Add ability to set custom username discriminators.

2025-12-22 03:58:48 +00:00 · 2024-01-09 11:37:39 -04:00
parent fb75440769
commit 17a6fcafa1
12 changed files with 952 additions and 75 deletions
--- a/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditFragment.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditFragment.java
@@ -3,14 +3,12 @@ package org.thoughtcrime.securesms.profiles.manage;
 import android.animation.LayoutTransition;
 import android.content.Intent;
 import android.content.res.ColorStateList;
-import android.graphics.drawable.Drawable;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.inputmethod.EditorInfo;
 import android.widget.EditText;
-import android.widget.TextView;
 import android.widget.Toast;

 import androidx.annotation.NonNull;
@@ -25,25 +23,22 @@ import androidx.navigation.fragment.NavHostFragment;
 import com.google.android.material.dialog.MaterialAlertDialogBuilder;
 import com.google.android.material.textfield.TextInputLayout;

-import org.signal.core.util.DimensionUnit;
 import org.thoughtcrime.securesms.LoggingFragment;
 import org.thoughtcrime.securesms.PassphraseRequiredActivity;
 import org.thoughtcrime.securesms.R;
 import org.thoughtcrime.securesms.contactshare.SimpleTextWatcher;
 import org.thoughtcrime.securesms.databinding.UsernameEditFragmentBinding;
 import org.thoughtcrime.securesms.keyvalue.SignalStore;
-import org.thoughtcrime.securesms.recipients.Recipient;
 import org.thoughtcrime.securesms.util.FragmentResultContract;
 import org.signal.core.util.concurrent.LifecycleDisposable;
 import org.thoughtcrime.securesms.util.UsernameUtil;
 import org.thoughtcrime.securesms.util.ViewUtil;
 import org.thoughtcrime.securesms.util.views.CircularProgressMaterialButton;

-import java.util.Objects;
-
 public class UsernameEditFragment extends LoggingFragment {

  private static final float DISABLED_ALPHA           = 0.5f;
+  public static final String IGNORE_TEXT_CHANGE_EVENT = "ignore.text.change.event";

  private UsernameEditViewModel       viewModel;
  private UsernameEditFragmentBinding binding;
@@ -99,6 +94,7 @@ public class UsernameEditFragment extends LoggingFragment {

    lifecycleDisposable.add(viewModel.getUiState().subscribe(this::onUiStateChanged));
    lifecycleDisposable.add(viewModel.getEvents().subscribe(this::onEvent));
+    lifecycleDisposable.add(viewModel.getUsernameInputState().subscribe(this::presentUsernameInputState));

    binding.usernameSubmitButton.setOnClickListener(v -> viewModel.onUsernameSubmitted());
    binding.usernameDeleteButton.setOnClickListener(v -> viewModel.onUsernameDeleted());
@@ -112,10 +108,23 @@ public class UsernameEditFragment extends LoggingFragment {
    binding.usernameText.addTextChangedListener(new SimpleTextWatcher() {
      @Override
      public void onTextChanged(@NonNull String text) {
+        if (binding.usernameText.getTag() != IGNORE_TEXT_CHANGE_EVENT) {
          viewModel.onNicknameUpdated(text);
        }
+      }
    });
-    binding.usernameText.setOnEditorActionListener((v, actionId, event) -> {
+
+    binding.discriminatorText.setText(usernameState.getDiscriminator());
+    binding.discriminatorText.addTextChangedListener(new SimpleTextWatcher() {
+      @Override
+      public void onTextChanged(@NonNull String text) {
+        if (binding.discriminatorText.getTag() != IGNORE_TEXT_CHANGE_EVENT) {
+          viewModel.onDiscriminatorUpdated(text);
+        }
+      }
+    });
+
+    binding.discriminatorText.setOnEditorActionListener((v, actionId, event) -> {
      if (actionId == EditorInfo.IME_ACTION_DONE) {
        viewModel.onUsernameSubmitted();
        return true;
@@ -127,24 +136,9 @@ public class UsernameEditFragment extends LoggingFragment {
    binding.usernameDescription.setLearnMoreVisible(true);
    binding.usernameDescription.setOnLinkClickListener(this::onLearnMore);

-    initializeSuffix();
    ViewUtil.focusAndShowKeyboard(binding.usernameText);
  }

-  private void initializeSuffix() {
-    TextView suffixTextView = binding.usernameTextWrapper.getSuffixTextView();
-    Drawable pipe           = Objects.requireNonNull(ContextCompat.getDrawable(requireContext(), R.drawable.pipe_divider));
-
-    pipe.setBounds(0, 0, (int) DimensionUnit.DP.toPixels(1f), (int) DimensionUnit.DP.toPixels(20f));
-    suffixTextView.setCompoundDrawablesRelative(pipe, null, null, null);
-
-    ViewUtil.setLeftMargin(suffixTextView, (int) DimensionUnit.DP.toPixels(16f));
-
-    binding.usernameTextWrapper.getSuffixTextView().setCompoundDrawablePadding((int) DimensionUnit.DP.toPixels(16f));
-
-    suffixTextView.setOnClickListener(this::onLearnMore);
-  }
-
  @Override
  public void onDestroyView() {
    super.onDestroyView();
@@ -162,7 +156,7 @@ public class UsernameEditFragment extends LoggingFragment {
  private void onUiStateChanged(@NonNull UsernameEditViewModel.State state) {
    TextInputLayout usernameInputWrapper = binding.usernameTextWrapper;

-    presentSuffix(state.username);
+    presentProgressState(state.username);
    presentButtonState(state.buttonState);
    presentSummary(state.username);

@@ -174,7 +168,7 @@ public class UsernameEditFragment extends LoggingFragment {
        break;
      case TOO_SHORT:
      case TOO_LONG:
-        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment_usernames_must_be_between_a_and_b_characters, UsernameUtil.MIN_LENGTH, UsernameUtil.MAX_LENGTH));
+        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment_usernames_must_be_between_a_and_b_characters, UsernameUtil.MIN_NICKNAME_LENGTH, UsernameUtil.MAX_NICKNAME_LENGTH));
        usernameInputWrapper.setErrorTextColor(ColorStateList.valueOf(getResources().getColor(R.color.signal_colorError)));

        break;
@@ -197,6 +191,22 @@ public class UsernameEditFragment extends LoggingFragment {
        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment_this_username_is_taken));
        usernameInputWrapper.setErrorTextColor(ColorStateList.valueOf(getResources().getColor(R.color.signal_colorError)));

