[otlp-exporter] web exporters should set User-Agent header upon requests.

[llc1123]

        Error: Uncaught AssertionError: 'Refused to set unsafe header "User-Agent"' === 'Request Timeout' (webpack-internal:///../../../node_modules/assert/assert.js:199)

Originally posted by @JamieDanielson in #3790 (comment)

The current test based on headless Chrome will return above error due to Chrome's limitation.

Setting the user-agent header in Chrome browser by Headers object or using fetch() will have no effect but won't throw any error.
Using XMLHttpRequest.setRequestHeader() will throw the above error.

As other browsers (tested on latest Firefox and Safari) work as expected, I suggest we use a try...catch block and ignore the output and complete the implementation as per specification.

Another thing is that the current implementation uses sendBeacon if available and if no custom header being set. As the user-agent header should be present as per spec. We should remove the use of sendBeacon.

We can also rely solely on fetch and drop XMLHttpRequest. Users should use a polyfill for fetch if they want to support legacy browsers.

Related: #3790 #3806 #3291

[llc1123]

Also, if the user-agent header is not allowed to be overwritten by the user (which I believe the spec says so), we can implement this in the base packages instead of in separate exporter packages (simply apply user-agent after applying the configured headers). We can also warn the user if they attempt to set user-agent by config.

[llc1123]

We can also rely solely on fetch and drop XMLHttpRequest. Users should use a polyfill for fetch if they want to support legacy browsers.

I found some usages of modern javascript features (such as Object.entries()) in the sendWithXhr function. Is there a guideline of browser compatibility or I suggest we just use fetch instead.

[llc1123]

I've finished the user-agent part in #3811. Should I replace sendWithXhr with fetch?

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This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[dyladan]

not stale

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[github-actions]

This issue was closed because it has been stale for 14 days with no activity.