fix(node): Compression headers leak between requests

[timfish]

#5139 introduced a subtle bug where options.headers was modified which causes headers to leak between requests. This means requests after a compressed request will be incorrectly marked with content-encoding: gzip.

[lforst]

Nice thanks!

[timfish]

This took me so long to work out what was going on and I found it after telling Abhi the PR was good to go...

I'm trying to think how we can make bugs like this less likely. Making the options ReadOnly would have stopped this as options should be immutable?

[lforst]

Yup. Thought exactly the same thing. readonly would have caught this. I'll bounce this off the rest of the team and create an issue for it if we think it's a good idea.

[timfish]

At a minimum we could make the parameters in transports Readonly<T>.

export function makeNodeTransport(options: Readonly<NodeTransportOptions>): Transport {

We can't make transportOptions on the client options readonly because of this:

sentry-javascript/packages/node/src/client.ts

Lines 36 to 40 in 409f8fd

	// Until node supports global TextEncoder in all versions we support, we are forced to pass it from util
	options.transportOptions = {
	textEncoder: new TextEncoder(),
	...options.transportOptions,
	};

[lforst]

I think we could rewrite the constructor of the clients so that it passes a new options object to super instead of a modified one. But yeah bare minimum we could make the node transport options readonly. I believe it's generally good practice to make as much readonly as possible.