Deep linking to the Perfetto UI

This document describes how to open traces hosted on external servers with the Perfetto UI. This can help integrating the Perfetto UI with custom dashboards and implement 'Open with Perfetto UI'-like features.

Using window.open and postMessage

The supported way of doing this is to inject the trace as an ArrayBuffer via window.open('https://ui.perfetto.dev') and postMessage(). In order to do this you need some minimal JavaScript code running on some hosting infrastructure you control which can access the trace file. In most cases this is some dashboard which you want to deep-link to the Perfetto UI.

Open ui.perfetto.dev via window.open

The source dashboard, the one that knows how to locate a trace and deal with ACL checking / oauth authentication and the like, creates a new tab by doing

var handle = window.open('https://ui.perfetto.dev');

The window handle allows bidirectional communication using postMessage() between the source dashboard and the Perfetto UI.

Wait for the UI to be ready via PING/PONG

Wait for the UI to be ready. The window.open() message channel is not buffered. If you send a message before the opened page has registered an onmessage listener the messagge will be dropped on the floor. In order to avoid this race, you can use a very basic PING/PONG protocol: keep sending a 'PING' message until the opened window replies with a 'PONG'. When this happens, that is the signal that the Perfetto UI is ready to open traces.

Post the trace data

Once the PING/PONG handshake is complete, you can post a message to the Perfetto UI window. The message should be a JavaScript object with a single perfetto key.

  {
    'perfetto': {
      buffer: ArrayBuffer;
      title: string;
      fileName?: string;    // Optional
      url?: string;         // Optional
      appStateHash?: string // Optional
    }
  }

The properties of the perfetto object are:

buffer: An ArrayBuffer containing the raw trace data. You would typically get this by fetching a trace file from your backend.
title: A human-readable string that will be displayed as the title of the trace in the UI. This helps users to distinguish between different traces if they have multiple tabs open.
fileName (optional): The suggested file name if a user decides to download the trace from the Perfetto UI. If omitted, a generic name will be used.
url (optional): A URL for sharing the trace. See the "Sharing" section below.
appStateHash (optional): A hash for restoring the UI state when sharing. See the "Sharing" section below.

Sharing Traces and UI State

When traces are opened via postMessage, Perfetto avoids storing the trace as doing so may violate the retention policy of the original trace source. That is to say the trace is not uploaded anywhere. Thus, you must provide a URL that provides a direct link to the same trace via your infrastructure, which should automatically re-open Perfetto perfetto and use postmessage to supply the same trace.

The url and appStateHash properties work together to allow users to share a link to a trace that, when opened, restores the trace and the UI to the same state (e.g. zoom level, selected event).

When a user clicks the "Share" button in the Perfetto UI, Perfetto looks at the url you provided when opening the trace. If this url contains the special placeholder perfettoStateHashPlaceholder, Perfetto will:

Save the current UI state and generate a unique hash for it.
Replace perfettoStateHashPlaceholder in your url with this new hash.
Present this final URL to the user for sharing.

For example, if you provided this url: 'https://my-dashboard.com/trace?id=1234&state=perfettoStateHashPlaceholder'

Perfetto might generate a shareable URL like this: 'https://my-dashboard.com/trace?id=1234&state=a1b2c3d4'

When another user opens this shared URL, your application should:

Extract the state hash (a1b2c3d4 in this example) from the URL.
postMessage the trace buffer as usual, but this time also include the appStateHash property with the extracted hash.

Perfetto will then load the trace and automatically restore the UI state associated with that hash.

If the url property is omitted, the share functionality will be disabled. If the perfettoStateHashPlaceholder is omitted from the url, the trace can be shared but the UI state will not be saved.

Code samples

See this example caller, for which the code is in this GitHub gist.

Googlers: take a look at the existing examples in the internal codesearch

Common pitfalls

Many browsers sometimes block window.open() requests prompting the user to allow popups for the site. This usually happens if:

The window.open() is NOT initiated by a user gesture.
Too much time is passed from the user gesture to the window.open()

If the trace file is big enough, the fetch() might take long time and pass the user gesture threshold. This can be detected by observing that the window.open() returned null. When this happens the best option is to show another clickable element and bind the fetched trace ArrayBuffer to the new onclick handler, like the code in the example above does.

Some browser can have a variable time threshold for the user gesture timeout which depends on the website engagement score (how much the user has visited the page that does the window.open() before). It's quite common when testing this code to see a popup blocker the first time the new feature is used and then not see it again.

This scheme will not work from a file:// based URL. This is due to browser security context for file:// URLs.

The source website must not be served with the Cross-Origin-Opener-Policy: same-origin header. For example see this issue.

Where does the posted trace go?

The Perfetto UI is client-only and doesn't require any server-side interaction. Traces pushed via postMessage() are kept only in the browser memory/cache and are not sent to any server.

Why can't I just pass a URL?

"Why you don't let me just pass a URL to the Perfetto UI (e.g. ui.perfetto.dev?url=...) and you deal with all this?"

The answer to this is manifold and boils down to security.

Cross origin requests blocking

If ui.perfetto.dev had to do a fetch('https://yourwebsite.com/trace') that would be a cross-origin request. Browsers disallow by default cross-origin fetch requests. In order for this to work, the web server that hosts yourwebsite.com would have to expose a custom HTTP response header (Access-Control-Allow-Origin: https://ui.perfetto.dev) to allow the fetch. In most cases customizing the HTTP response headers is outside of dashboard's owners control.

You can learn more about CORS at https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

Content Security Policy

Perfetto UI uses a strict Content Security Policy which disallows foreign fetches and subresources, as a security mitigation about common attacks. Even assuming that CORS headers are properly set and your trace files are publicly accessible, fetching the trace from the Perfetto UI would require allow-listing your origin in our CSP policy. This is not scalable.

You can learn more about CSP at https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP

Dealing with OAuth2 or other authentication mechanisms

Even ignoring CORS, the Perfetto UI would have to deal with OAuth2 or other authentication mechanisms to fetch the trace file. Even if all the dashboards out there used OAuth2, that would still mean that Perfetto UI would have to know about all the possible OAuth2 scopes, one for each dashboard. This is not scalable.

Opening the trace at a specific event or time

Using the fragment query string allows for more control over the UI after the trace opens. For example this URL:

https://ui.perfetto.dev/#!/?visStart=261191575272856&visEnd=261191675272856

Will open the pushed trace at 261191575272856ns (~261192s) and the viewing window will be 261191675272856ns -261191575272856ns = 100ms wide.

Selecting a slice on load:

You can pass the following parameters: ts, dur, pid, tid. The UI will query the slice table and find a slice that matches the parameters passed. If a slice is found it's highlighted. You don't have to provide all the parameters. Usually ts and dur suffice to uniquely identifying a slice.

We deliberately do NOT support linking by slice id. This is because slice IDs are not stable across perfetto versions. Instead you can link a slice by passing the exact start and duration (ts and dur), as you see them by issuing a query SELECT ts, dur FROM slices WHERE id=....

Zooming into a region of the trace on load:

Pass visStart, visEnd. These values are the raw values in ns as seen in the sql tables.

Issuing a query on load:

Pass the query in the query parameter.

Try the following examples:

You must take care to correctly escape strings where needed.

Source links

The source code that deals with the postMessage() in the Perfetto UI is post_message_handler.ts.