Update API for refreshing currency exchange rates.

CHANGELOG.md

@@ -5,10 +5,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 # Unreleased
+
 ## Added
-- `Synchronizer.getExchangeRateUSD() -> NSDecimalNumber`, which fetches the latest USD/ZEC
-  exchange rate. Prices are queried over Tor (to hide the wallet's IP address) on Binance,
-  Coinbase, and Gemini.
+- `Synchronizer.exchangeRateUSDStream: AnyPublisher<FiatCurrencyResult?, Never>`,
+  which returns the currently-cached USD/ZEC exchange rate, or `nil` if it has not yet been
+  fetched.
+- `Synchronizer.refreshExchangeRateUSD()`, which refreshes the rate returned by
+  `Synchronizer.exchangeRateUSDStream`. Prices are queried over Tor (to hide the wallet's
+  IP address).
 
 # 2.1.12 - 2024-07-04
 

Example/ZcashLightClientSample/ZcashLightClientSample/Get Balance/GetBalanceViewController.swift

@@ -8,25 +8,49 @@
 
 import UIKit
 import ZcashLightClientKit
+import Combine
 
 class GetBalanceViewController: UIViewController {
     @IBOutlet weak var balance: UILabel!
     @IBOutlet weak var verified: UILabel!
 
+    var cancellable: AnyCancellable?
+
+    var accountBalance: AccountBalance?
+    var rate: FiatCurrencyResult?
+
     override func viewDidLoad() {
         super.viewDidLoad()
         let synchronizer = AppDelegate.shared.sharedSynchronizer
         self.title = "Account 0 Balance"
 
-        Task { @MainActor in
-            let balance = try? await synchronizer.getAccountBalance()
-            let balanceText = (balance?.saplingBalance.total().formattedString) ?? "0.0"
-            let verifiedText = (balance?.saplingBalance.spendableValue.formattedString) ?? "0.0"
-            let usdZecRate = try await synchronizer.getExchangeRateUSD()
-            let usdBalance = (balance?.saplingBalance.total().decimalValue ?? 0).multiplying(by: usdZecRate)
-            let usdVerified = (balance?.saplingBalance.spendableValue.decimalValue ?? 0).multiplying(by: usdZecRate)
-            self.balance.text = "\(balanceText) ZEC\n\(usdBalance) USD\n\n(\(usdZecRate) USD/ZEC)"
-            self.verified.text = "\(verifiedText) ZEC\n\(usdVerified) USD"
+        Task { @MainActor [weak self] in
+            self?.accountBalance = try? await synchronizer.getAccountBalance()
+            self?.updateLabels()
+        }
+
+        cancellable = synchronizer.exchangeRateUSDStream.sink { [weak self] result in
+            self?.rate = result
+            self?.updateLabels()
+        }
+
+        synchronizer.refreshExchangeRateUSD()
+    }
+
+    func updateLabels() {
+        DispatchQueue.main.async { [weak self] in
+            let balanceText = (self?.accountBalance?.saplingBalance.total().formattedString) ?? "0.0"
+            let verifiedText = (self?.accountBalance?.saplingBalance.spendableValue.formattedString) ?? "0.0"
+
+            if let usdZecRate = self?.rate {
+                let usdBalance = (self?.accountBalance?.saplingBalance.total().decimalValue ?? 0).multiplying(by: usdZecRate.rate)
+                let usdVerified = (self?.accountBalance?.saplingBalance.spendableValue.decimalValue ?? 0).multiplying(by: usdZecRate.rate)
+                self?.balance.text = "\(balanceText) ZEC\n\(usdBalance) USD\n\n(\(usdZecRate.rate) USD/ZEC)"
+                self?.verified.text = "\(verifiedText) ZEC\n\(usdVerified) USD"
+            } else {
+                self?.balance.text = "\(balanceText) ZEC"
+                self?.verified.text = "\(verifiedText) ZEC"
+            }
         }
     }
 }

Sources/ZcashLightClientKit/ClosureSynchronizer.swift

@@ -129,8 +129,7 @@ public protocol ClosureSynchronizer {
 
     func getAccountBalance(accountIndex: Int, completion: @escaping (Result<AccountBalance?, Error>) -> Void)
 
-    /// Fetches the latest ZEC-USD exchange rate.
-    func getExchangeRateUSD(completion: @escaping (Result<NSDecimalNumber, Error>) -> Void)
+    func refreshExchangeRateUSD()
 
     /*
      It can be missleading that these two methods are returning Publisher even this protocol is closure based. Reason is that Synchronizer doesn't