+        break;
+      case DISCRIMINATOR_HAS_INVALID_CHARACTERS:
+      case DISCRIMINATOR_NOT_AVAILABLE:
+        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment__this_username_is_not_available_try_another_number));
+        usernameInputWrapper.setErrorTextColor(ColorStateList.valueOf(getResources().getColor(R.color.signal_colorError)));
+
+        break;
+      case DISCRIMINATOR_TOO_LONG:
+        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment__invalid_username_enter_a_maximum_of_d_digits, UsernameUtil.MAX_DISCRIMINATOR_LENGTH));
+        usernameInputWrapper.setErrorTextColor(ColorStateList.valueOf(getResources().getColor(R.color.signal_colorError)));
+
+        break;
+      case DISCRIMINATOR_TOO_SHORT:
+        usernameInputWrapper.setError(getResources().getString(R.string.UsernameEditFragment__invalid_username_enter_a_minimum_of_d_digits, UsernameUtil.MIN_DISCRIMINATOR_LENGTH));
+        usernameInputWrapper.setErrorTextColor(ColorStateList.valueOf(getResources().getColor(R.color.signal_colorError)));
+
        break;
    }

@@ -302,9 +312,25 @@ public class UsernameEditFragment extends LoggingFragment {
    }
  }

-  private void presentSuffix(@NonNull UsernameState usernameState) {
-    binding.usernameTextWrapper.setSuffixText(usernameState.getDiscriminator());
+  private void presentUsernameInputState(@NonNull UsernameEditStateMachine.State state) {
+    binding.usernameText.setTag(IGNORE_TEXT_CHANGE_EVENT);
+    String nickname = state.getNickname();
+    if (!binding.usernameText.getText().toString().equals(nickname)) {
+      binding.usernameText.setText(state.getNickname());
+      binding.usernameText.setSelection(binding.usernameText.length());
+    }
+    binding.usernameText.setTag(null);

+    binding.discriminatorText.setTag(IGNORE_TEXT_CHANGE_EVENT);
+    String discriminator = state.getDiscriminator();
+    if (!binding.discriminatorText.getText().toString().equals(discriminator)) {
+      binding.discriminatorText.setText(state.getDiscriminator());
+      binding.discriminatorText.setSelection(binding.discriminatorText.length());
+    }
+    binding.discriminatorText.setTag(null);
+  }
+
+  private void presentProgressState(@NonNull UsernameState usernameState) {
    boolean isInProgress = usernameState.isInProgress();

