Add a developer option for history sharing on invite

Adds a new developer flag, enabling our experimental support for MSC4268.

ElementX/Sources/Application/AppSettings.swift

@@ -17,6 +17,7 @@ protocol CommonSettingsProtocol {
     var logLevel: LogLevel { get }
     var traceLogPacks: Set<TraceLogPack> { get }
     var enableOnlySignedDeviceIsolationMode: Bool { get }
+    var enableKeyShareOnInvite: Bool { get }
     var hideQuietNotificationAlerts: Bool { get }
 }
 
@@ -52,6 +53,7 @@ final class AppSettings {
         case publicSearchEnabled
         case fuzzyRoomListSearchEnabled
         case enableOnlySignedDeviceIsolationMode
+        case enableKeyShareOnInvite
         case knockingEnabled
         case threadsEnabled
         case developerOptionsEnabled
@@ -363,7 +365,11 @@ final class AppSettings {
     /// Configuration to enable only signed device isolation mode for  crypto. In this mode only devices signed by their owner will be considered in e2ee rooms.
     @UserPreference(key: UserDefaultsKeys.enableOnlySignedDeviceIsolationMode, defaultValue: false, storageType: .userDefaults(store))
     var enableOnlySignedDeviceIsolationMode
-    
+
+    /// Configuration to enable encrypted history sharing on invite, and accepting keys from inviters.
+    @UserPreference(key: UserDefaultsKeys.enableKeyShareOnInvite, defaultValue: false, storageType: .userDefaults(store))
+    var enableKeyShareOnInvite
+
     @UserPreference(key: UserDefaultsKeys.hideQuietNotificationAlerts, defaultValue: false, storageType: .userDefaults(store))
     var hideQuietNotificationAlerts
 }

ElementX/Sources/Other/Extensions/ClientBuilder.swift

@@ -16,6 +16,7 @@ extension ClientBuilder {
                             sessionDelegate: ClientSessionDelegate,
                             appHooks: AppHooks,
                             enableOnlySignedDeviceIsolationMode: Bool,
+                            enableKeyShareOnInvite: Bool,
                             requestTimeout: UInt64? = 30000,
                             maxRequestRetryTime: UInt64? = nil) -> ClientBuilder {
         var builder = ClientBuilder()
@@ -37,6 +38,7 @@ extension ClientBuilder {
             builder = builder
                 .autoEnableCrossSigning(autoEnableCrossSigning: true)
                 .backupDownloadStrategy(backupDownloadStrategy: .afterDecryptionFailure)
+                .enableShareHistoryOnInvite(enableShareHistoryOnInvite: enableKeyShareOnInvite)
                 .autoEnableBackups(autoEnableBackups: true)
                 
             if enableOnlySignedDeviceIsolationMode {

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/DeveloperOptionsScreenModels.swift

@@ -42,6 +42,7 @@ protocol DeveloperOptionsProtocol: AnyObject {
     var hideUnreadMessagesBadge: Bool { get set }
     var fuzzyRoomListSearchEnabled: Bool { get set }
     var enableOnlySignedDeviceIsolationMode: Bool { get set }
+    var enableKeyShareOnInvite: Bool { get set }
     var elementCallBaseURLOverride: URL? { get set }
     var knockingEnabled: Bool { get set }
     var threadsEnabled: Bool { get set }

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/View/DeveloperOptionsScreen.swift

@@ -75,6 +75,16 @@ struct DeveloperOptionsScreen: View {
                 Text("This setting controls how end-to-end encryption (E2EE) keys are exchanged. Enabling it will prevent the inclusion of devices that have not been explicitly verified by their owners.")
             }
 
+            Section {
+                Toggle(isOn: $context.enableKeyShareOnInvite) {
+                    Text("Share encrypted history with new members")
+                    Text("Requires app reboot")
+                }
+            } footer: {
+                Text("When inviting a user to an encrypted room that has history visibility set to \"shared\", share encrypted history with that user, and accept encrypted history when you are invited to such a room.")
+                Text("WARNING: this feature is EXPERIMENTAL and not all security precautions are implemented. Do not enable on production accounts.")
+            }
+
             Section {
                 TextField("Leave empty to use EC locally", text: $elementCallURLOverrideString)
                     .autocorrectionDisabled(true)

ElementX/Sources/Services/Authentication/AuthenticationClientBuilder.swift

@@ -48,7 +48,8 @@ struct AuthenticationClientBuilder: AuthenticationClientBuilderProtocol {
                          slidingSync: .discover,
                          sessionDelegate: clientSessionDelegate,
                          appHooks: appHooks,
-                         enableOnlySignedDeviceIsolationMode: appSettings.enableOnlySignedDeviceIsolationMode)
+                         enableOnlySignedDeviceIsolationMode: appSettings.enableOnlySignedDeviceIsolationMode,
+                         enableKeyShareOnInvite: appSettings.enableKeyShareOnInvite)
             .sessionPaths(dataPath: sessionDirectories.dataPath,
                           cachePath: sessionDirectories.cachePath)
             .sessionPassphrase(passphrase: passphrase)

ElementX/Sources/Services/UserSession/UserSessionStore.swift

@@ -123,7 +123,8 @@ class UserSessionStore: UserSessionStoreProtocol {
                          slidingSync: .restored,
                          sessionDelegate: keychainController,
                          appHooks: appHooks,
-                         enableOnlySignedDeviceIsolationMode: appSettings.enableOnlySignedDeviceIsolationMode)
+                         enableOnlySignedDeviceIsolationMode: appSettings.enableOnlySignedDeviceIsolationMode,
+                         enableKeyShareOnInvite: appSettings.enableKeyShareOnInvite)
             .sessionPaths(dataPath: credentials.restorationToken.sessionDirectories.dataPath,
                           cachePath: credentials.restorationToken.sessionDirectories.cachePath)
             .username(username: credentials.userID)

NSE/Sources/NSEUserSession.swift

@@ -61,6 +61,7 @@ final class NSEUserSession {
                          sessionDelegate: clientSessionDelegate,
                          appHooks: appHooks,
                          enableOnlySignedDeviceIsolationMode: appSettings.enableOnlySignedDeviceIsolationMode,
+                         enableKeyShareOnInvite: appSettings.enableKeyShareOnInvite,
                          requestTimeout: 15000,
                          maxRequestRetryTime: 5000)
             .systemIsMemoryConstrained()