It works ! Thank you for the expanded explanation, it helped a lot. I
initially though there would be a "prettier" out-of-the-box solution, but as
long as it works...
While I have you, I have a more general question. Is it common case to
distribute Cap'n'Proto genererated headers as part of a library, or
everything must stay private ?
Let's say I have defined some enum in the .capnp and I want the users of my
library to use them.
For the moment I have a duplicated the definition of this enum in a public
header, and I do static casts before serialization.
Le lundi 26 avril 2021 à 17:40:59 UTC+2, ken...@cloudflare.com a écrit :
> You need your `SubscriberImpl` to hold a regular C++ pointer back to the
> `MediaLibraryImpl` that created it, so that you can access its
> `publishers_` set through that pointer. You can pass the pointer to
> `SubscriberImpl`'s constructor.
>
> You'll also want to make sure the pointer doesn't become a dangling
> pointer, so `SubscriberImpl` should also hold a `MediaLibrary::Client`
> which points to the same `MediaLibraryImpl` -- holding this counts as a
> strong reference so Cap'n Proto won't destroy the `MediaLibraryImpl`.
> Inside `addSubscriber()` you can use `thisCap()` to get a
> `MediaLibrary::Client` pointing to `this`, then you'd pass that to
> `SubscriberImpl`'s constructor, along with the plain C++ pointer to `this`.
>
> -Kenton
>
> On Mon, Apr 26, 2021 at 10:25 AM Théophile B. <theophi...@gmail.com>
> wrote:
>
>> Thank you for your quick answer!
>>
>> The `Server` to `Client` "conversion" is done via the bootstrap
>> capability, but I need the underlying `Server` back when calling
>> capabilities returned by the bootstrap capability.
>> Here is a simplified example where I (tried) to implement your advice:
>>
>> interface MediaLibrary {
>> addPublisher @0 (name :Text) -> (pub :Publisher);
>> addSubscriber @1 (name :Text) -> (sub :Subscriber);
>>
>> interface Publisher {}
>>
>> interface Subscriber {
>> listenTo @0 (publisher :Publisher);
>> }
>> }
>>
>> class MediaLibraryImpl final : public MediaLibrary::Server {
>> public:
>> kj::Promise<void> addPublisher(AddPublisherContext context) override {
>> my_underlying_library::Publisher* output = ...; // call the
>> underlying lib
>> MediaLibrary::Publisher::Client pub = publishers_.add(kj::heap<
>> PublisherImpl>(output));
>> context.getResults().setPub(pub);
>> return kj::READY_NOW;
>> }
>>
>> kj::Promise<void> addSubscriber(AddSubscriberContext context) override {
>> my_underlying_library::Subscriber* output = ...; // call the
>> underlying lib
>> MediaLibrary::Subscriber::Client sub = subscribers_.add(kj::heap<
>> SubscriberImpl>(output));
>> context.getResults().setSub(sub);
>> return kj::READY_NOW;
>> }
>>
>> private:
>> capnp::CapabilityServerSet<MediaLibrary::Subscriber> subscribers_;
>> capnp::CapabilityServerSet<MediaLibrary::Publisher> publishers_;
>> };
>>
>> class PublisherImpl : public virtual GstDaemon::Publisher::Server {
>> protected:
>> PublisherImpl(my_underlying_library::Publisher* pub) : pub_(pub) {}
>>
>> private:
>> my_underlying_library::Publisher* pub_;
>> }
>>
>> class SubscriberImpl : public virtual GstDaemon::Subscriber::Server {
>> protected:
>> SubscriberImpl(my_underlying_library::Subscriber* sub) : sub_(sub) {}
>>
>> kj::Promise<void> listenTo(ListenToContext context) override {
>> auto pub = context.getParams().getPublisher(); // GstDaemon::Publisher
>> ::Client
>> // No access to CapabilityServerSet !
>> // We we would like to do: sub_->listenTo("pub_")
>> }
>>
>> private:
>> my_underlying_library::Subscriber* sub_;
>> }
>>
>> If I understand well, I can now do subscribers_.getLocalServer("
>> GstDaemon::Publisher::Client") from `MediaLibraryImpl`.
