Thanks for the explanation on the interaction between schema evolution and
copying structures, that makes sense.
It may not be a common requirement to want to copy over the entire request
structure, rather than just initialise a member from an existing reader.
For the moment, I only care about copying content from JSON, but
typelessRequests might be a nice approach for generally recording and
replaying RPC calls.
Thanks,
Vaci
On Friday, 4 June 2021 at 20:33:59 UTC+1 ken...@cloudflare.com wrote:
> I see. There isn't a great API for this right now. The problem is, once a
> struct Builder is already allocated, the struct can't be resized. But if
> you're trying to copy the content of another struct into it, it's possible
> that other struct was originally created with a newer version of the schema
> which had new fields defined, and so it is larger. If the data were copied
> from that larger struct into the smaller struct that has been allocated,
> the new fields would be silently dropped. I wanted to avoid that situation.
>
> One thing you could do is manually invoke
> Capability::Client::typelessReuqest(), manually passing the
> appropriate interface and method IDs. Then you get a request where the root
> type is AnyPointer, which you can set to an existing struct. This avoids
> the problem of dropping unknown fields, since the destination struct isn't
> allocated until the source is known, and it is then allocated with the same
> size as the source.
>
> Perhaps we should update the code generator to generate RPC client methods
> that can accept an existing struct Reader as input, to make this nicer.
>
> -Kenton
>
> On Thu, Jun 3, 2021 at 8:59 AM Vaci <va...@vaci.org> wrote:
>
>> Ah, I figured out that I can use the layered API to decode each item in
>> the list individually:
>>
>> Bar::Client cap;
>> kj::ArrayPtr<const char> text;
>> capnp::MallocMessageBuilder mb;
>> capnp::JsonCodec codec;
>> kj::ArrayBuilder<kj::Promise<void>> promises;
>>
>> auto value = mb.initRoot<capnp::JsonValue>();
>> codec.decodeRaw(text, value);
>>
>> for (auto&& entry: value.getArray()) {
>> auto request = cap.fooRequest();
>> codec.decode(entry, request);
>> promises.add(request.send().ignoreResult());
>> }
>>
>> However, I'd still be curious to know how to create a request from an
>> existing struct, if that's at all possible!
>>
>> Many thanks,
>> Vaci
>>
>> On Thursday, 3 June 2021 at 09:10:32 UTC+1 Vaci wrote:
>>
>>> That's not quite what I want to do. Given that a request is a struct
>>> type, I want to copy or assign an existing struct to the whole request.
>>>
>>> I can use the json decoder to write content into the request struct, but
>>> I don't see a way to do that when I'm holding an orphan pointer to a struct
>>> that is of the same type as the request.
>>>
>>> Vaci
>>>
>>> On Wednesday, 2 June 2021 at 15:36:55 UTC+1 ken...@cloudflare.com wrote:
>>>
>>>> Hi Vaci,
>>>>
>>>> An RPC request is always a struct type, not a list, so I assume what
>>>> you really mean here is that you want to use the list as a field of the
>>>> request? E.g. you have:
>>>>
>>>> struct Foo {}
>>>>
>>>> interface Bar {
>>>> foo @0 (foos :List(Foo));
>>>> }
>>>>
>>>>
>>>> Then you would do:
>>>>
>>>> auto req = bar.fooRequest();
>>>>
>>>> auto orphanage = capnp::Orphanage::getForMessageContaining(req);
>>>>
>>>> auto orphan = json.decode<capnp::List<Foo>>(txt, orphanage);
>>>>
>>>> req.adoptFoos(kj::mv(orphan));
>>>>
>>>>
>>>> -Kenton
>>>>
>>>> On Wed, Jun 2, 2021 at 6:29 AM Vaci <va...@vaci.org> wrote:
>>>>
>>>>> I may be missing something obvious, but is it possible to copy the
>>>>> content of a struct into the body of a request builder?
>>>>>
>>>>> I have an interface of the form:
>>>>>
>>>>> struct Foo {};
>>>>>
>>>>> interface Bar {
>>>>> foo @0 Foo;
>>>>> };
>>>>>
>>>>> I want to import a bunch of Foo structures using the json reader and
>>>>> use them to populate the requests. This works fine with a single item,
>>>>> because I can just decode directly into the request body:
>>>>>
>>>>> auto foo = bar.fooRequest();
>>>>> capnp::JsonCodec json;
>>>>> json.decode(txt, foo);
>>>>>
>>>>> ...but if my input is a list of items, the json decoder will return an
>>>>> (orphaned) list of Foo structures, and I can't see a way to use each item
>>>>> as request params.
>>>>>
>>>>> Vaci
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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