This needs #6632 to be merged first

Friendly ping

Another ping: this is just the custom_metadata interop test for PHP now

LGTM

test this please

re-based and PHP tests passed

Let's un-blacklist the custom_metadata interop test for PHP, otherwise this change is pointless.

https://github.com/grpc/grpc/blob/master/tools/run_tests/run_interop_tests.py#L255

@murgatroid99 Please review this again, thanks!

So I end up implementing all of custom_metadata, status_code_and_message, unimplemented_method interop tests so that I can remove the _SKIP_ADVANCED blacklist.

Two things:

1. Since PHP is still on proto2, I need to copy over some missing fields for messages.proto.
2. For the unimplemented_method interop test, I cheated a little bit - if the method is truly undefined even in the proto, the method won't be in the generated stub, and if I try to call that, PHP will throw a Fatal Error. So I make an unimplemented method in the proto so that I can call it, which correspond to an unimplemented method on the server, and I get the desired response code.

The existing test.proto file already has an UnimplementedService definition. You should copy that to your proto file instead of making a different one.

@murgatroid99 Thanks for the pointer. Fixed by copying and using UnimplementedService.

LGTM