Request priority in HAR file for Chromium based browsers by ozcoder · Pull Request #164 · cloudflare/telescope

ozcoder · 2026-03-02T05:59:42Z

Adds _priority and _initialPriority to the HAR file when testing with a Chromium based browser.

Closes #16

Store the initial priority of each request. Store if the priority changes. Insert the initial priority value into the HAR file. Insert the final priority value into the HAR file.

Set types correctly on newPriorities and priorities. Check before using variables. Removed console debugging. Added fields to HarEntry.

sufian-cf · 2026-03-09T18:59:38Z

The change itself looks reasonable, but I'm not able to verify it locally. How can I run telescope so that there are _priority and _initialPriority fields produced within the har?

ozcoder · 2026-03-10T07:21:05Z

@sufian-cf if you run from the command line
npx . -u https://www.cloudflare.com/ -b chrome --timeout 60000 --debug
it will generate the files in a sub directory of the results directory.
Inside that is the pageload.har file which you can make pretty however you want (command or online) to make it easier to read. Eg. cat pageload.har | jq . > pageload.har.json
Edit that JSON file and search for a url entry that has Hero-globe as part of the filename. At the end of its entry it should have "_initialPriority": "Low" and the _priority value should be different, probably High since the browser would want to upgrade the priority of that image.
Other images would be upgraded too, but not all of them.

MildMax

verified working order of the initialPriority , priority, and resourceType in the chrome browser

sergeychernyshev

Looks like a good solution, we can make a couple improvements, see comments below.

Also, if you can make a fixture for testing the case with changing priority, it would be great. And maybe for testing duplicate requests.

sergeychernyshev · 2026-03-19T21:40:58Z

+      const fullURL = request.url + (request.urlFragment || '');
+      const resourceType = type || 'Other';
+
+      if (occasion.priorities[fullURL as keyof PriorityInfo]) {


Can we use requestId as a key instead of request URL?

Mapping by URL will break if there are multiple requests to the same URL.

I was using an array to get around that.
Now, using a slightly more complicated way, I can get the requestId from the CDP universe to the Playwright universe.

Create mapping of hash of url and starting time to requestId. Gather resourceType is a better place. Fixup types.

sufian-cf · 2026-04-16T13:42:33Z

+      const { requestId, response } = params;
+
+      if (response.timing) {
+        const hashString = crypto.createHash('sha256').update(response.url + response.timing.sendStart).digest('hex');


Here we hash response.url + response.timing.sendStart

But when we look the hash up (in src/testRunner.ts), we use request.url + request.timing.requestStart

Is this difference intentional?

They are the same value. It's because we are dealing with the CDP universe in one place and the Playwright universe in the other place. I had to find a stable attribute that was known to the request and the response and would be different when the same URL is requested more than once.

sufian-cf · 2026-04-16T13:50:21Z

    const client: CDPSession = await page.context().newCDPSession(page);
+    await client.send('Network.enable');
+
+    let occasion = this;


Nit: this closure isn't needed -- this will still be bound to the same object in the event handlers below, since they're arrow functions.

Ah, yes. Old habit.

sufian-cf · 2026-04-16T13:50:46Z

  async createPage(browser: BrowserContext): Promise<Page> {
    const page = browser.pages()[0];
    const client: CDPSession = await page.context().newCDPSession(page);
+    await client.send('Network.enable');


Is it possible Network.requestWillBeSent / other events below will fire before this client.send('Network.enable')?

Shouldn't happen since even preparePage hasn't been called until the end of this method.

sufian-cf · 2026-04-16T14:38:31Z

Hey @ozcoder, my apologies for the delay. I've taken a look at this approach and have manually verified that it sometimes works, but not for all requests. I've left a few comments, and overall am a bit concerned with the approach.

That being said, I think this has surfaced a real bug in our existing code. If the page load triggers multiple requests with the same URL, we're going to only be updating performance information on the first one, since we look up the corresponding entry via findIndex on just the URL.

I've just created #243 and will follow up with a fix that introduces a unique id per request we can use to match things.

sufian-cf · 2026-04-16T21:32:32Z

Ok, I have a PR for the fix in #243 which should give each request a unique identifier that can be used to cross-reference: #244

Once that mechanism is used, and there's some automated test coverage verifying the presence of the priority fields in the HAR, this PR should be good to get in

ozcoder added 6 commits December 6, 2025 17:30

Enable getting Network events from the Chrome Devtools Protocol Session.

8fca6f3

Store the initial priority of each request. Store if the priority changes. Insert the initial priority value into the HAR file. Insert the final priority value into the HAR file.

Merge branch 'main' into request_priority

a4b7834

Merge branch 'main' into request_priority

4635990

Tidyup

bbe0298

Merge branch 'main' into request_priority

ce9fb36

Renamed variables to be like other ones.

732b58a

Set types correctly on newPriorities and priorities. Check before using variables. Removed console debugging. Added fields to HarEntry.

ozcoder requested a review from a team March 2, 2026 05:59

sergeychernyshev added the ticket This label indicates that internal ticket was created to track it. label Mar 2, 2026

MildMax previously approved these changes Mar 16, 2026

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sergeychernyshev requested changes Mar 19, 2026

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ozcoder added 2 commits March 22, 2026 12:30

Merge branch 'main' into request_priority

10af114

Use requestId as key to priorities.

6577666

Create mapping of hash of url and starting time to requestId. Gather resourceType is a better place. Fixup types.

ozcoder dismissed MildMax’s stale review via 6577666 March 22, 2026 10:27

ozcoder requested a review from sergeychernyshev March 22, 2026 10:32

sufian-cf reviewed Apr 16, 2026

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ozcoder commented Mar 2, 2026

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sufian-cf commented Mar 9, 2026

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ozcoder commented Mar 10, 2026

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sufian-cf commented Apr 16, 2026

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sufian-cf commented Apr 16, 2026

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