    if (isInProgress) {
--- a/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditStateMachine.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditStateMachine.kt
@@ -0,0 +1,216 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.profiles.manage
+
+object UsernameEditStateMachine {
+
+  enum class StateModifier {
+    USER,
+    SYSTEM
+  }
+
+  sealed class State {
+    abstract val nickname: String
+    abstract val discriminator: String
+    abstract val stateModifier: StateModifier
+
+    abstract fun onUserChangedNickname(nickname: String): State
+    abstract fun onUserChangedDiscriminator(discriminator: String): State
+    abstract fun onSystemChangedNickname(nickname: String): State
+    abstract fun onSystemChangedDiscriminator(discriminator: String): State
+  }
+
+  /**
+   * This state is representative of when the user has not manually changed either field in
+   * the form, and it is assumed that both values are either blank or system provided.
+   *
+   * This can be thought of as our "initial state" and can be pre-populated with username information
+   * for the local user.
+   */
+  data class NoUserEntry(
+    override val nickname: String,
+    override val discriminator: String,
+    override val stateModifier: StateModifier
+  ) : State() {
+    override fun onUserChangedNickname(nickname: String): State {
+      return if (nickname.isBlank()) {
+        NoUserEntry(
+          nickname = "",
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      } else {
+        UserEnteredNickname(
+          nickname = nickname,
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      }
+    }
+
+    override fun onUserChangedDiscriminator(discriminator: String): State {
+      return if (discriminator.isBlank()) {
+        NoUserEntry(
+          nickname = nickname,
+          discriminator = "",
+          stateModifier = StateModifier.USER
+        )
+      } else {
+        UserEnteredDiscriminator(
+          nickname = nickname,
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      }
+    }
+
+    override fun onSystemChangedNickname(nickname: String): State {
+      return copy(nickname = nickname, stateModifier = StateModifier.SYSTEM)
+    }
+
+    override fun onSystemChangedDiscriminator(discriminator: String): State {
+      return copy(discriminator = discriminator, stateModifier = StateModifier.SYSTEM)
+    }
+  }
+
+  /**
+   * The user has altered the nickname field with something that is non-empty.
+   * The user has not altered the discriminator field.
+   */
+  data class UserEnteredNickname(
+    override val nickname: String,
+    override val discriminator: String,
+    override val stateModifier: StateModifier
+  ) : State() {
+    override fun onUserChangedNickname(nickname: String): State {
+      return if (nickname.isBlank()) {
+        NoUserEntry(
+          nickname = "",
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      } else {
+        copy(nickname = nickname, stateModifier = StateModifier.USER)
+      }
+    }
+
+    override fun onUserChangedDiscriminator(discriminator: String): State {
+      return if (discriminator.isBlank()) {
+        copy(discriminator = "", stateModifier = StateModifier.USER)
+      } else {
+        UserEnteredNicknameAndDiscriminator(
+          nickname = nickname,
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      }
+    }
+
+    override fun onSystemChangedNickname(nickname: String): State {
+      return NoUserEntry(
+        nickname = nickname,
+        discriminator = discriminator,
+        stateModifier = StateModifier.SYSTEM
+      )
+    }
+
+    override fun onSystemChangedDiscriminator(discriminator: String): State {
+      return copy(discriminator = discriminator, stateModifier = StateModifier.SYSTEM)
+    }
+  }
+
+  /**
+   * The user has altered the discriminator field with something that is non-empty.
+   * The user has not altered the nickname field.
+   */
+  data class UserEnteredDiscriminator(
+    override val nickname: String,
+    override val discriminator: String,
+    override val stateModifier: StateModifier
+  ) : State() {
+    override fun onUserChangedNickname(nickname: String): State {
+      return if (nickname.isBlank()) {
+        copy(nickname = nickname, stateModifier = StateModifier.USER)
+      } else if (discriminator.isBlank()) {
+        UserEnteredNickname(
+          nickname = nickname,
+          discriminator = "",
+          stateModifier = StateModifier.USER
+        )
+      } else {
+        UserEnteredNicknameAndDiscriminator(
+          nickname = nickname,
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      }
+    }
+
+    override fun onUserChangedDiscriminator(discriminator: String): State {
+      return copy(discriminator = discriminator, stateModifier = StateModifier.USER)
+    }
+
+    override fun onSystemChangedNickname(nickname: String): State {
+      return copy(nickname = nickname, stateModifier = StateModifier.SYSTEM)
+    }
+
+    override fun onSystemChangedDiscriminator(discriminator: String): State {
+      return NoUserEntry(
+        nickname = nickname,
+        discriminator = discriminator,
+        stateModifier = StateModifier.SYSTEM
+      )
+    }
+  }
+
+  /**
+   * The user has altered the nickname field with something that is non-empty.
+   * The user has altered the discriminator field with something that is non-empty.
+   */
+  data class UserEnteredNicknameAndDiscriminator(
+    override val nickname: String,
+    override val discriminator: String,
+    override val stateModifier: StateModifier
+  ) : State() {
+    override fun onUserChangedNickname(nickname: String): State {
+      return if (nickname.isBlank()) {
+        UserEnteredDiscriminator(
+          nickname = "",
+          discriminator = discriminator,
+          stateModifier = StateModifier.USER
+        )
+      } else if (discriminator.isBlank()) {
+        UserEnteredNickname(
+          nickname = nickname,
+          discriminator = "",
+          stateModifier = StateModifier.USER
+        )
+      } else {
+        copy(nickname = nickname, stateModifier = StateModifier.USER)
+      }
+    }
+
+    override fun onUserChangedDiscriminator(discriminator: String): State {
+      return copy(discriminator = discriminator, stateModifier = StateModifier.USER)
+    }
+
+    override fun onSystemChangedNickname(nickname: String): State {
+      return UserEnteredDiscriminator(
+        nickname = nickname,
+        discriminator = discriminator,
+        stateModifier = StateModifier.SYSTEM
+      )
+    }
+
+    override fun onSystemChangedDiscriminator(discriminator: String): State {
+      return UserEnteredNickname(
+        nickname = nickname,
+        discriminator = discriminator,
+        stateModifier = StateModifier.SYSTEM
+      )
+    }
+  }
+}
--- a/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditViewModel.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditViewModel.kt
@@ -5,9 +5,10 @@ import androidx.lifecycle.ViewModelProvider
 import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
 import io.reactivex.rxjava3.core.Flowable
 import io.reactivex.rxjava3.core.Observable
+import io.reactivex.rxjava3.core.Single
 import io.reactivex.rxjava3.disposables.CompositeDisposable
 import io.reactivex.rxjava3.kotlin.plusAssign
-import io.reactivex.rxjava3.processors.PublishProcessor
+import io.reactivex.rxjava3.kotlin.subscribeBy
 import io.reactivex.rxjava3.schedulers.Schedulers
 import io.reactivex.rxjava3.subjects.PublishSubject
 import org.signal.core.util.Result
@@ -15,6 +16,7 @@ import org.thoughtcrime.securesms.keyvalue.SignalStore
 import org.thoughtcrime.securesms.profiles.manage.UsernameRepository.UsernameDeleteResult
 import org.thoughtcrime.securesms.profiles.manage.UsernameRepository.UsernameSetResult
 import org.thoughtcrime.securesms.util.UsernameUtil.InvalidReason
+import org.thoughtcrime.securesms.util.UsernameUtil.checkDiscriminator
 import org.thoughtcrime.securesms.util.UsernameUtil.checkUsername
 import org.thoughtcrime.securesms.util.rx.RxStore
 import java.util.concurrent.TimeUnit
@@ -32,7 +34,6 @@ import java.util.concurrent.TimeUnit
 */
 internal class UsernameEditViewModel private constructor(private val isInRegistration: Boolean) : ViewModel() {
  private val events: PublishSubject<Event> = PublishSubject.create()
-  private val nicknamePublisher: PublishProcessor<String> = PublishProcessor.create()
  private val disposables: CompositeDisposable = CompositeDisposable()

  private val uiState: RxStore<State> = RxStore(
@@ -44,10 +45,23 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
    scheduler = Schedulers.computation()
  )

+  private val stateMachineStore = RxStore<UsernameEditStateMachine.State>(
+    defaultValue = UsernameEditStateMachine.NoUserEntry(
+      nickname = SignalStore.account().username?.split(UsernameState.DELIMITER)?.first() ?: "",
+      discriminator = SignalStore.account().username?.split(UsernameState.DELIMITER)?.last() ?: "",
+      stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM
+    ),
+    scheduler = Schedulers.computation()
+  )
+
+  val usernameInputState: Flowable<UsernameEditStateMachine.State> = stateMachineStore.stateFlowable.observeOn(AndroidSchedulers.mainThread())
+
  init {
-    disposables += nicknamePublisher
+    disposables += stateMachineStore
+      .stateFlowable
+      .filter { it.stateModifier == UsernameEditStateMachine.StateModifier.USER }
      .debounce(NICKNAME_PUBLISHER_DEBOUNCE_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)
-      .subscribe { nickname: String -> onNicknameUpdatedDebounced(nickname) }
+      .subscribeBy(onNext = this::onUsernameStateUpdateDebounced)
  }

  override fun onCleared() {
@@ -85,7 +99,31 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
      }
    }

