This PR is the first step in getting a groth16 proving system fully
integrated with the rest of zebra. This PR implements the initial async
API, but none of the actual batching logic necessary for our eventual
verifier design.
Once the batch verification API from bellman has been implemented we
will need to swap out the "Batch" type defined in this crate with the
new `batch::Verifier` defined in bellman.
This change is mostly mechanical, with the exception of the changes to the
`tower-batch` middleware. This middleware was adapted from `tower::buffer`,
and the `tower::buffer` code was changed to implement its own bounded queue,
because Tokio 0.3 removed the `mpsc::Sender::poll_send` method. See
ddc64e8d4d
for more context on the Tower changes. To match Tower as closely as possible
in order to be able to upstream `tower-batch`, those changes are copied from
`tower::Buffer` to `tower-batch`.
This addresses at least three pain points:
- we were affected by bugs that were already fixed in git, but not in
the released crate;
- we can use service combinators to transform requests and responses;
- we can use the hedge middleware.
The version in git is still marked as 0.3.1 but these changes will be
part of tower 0.4: https://github.com/tower-rs/tower/issues/431
Jane Lusby
teor
Deirdre Connolly
Henry de Valence