Vijay, thanks, yes very helpful.
On the streaming side - I'm not familiar with the intricacies of how the
streaming works. After your suggestion, I found the RouteGuide example
and was looking through it to try to understand exactly how the streaming
works. The example declares the ListFeatures rpc method as a streaming
method as follows:
rpc ListFeatures(Rectangle) returns (stream Feature) {}
However looking at the client C++ code, it looks almost like a synchronous
API that returns the current list of features at the time of the call
(albeit returned in streaming form). In my case, I would like to have a
dedicated thread waiting for updates from the server (I'm essentially
monitoring a page of data for updates). I'm not sure this is possible
without repeatedly polling which would be different to streaming. I'm new
to the grpc streaming so I am probably incorrect.
John
void ListFeatures() {
routeguide::Rectangle rect;
Feature feature;
ClientContext context;
rect.mutable_lo()->set_latitude(400000000);
rect.mutable_lo()->set_longitude(-750000000);
rect.mutable_hi()->set_latitude(420000000);
rect.mutable_hi()->set_longitude(-730000000);
std::cout << "Looking for features between 40, -75 and 42, -73"
<< std::endl;
std::unique_ptr<ClientReader<Feature> > reader(
stub_->ListFeatures(&context, rect));
while (reader->Read(&feature)) {
std::cout << "Found feature called "
<< feature.name() << " at "
<< feature.location().latitude()/kCoordFactor_ << ", "
<< feature.location().longitude()/kCoordFactor_ << std::endl;
}
Status status = reader->Finish();
if (status.ok()) {
std::cout << "ListFeatures rpc succeeded." << std::endl;
} else {
std::cout << "ListFeatures rpc failed." << std::endl;
}
}
On Tuesday, June 6, 2017 at 2:21:52 PM UTC-4, Vijay Pai wrote:
>
> You're on the right track with regard to the first question. A unary RPC
> has to have a response, but the response can be empty (which you can check
> with the appropriate has_ methods) or you can do a oneof. An alternative is
> to use a server-side streaming return value which allows 0 or more
> responses
>
> rpc GetPage(PageRequest) returns (stream PageResponse)
>
> And that ties in to the 2nd question re Push - that's exactly what
> streaming is for. You can send your updates back as subsequent responses on
> the return stream. Hope that helps!
> @vjpai
>
> On Tue, Jun 6, 2017 at 10:48 AM John Coffey <[email protected]
> <javascript:>> wrote:
>
>> I am creating an RPC service and I want to know how I would declare an
>> RPC method that returns (in my case) an optional response. The way the rpc
>> is defined below means that it always returns a PageResponse. I suppose I
>> could check to see if the page_title in the response has not been set but I
>> am sure that there is a more elegant solution to this (probably a
>> combination of 'empty' and 'oneof'?
>>
>> Also in a somewhat related question, Is it possible to change the rpc to
>> support some sort of push data? I have a cache managed by a GWService and
>> I would like the grpc client to act like a listener for updates to this
>> cache - other than polling for changes, I am not sure how I would do this.
>> Is that what streaming is for?
>>
>> Thanks in advance
>>
>> John
>>
>> //! Request a page object from the cache
>> message PageRequest {
>> string page_title = 1;
>> }
>>
>> //! cache page wrapper
>> message PageResponse {
>> // embed the page title in case we decide to stream
>> // many of these back to back using the streaming API
>> string page_title = 1;
>> Page page_data = 2;
>> }
>>
>>
>> //! Gateway Service.
>> service GWService {
>>
>> . . .
>>
>>
>> // request a specific
>> rpc GetPage(PageRequest) returns (PageResponse) {}
>> }
>>
>>
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