[#1466] Choose the best server by testing responses from multiple hosts

CHANGELOG.md

@@ -6,6 +6,11 @@ and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+## Added
+
+### [#1466] Choose the best server by testing responses from multiple hosts
+- Synchronizer's `evaluateBestOf(endpoints: [], ...) async -> [LightWalletEndpoint]` method takes a list of endpoints and evaluates top k best performant servers. 
+
 # 2.2.1 - 2024-08-21
 
 ## Fixed

Example/ZcashLightClientSample/ZcashLightClientSample.xcodeproj/project.pbxproj

@@ -53,6 +53,8 @@
 		343CB69829CDC05D0063BF41 /* SyncBlocksListViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 343CB69629CDC05D0063BF41 /* SyncBlocksListViewController.swift */; };
 		34CC8FD029CDC212001E06E9 /* SynchronizerCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = 34CC8FCF29CDC212001E06E9 /* SynchronizerCell.swift */; };
 		34CC8FD129CDC212001E06E9 /* SynchronizerCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = 34CC8FCF29CDC212001E06E9 /* SynchronizerCell.swift */; };
+		9EEFA3BF2C380DB900467ABC /* TestServersViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9EEFA3BE2C380DB900467ABC /* TestServersViewController.swift */; };
+		9EEFA3C02C380DB900467ABC /* TestServersViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9EEFA3BE2C380DB900467ABC /* TestServersViewController.swift */; };
 		F94912632790D7C4004BB3DE /* ZcashLightClientSample-Mainnet-Info.plist in Resources */ = {isa = PBXBuildFile; fileRef = F94912622790D7C4004BB3DE /* ZcashLightClientSample-Mainnet-Info.plist */; };
 		F9D63D1F27CD114A00F4DC5F /* ZcashLightClientKit in Frameworks */ = {isa = PBXBuildFile; productRef = F9D63D1E27CD114A00F4DC5F /* ZcashLightClientKit */; };
 		F9D63D2227CD125300F4DC5F /* KRProgressHUD in Frameworks */ = {isa = PBXBuildFile; productRef = F9D63D2127CD125300F4DC5F /* KRProgressHUD */; };
@@ -103,6 +105,7 @@
 		34CC8FCF29CDC212001E06E9 /* SynchronizerCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SynchronizerCell.swift; sourceTree = "<group>"; };
 		372CC57DB80CC242BA556A30 /* Pods_ZcashLightClientSampleUITests.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_ZcashLightClientSampleUITests.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		541D36743362A797BF085D14 /* Pods_ZcashLightClientSample_Mainnet.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_ZcashLightClientSample_Mainnet.framework; sourceTree = BUILT_PRODUCTS_DIR; };
+		9EEFA3BE2C380DB900467ABC /* TestServersViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TestServersViewController.swift; sourceTree = "<group>"; };
 		EBA186B246C4205F9BF71EED /* Pods_ZcashLightClientSample.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_ZcashLightClientSample.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		F94912622790D7C4004BB3DE /* ZcashLightClientSample-Mainnet-Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist; path = "ZcashLightClientSample-Mainnet-Info.plist"; sourceTree = SOURCE_ROOT; };
 		F9D63D1D27CD103E00F4DC5F /* ZcashLightClientKit */ = {isa = PBXFileReference; lastKnownFileType = folder; name = ZcashLightClientKit; path = ../..; sourceTree = "<group>"; };
@@ -219,6 +222,7 @@
 		0D907F142322CC5900D641FE /* ZcashLightClientSample */ = {
 			isa = PBXGroup;
 			children = (
+				9EEFA3BD2C380D7900467ABC /* Test Servers */,
 				0D76121426B1D5D7001CA417 /* Constants */,
 				0D1BE47D2581933C00F78BE3 /* Get UTXOs */,
 				0D6CE8BB252E3C1A0005D707 /* Sapling Parameters */,
@@ -300,6 +304,14 @@
 			path = "Paginated Transactions";
 			sourceTree = "<group>";
 		};
+		9EEFA3BD2C380D7900467ABC /* Test Servers */ = {
+			isa = PBXGroup;
+			children = (
+				9EEFA3BE2C380DB900467ABC /* TestServersViewController.swift */,
+			);
+			path = "Test Servers";
+			sourceTree = "<group>";
+		};
 		F93EF550279077B70063E43A /* Frameworks */ = {
 			isa = PBXGroup;
 			children = (
@@ -528,6 +540,7 @@
 				0DF53E6723A438F100D7249C /* PaginatedTransactionsViewController.swift in Sources */,
 				34CC8FD029CDC212001E06E9 /* SynchronizerCell.swift in Sources */,
 				343CB69729CDC05D0063BF41 /* SyncBlocksListViewController.swift in Sources */,
+				9EEFA3BF2C380DB900467ABC /* TestServersViewController.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -560,6 +573,7 @@
 				0DA1C4CD27D11D9500E5006E /* PaginatedTransactionsViewController.swift in Sources */,
 				34CC8FD129CDC212001E06E9 /* SynchronizerCell.swift in Sources */,
 				343CB69829CDC05D0063BF41 /* SyncBlocksListViewController.swift in Sources */,
+				9EEFA3C02C380DB900467ABC /* TestServersViewController.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Example/ZcashLightClientSample/ZcashLightClientSample/Base.lproj/Main.storyboard

