Never mind that, I figured out what I was doing wrong. One little tiny
character was missing:
[](kj::Maybe<Callable::Server> perhaps) {
... should have been ...
[](kj::Maybe<Callable::Server&> perhaps) {
On Wednesday, February 22, 2017 at 4:00:48 PM UTC+1, Johannes Zeppenfeld
wrote:
>
> I've tried pursuing the CapabilityServerSet option, and have run into a
> bit of a snag. Using the schema posted in the original post, here is the
> current implementation of the server's Bootstrap class:
>
> class BootstrapImpl : public Bootstrap::Server {
> private:
> kj::Promise<void> getCallable(GetCallableContext context) override {
> // Create a callable to return to the client, storing it in the
> // server capability set of callables.
> Callable::Client callable =
> _callables.add(kj::heap<CallableImpl>());
> context.getResults().setCallable(callable);
>
> // Test if the callable can be retrieved.
> // Normally I'd just return kj::READY_NOW here.
> return _callables.getLocalServer(callable).then(
> [](kj::Maybe<Callable::Server> perhaps) {
> KJ_IF_MAYBE(callable, perhaps) {
> std::cout << "Callable lookup: " << callable <<
> std::endl;
> } else {
> std::cout << "Callable lookup failed." << std::endl;
> }
> }
> );
> }
>
> private:
> capnp::CapabilityServerSet<Callable> _callables;
> };
>
> Unfortunately, the pointer returned by the getLocalServer lookup has
> nothing to do with the actual address of the instantiate CallableImpl...
>
> CallableImpl():0x8249b0
> Callable lookup: 0x7fffc33b44a8
> ~CallableImpl():0x8249b0
>
> Am I doing something wrong? Is this a bug in Cap'n Proto? Any suggestions
> for getting this to work?
>
> A full client and server code example is attached.
>
> Thanks!
> Johannes
>
>
>
> On Wednesday, February 22, 2017 at 9:22:47 AM UTC+1, Johannes Zeppenfeld
> wrote:
>>
>> Thanks for the tip! I knew I couldn't have been the first person to need
>> something like this, and installing from git is fine.
>>
>> However... getLocalServer returns a promise, which again makes it
>> impossible to call the Callable functions from within the process method.
>> Is there a way to get the server object directly? I don't see any way for
>> the Client object to be a promise at this point...
>>
>> Otherwise I suppose I'd have to split the process method into two parts,
>> first starting retrieval of all of the local server objects, joining the
>> returned promises and then processing them in a second step. This becomes
>> difficult when dealing with heterogeneous server object types though, e.g.
>> if there are Actions for Callable and another type, e.g., Executable. Is
>> there something similar to joinPromises that works with heterogeneous types?
>>
>> Thanks!
>> Johannes
>>
>> On Tuesday, February 21, 2017 at 7:21:43 PM UTC+1, David Renshaw wrote:
>>>
>>> You can accomplish that with CapabilityServerSet, which was added in
>>> this commit:
>>> https://github.com/sandstorm-io/capnproto/commit/8b8f8a2fc25d69c8a43ee0ac987521c2c4d5108c
>>>
>>> .
>>>
>>> Unfortunately, there has not yet been a release that includes
>>> CapabilityServerSet, so you would need to install Cap'n Proto from git to
>>> make use of it.
>>>
>>> On Tue, Feb 21, 2017 at 1:06 PM, Johannes Zeppenfeld <[email protected]>
>>> wrote:
>>>
>>>> Knowing that the answer to the question in the subject is probably
>>>> "don't do that", I'm looking for a way to support database-like
>>>> transactions (i.e., event-loop atomic operations) spanning multiple server
>>>> objects.
>>>>
>>>> Here's a simplified schema to help explain the problem:
>>>>
>>>> # A transaction holds a list of actions that should be processed in a
>>>> single
>>>> # event-loop atomic operation.
>>>> struct Transaction {
>>>> actions @0 :List(Action);
>>>>
>>>> struct Action {
>>>> union {
>>>> nop @0 :Void;
>>>> execute @1 :Callable;
>>>> #doSomething @2 :AnotherType;
>>>> #etc...
>>>> }
>>>> }
>>>> }
>>>>
>>>> # A callable is a server-side object conveying the capability of calling
>>>> # some server function as part of a transaction.
>>>> interface Callable { }
>>>>
>>>> # Some other interface that serves callables (simplified example) and
>>>> # processes transactions.
>>>> interface Bootstrap {
>>>> getCallable @0 (name :Text) -> (callable :Callable);
>>>>
>>>> process @1 (transaction :Transaction);
>>>> }
>>>>
>>>> A client can obtain Callables from the server through e.g. the
>>>> Bootstrap interface, and should then be able to pass that Callable as part
>>>> of a Transaction back to the server. The Callable::Server implementation
>>>> contains a std::function that should be called for any Callable that is
>>>> executed as part of a transaction.
>>>>
>>>> Unfortunately (although it totally makes sense), the Transaction Reader
>>>> available in the Bootstrap implementation's process method only provides a
>>>> Callable::Client, without a possibility (as far as I can tell) of
>>>> retrieving the associated Callable::Server object. Thus it is not possible
>>>> to retrieve nor call the std::function object associated with the Callable.
>>>>
>>>> Adding a call method to the Callable interface would allow it to be
>>>> called by the process method or directly by the client, but not (again as
>>>> far as I can tell) in an event-loop atomic manner as part of a transaction.
>>>>
>>>> I hope that the scenario above is understandable. If not I'd be more
>>>> than happy to elaborate on points that are not clear.
>>>>
>>>> Am I overlooking something that would allow somehow calling the
>>>> std::function of a Callable implementation from within the process method?
>>>> Does anyone have a different suggestion for achieving something like this?
>>>>
>>>> I would like to avoid implementing a custom capability system that
>>>> replaces Callable with a struct containing an id. But perhaps it is the
>>>> only way?
>>>>
>>>> Thanks!
>>>> Johannes
>>>>
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>>>>
>>>
>>>
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