-    nicknamePublisher.onNext(nickname)
+    stateMachineStore.update {
+      it.onUserChangedNickname(nickname)
+    }
+  }
+
+  fun onDiscriminatorUpdated(discriminator: String) {
+    uiState.update { state: State ->
+      if (discriminator.isBlank() && SignalStore.account().username != null) {
+        return@update State(
+          buttonState = if (isInRegistration) ButtonState.SUBMIT_DISABLED else ButtonState.DELETE,
+          usernameStatus = UsernameStatus.NONE,
+          username = UsernameState.NoUsername
+        )
+      }
+
+      State(
+        buttonState = ButtonState.SUBMIT_DISABLED,
+        usernameStatus = UsernameStatus.NONE,
+        username = state.username
+      )
+    }
+
+    stateMachineStore.update {
+      it.onUserChangedDiscriminator(discriminator)
+    }
  }

  fun onUsernameSkipped() {
@@ -94,26 +132,38 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
  }

  fun onUsernameSubmitted() {
+    val state = stateMachineStore.state
+
+    if (isCaseChange(state)) {
+      handleUserConfirmation(UsernameRepository::updateUsername)
+    } else {
+      handleUserConfirmation(UsernameRepository::confirmUsername)
+    }
+  }
+
+  private inline fun <reified T : UsernameState> handleUserConfirmation(
+    repositoryWorkerMethod: (T) -> Single<UsernameSetResult>
+  ) {
    val usernameState = uiState.state.username
-    if (usernameState !is UsernameState.Reserved) {
+    if (usernameState !is T) {
      uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.NONE, it.username) }
      return
    }

-    if (usernameState.username == SignalStore.account().username) {
+    if (usernameState.requireUsername() == SignalStore.account().username) {
      uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.NONE, it.username) }
      return
    }

    val invalidReason = checkUsername(usernameState.getNickname())
    if (invalidReason != null) {
-      uiState.update { State(ButtonState.SUBMIT_DISABLED, mapUsernameError(invalidReason), it.username) }
+      uiState.update { State(ButtonState.SUBMIT_DISABLED, mapNicknameError(invalidReason), it.username) }
      return
    }

    uiState.update { State(ButtonState.SUBMIT_LOADING, UsernameStatus.NONE, it.username) }

-    disposables += UsernameRepository.confirmUsername(usernameState).subscribe { result: UsernameSetResult ->
+    disposables += repositoryWorkerMethod(usernameState).subscribe { result: UsernameSetResult ->
      val nickname = usernameState.getNickname()

      when (result) {
@@ -169,19 +219,49 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
    return events.observeOn(AndroidSchedulers.mainThread())
  }

+  private fun isCaseChange(state: UsernameEditStateMachine.State): Boolean {
+    if (state is UsernameEditStateMachine.UserEnteredDiscriminator || state is UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator) {
+      return false
+    }
+
+    val newLower = state.nickname.lowercase()
+    val oldLower = SignalStore.account().username?.split(UsernameState.DELIMITER)?.firstOrNull()?.lowercase()
+
+    return newLower == oldLower
+  }
+
  /** Triggered when the debounced nickname event stream fires. */
-  private fun onNicknameUpdatedDebounced(nickname: String) {
+  private fun onUsernameStateUpdateDebounced(state: UsernameEditStateMachine.State) {
+    val nickname = state.nickname
    if (nickname.isBlank()) {
      return
    }

+    if (state is UsernameEditStateMachine.NoUserEntry || state.stateModifier == UsernameEditStateMachine.StateModifier.SYSTEM) {
+      return
+    }
+
+    if (isCaseChange(state)) {
+      val discriminator = SignalStore.account().username?.split(UsernameState.DELIMITER)?.lastOrNull() ?: error("Unexpected case change, no discriminator!")
+      uiState.update {
+        State(
+          buttonState = ButtonState.SUBMIT,
+          usernameStatus = UsernameStatus.NONE,
+          username = UsernameState.CaseChange("${state.nickname}${UsernameState.DELIMITER}$discriminator")
+        )
+      }
+
+      stateMachineStore.update { s -> s.onSystemChangedDiscriminator(discriminator) }
+      return
+    }
+
    val invalidReason: InvalidReason? = checkUsername(nickname)
    if (invalidReason != null) {
-      uiState.update { state ->
+      uiState.update { uiState ->
        State(
          buttonState = ButtonState.SUBMIT_DISABLED,
-          usernameStatus = mapUsernameError(invalidReason),
-          username = state.username
+          usernameStatus = mapNicknameError(invalidReason),
+          username = uiState.username
        )
      }
      return
@@ -189,26 +269,60 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr

    uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.NONE, UsernameState.Loading) }

-    disposables += UsernameRepository.reserveUsername(nickname).subscribe { result: Result<UsernameState.Reserved, UsernameSetResult> ->
+    val isDiscriminatorSetByUser = state is UsernameEditStateMachine.UserEnteredDiscriminator || state is UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator
+    val discriminator = if (isDiscriminatorSetByUser) {
+      state.discriminator
+    } else {
+      null
+    }
+
+    val discriminatorInvalidReason = checkDiscriminator(discriminator)
+    if (isDiscriminatorSetByUser && discriminatorInvalidReason != null) {
+      uiState.update { s ->
+        State(
+          buttonState = ButtonState.SUBMIT_DISABLED,
+          usernameStatus = mapDiscriminatorError(discriminatorInvalidReason),
+          username = s.username
+        )
+      }
+      return
+    }
+
+    disposables += UsernameRepository.reserveUsername(nickname, discriminator).subscribe { result: Result<UsernameState.Reserved, UsernameSetResult> ->
      result.either(
        onSuccess = { reserved: UsernameState.Reserved ->
          uiState.update { State(ButtonState.SUBMIT, UsernameStatus.NONE, reserved) }
+
+          val d = reserved.getDiscriminator()
+          if (!isDiscriminatorSetByUser && d != null) {
+            stateMachineStore.update { s -> s.onSystemChangedDiscriminator(d) }
+          }
        },
        onFailure = { failure: UsernameSetResult ->
          when (failure) {
            UsernameSetResult.SUCCESS -> {
              throw AssertionError()
            }
+
            UsernameSetResult.USERNAME_INVALID -> {
              uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.INVALID_GENERIC, UsernameState.NoUsername) }
            }
+
            UsernameSetResult.USERNAME_UNAVAILABLE -> {
-              uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.TAKEN, UsernameState.NoUsername) }
+              val status = if (isDiscriminatorSetByUser) {
+                UsernameStatus.DISCRIMINATOR_NOT_AVAILABLE
+              } else {
+                UsernameStatus.TAKEN
              }
+
+              uiState.update { State(ButtonState.SUBMIT_DISABLED, status, UsernameState.NoUsername) }
+            }
+
            UsernameSetResult.NETWORK_ERROR -> {
              uiState.update { State(ButtonState.SUBMIT, UsernameStatus.NONE, UsernameState.NoUsername) }
              events.onNext(Event.NETWORK_FAILURE)
            }
+
            UsernameSetResult.CANDIDATE_GENERATION_ERROR -> {
              // TODO -- Retry
              uiState.update { State(ButtonState.SUBMIT_DISABLED, UsernameStatus.TAKEN, UsernameState.NoUsername) }
@@ -226,7 +340,17 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
  )

