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 the same or slightly modified message using an outdated scheme and place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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