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I'm struggling with that one.

The goal is:

I plan to build a chrome extension, that would allow me to visualize an application's traces inside chrome://Tracing.

The extension should :

  1. receive a json file from some source
  2. open a new tab on url "chrome://tracing".
  3. load the json file in this tab

I fail to achieve the thirs step

The goal is not:

  • to capture trace from my extension. The extension is not what is generating traces. The traces were generated elsewhere, I'm just trying to visualize them
  • to capture traces from something else. The traces were generated in the past, and stored in a database. There's nothing left to plug on.

The question

Is there a way for a Chrome extension to ask or force a tab that loaded the url "chrome://tracing" to load a json file ?

What I tried

Inject javascript into the new tab

Obviously, my first attempt was to insert javascript into the new tab page. I managed to do it on any other page, using things like : 

chrome.tabs.onUpdated.addListener
document.createElement
appendChild

Like it is proposed here

I achieved to inject scripts on a tab with urml "https://google.com" for instance. But as soon as I target the url : "chrome://Tracing" injection fails with a cryptic error message in the devTool's console.

I eventually figured out, it's not possible to inject code into chrome extensions. Or maybe it is in a very hacky way if I trust this.

Send messages to the new tab

I hoped that some way, this feature was already planned inside chrome://tracing. So I red the javascript content of tracing.js, in order to find any message I could send to it to ask him to load my file.

But tracing.js is about 80k lines long (beautified), which means that if this message listener exists, I probably missed it.

Use url parameters

With the same amount of optimism, I tried to find any url parameter that would ask the new tab to load this file. But it already was looking like a desperate solution.

Extending DevTools

I assumed that maybe I had different permissions from a DevTools extension than from a regular extension. But the results were the very same. Either I failed to do it properly or my assumption was false.

Working around

Finally I show a message to user, with the path of the file and I ask him to manually click on the "load" button and choose his file.

This is not a good way to do.

What I didn't try

Making my own page that embed tracing.js

I just figure out, my approach may be wrong and I should try to make my own page, instead of trying to use chrome://Tracing.

A quick search show me that there is documentation on embedding catapult's trace-viewer, that I cannot post here due to my low reputation.

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mgueydan
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  • 1. Extensions can't run on chrome:// urls unless you enable a hidden flag. 2. DevTools is all-powerful because it has a back-end in the browser itself, the UI we see is only a front-end that queries the internals of the browser. – wOxxOm Feb 06 '17 at 20:32
  • Makyen link allowed my injection to work. Thanks. I wish I'd found this link before posting, but I was looking for "chrome://tracing" instead of "chrome://". – mgueydan Feb 07 '17 at 20:18
  • Thanks also to wOxxOm. I really wonder how my DevTools extensions fails, despite the fact DevTools is supposed to be Omnipotent. – mgueydan Feb 07 '17 at 20:21
  • Well, chromium developers decided to limit what the extensions can do. I guess "for security reasons" as usual. – wOxxOm Feb 07 '17 at 21:51

0 Answers0