Thanks!
Previously i tried to reinterpret messages knowing a generic scheme, can i
somehow iterate over additional lists that aren't in my generic scheme?
For example i have a message with a few consecutive Lists of any structs,
let's say 3 of them and in an incoming message there are 2 more lists of
any structs, 5 total:
can i iterate over them and then later pack them in the same manner back?
How it can be done?
On Monday, July 29, 2019 at 10:18:57 PM UTC+3, Kenton Varda wrote:
>
> You can get the offset and size of a field via the schema API. Check out
> schema.h and schema.capnp.
>
> auto fieldDef = KJ_ASSERT_NONNULL(
>
> capnp::Schema::from<MyStruct>().findFieldByName("myField")).getProto().getSlot();
> auto offset = fieldDef.getOffset(); // multiply by field size to get
> byte offset
> switch (fieldDef.getType()) { ... }
>
> -Kenton
>
> On Mon, Jul 29, 2019 at 5:26 AM Dmitry Shmorgun <[email protected]
> <javascript:>> wrote:
>
>> I tried it, so any message can be reinterpret by a proper generic message
>> that has AnyPointer fields in a scheme. Where AnyPointer can be any
>> construction like List<List<AnyStruct>> for example, so i can serialize,
>> store, manipulate, serialize back any message only knowing a generic
>> structure. It works well.
>> I saw an example of a list truncation:
>> auto orphan = myStruct.disownMyList();
>> orphan.truncate(size);
>> myStruct.adoptMyList(kj::mv(orphan));
>>
>> though i haven't found how to do so for AnyList<AnyStruct> structure, so
>> it was necessary to calculate m_filledEntries before the creation of the
>> list:
>>
>> auto entriesBuilder =
>> AnyPointer::Builder(r1.getEntries()).initAsListOfAnyStruct(m_entrySize,
>> m_filledEntries, m_filledEntries);
>>
>> for (size_t i = 0, j = 0; i < m_entries.size(); ++i) {
>> if (!m_entries[i].isBlank) {
>> auto dataSection = entriesBuilder[j++].getDataSection();
>> std::copy(m_entries[i].buff.begin(),
>> m_entries[i].buff.begin() + m_entrySize, dataSection.begin());
>> }
>> }
>>
>> Now i'm trying to tell a server that uses generic messages that in a
>> struct of a received message there is a key on the byte offset X with the
>> size N. The server reads a special message that convey this information. So
>> the server can keep a data snapshot in a hash key-value storage and
>> manipulate entries by the the byte-key. The problem is how to find the
>> offset and size of the specific key field to encode in the message with
>> settings. It seems all these things are deeply hidden.
>> Any ideas maybe?
>>
>> Thanks for your help.
>>
>>
>> On Thursday, July 25, 2019 at 6:25:49 PM UTC+3, Dmitry Shmorgun wrote:
>>>
>>> Hi!
>>>
>>> According to
>>> https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html there
>>> is a way to extract new unknown fields from a message and then construct
>>> the same or slightly modified message using an outdated scheme and place
>>> these fields back.
>>> But how actually this can be done? I don't find any example.
>>> I assume there should be something else than dynamic scheme loading.
>>> Can I go further and just reinterpret a message type A as an message
>>> containing a header and a one struct that can be specified as a generic
>>> message B, modify and pack back as A? So in this way, I can even not know
>>> the scheme of A at all.
>>>
>>> Many thanks
>>>
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