Sources/ZcashLightClientKit/CombineSynchronizer.swift

@@ -129,10 +129,7 @@ public protocol CombineSynchronizer {
 
     func refreshUTXOs(address: TransparentAddress, from height: BlockHeight) -> SinglePublisher<RefreshedUTXOs, Error>
 
-    func getAccountBalance(accountIndex: Int) -> SinglePublisher<AccountBalance?, Error>
-
-    /// Fetches the latest ZEC-USD exchange rate.
-    func getExchangeRateUSD() -> SinglePublisher<NSDecimalNumber, Error>
+    func refreshExchangeRateUSD()
 
     func rewind(_ policy: RewindPolicy) -> CompletablePublisher<Error>
     func wipe() -> CompletablePublisher<Error>

Sources/ZcashLightClientKit/Model/FiatCurrencyResult.swift

@@ -0,0 +1,13 @@
+//
+//  FiatCurrencyResult.swift
+//
+//
+//  Created by Lukáš Korba on 31.07.2024.
+//
+
+import Foundation
+
+public struct FiatCurrencyResult: Equatable {
+    public let rate: NSDecimalNumber
+    public let date: Date
+}

Sources/ZcashLightClientKit/Synchronizer.swift

@@ -101,6 +101,9 @@ public protocol Synchronizer: AnyObject {
     /// This stream is backed by `PassthroughSubject`. Check `SynchronizerEvent` to see which events may be emitted.
     var eventStream: AnyPublisher<SynchronizerEvent, Never> { get }
 
+    /// This stream emits the latest known USD/ZEC exchange rate, paired with the time it was queried. See `FiatCurrencyResult`.
+    var exchangeRateUSDStream: AnyPublisher<FiatCurrencyResult?, Never> { get }
+
     /// Initialize the wallet. The ZIP-32 seed bytes can optionally be passed to perform
     /// database migrations. most of the times the seed won't be needed. If they do and are
     /// not provided this will fail with `InitializationResult.seedRequired`. It could
@@ -309,8 +312,8 @@ public protocol Synchronizer: AnyObject {
     /// - Returns: `AccountBalance`, struct that holds sapling and unshielded balances or `nil` when no account is associated with `accountIndex`
     func getAccountBalance(accountIndex: Int) async throws -> AccountBalance?
 
-    /// Fetches the latest ZEC-USD exchange rate.
-    func getExchangeRateUSD() async throws -> NSDecimalNumber
+    /// Fetches the latest ZEC-USD exchange rate and updates `exchangeRateUSDSubject`.
+    func refreshExchangeRateUSD()
 
     /// Rescans the known blocks with the current keys.
     ///

Sources/ZcashLightClientKit/Synchronizer/ClosureSDKSynchronizer.swift

@@ -194,10 +194,8 @@ extension ClosureSDKSynchronizer: ClosureSynchronizer {
         }
     }
 
-    public func getExchangeRateUSD(completion: @escaping (Result<NSDecimalNumber, Error>) -> Void) {
-        AsyncToClosureGateway.executeThrowingAction(completion) {
-            try await self.synchronizer.getExchangeRateUSD()
-        }
+    public func refreshExchangeRateUSD() {
+        synchronizer.refreshExchangeRateUSD()
     }
 
     /*

Sources/ZcashLightClientKit/Synchronizer/CombineSDKSynchronizer.swift

@@ -196,10 +196,8 @@ extension CombineSDKSynchronizer: CombineSynchronizer {
         }
     }
 
-    public func getExchangeRateUSD() -> SinglePublisher<NSDecimalNumber, Error> {
-        AsyncToCombineGateway.executeThrowingAction() {
-            try await self.synchronizer.getExchangeRateUSD()
-        }
+    public func refreshExchangeRateUSD() {
+        synchronizer.refreshExchangeRateUSD()
     }
 
     public func rewind(_ policy: RewindPolicy) -> CompletablePublisher<Error> { synchronizer.rewind(policy) }

Sources/ZcashLightClientKit/Synchronizer/SDKSynchronizer.swift

@@ -22,6 +22,9 @@ public class SDKSynchronizer: Synchronizer {
     private let eventSubject = PassthroughSubject<SynchronizerEvent, Never>()
     public var eventStream: AnyPublisher<SynchronizerEvent, Never> { eventSubject.eraseToAnyPublisher() }
 