  enum class UsernameStatus {
-    NONE, TAKEN, TOO_SHORT, TOO_LONG, CANNOT_START_WITH_NUMBER, INVALID_CHARACTERS, INVALID_GENERIC
+    NONE,
+    TAKEN,
+    TOO_SHORT,
+    TOO_LONG,
+    CANNOT_START_WITH_NUMBER,
+    INVALID_CHARACTERS,
+    INVALID_GENERIC,
+    DISCRIMINATOR_NOT_AVAILABLE,
+    DISCRIMINATOR_TOO_SHORT,
+    DISCRIMINATOR_TOO_LONG,
+    DISCRIMINATOR_HAS_INVALID_CHARACTERS
  }

  enum class ButtonState {
@@ -246,7 +370,7 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
  companion object {
    private const val NICKNAME_PUBLISHER_DEBOUNCE_TIMEOUT_MILLIS: Long = 1000

-    private fun mapUsernameError(invalidReason: InvalidReason): UsernameStatus {
+    private fun mapNicknameError(invalidReason: InvalidReason): UsernameStatus {
      return when (invalidReason) {
        InvalidReason.TOO_SHORT -> UsernameStatus.TOO_SHORT
        InvalidReason.TOO_LONG -> UsernameStatus.TOO_LONG
@@ -255,5 +379,14 @@ internal class UsernameEditViewModel private constructor(private val isInRegistr
        else -> UsernameStatus.INVALID_GENERIC
      }
    }
+
+    private fun mapDiscriminatorError(invalidReason: InvalidReason): UsernameStatus {
+      return when (invalidReason) {
+        InvalidReason.TOO_SHORT -> UsernameStatus.DISCRIMINATOR_TOO_SHORT
+        InvalidReason.TOO_LONG -> UsernameStatus.DISCRIMINATOR_TOO_LONG
+        InvalidReason.INVALID_CHARACTERS -> UsernameStatus.DISCRIMINATOR_HAS_INVALID_CHARACTERS
+        else -> UsernameStatus.INVALID_GENERIC
+      }
+    }
  }
 }
--- a/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameRepository.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameRepository.kt
@@ -88,12 +88,21 @@ object UsernameRepository {

  private val accountManager: SignalServiceAccountManager get() = ApplicationDependencies.getSignalServiceAccountManager()

+  /**
+   * Given a username, update the username link, given that all was changed was the casing of the nickname.
+   */
+  fun updateUsername(caseChange: UsernameState.CaseChange): Single<UsernameSetResult> {
+    return Single
+      .fromCallable { updateUsernameInternal(caseChange) }
+      .subscribeOn(Schedulers.io())
+  }
+
  /**
   * Given a nickname, this will temporarily reserve a matching discriminator that can later be confirmed via [confirmUsername].
   */
-  fun reserveUsername(nickname: String): Single<Result<UsernameState.Reserved, UsernameSetResult>> {
+  fun reserveUsername(nickname: String, discriminator: String?): Single<Result<UsernameState.Reserved, UsernameSetResult>> {
    return Single
-      .fromCallable { reserveUsernameInternal(nickname) }
+      .fromCallable { reserveUsernameInternal(nickname, discriminator) }
      .subscribeOn(Schedulers.io())
  }

@@ -295,9 +304,13 @@ object UsernameRepository {
  }

  @WorkerThread
-  private fun reserveUsernameInternal(nickname: String): Result<UsernameState.Reserved, UsernameSetResult> {
+  private fun reserveUsernameInternal(nickname: String, discriminator: String?): Result<UsernameState.Reserved, UsernameSetResult> {
    return try {
-      val candidates: List<Username> = Username.candidatesFrom(nickname, UsernameUtil.MIN_LENGTH, UsernameUtil.MAX_LENGTH)
+      val candidates: List<Username> = if (discriminator == null) {
+        Username.candidatesFrom(nickname, UsernameUtil.MIN_NICKNAME_LENGTH, UsernameUtil.MAX_NICKNAME_LENGTH)
+      } else {
+        listOf(Username("$nickname${UsernameState.DELIMITER}$discriminator"))
+      }

      val hashes: List<String> = candidates
        .map { Base64.encodeUrlSafeWithoutPadding(it.hash) }
@@ -327,6 +340,31 @@ object UsernameRepository {
    }
  }

