Using ExtEditorR with Flatpak

[tyalie]

I've got a (probably) working config of ExtEditorR while having Thunderbird be sandboxed in a flatpak. This trick is to allow Thunderbird to call external application using the flatpak commands and giving it permission to read the files in ~/.mozilla/native-messaging-hosts.

So first I've created a wrapper script around the ExtEditorR native daemon, which looks like this (filename external-editor-revived.sh)

#!/bin/bash
flatpak-spawn --host ./external-editor-revived "$@"

The native messaging host ofc needs to be in the same folder. I've then modified the external_editor_revived.json by appending .sh to the path field. i.e.

{
  "name": "external_editor_revived",
  "path": "/home/USER/.mozilla/native-messaging-hosts/external-editor-revived.sh",
  ...
}

The last step to remain is allowing the thunderbird application to access the folders and be able to call external applications. One can fix this using the following

# allow thunderbird to access the native-messaging-hosts folder
flatpak override --filesystem=~/.mozilla/native-messaging-hosts:ro org.mozilla.Thunderbird
# allow thunderbird to talk to flatpak for i.e. executing `flatpak-spawn`
flatpak override --talk-name=org.freedesktop.Flatpak org.mozilla.Thunderbird

Warning
This circumvents the Thunderbird sandbox provided by Flatpak quite significantly. Setting the talk-name property basically allows Thunderbird to access your whole system. So don't do this, if you want your Thunderbird to be isolated away.

[tyalie]

Just as a note. Often times I've hit upon some unexpected wall and didn't knew how to debug it. I've been able to get the stdout by the external-editor-revived dumped into a file for debugging by using this line in the above mentioned .sh:

flatpak-spawn --host ./external-editor-revived "$@" 2>&1 | tee /tmp/exteditorr.log

As Flatpak /tmp folders are their own tmpfs, you cannot find this log in the system /tmp. You can find it in /run/user/USERID/.flatpak/org.mozilla.Thunderbird/tmp/exteditorr.log instead