Make extension background non-persistent

[bershanskiy]

Describe the bug
Background page should not be persistent.

To Reproduce
Steps to reproduce the behavior:

1. Install extension in Chrome and close all dev tools, including Svelte.
2. Open Chrome Task manager (click Shift+ESC).
3. See "Extension: Svelte Devtools" in the process list, even though extension is not in use.

Expected behavior
When extension is not in use, it should not consume computer resources (RAM).

Environment

• Browser: Any (Chrome 91)
• Devtools version: Any (built from master)
• Svelte version: Any (3.38.2)

Additional context
If you are interested, I can file a PR to fix this. Right now, only Chrome supports non-persistent pages, but Firefox plans to add support soon^TM.

Plan
I will break up this into a few PRs. Here is a tentative plan (no particular order):

WIP (all these are blocked on already opened PRs):

1. (TODO) Store and retreive Background context variables from chrome.storage.local when needed
2. (TODO) Optimization: let background open and close persistent ports with DevTools only when needed
3. (TODO) Declare background non-persistent in manifest.json and test it!

Review:

1. Avoid excessive chrome.tabs.onUpdated invocations #62
   Optimization: avoid chrome.tabs.onUpdated because it is triggered for every single other tab.
   Frequent callback runs restore background into active state unnecessarily.
2. Send messages from DevTools to BG via one-time messages #60

Done:

1. Avoid persistent ports in content scripts #54 Removes pagePorts in src/background.js
2. Store profiler enabled/disabled state in inspected window's sessionStorage #53 Fix: background has two handlers for 'startProfiler' (one is dead) and no handler for 'stopProfiler'
3. Store profiler enabled/disabled state in inspected window's sessionStorage #53 Get rid of gloal profilerEnabledList in src/background.js
   Value of this variable is set in DevTools tab and is used in content script. It makes sense to store it in either one, but not in background.

Edit: add plan!

[RedHatter]

I spent some time attempting to move to a non-persistent background script today but was unable to get it working.

If I'm understanding correctly in order to use a non-persistent background script correctly I would need to move the toolsPorts and pagePorts maps into chrome.storage.local but, unfortunately, these maps store message passing ports which are not serializable.

You are welcome to take a crack at it if you wish but I do not believe it will work with the current architecture.

[bershanskiy]

If I'm understanding correctly in order to use a non-persistent background script correctly I would need to move the toolsPorts and pagePorts maps into chrome.storage.local but, unfortunately, these maps store message passing ports which are not serializable.

Not exactly. Chrome persists the background context for as long as it has at least one open port, so you don't need to serialize ports. This persistence is both a blessing (ease of development) and a curse (efficiency loss), so I personally prefer avoiding ports and using messages.

I spent some time attempting to move to a non-persistent background script today but was unable to get it working.

What problem are you facing?

You are welcome to take a crack at it if you wish but I do not believe it will work with the current architecture.

I'd actually prefer just using regular message passing, if that's OK with you. I have a working local repo which works for me, can file a PR if you are interested.

[RedHatter]

If you have something working by all means create a pull request and I'll look at it.

[bershanskiy]

I didn't document my changes very well by making small commits, so the diffs are rateher long and not all changes are relevant. I'll split changes out in logical chuncks for simpler review and file incremental PRs. I'll make sure to reference this bug to help keep track.

[RedHatter]

Take your time. I appreciate the help.

[bershanskiy]

@RedHatter I have updated the top comment with a tentative plan. Feedback is welcome.

Edit: typo

[bershanskiy]

Technically, it would be fine to declare background non-persistent already (because background would be kept alive all the time when at least one Svelte DevTool tab is open), but I'd like to get #53 merged and do task 5 before that.

[bershanskiy]

@RedHatter I filed all the PRs which I could without depending on already existing PR. I still expect some PRs to have merge conflict which I can resolve after the first PR is merged. What do you think of what is already there?

[bershanskiy]

Closing as obsolete.