Error: Cannot assign to read only property 'headers' of object '[object Request]'

[kkruk-sumo]

What version of OpenTelemetry are you using?

0.9.0

What version of Node are you using?

12.7.0

What did you do?

fetch(new Request('/api'))

What did you expect to see?

Fetch request to be sent and auto-instrumented by opentelemetry-plugin-fetch.

What did you see instead?

An error:

Error: Cannot assign to read only property 'headers' of object '[object Request]

Additional context

opentelemetry-plugn-fetch is trying to change the headers attribute on a given fetch constructor parameter (see

opentelemetry-js/packages/opentelemetry-plugin-fetch/src/fetch.ts

Line 112 in 0d939d2

options.headers = Object.assign({}, headers, options.headers || {});

).
It fails, because the fetch constructor accepts an object or an instance of Request and the headers of a Request has no setter.

[dyladan]

PTAL at #1274 as a fix