Restore contacts from backup

XXClient library

• Improve error handling in UdMultiLookupCallback.

xx-messenger example

• Improve backup restoration.
• Restore contacts.
• Add contact lookup feature.
• Display contact ids.
• Improve sending requests.
• Restore username from restored facts, not from restored params.

Examples/xx-messenger/Sources/ContactLookupFeature/ContactLookupView.swift

+import AppCore
+import ComposableArchitecture
+import SwiftUI
+
+public struct ContactLookupView: View {
+  public init(store: Store<ContactLookupState, ContactLookupAction>) {
+    self.store = store
+  }
+
+  let store: Store<ContactLookupState, ContactLookupAction>
+
+  struct ViewState: Equatable {
+    init(state: ContactLookupState) {
+      id = state.id
+      isLookingUp = state.isLookingUp
+      failure = state.failure
+    }
+
+    var id: Data
+    var isLookingUp: Bool
+    var failure: String?
+  }
+
+  public var body: some View {
+    WithViewStore(store, observe: ViewState.init) { viewStore in
+      Form {
+        Section {
+          Label(viewStore.id.hexString(), systemImage: "number")
+            .font(.footnote.monospaced())
+
+          Button {
+            viewStore.send(.lookupTapped)
+          } label: {
+            HStack {
+              Text("Lookup")
+              Spacer()
+              if viewStore.isLookingUp {
+                ProgressView()
+              } else {
+                Image(systemName: "magnifyingglass")
+              }
+            }
+          }
+          .disabled(viewStore.isLookingUp)
+        } header: {
+          Text("Contact ID")
+        }
+
+        if let failure = viewStore.failure {
+          Section {
+            Text(failure)
+          } header: {
+            Text("Error")
+          }
+        }
+      }
+      .navigationTitle("Lookup")
+    }
+  }
+}
+
+#if DEBUG
+public struct ContactLookupView_Previews: PreviewProvider {
+  public static var previews: some View {
+    NavigationView {
+      ContactLookupView(store: Store(
+        initialState: ContactLookupState(
+          id: "1234".data(using: .utf8)!
+        ),
+        reducer: .empty,
+        environment: ()
+      ))
+    }
+  }
+}
+#endif