https://github.com/mitar/chromium-1415291

Reproduction for https://bugs.chromium.org/p/chromium/issues/detail?id=1415291
https://github.com/mitar/chromium-1415291

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Reproduction for https://bugs.chromium.org/p/chromium/issues/detail?id=1415291

• Host: GitHub
• URL: https://github.com/mitar/chromium-1415291
• Owner: mitar
• Created: 2023-07-20T08:48:18.000Z (about 1 year ago)
• Default Branch: main
• Last Pushed: 2023-07-20T08:48:28.000Z (about 1 year ago)
• Last Synced: 2024-04-15T02:51:10.092Z (6 months ago)
• Language: Go
• Size: 4.88 KB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
This repository is a reproduction for [Chromium issue 1415291](https://bugs.chromium.org/p/chromium/issues/detail?id=1415291).

The issue is that since Chromium disabled HTTP2 PUSH there is no way to preload content negotiated data (i.e., where data

depends on the `Accept` header) which is a problem when you have a server which serves both HTML and JSON at the same path

and you want to preload JSON when HTML is requested.

To run, you should use [Go](https://go.dev/):

```

go run main.go

```

And then open [http://localhost:8000/](http://localhost:8000/) in Chromium. Open network tab in DevTools.

## Expected

You should see three requests being made very soon after the other, one for `/` for `text/html`, another for

`/` for `application/json`, and another for `/data.json` for `application/json`. After 2 seconds that JSON data

should be shown in the page when JavaScript calls `fetch` and gets preloaded data without doing another

server equest.

## Actual

You see three requests, one for `/`, anther for `/` and the third for `/data.json`, but all of them

`text/html`. After 2 seconds no additional requests are made (good), but `fetch` gets HTML responses

which are invalid JSON so error is shown in the page by JavaScript (bad).

## Discussion

There are multiple issues here:

- Preload requests are made with `Accept` set to `*/*` so HTML responses are returned. Instead,

  `type="application/json"` from `Link` header should be respected to load JSON responses.

- When JavaScript calls `fetch` 2 seconds later, it is called with `Accept` header set to

  `application/json` but Chromium still returns preloaded HTML content instead of doing another

  request with `application/json`. So not just that performance is degraded (invalid and unnecessary

  preloading of HTML is done) but also correctness of execution of the page is impacted.

- No preloading happens if just `>; rel="preload"; as="fetch"; type="application/json"; crossorigin="anonymous"`

  `Link` header is issued by the server. If both `>; rel="preload"; as="fetch"; type="application/json"; crossorigin="anonymous"`

  and `; rel="preload"; as="fetch"; type="application/json"; crossorigin="anonymous"` headers are issued, then

  both of them are preloaded. (This is the reason why I included additional `/data.json` loading. Originally the plan was

  to have loading of HTML and JSON just from `/`.)

Tested on Chromium 114.0.5735.198.

Firefox 115.0.2 behaves the same but it does not require two `Link` headers to load from `/` and

it still has HTTP2 PUSH.