Device dehydration not working

[chagai95]

I search for a ticket for this issue but could not find any, I'm not sure if this is a synapse issue or an Element issue, but I'm betting on Element, also I don't have access to the synapse logs, so I am putting this here with the Element logs. If there is another issue already/the issue is synapse, then I'm sorry just ignore this issue.

Steps to reproduce

1. Activate the device dehydration feature.
2. log out of all sessions.
3. send a message from another account.
4. login and enter passphrase.

Outcome

What did you expect?

The message should be visible

What happened instead?

The message was not decrypted:

{
  "type": "[m.room](http://m.room/).message",
  "content": {
    "msgtype": "m.bad.encrypted",
    "body": "** Unable to decrypt: DecryptionError: This message was sent before this device logged in. Key backup is working, but we still do not (yet) have the key. **"
  }
}

More info

Here is a video showing us trying:
https://fair.tube/w/2t6GdDmrcfLLYHHc52zbY8

Unfortunately we refreshed once in the middle so that might affect the logs, we can reproduce this if it's still relevant, I'm wondering if this has anything to do with Firefox on Ubuntu? Do you need the versions of that? How can we check the logs/db to see if the dehydrated device was actually registered? We would love to help debugging this.

I'm wondering also if this is related to Device dehydration v2 there is a mention there of v1 being tricky to implement, is that because you have had experience with this being buggy? We are wondering if turning the feature on and off might be a bit unstable, which is something we did. Also we tried seeing something in the network tab, we didn't see any request going out, which seemed weird. Also, every new login it was turned off, I guess that's just how it works but it was a bit confusing, we were just not sure if it actually registered a device on the server.

Operating system

Ubuntu

Browser information

Firefox

URL for webapp

app.element.io

Application version

Element version: 1.11.69 Crypto version: Rust SDK 0.7.0 (068a0af), Vodozemac 0.6.0

Homeserver

matrix.org

Will you send logs?

Yes

[t3chguy]

Your steps are the problem. When you log out you deactivate the dehydration labs flag, so you'd need to use an instance which has it enabled in the config otherwise dehydration will not be used at login to bootstrap your new session. app.element.io does not have such labs config.

[chagai95]

Thx, that's very useful information, we actually tried this with an element web instance that does have labs activated by default, do you mean we need to also have device dehydration enabled in the config? Or just the labs?

[t3chguy]

do you mean we need to also have device dehydration enabled in the config?

Yes

[chagai95]

do you mean the labs feature "feature_dehydration"? Thx so much!

[t3chguy]

This isn't a support forum, I suggest asking in the support room where you'd get an answer from someone who knows more about dehydration.