Thanks for getting back to me.
I'm currently doing:
@Override
public <ReqT, RespT> Listener<ReqT> interceptCall(ServerCall<ReqT, RespT
> call,
Metadata headers, ServerCallHandler<ReqT, RespT> next) {
if (!cacheableMethods.contains(call.getMethodDescriptor())) {
return next.startCall(call, headers);
}
ServerCall.Listener<ReqT> no_op = new ServerCall.Listener<ReqT>() {
};
return new ForwardingServerCallListener<ReqT>() {
ServerCall.Listener<ReqT> delegate = no_op;
@Override
protected ServerCall.Listener<ReqT> delegate() {
return delegate;
}
@Override
public void onMessage(ReqT message) {
if (delegate == no_op) {
Message request = (Message) message;
Message resp = cache.getIfPresent(request);
if (resp != null) {
call.sendHeaders(headers);
call.sendMessage((RespT) resp);
call.close(Status.OK, new Metadata());
return;
}
delegate = next.startCall(call, headers);
}
onMessage(message);
}
};
}
and running a unit test using the InProcessServerBuilder. The test times
out, and when I step through with a debugger it doesn't look like onMessage is
ever called. If the above offers no clues, I can spend some time setting up
a minimal example project I can share.
On Friday, 18 June 2021 at 03:38:22 UTC+2 [email protected] wrote:
> The idea in
> https://github.com/grpc/grpc-java/issues/5414#issuecomment-468754271
> should work for your use case and the code should be almost same as that.
> Can you post a snippet for your code so that we can see what went wrong?
> The idea is to have your ServerInterceptor produce a ServerCall.Listener
> that delays calling into the real ServerCall.Listener (or more precisely,
> avoid calling into the real ServerCall.Listener if the cache-lookup
> ServerCall.Listener can end the call early with cached data).
>
> On Thursday, May 27, 2021 at 8:25:37 AM UTC-7 Alexander Chiu wrote:
>
>> Hi
>>
>> I'm trying to build a caching ServerInterceptor which will be the first
>> in a chain of interceptors. I managed to get the basic functionality
>> working by returning a SimpleForwardingServerCallListener which checks a
>> cache in the onMessage method, and manually sending the headers and
>> response and closing the call in case of a cache hit, otherwise delegating
>> to next.startCall(...). However, it seems like next.startCall(...) causes
>> the call to cascade to the subsequent interceptors, and onMessage on the
>> listener is only called after that.
>>
>> My searches have come across:
>>
>> - https://gitter.im/grpc/grpc?at=5b59f01bbd17b9615905d7b5
>> -
>>
>> https://stackoverflow.com/questions/39389771/validate-request-using-grpc-server-interceptor
>>
>> and a few others where it seems like it possible to delay
>> next.startCall(...) until after the first message is received. I tried
>> to do something akin to
>> https://github.com/grpc/grpc-java/issues/5414#issuecomment-468754271 using
>> a noop listener, but then the onMessage on the listener never seems to
>> be called at all.
>>
>> Am I missing something obvious?
>>
>> PS. A big thank you to all the maintainers
>>
>
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