+  @WorkerThread
+  private fun updateUsernameInternal(caseChange: UsernameState.CaseChange): UsernameSetResult {
+    return try {
+      val oldUsernameLink = SignalStore.account().usernameLink ?: return UsernameSetResult.USERNAME_INVALID
+      val username = Username(caseChange.username)
+      val newUsernameLink = username.generateLink(oldUsernameLink.entropy)
+      val usernameLinkComponents = accountManager.updateUsernameLink(newUsernameLink)
+
+      SignalStore.account().username = username.username
+      SignalStore.account().usernameLink = usernameLinkComponents
+      SignalDatabase.recipients.setUsername(Recipient.self().id, username.username)
+      SignalStore.account().usernameSyncState = AccountValues.UsernameSyncState.IN_SYNC
+      SignalStore.account().usernameSyncErrorCount = 0
+
+      SignalDatabase.recipients.markNeedsSync(Recipient.self().id)
+      StorageSyncHelper.scheduleSyncForDataChange()
+      Log.i(TAG, "[updateUsername] Successfully updated username.")
+
+      UsernameSetResult.SUCCESS
+    } catch (e: IOException) {
+      Log.w(TAG, "[updateUsername] Generic network exception.", e)
+      UsernameSetResult.NETWORK_ERROR
+    }
+  }
+
  @WorkerThread
  private fun confirmUsernameInternal(reserved: UsernameState.Reserved): UsernameSetResult {
    return try {
--- a/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameState.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/profiles/manage/UsernameState.kt
@@ -10,6 +10,8 @@ sealed class UsernameState {
  protected open val username: String? = null
  open val isInProgress: Boolean = false

+  fun requireUsername(): String = username!!
+
  object Loading : UsernameState() {
    override val isInProgress: Boolean = true
  }
@@ -21,6 +23,10 @@ sealed class UsernameState {
    val reserveUsernameResponse: ReserveUsernameResponse
  ) : UsernameState()

+  data class CaseChange(
+    public override val username: String
+  ) : UsernameState()
+
  data class Set(
    override val username: String
  ) : UsernameState()
--- a/app/src/main/java/org/thoughtcrime/securesms/util/UsernameUtil.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/util/UsernameUtil.kt
@@ -6,9 +6,11 @@ import java.util.regex.Pattern

 object UsernameUtil {
  private val TAG = Log.tag(UsernameUtil::class.java)
-  const val MIN_LENGTH = 3
-  const val MAX_LENGTH = 32
-  private val FULL_PATTERN = Pattern.compile(String.format(Locale.US, "^[a-zA-Z_][a-zA-Z0-9_]{%d,%d}$", MIN_LENGTH - 1, MAX_LENGTH - 1), Pattern.CASE_INSENSITIVE)
+  const val MIN_NICKNAME_LENGTH = 3
+  const val MAX_NICKNAME_LENGTH = 32
+  const val MIN_DISCRIMINATOR_LENGTH = 2
+  const val MAX_DISCRIMINATOR_LENGTH = 10
+  private val FULL_PATTERN = Pattern.compile(String.format(Locale.US, "^[a-zA-Z_][a-zA-Z0-9_]{%d,%d}$", MIN_NICKNAME_LENGTH - 1, MAX_NICKNAME_LENGTH - 1), Pattern.CASE_INSENSITIVE)
  private val DIGIT_START_PATTERN = Pattern.compile("^[0-9].*$")
  private const val BASE_URL_SCHEMELESS = "signal.me/#eu/"
  private const val BASE_URL = "https://$BASE_URL_SCHEMELESS"
@@ -17,8 +19,8 @@ object UsernameUtil {
    String.format(
      Locale.US,
      "^@?[a-zA-Z_][a-zA-Z0-9_]{%d,%d}(.[0-9]+)?$",
-      MIN_LENGTH - 1,
-      MAX_LENGTH - 1,
+      MIN_NICKNAME_LENGTH - 1,
+      MAX_NICKNAME_LENGTH - 1,
      Pattern.CASE_INSENSITIVE
    )
  )
@@ -39,10 +41,10 @@ object UsernameUtil {
      value == null -> {
        InvalidReason.TOO_SHORT
      }
-      value.length < MIN_LENGTH -> {
+      value.length < MIN_NICKNAME_LENGTH -> {
        InvalidReason.TOO_SHORT
      }
-      value.length > MAX_LENGTH -> {
+      value.length > MAX_NICKNAME_LENGTH -> {
        InvalidReason.TOO_LONG
      }
      DIGIT_START_PATTERN.matcher(value).matches() -> {
@@ -57,6 +59,26 @@ object UsernameUtil {
    }
  }

+  fun checkDiscriminator(value: String?): InvalidReason? {
+    return when {
+      value == null -> {
+        null
+      }
+      value.length < MIN_DISCRIMINATOR_LENGTH -> {
+        InvalidReason.TOO_SHORT
+      }
+      value.length > MAX_DISCRIMINATOR_LENGTH -> {
+        InvalidReason.TOO_LONG
+      }
+      value.toIntOrNull() == null -> {
+        InvalidReason.INVALID_CHARACTERS
+      }
+      else -> {
+        null
+      }
+    }
+  }
+
  enum class InvalidReason {
    TOO_SHORT,
    TOO_LONG,
--- a/app/src/main/res/layout/username_edit_fragment.xml
+++ b/app/src/main/res/layout/username_edit_fragment.xml
@@ -35,24 +35,34 @@
        app:srcCompat="@drawable/symbol_at_24"
        app:tint="@color/signal_colorOnSurface" />

+    <View
+        android:id="@+id/username_box_fill"
+        android:layout_width="0dp"
+        android:layout_height="0dp"
+        android:background="@color/signal_colorSurfaceVariant"
+        app:layout_constraintBottom_toBottomOf="@id/username_text_wrapper"
+        app:layout_constraintEnd_toEndOf="@id/discriminator_text"
+        app:layout_constraintStart_toStartOf="@id/username_text_wrapper"
+        app:layout_constraintTop_toTopOf="@id/username_text_wrapper" />
+
    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/username_text_wrapper"
        style="@style/Widget.Signal.TextInputLayout"
-        android:layout_width="match_parent"
+        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="@dimen/dsl_settings_gutter"
        android:layout_marginTop="24dp"
-        android:layout_marginEnd="@dimen/dsl_settings_gutter"
+        android:layout_marginEnd="16dp"
        app:boxStrokeColor="@color/signal_colorPrimary"
-        app:boxStrokeWidthFocused="2dp"
+        app:boxStrokeWidth="0dp"
+        app:boxStrokeWidthFocused="0dp"
        app:errorTextAppearance="@style/Signal.Text.Zero"
        app:expandedHintEnabled="false"
-        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constrainedWidth="true"
+        app:layout_constraintEnd_toStartOf="@id/suffix_progress"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/summary"
-        app:suffixTextColor="@color/signal_colorOnSurface"
-        tools:errorEnabled="true"
-        tools:suffixText="| .1234">
+        app:suffixTextColor="@color/signal_colorOnSurface">

