feat: Use REST

[schmidt-sebastian]

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Fixes #<issue_number_goes_here> 🦕

[bcoe]

@schmidt-sebastian this is cool, is your intention to default to gRPC, and document REST?

[schmidt-sebastian]

@bcoe I haven't decided yet. We need to fix one more issue with queries and then compare performance data to see what mode should be the default.

[alexander-fenster]

@MarkDuckworth It works now! When I throw new Error('...') in node_modules/@grpc/grpc-js/build/src/index.js and run npm run system-test:rest, only a handful of tests that actually require gRPC fail, most tests pass.

Note: I'm using the pre-released version of google-gax because of the bug. I will remove the package.json change when gax is released later today.

The main change is in the client factory here: https://github.com/googleapis/nodejs-firestore/pull/1698/files#diff-33330e7a0daf2387ffc6f936c4d6cb4dd23b4b404446a5e34d2cab779e47cb50R552

[MarkDuckworth]

Looks great! One minor suggestion but I don't feel very strongly about it.

[MarkDuckworth]

I'm wondering if instead of using this path to fallback, we can use a subpath export to the fallback? https://nodejs.org/api/packages.html#subpath-exports

Maybe it's already set up that way, I didn't look at gax source yet. But the path indicates maybe it is not.

[alexander-fenster]

That's a great idea (and "today I learned" as well).

We will be able to safely start using it when we drop Node 12 support. The documentation says subpath exports were added in v12.7.0 but we have "engines.node" set to ">=12" now, so we cannot possibly start using it without making a semver major. But for the next major I definitely want to do it. I filed googleapis/gax-nodejs#1337 so that we don't forget.

[hspak]

Hello! Sorry for reviving an old pull request, but was this data published anywhere?

We need to fix one more issue with queries and then compare performance data to see what mode should be the default.

[MarkDuckworth]

Performance data was not published. From what I have seen, internal tests and customer reports indicate a speedup when using preferRest in the cold start of functions. However, I cannot give specific numbers.

We did not change the default mode, which is still gRPC.