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Integration between the Zebra and the zcash_client_backend memory wallet interface

Introduction

This document outlines a potential design for integrating Zebra with the zcash_client_backend.

The outlined design is subject to further refinement and iteration, as it represents uncharted territory with room for modifications or complete reconsideration based on input from involved design and development teams.

This design is not a plan to develop a wallet in Zebra but a possible path to follow to integrate zcash_client_backend memory wallet code with Zebra opening the possibility to develop external clients. These abstract external client might be a wallet but it is outside of the scope to plan that work here.

Motivation

As the transition away from zcashd draws near, zebrad emerges as the natural successor. However, external client functionality, specifically the librustzcash library with the zcash_client_backend, must persist.

With the development of the scanning capabilities in Zebra (learn more), new opportunities for having external client support within Zebra arise. To optimize resource utilization, integrating these components rather than building something entirely new is preferred. This specification leverages components from both sides to create a bridge between them.

Design diagram

At the core of the system lies the zcash_client_backend, hosting the memory wallet code. The memory wallet has services for reading, writing data, and creating a new memory wallet database.

On the Zebra side, a feature will enable external client functionality when the node gets started. If the feature is enabled, external-client component will be imported which exposes various RPC methods, including z_getnewaccount, which invokes the create_account in the zcash_client_backend crate.

The external-client also do the scanning, this was originally the zebra-scan crate of Zebra where it's name was changed to external-client and additional functionality (RPC interface, etc) is added.

An additional RPC method z_getbalanceforaccount was added to the spec for more clarity.

%%{init: {"flowchart": {"htmlLabels": false}} }%%
flowchart TD
    subgraph librustzcash [zcash_client_backend side]
        zcash_client_backend{{zcash_client_backend}} --> |Host the memory wallet code|memory_wallet[Memory Wallet]
        memory_wallet ----> |Available services|read[(Read Service)]
        memory_wallet ----> |Available services|write[(Write Service)]
        memory_wallet --> |Available services|read[(Read Service)]
        memory_wallet --> |Create a new memory wallet database|new
        write --> |Service call|create_account_zcash_client_backend[create_account]
        write ----> |Service call|put_blocks
        read --> |Service call|get_wallet_summary
    end
    subgraph zebra [Zebra side]
        zebrad{{zebrad}} --> |Blocks permanent storage database|blocks_database[Blocks Database]
        zebrad{{zebrad}} --> |Last 100 blocks|non_finalized_blocks[Non-Finalized Blocks]
        blocks_database <-->|RocksDB access| external-client{{external-client}}
        non_finalized_blocks <-->|Some sort of pipe or rpc| external-client{{external-client}}
    end
    subgraph external [external-client side]
        external-client -->|Start scan task| scan_task[Scan Task]
        external-client --> |RPC methods|rpc-methods[RPC Interface]
        rpc-methods --> |Method|z_getbalanceforaccount
        rpc-methods --> |Method|z_getnewaccount
        z_getbalanceforaccount --> |Call the memory wallet method|get_wallet_summary
        z_getnewaccount --> |Call the memory wallet method|create_account_zcash_client_backend

        external-client -->|Services available| Services
        Services --> |Service call|Register[(Register Service)]
        Services --> |Service call|Create[(Create Service)]
        z_getnewaccount --> Create
        Create --> |Internally|Register
        scan_task -.-> |Send scanned blocks if any|insert_blocks
        insert_blocks --> |Call the memory wallet method|put_blocks
        scan_task --> |Initializes an empty memory wallet|init_mem_wallet
        scan_task --> |Start scanning for a new key|start-scanning
        init_mem_wallet --> |Create a new memory wallet database|new
        Register --> |Register service start scanning for key|start-scanning[Start scanning]
    end
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Specification

This specification simulates the integration of a memory wallet with Zebra, facilitating communication among various components, including the memory wallet, Zebra, and the zcash_client_backend crate.

The simulation starts with a call to the z_getnewaccount method from the main process. Subsequent processes handle service requests, interact with the zcash_client_backend crate, and manage scan tasks as required.

Client Integration Specification