xds: override bootstrap for xds server

[YifeiZhuang]

#7819

[ejona86]

"#7819" should be part of the commit message.

[ejona86]

Remove extra line

[ejona86]

XdsClientPoolFactory is not public, and we don't want it to be public. We just want the bootstrap. And we should probably put "for test" or the like in the name.

[ejona86]

This PR seems to do essentially nothing. What method is the user intended to call?

[YifeiZhuang]

This PR seems to do essentially nothing. What method is the user intended to call?

I was thinking they can override bootstrap for their server:
XdsServerBuilder.forPort().xdsClientPoolFactoryForTest(null, bootstrapOverride).build()

[ejona86]

But they can't call xdsClientPoolFactoryForTest; it is package-private.

We don't want XdsClientPoolFactory part of the public API. We need a new method. Also, a name like "xdsClientPoolFactory" is very poor for the user; we should choose a name that has more meaning to the user.

[YifeiZhuang]

But they can't call xdsClientPoolFactoryForTest; it is package-private.

We don't want XdsClientPoolFactory part of the public API. We need a new method. Also, a name like "xdsClientPoolFactory" is very poor for the user; we should choose a name that has more meaning to the user.

Yea, because bootstrap is directly related to xdsClientPoolFactory so i put them together, the main reason I had one method is to prevent the situation overrideBootstrap() called first and then xdsClientPoolFactory() would erase the first call, e.g.

XdsServerBuilder xdsClientPoolFactory(XdsClientPoolFactory xdsClientPoolFactory) {
this.xdsClientPoolFactory = xdsClientPoolFactory;
}

public XdsServerBuilder overrideBootstrapForTest(Map<?,?> rawMap ) {
this.xdsClientPoolFactory.setBootstrapOverride(rawMap);
}

but yea they usually can not call xdsClientPoolFactory because it is package private. Our own tests will have the issue at least. We can sure do some trick to always save the bootstrap, but i don't think that is a clean solution.

[ejona86]

This is mutating a singleton.

[YifeiZhuang]

why we can't?

[ejona86]

That means it would change channels and other servers. We went through this before on client-side. https://github.com/grpc/grpc-java/pull/8358/files/8f38f34705f34db27e9103928dc27dd856dc467e#r684332029