@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="22505" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="Ewq-Xy-xHb">
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="32700.99.1234" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="Ewq-Xy-xHb">
     <device id="retina6_0" orientation="portrait" appearance="light"/>
     <dependencies>
         <deployment identifier="iOS"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="22504"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="22685"/>
         <capability name="Safe area layout guides" minToolsVersion="9.0"/>
         <capability name="System colors in document resources" minToolsVersion="11.0"/>
         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
@@ -297,6 +297,26 @@
                                             <segue destination="Ugl-B2-O3O" kind="show" id="hk7-2x-BJl"/>
                                         </connections>
                                     </tableViewCell>
+                                    <tableViewCell clipsSubviews="YES" contentMode="scaleToFill" preservesSuperviewLayoutMargins="YES" selectionStyle="default" indentationWidth="10" textLabel="Cuf-Pp-TrG" style="IBUITableViewCellStyleDefault" id="B0F-J8-vVs">
+                                        <rect key="frame" x="0.0" y="661.33335113525391" width="390" height="43.666667938232422"/>
+                                        <autoresizingMask key="autoresizingMask"/>
+                                        <tableViewCellContentView key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" preservesSuperviewLayoutMargins="YES" insetsLayoutMarginsFromSafeArea="NO" tableViewCell="B0F-J8-vVs" id="7IF-Qw-50i">
+                                            <rect key="frame" x="0.0" y="0.0" width="390" height="43.666667938232422"/>
+                                            <autoresizingMask key="autoresizingMask"/>
+                                            <subviews>
+                                                <label opaque="NO" multipleTouchEnabled="YES" contentMode="left" insetsLayoutMarginsFromSafeArea="NO" text="Test servers" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" id="Cuf-Pp-TrG">
+                                                    <rect key="frame" x="20" y="0.0" width="350" height="43.666667938232422"/>
+                                                    <autoresizingMask key="autoresizingMask"/>
+                                                    <fontDescription key="fontDescription" type="system" pointSize="17"/>
+                                                    <nil key="textColor"/>
+                                                    <nil key="highlightedColor"/>
+                                                </label>
+                                            </subviews>
+                                        </tableViewCellContentView>
+                                        <connections>
+                                            <segue destination="YrC-gV-U7F" kind="show" id="L7C-z0-MKd"/>
+                                        </connections>
+                                    </tableViewCell>
                                 </cells>
                             </tableViewSection>
                         </sections>
@@ -1391,6 +1411,44 @@
             </objects>
             <point key="canvasLocation" x="1880" y="1126"/>
         </scene>
+        <!--Test Servers View Controller-->
+        <scene sceneID="b7C-1S-hZW">
+            <objects>
+                <viewController id="YrC-gV-U7F" customClass="TestServersViewController" customModule="ZcashLightClientSample" customModuleProvider="target" sceneMemberID="viewController">
+                    <view key="view" contentMode="scaleToFill" id="Iha-sQ-HNt">
+                        <rect key="frame" x="0.0" y="0.0" width="390" height="844"/>
+                        <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
+                        <subviews>
+                            <button opaque="NO" contentMode="scaleToFill" fixedFrame="YES" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="system" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="oOW-JY-WzN">
+                                <rect key="frame" x="136" y="109" width="119" height="35"/>
+                                <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
+                                <state key="normal" title="Button"/>
+                                <buttonConfiguration key="configuration" style="plain" title="Test Servers"/>
+                                <connections>
+                                    <action selector="testServers:" destination="YrC-gV-U7F" eventType="touchUpInside" id="El4-aw-aUF"/>
+                                </connections>
+                            </button>
+                            <label opaque="NO" userInteractionEnabled="NO" contentMode="top" horizontalHuggingPriority="251" verticalHuggingPriority="251" fixedFrame="YES" text="asdasd" lineBreakMode="tailTruncation" numberOfLines="0" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="TVg-m2-N4p">
+                                <rect key="frame" x="24" y="162" width="344" height="469"/>
+                                <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
+                                <fontDescription key="fontDescription" type="system" pointSize="17"/>
+                                <nil key="textColor"/>
+                                <nil key="highlightedColor"/>
+                            </label>
+                        </subviews>
+                        <viewLayoutGuide key="safeArea" id="fec-YN-6id"/>
+                        <color key="backgroundColor" systemColor="systemBackgroundColor"/>
+                    </view>
+                    <navigationItem key="navigationItem" id="jfe-3q-9Oj"/>
+                    <connections>
+                        <outlet property="resultsLabel" destination="TVg-m2-N4p" id="t2g-vv-hbe"/>
+                        <outlet property="testServersBtn" destination="oOW-JY-WzN" id="Bqh-QJ-s56"/>
+                    </connections>
+                </viewController>
+                <placeholder placeholderIdentifier="IBFirstResponder" id="bDV-rt-CHM" userLabel="First Responder" customClass="UIResponder" sceneMemberID="firstResponder"/>
+            </objects>
+            <point key="canvasLocation" x="-1623.0769230769231" y="1124.6445497630332"/>
+        </scene>
     </scenes>
     <inferredMetricsTieBreakers>
         <segue reference="oxP-eV-1Z2"/>