        <EditText
            android:id="@+id/username_text"
@@ -60,7 +70,7 @@
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="@string/UsernameEditFragment_username"
-            android:imeOptions="actionDone"
+            android:imeOptions="actionNext"
            android:importantForAutofill="no"
            android:inputType="text"
            android:maxLines="1"
@@ -71,18 +81,54 @@

    </com.google.android.material.textfield.TextInputLayout>

+    <EditText
+        android:id="@+id/discriminator_text"
+        style="@style/Signal.Text.Body"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginEnd="@dimen/dsl_settings_gutter"
+        android:background="@null"
+        android:hint="@string/UsernameEditFragment__00"
+        android:imeOptions="actionDone"
+        android:importantForAutofill="no"
+        android:inputType="number"
+        android:maxLines="1"
+        android:paddingHorizontal="16dp"
+        android:minHeight="48dp"
+        app:layout_constrainedWidth="true"
+        app:layout_constraintBottom_toBottomOf="@id/username_text_wrapper"
+        app:layout_constraintEnd_toEndOf="parent"
+        tools:text="21" />
+
    <com.google.android.material.progressindicator.CircularProgressIndicator
        android:id="@+id/suffix_progress"
        android:layout_width="16dp"
        android:layout_height="16dp"
-        android:layout_marginEnd="16dp"
        android:layout_marginBottom="10dp"
-        app:layout_constraintEnd_toEndOf="@id/username_text_wrapper"
-        app:layout_constraintBottom_toBottomOf="@id/username_text_wrapper"
+        app:indicatorColor="@color/signal_colorOnSurfaceVariant"
        app:indicatorSize="16dp"
-        app:trackThickness="1dp"
+        app:layout_constraintBottom_toBottomOf="@id/username_text_wrapper"
+        app:layout_constraintEnd_toStartOf="@id/discriminator_text"
        app:trackColor="@color/transparent"
-        app:indicatorColor="@color/signal_colorOnSurfaceVariant"/>
+        app:trackThickness="1dp" />
+
+    <View
+        android:id="@+id/divider"
+        android:layout_width="1dp"
+        android:layout_height="20dp"
+        android:background="@color/signal_colorOutline"
+        app:layout_constraintBottom_toBottomOf="@id/discriminator_text"
+        app:layout_constraintStart_toStartOf="@id/discriminator_text"
+        app:layout_constraintTop_toTopOf="@id/discriminator_text" />
+
+    <View
+        android:id="@+id/username_text_focused_stroke"
+        android:layout_width="0dp"
+        android:layout_height="2dp"
+        android:background="@color/signal_colorPrimary"
+        app:layout_constraintBottom_toBottomOf="@id/username_text_wrapper"
+        app:layout_constraintEnd_toEndOf="@id/discriminator_text"
+        app:layout_constraintStart_toStartOf="@id/username_text_wrapper" />

    <TextView
        android:id="@+id/username_error"
@@ -92,8 +138,8 @@
        android:textAppearance="@style/Signal.Text.BodyMedium"
        android:textColor="@color/signal_colorError"
        android:visibility="gone"
-        app:layout_constraintStart_toStartOf="@id/username_description"
        app:layout_constraintEnd_toEndOf="@id/username_description"
+        app:layout_constraintStart_toStartOf="@id/username_description"
        app:layout_constraintTop_toBottomOf="@id/username_text_wrapper"
        tools:text="Error something bad happened. Very super long error message that wraps"
        tools:visibility="visible" />
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -2202,6 +2202,8 @@
    <string name="UnverifiedSendDialog_send">Send</string>

    <!-- UsernameEditFragment -->
+    <!-- Placeholder text for custom discriminator -->
+    <string name="UsernameEditFragment__00">00</string>
    <!-- Toolbar title when entering from registration -->
    <string name="UsernameEditFragment__add_a_username">Add a username</string>
    <!-- Instructional text at the top of the username edit screen -->
@@ -2224,6 +2226,12 @@
    <string name="UsernameEditFragment__skip">Skip</string>
    <!-- Content description for done button -->
    <string name="UsernameEditFragment__done">Done</string>
+    <!-- Displayed when the chosen discriminator is not available for the given nickname -->
+    <string name="UsernameEditFragment__this_username_is_not_available_try_another_number">This username is not available, try another number.</string>
+    <!-- Displayed when the chosen discriminator is too short -->'
+    <string name="UsernameEditFragment__invalid_username_enter_a_minimum_of_d_digits">Invalid username, enter a minimum of %1$d digits.</string>
+    <!-- Displayed when the chosen discriminator is too long -->'
+    <string name="UsernameEditFragment__invalid_username_enter_a_maximum_of_d_digits">Invalid username, enter a maximum of %1$d digits.</string>

