当我使用SimpleForwardingServerCallListener时，gRPC上下文返回null

Question

我想覆盖ServerInterceptor(使用Context(中的sendMessage、sendHeaders、onMessage、onHalfClose方法：

val context = Context.current().withValue(TestConstants.CONTEXT_KEY, "testValue1")
val delegatedCall = object : SimpleForwardingServerCall<ReqT, RespT>(call) {
override fun sendMessage(message: RespT) {
[e-mail](message)
super.sendMessage(message)
}
override fun sendHeaders(headers: Metadata) {
[e-mail](headers)
super.sendHeaders(headers)
}
override fun close(status: Status, trailers: Metadata) {
[e-mail](status, trailers)
super.close(status, trailers)
}
}
val delegatedListener: ServerCall.Listener<ReqT> =
if (context === null)
next.startCall(delegatedCall, headers)
else
Contexts.interceptCall(context, delegatedCall, headers, next)
return object : ForwardingServerCallListener.SimpleForwardingServerCallListener<ReqT>(delegatedListener) {
override fun onMessage(message: ReqT) {
[e-mail](message, headers)
super.onMessage(message)
}
override fun onHalfClose() {
[e-mail](headers)
super.onHalfClose()
}
override fun onCancel() {
[e-mail](headers)
super.onCancel()
}
override fun onComplete() {
[e-mail](headers)
super.onComplete()
}
override fun onReady() {
[e-mail](headers)
super.onReady()
}
}

这是输出：

>>>>intercept1
>>>>intercept2: testValue1
>>>>onReady1: null
>>>>onMessage1: null
>>>>onHalfClose1: null
HelloService3.hello: testValue1
>>>>sendHeaders2: testValue1
>>>>sendHeaders1: testValue1
>>>>sendMessage2: testValue1
>>>>sendMessage1: testValue1

您可以看到Context对delegatedCall(sendMessage、sendHeaders(有效，但对delegatedListener(onMessage、onHalfClose(无效。

为什么以及如何解决这个问题？

Answer 1

我认为问题是特定SimpleForwardingServerCallListener的没有看到更改，因为它是在Contexts.interceptCall()中的侦听器之前执行的。侦听器用于回调，因此它们由gRPC调用。gRPC将调用返回的侦听器，该侦听器最终将调用delegatedListener，而delegatedListener是执行上下文调整的侦听器。Contexts.interceptCall()根本不会更改call，因此调用看到上下文的事实意味着Listener必须正常工作。

我建议制作一个ServerCallHandler来完成对SimpleServerInterceptor的所有调用，并将该处理程序传递给Contexts.interceptCall()。

(只是一个草图，因为我不熟悉Kotlin(

val context = Context.current().withValue(TestConstants.CONTEXT_KEY, "testValue1")
if (context === null) // Unclear how this will be null
return next.startCall(delegatedCall, headers)
else
return Contexts.interceptCall(context, delegatedCall, headers, new SimpleServerInterceptorHandler(next))
...
// Within SimpleServerInterceptorHandler
val delegatedCall = object : SimpleForwardingServerCall<ReqT, RespT>(call) {
...
}
val delegatedListener: ServerCall.Listener<ReqT> =
next.startCall(delegatedCall, headers)
return object : ForwardingServerCallListener.SimpleForwardingServerCallListener<ReqT>(delegatedListener) {
...
}