Example/ZcashLightClientSample/ZcashLightClientSample/Test Servers/TestServersViewController.swift

@@ -0,0 +1,68 @@
+//
+//  TestServersViewController.swift
+//  ZcashLightClientSample
+//
+//  Created by Lukáš Korba on 05.07.2024.
+//  Copyright © 2024 Electric Coin Company. All rights reserved.
+//
+
+import UIKit
+import ZcashLightClientKit
+
+class TestServersViewController: UIViewController {
+    let endpoints: [LightWalletEndpoint] = [
+        LightWalletEndpoint(address: "zec.rocks", port: 443),
+        LightWalletEndpoint(address: "na.zec.rocks", port: 443),
+        LightWalletEndpoint(address: "sa.zec.rocks", port: 443),
+        LightWalletEndpoint(address: "eu.zec.rocks", port: 443),
+        LightWalletEndpoint(address: "ap.zec.rocks", port: 443),
+        LightWalletEndpoint(address: "lwd1.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd2.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd3.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd4.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd5.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd6.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd7.zcash-infra.com", port: 9067),
+        LightWalletEndpoint(address: "lwd8.zcash-infra.com", port: 9067)
+    ]
+
+    @IBOutlet weak var resultsLabel: UILabel!
+    @IBOutlet weak var testServersBtn: UIButton!
+
+    var startTime: TimeInterval = 0.0
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+    }
+
+    @IBAction func testServers(_ sender: Any) {
+        let synchronizer = AppDelegate.shared.sharedSynchronizer
+        testServersBtn.isEnabled = false
+
+        startTime = Date().timeIntervalSince1970
+
+        Task {
+            let results = await synchronizer.evaluateBestOf(endpoints: endpoints)
+
+            await showResults(results)
+        }
+    }
+
+    @MainActor func showResults(_ endpoints: [LightWalletEndpoint]) async {
+        testServersBtn.isEnabled = true
+
+        var resultStr = ""
+
+        var counter = 1
+        endpoints.forEach {
+            resultStr = "\(resultStr) \(counter). \($0.host):\($0.port)\n"
+            counter += 1
+        }
+
+        resultStr = "\(resultStr) \n"
+
+        resultStr = "\(resultStr) time to evaluate all: \(Date().timeIntervalSince1970 - startTime)s"
+
+        resultsLabel.text = resultStr
+    }
+}

Sources/ZcashLightClientKit/Block/CompactBlockProcessor.swift

@@ -292,6 +292,10 @@ extension CompactBlockProcessor {
     func latestHeight() async throws -> BlockHeight {
         try await blockDownloaderService.latestBlockHeight()
     }
+
+    func consensusBranchIdFor(_ height: Int32) -> Int32? {
+        try? rustBackend.consensusBranchIdFor(height: height)
+    }
 }
 
 // MARK: - Rewind

Sources/ZcashLightClientKit/Constants/ZcashSDK.swift

@@ -147,6 +147,9 @@ public enum ZcashSDK {
     public static let outputParamFilename = "sapling-output.params"
     // swiftlint:disable:next force_unwrapping
     public static let outputParamFileURL = URL(string: cloudParameterURL)!.appendingPathComponent(outputParamFilename)
+
+    /// A constant that helps determine if a server’s chain tip is so far away from the estimated height that we consider the server out of sync
+    public static let syncedThresholdBlocks = UInt64(288)
 }
 
 public protocol NetworkConstants {

Sources/ZcashLightClientKit/Synchronizer.swift

@@ -367,6 +367,23 @@
     ///
     /// - parameter seed: byte array of the seed
     func isSeedRelevantToAnyDerivedAccount(seed: [UInt8]) async throws -> Bool
+
+    /// Takes the list of endpoints and runs it through a series of checks to evaluate its performance.
+    /// - Parameters:
+    ///    - endpoints: Array of endpoints to evaluate.
+    ///    - latencyThresholdMillis: The mean latency of `getInfo` and `getTheLatestHeight` calls must be below this threshold. The default is 300 ms.
+    ///    - fetchThresholdSeconds: The time to download `nBlocksToFetch` blocks from the stream must be below this threshold. The default is 60 seconds.
+    ///    - nBlocksToFetch: The number of blocks expected to be downloaded from the stream, with the time compared to `fetchThresholdSeconds`. The default is 100.
+    ///    - kServers: The expected number of endpoints in the output. The default is 3.
+    ///    - network: Mainnet or testnet. The default is mainnet.
+    func evaluateBestOf(
+        endpoints: [LightWalletEndpoint],
+        latencyThresholdMillis: Double,
+        fetchThresholdSeconds: Double,
+        nBlocksToFetch: UInt64,
+        kServers: Int,
+        network: NetworkType
+    ) async -> [LightWalletEndpoint]
 }
 
 public enum SyncStatus: Equatable {