>> Bu what about SubscriberImpl, where the `listenTo` needs `PublisherImpl`
>> ?
>> Is it possible to have access to `MediaLibraryImpl` from `SubscriberImpl`
>> ?
>> Instead, should I pass references to the `CapabilityServerSet` to `
>> PublisherImpl` and `SubscriberImpl` ?
>>
>> Le lundi 26 avril 2021 à 16:30:55 UTC+2, ken...@cloudflare.com a écrit :
>>
>>> Hi Théophile,
>>>
>>> Take a look at CapabilityServerSet:
>>>
>>>
>>> https://github.com/capnproto/capnproto/blob/6b5bcc2c6e954bc6e167ac581eb628e5a462a469/c++/src/capnp/capability.h#L607-L633
>>>
>>> When you convert your `Server` object to a `Client`, you need to do it
>>> using a CapabilityServerSet. Later, you can use the same set to unwrap the
>>> `Client` and get the underlying `Server` back -- even if the client has
>>> been passed over the network and back in the meantime.
>>>
>>> -Kenton
>>>
>>> On Mon, Apr 26, 2021 at 9:25 AM Théophile B. <theophi...@gmail.com>
>>> wrote:
>>>
>>>> I'm not sure I'm usign the right terminology in my question, but I hope
>>>> you will understand my problem with the following example.
>>>>
>>>> I'm developing a media library where the user can play/pause/stop
>>>> different kinds of "pipelines" (source ~ camera, filter ~ processing, sink
>>>> ~ display). Depending on their type, these pipeline can listen to each
>>>> other, or not (e.g: a source pipeline cannot listen). I'm now working on a
>>>> "capnp wrapper" of the library, so that it can be controlled via RPC.
>>>>
>>>> I have replicated the class inheritance with success:
>>>>
>>>> interface Publisher {}
>>>>
>>>> interface Subscriber {
>>>> listenTo @0 (publisher :Publisher);
>>>> }
>>>>
>>>> interface Pipeline {
>>>> play @0 ();
>>>> pause @1 ();
>>>> stop @2 ();
>>>> }
>>>>
>>>> interface SourcePipeline extends(Pipeline, Publisher) {}
>>>>
>>>> interface FilterPipeline extends(Pipeline, Publisher, Subscriber) {}
>>>>
>>>> interface SinkPipeline extends(Pipeline, Subscriber) {}
>>>>
>>>> Server-side I have those impl classes, which holds the references to
>>>> the underlying objects of the media library (pub_ & sub_).
>>>>
>>>> class PublisherImpl : public virtual GstDaemon::Publisher::Server {
>>>> protected:
>>>> PublisherImpl(my_underlying_library::Publisher* pub) : pub_(pub) {}
>>>> private:
>>>> my_underlying_library::Publisher* pub_;
>>>> };
>>>>
>>>> class SubscriberImpl : public virtual GstDaemon::Subscriber::Server {
>>>> protected:
>>>> SubscriberImpl(my_underlying_library::Subscriber* sub) : sub_(sub) {}
>>>>
>>>> kj::Promise<void> listenTo(ListenToContext context) override {
>>>> auto pub = context.getParams().getPublisher(); // GstDaemon::Publisher
>>>> ::Client
>>>> // ??? = PublisherImpl::pub_
>>>> sub_->listenTo(???)
>>>> }
>>>>
>>>> private:
>>>> my_underlying_library::Subscriber* sub_;
>>>> };
>>>>
>>>> Now, from the client, I wanted to do something like this:
>>>> //GstDaemon::Subscriber::Client subscriber; // already returned by the
>>>> server
>>>> //GstDaemon::Publisher::Client publisher; // already returned by the
>>>> server
>>>> auto request = subscriber.listenToRequest();
>>>> request.setPublisher(publisher);
>>>> auto promise = request.send();
>>>>
>>>> However, as you can see, on the server it's not possible to get the pub_
>>>> pointer when the listenTo method is called. Is there any way I can get
>>>> a reference to the PublisherImpl here ?
>>>>
>>>> --
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>>>>
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>>>> .
>>>>
>>> --
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>>
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>>
>
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