Minimal Repro of BatchHTTPClient not functioning correctly

Datadog RUM attaches headers to outgoing fetch and XHR requests to be able to link together traces. When using Apollo's HTTPLink, this functions correctly, but it doesn't with BatchHTTPLink.

This was previously reported as an issue and fixed for HTTPLink in PR #8603 but the same fix needs to be applied to BatchHTTPLink.

Repo Setup

# Assuming you have nvm installed, if not skip this step or install the latest node version
nvm install 
corepack enable
yarn install
yarn start

Repro

Error Case

• Open localhost:9000 in a browser
• open the network tab
• You should see a request to http://localhost:9000/graphql
• Examine the request headers for the request and see that there are no x-datadog- headers attached.

Working Case

• Change the client passed to the ApolloProvider in app/Component.js to use unbatchedClient
• Refresh the browser
• Examine the request headers again for the /graphql request
• There are now several x-datadog- headers attached to the request

Workaround Hack

By passing in a custom function for fetch which forces the fetch to be reevaluated, we can get around the issues with BatchHTTPClient.

• Change the client passed to the ApolloProvider in app/Component.js to use batchedClientWithHack
• Refresh the browser
• Examine the request headers again for the /graphql request
• There are now several x-datadog- headers attached to the request