    <plurals name="UserNotificationMigrationJob_d_contacts_are_on_signal">
        <item quantity="one">%d contact is on Signal!</item>
--- a/app/src/test/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditStateMachineTest.kt
+++ b/app/src/test/java/org/thoughtcrime/securesms/profiles/manage/UsernameEditStateMachineTest.kt
@@ -0,0 +1,376 @@
+package org.thoughtcrime.securesms.profiles.manage
+
+import org.junit.Test
+import org.thoughtcrime.securesms.assertIs
+
+class UsernameEditStateMachineTest {
+  @Test
+  fun `Given NoUserEntry, when user clears the username field, then I expect NoUserEntry with empty username and copied discriminator`() {
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = "MilesMorales", discriminator = "07", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = "", discriminator = "07", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when user enters text into the username field, then I expect UserEnteredNickname with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when user clears the discriminator field, then I expect NoUserEntry with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when user enters text into the discriminator field, then I expect UserEnteredDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when system clears the username field, then I expect NoUserEntry with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when system enters text into the username field, then I expect NoUserEntry with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when system clears the discriminator field, then I expect NoUserEntry with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given NoUserEntry, when system enters text into the discriminator field, then I expect UserEnteredDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when user clears the username field, then I expect NoUserEntry with empty username and copied discriminator`() {
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = "MilesMorales", discriminator = "07", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = "", discriminator = "07", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when user enters text into the username field, then I expect UserEnteredNickname with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when user clears the discriminator field, then I expect UserEnteredNickname with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when user enters text into the discriminator field, then I expect UserEnteredNicknameAndDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when system clears the username field, then I expect NoUserEntry with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when system enters text into the username field, then I expect NoUserEntry with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when system clears the discriminator field, then I expect UserEnteredNickname with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNickname, when system enters text into the discriminator field, then I expect UserEnteredDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when user clears the username field, then I expect NoUserEntry with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when user enters text into the username field, then I expect UserEnteredNicknameAndDiscriminator with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator with an empty discriminator, when user enters text into the username field, then I expect UserEnteredNickname with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = ""
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when user clears the discriminator field, then I expect UserEnteredDiscriminator with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when user enters text into the discriminator field, then I expect UserEnteredDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when system clears the username field, then I expect UserEnteredDiscriminator with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when system enters text into the username field, then I expect UserEnteredDiscriminator with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when system clears the discriminator field, then I expect NoUserEntry with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredDiscriminator, when system enters text into the discriminator field, then I expect NoUserEntry with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.NoUserEntry(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when user clears the username field, then I expect UserEnteredDiscriminator with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when user enters text into the username field, then I expect UserEnteredNicknameAndDiscriminator with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator with empty discriminator, when user enters text into the username field, then I expect UserEnteredNickname with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = ""
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when user clears the discriminator field, then I expect UserEnteredNicknameAndDiscriminator with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when user enters text into the discriminator field, then I expect UserEnteredNicknameAndDiscriminator with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val expected = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val actual = given.onUserChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when system clears the username field, then I expect UserEnteredDiscriminator with empty username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = "", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when system enters text into the username field, then I expect NoUserEntry with given username and copied discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = "MilesMorales", discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedNickname(nickname)
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when system clears the discriminator field, then I expect UserEnteredNickname with given username and empty discriminator`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = "", stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator("")
+
+    actual assertIs expected
+  }
+
+  @Test
+  fun `Given UserEnteredNicknameAndDiscriminator, when system enters text into the discriminator field, then I expect NoUserEntry with given discriminator and copied nickname`() {
+    val nickname = "Nick"
+    val discriminator = "07"
+    val given = UsernameEditStateMachine.UserEnteredNicknameAndDiscriminator(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.USER)
+    val expected = UsernameEditStateMachine.UserEnteredNickname(nickname = nickname, discriminator = discriminator, stateModifier = UsernameEditStateMachine.StateModifier.SYSTEM)
+    val actual = given.onSystemChangedDiscriminator(discriminator)
+
+    actual assertIs expected
+  }
+}
--- a/libsignal-service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java
+++ b/libsignal-service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java
@@ -787,6 +787,12 @@ public class SignalServiceAccountManager {
    this.pushServiceSocket.confirmUsername(username, reserveUsernameResponse);
  }

+  public UsernameLinkComponents updateUsernameLink(UsernameLink newUsernameLink) throws IOException {
+      UUID serverId = this.pushServiceSocket.createUsernameLink(Base64.encodeUrlSafeWithoutPadding(newUsernameLink.getEncryptedUsername()), true);
+
+      return new UsernameLinkComponents(newUsernameLink.getEntropy(), serverId);
+  }
+
  public void deleteUsername() throws IOException {
    this.pushServiceSocket.deleteUsername();
  }
@@ -794,7 +800,7 @@ public class SignalServiceAccountManager {
  public UsernameLinkComponents createUsernameLink(Username username) throws IOException {
    try {
      UsernameLink link     = username.generateLink();
-      UUID         serverId = this.pushServiceSocket.createUsernameLink(Base64.encodeUrlSafeWithPadding(link.getEncryptedUsername()));
+      UUID         serverId = this.pushServiceSocket.createUsernameLink(Base64.encodeUrlSafeWithPadding(link.getEncryptedUsername()), false);

      return new UsernameLinkComponents(link.getEntropy(), serverId);
    } catch (BaseUsernameException e) {
--- a/libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java
+++ b/libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java
@@ -1147,8 +1147,8 @@ public class PushServiceSocket {
   * @param encryptedUsername URL-safe base64-encoded encrypted username
   * @return The serverId for the generated link.
   */
-  public UUID createUsernameLink(String encryptedUsername) throws IOException {
-    String                      response = makeServiceRequest(USERNAME_LINK_PATH, "PUT", JsonUtil.toJson(new SetUsernameLinkRequestBody(encryptedUsername)));
+  public UUID createUsernameLink(String encryptedUsername, boolean keepLinkHandle) throws IOException {
+    String                      response = makeServiceRequest(USERNAME_LINK_PATH, "PUT", JsonUtil.toJson(new SetUsernameLinkRequestBody(encryptedUsername, keepLinkHandle)));
    SetUsernameLinkResponseBody parsed   = JsonUtil.fromJson(response, SetUsernameLinkResponseBody.class);

    return parsed.getUsernameLinkHandle();
--- a/libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/SetUsernameLinkRequestBody.kt
+++ b/libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/SetUsernameLinkRequestBody.kt
@@ -3,4 +3,4 @@ package org.whispersystems.signalservice.internal.push
 import com.fasterxml.jackson.annotation.JsonProperty

 /** Request body for setting a username link on the service. */
-data class SetUsernameLinkRequestBody(@JsonProperty val usernameLinkEncryptedValue: String)
+data class SetUsernameLinkRequestBody(@JsonProperty val usernameLinkEncryptedValue: String, @JsonProperty val keepLinkHandle: Boolean)