1.5 - Implement lightwalletd gRPC functionality in Rust using JSONRPC interface for backwards compatibility.

[idky137]

Currently Zaino only has the subset of lightwallet gRPC services that Zingolib uses implemented. The full set of services should be implemented in Zaino-Fetch (backed by Zebra's JsonRPC Service) for backwards compatibility. The deprecated services can then use these implementations until they are fully removed.

Tasks

• Task 1: implement remaining lightwallet gRPC services (shown in Snapshot of unimplemented RPCs #40).

NOTE 1: Currently compact blocks are fetched as full blocks are parsed to compact blocks before being served to the client. This is inefficient and compact block should be served directly from disc / memory. This work will be completed in #55.

NOTE 2: Currently Lightwalletd does not return the correct error types from its gRPC services [https://github.com/zcash/lightwalletd/issues/497]. We will implement Zaino to use the correct tonic statuses [https://github.com/grpc/grpc/blob/master/doc/statuscodes.md#status-codes-and-their-use-in-grpc] rather than implement functionality as it is in Lightwalletd.

[idky137]

• Merging linked open PRs and completing Implement subtree roots RPCs #95, Implement Utxo RPCs #94 and Implement address balance RPCs #93 will complete this deliverable.