+    private let exchangeRateUSDSubject = CurrentValueSubject<FiatCurrencyResult?, Never>(nil)
+    public var exchangeRateUSDStream: AnyPublisher<FiatCurrencyResult?, Never> { exchangeRateUSDSubject.eraseToAnyPublisher() }
+
     let metrics: SDKMetrics
     public let logger: Logger
 
@@ -508,21 +511,16 @@ public class SDKSynchronizer: Synchronizer {
         try await initializer.rustBackend.getWalletSummary()?.accountBalances[UInt32(accountIndex)]
     }
 
-    public func getExchangeRateUSD() async throws -> NSDecimalNumber {
-        logger.info("Bootstrapping Tor client for fetching exchange rates")
-        let tor: TorClient
-        do {
-            tor = try await TorClient(torDir: initializer.torDirURL)
-        } catch {
-            logger.error("failed to bootstrap Tor client: \(error)")
-            throw error
-        }
+    /// Fetches the latest ZEC-USD exchange rate.
+    public func refreshExchangeRateUSD() {
+        Task {
+            logger.info("Bootstrapping Tor client for fetching exchange rates")
 
-        do {
-            return try await tor.getExchangeRateUSD()
-        } catch {
-            logger.error("Failed to fetch exchange rate through Tor: \(error)")
-            throw error
+            guard let tor = try? await TorClient(torDir: initializer.torDirURL) else {
+                return
+            }
+
+            exchangeRateUSDSubject.send(try? await tor.getExchangeRateUSD())
         }
     }
 

Sources/ZcashLightClientKit/Tor/TorClient.swift

@@ -36,13 +36,16 @@ public class TorClient {
         zcashlc_free_tor_runtime(runtime)
     }
 
-    public func getExchangeRateUSD() async throws -> NSDecimalNumber {
+    public func getExchangeRateUSD() async throws -> FiatCurrencyResult {
         let rate = zcashlc_get_exchange_rate_usd(runtime)
 
         if rate.is_sign_negative {
             throw ZcashError.rustTorClientGet(lastErrorMessage(fallback: "`TorClient.get` failed with unknown error"))
         }
 
-        return NSDecimalNumber(mantissa: rate.mantissa, exponent: rate.exponent, isNegative: rate.is_sign_negative)
+        return FiatCurrencyResult(
+            rate: NSDecimalNumber(mantissa: rate.mantissa, exponent: rate.exponent, isNegative: rate.is_sign_negative),
+            date: Date()
+        )
     }
 }

Tests/TestUtils/Sourcery/GeneratedMocks/AutoMockable.generated.swift

@@ -1311,6 +1311,10 @@ class SynchronizerMock: Synchronizer {
         get { return underlyingEventStream }
     }
     var underlyingEventStream: AnyPublisher<SynchronizerEvent, Never>!
+    var exchangeRateUSDStream: AnyPublisher<FiatCurrencyResult?, Never> {
+        get { return underlyingExchangeRateUSDStream }
+    }
+    var underlyingExchangeRateUSDStream: AnyPublisher<FiatCurrencyResult?, Never>!
     var transactions: [ZcashTransaction.Overview] {
         get async { return underlyingTransactions }
     }
@@ -1798,26 +1802,17 @@ class SynchronizerMock: Synchronizer {
         }
     }
 
-    // MARK: - getExchangeRateUSD
+    // MARK: - refreshExchangeRateUSD
 
-    var getExchangeRateUSDThrowableError: Error?
-    var getExchangeRateUSDCallsCount = 0
-    var getExchangeRateUSDCalled: Bool {
-        return getExchangeRateUSDCallsCount > 0
+    var refreshExchangeRateUSDCallsCount = 0
+    var refreshExchangeRateUSDCalled: Bool {
+        return refreshExchangeRateUSDCallsCount > 0
     }
-    var getExchangeRateUSDReturnValue: NSDecimalNumber!
-    var getExchangeRateUSDClosure: (() async throws -> NSDecimalNumber)?
+    var refreshExchangeRateUSDClosure: (() -> Void)?
 
-    func getExchangeRateUSD() async throws -> NSDecimalNumber {
-        if let error = getExchangeRateUSDThrowableError {
-            throw error
-        }
-        getExchangeRateUSDCallsCount += 1
-        if let closure = getExchangeRateUSDClosure {
-            return try await closure()
-        } else {
-            return getExchangeRateUSDReturnValue
-        }
+    func refreshExchangeRateUSD() {
+        refreshExchangeRateUSDCallsCount += 1
+        refreshExchangeRateUSDClosure!()
     }
 
     // MARK: - rewind