Crate zcash_client_backend 

A crate for implementing Zcash light clients.

zcash_client_backend contains Rust structs and traits for creating shielded Zcash light clients.

Design

Wallet sync

The APIs in the data_api::chain module can be used to implement the following synchronization flow:

                         ┌─────────────┐  ┌─────────────┐
                         │Get required │  │   Update    │
                         │subtree root │─▶│subtree roots│
                         │    range    │  └─────────────┘
                         └─────────────┘         │
                                                 ▼
                                            ┌─────────┐
                                            │ Update  │
          ┌────────────────────────────────▶│chain tip│◀──────┐
          │                                 └─────────┘       │
          │                                      │            │
          │                                      ▼            │
   ┌─────────────┐        ┌────────────┐  ┌─────────────┐     │
   │  Truncate   │        │Split range │  │Get suggested│     │
   │  wallet to  │        │into batches│◀─│ scan ranges │     │
   │rewind height│        └────────────┘  └─────────────┘     │
   └─────────────┘               │                            │
          ▲                     ╱│╲                           │
          │      ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─              │
     ┌────────┐         ┌───────────────┐       │             │
     │ Choose │  │      │Download blocks│                     │
     │ rewind │         │   to cache    │       │             │
     │ height │  │      └───────────────┘           .───────────────────.
     └────────┘                 │               │  ( Scan ranges updated )
          ▲      │              ▼                   `───────────────────'
          │               ┌───────────┐         │             ▲
 .───────────────┴─.      │Scan cached│    .─────────.        │
( Continuity error  )◀────│  blocks   │──▶(  Success  )───────┤
 `───────────────┬─'      └───────────┘    `─────────'        │
                                │               │             │
                 │       ┌──────┴───────┐                     │
                         ▼              ▼       │             ▼
                 │┌─────────────┐┌─────────────┐  ┌──────────────────────┐
                  │Delete blocks││   Enhance   ││ │Update wallet balance │
                 ││ from cache  ││transactions │  │  and sync progress   │
                  └─────────────┘└─────────────┘│ └──────────────────────┘
                 └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─

Feature flags

• lightwalletd-tonic — Enables the tonic gRPC client bindings for connecting to a lightwalletd server.

• lightwalletd-tonic-tls-webpki-roots — Enables the tls-webpki-roots feature of tonic.

• lightwalletd-tonic-transport — Enables the transport feature of tonic producing a fully-featured client and server implementation

• transparent-inputs — Enables receiving transparent funds and shielding them.

• spend-index — Enables per-outpoint transparent spend queries, for consumers that have access to a spent-outpoint index (e.g. a full node’s spend index). Adds the TransactionDataRequest::GetSpendingTx request variant and the WalletWrite::notify_output_verified_unspent method, and is what a wallet targeting such a data source enables instead of relying on address-based TransactionsInvolvingAddress requests for transparent spend detection.

• orchard (enabled by default) — Enables receiving and spending Orchard funds.

  The orchard crate itself is an unconditional dependency (via zcash_primitives, which always requires it because every v5+ transaction carries an Orchard bundle type); this feature gates the wallet’s Orchard note-handling code, not the crate linkage.

• zcashd-compat — Enables compatibility with legacy zcashd wallet data

• pczt — Enables creating partially-constructed transactions for use in hardware wallet and multisig scenarios.

• sync — Exposes a wallet synchronization function that implements the necessary state machine.

• sync-decryptor — Exposes a batch decryption engine for use within syncing.

  This feature flag will eventually be removed when the sync::run function behind the sync feature flag is replaced with a sync engine that makes use of the batch decryption engine.

• tor — Exposes a Tor client for hiding a wallet’s IP address while performing certain wallet operations.

• test-dependencies — Exposes APIs that are useful for testing, such as proptest strategies.

  NOTE: Semver-breaking changes to the APIs exposed by this feature may be present in any release version, including patch releases.

• non-standard-fees — Exposes APIs that allow calculation of non-standard fees.

Experimental features

• unstable — Exposes unstable APIs. Their behaviour may change at any time.
• unstable-serialization — Exposes APIs for unstable serialization formats. These may change at any time.
• unstable-spanning-tree — Exposes the data_api::scanning::spanning_tree module.

Modules

addressDeprecated

data_api

Utilities for Zcash wallet construction

encodingDeprecated

fees

keysDeprecated

proposal

Types related to the construction and evaluation of transaction proposals.

proto

This module contains generated code for handling light client protobuf structs.

scan

scanning

Tools for scanning a compact representation of the Zcash block chain.

serializationunstable-serialization

syncsync-decryptor or sync

Implementation of the synchronization flow described in the crate root.

tortor

Tor support for Zcash wallets.

wallet

Structs representing transaction data scanned from the block chain by a wallet or light client.

zip321Deprecated

Structs

DecryptedOutput

A decrypted shielded output.

Enums

TransferType

An enumeration of the possible relationships a TXO can have to the wallet.

Functions

decrypt_transaction

Scans a Transaction for any information that can be decrypted by the set of UnifiedFullViewingKeys.

Type Aliases

PoolTypeDeprecated

ShieldedPoolDeprecated