Support Value well known type

[codebien]

Context

From the community we got a report regarding the missing support for Value Protobuf type: https://community.grafana.com/t/k6-is-sending-empty-text-for-datetime-string/105656.

An edited version of our internal test for Any confirms the issue. Sharing the patch below.

grpc-value-type-test.txt

[olegbespalov]

@codebien we do support (well actually we do after #49 which means it's v0.47) this type, check this PR #56

I believe we're missing more examples (maybe here, but for sure in grafana/k6-docs#1378) of how to use these wrappers. It's not so transparent that in the case of the wrapper, there is no need to pack this into the structure, like:

let respString = client.invoke("grpc.wrappers.testing.Service/TestValue", "John")
if (respString.message !== "hey John") {
	throw new Error("expected to get 'hey John', but got a " + respString.message)
}

let respNumber = client.invoke("grpc.wrappers.testing.Service/TestValue", 12)
if (respNumber.message !== 42) {
	throw new Error("expected to get '42', but got a " + respNumber.message)
}

[codebien]

@olegbespalov I'm struggling to find some good references about it. Reading https://protobuf.dev/reference/protobuf/google.protobuf/#value I had the impression that what the user suggested is a correct form. Do you have other references with better documentation?

[olegbespalov]

@codebien, the link that you've suggested is the right one. But keep in mind that this is the definition of the specification of the protobuf language. It's lacking of language-specific.

For instance, there is no direct access to string_value. It's the responsibility of the serializer (in our case, it's https://pkg.go.dev/google.golang.org/protobuf/encoding/protojson) to put the correct value there, or at least it's what's happening for the most cases.