The ability to send arbitrarily large data with a query has emerged from multiple use cases. To fullfill this need, Zenoh provides a way to optionally attach a Value (Encoding and Payload) to sent queries.
The Query message has a flag B that indicates the presence or absence of a QueryBody.
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
|K|B|T| QUERY |
+-+-+-+---------+
~ KeyExpr ~ if K==1 then key_expr has suffix
+---------------+
~selector_params~
+---------------+
~ qid ~
+---------------+
~ target ~ if T==1
+---------------+
~ consolidation ~
+---------------+
~ QueryBody ~ if B==1
+---------------+
The QueryBody contains a DataInfo and a Payload:
7 6 5 4 3 2 1 0
+---------------+
~ DataInfo ~
+---------------+
~ Payload ~
+---------------+
The DataInfo optionally contains more fields than the needed Encoding in this context. This allows the API to be enriched with no protocol change in the future.
The GetBuilder has 2 functions that allow to attach a Value to the query:
pub fn with_value<IntoValue>(mut self, value: IntoValue) -> Self
where IntoValue: Into<Value>;The Query struct (received by Queryables) has a function to access the optionally attached Value:
pub fn value(&self) -> Option<&Value>;