?

/cc @georgeclaghorn @pixeltrix