Add UI and logic for displaying redirect suggestion on the BAD_URL error page

app/src/main/java/com/duckduckgo/app/browser/BrowserTabFragment.kt

@@ -40,6 +40,8 @@ import android.print.PrintDocumentAdapter
 import android.print.PrintManager
 import android.provider.MediaStore
 import android.text.Spanned
+import android.text.SpannedString
+import android.text.TextUtils
 import android.view.ContextMenu
 import android.view.ContextThemeWrapper
 import android.view.LayoutInflater
@@ -179,6 +181,7 @@ import com.duckduckgo.app.browser.print.PrintDocumentAdapterFactory
 import com.duckduckgo.app.browser.print.PrintInjector
 import com.duckduckgo.app.browser.session.WebViewSessionStorage
 import com.duckduckgo.app.browser.shortcut.ShortcutBuilder
+import com.duckduckgo.app.browser.suggestredirect.RedirectSuggestion
 import com.duckduckgo.app.browser.tabpreview.WebViewPreviewGenerator
 import com.duckduckgo.app.browser.tabpreview.WebViewPreviewPersister
 import com.duckduckgo.app.browser.ui.dialogs.AutomaticFireproofDialogOptions
@@ -293,6 +296,7 @@ import com.duckduckgo.common.ui.menu.PopupMenu
 import com.duckduckgo.common.ui.store.BrowserAppTheme
 import com.duckduckgo.common.ui.tabs.SwipingTabsFeatureProvider
 import com.duckduckgo.common.ui.view.DaxDialog
+import com.duckduckgo.common.ui.view.addClickableLink
 import com.duckduckgo.common.ui.view.dialog.ActionBottomSheetDialog
 import com.duckduckgo.common.ui.view.dialog.CustomAlertDialogBuilder
 import com.duckduckgo.common.ui.view.dialog.DaxAlertDialog
@@ -1314,6 +1318,7 @@ class BrowserTabFragment :
                 errorView.yetiIcon.isSaveEnabled = false
                 errorView.errorTitle.isSaveEnabled = false
                 errorView.errorMessage.isSaveEnabled = false
+                errorView.redirectSuggestionMessage.isSaveEnabled = false
 
                 omnibar.disableViewStateSaving()
                 sslErrorView.disableViewStateSaving()
@@ -2373,6 +2378,7 @@ class BrowserTabFragment :
         newBrowserTab.newTabRootLayout.gone()
         sslErrorView.gone()
         maliciousWarningView.gone()
+        renderRedirectSuggestion(viewModel.browserViewState.value?.redirectSuggestion)
         hidePdf()
         omnibar.setViewMode(ViewMode.Error)
         webView?.onPause()
@@ -2388,6 +2394,21 @@ class BrowserTabFragment :
         browserNavigationBarIntegration.configureBrowserViewMode()
     }
 
+    private fun renderRedirectSuggestion(suggestion: RedirectSuggestion?) {
+        if (suggestion == null) {
+            errorView.redirectSuggestionMessage.gone()
+            return
+        }
+        // Use expandTemplate(), getString() would otherwise strip the annotation altogether
+        val message = SpannedString(TextUtils.expandTemplate(getText(R.string.webViewErrorRedirectSuggestionMessage), suggestion.domain))
+        with(errorView.redirectSuggestionMessage) {
+            addClickableLink("redirect_link", message) {
+                viewModel.onRedirectSuggestionClicked(suggestion.url)
+            }
+            show()
+        }
+    }
+
     private fun showDuckAI(browserViewState: BrowserViewState) {
         renderBrowserMenu(viewState = browserViewState, omnibarViewMode = ViewMode.DuckAI)
         omnibar.setViewMode(ViewMode.DuckAI)
@@ -6104,6 +6125,7 @@ class BrowserTabFragment :
                 val browserShowing = viewState.browserShowing
                 val browserShowingChanged = viewState.browserShowing != lastSeenBrowserViewState?.browserShowing
                 val errorChanged = viewState.browserError != lastSeenBrowserViewState?.browserError
+                val redirectSuggestionChanged = viewState.redirectSuggestion != lastSeenBrowserViewState?.redirectSuggestion
                 val sslErrorChanged = viewState.sslError != lastSeenBrowserViewState?.sslError
 
                 lastSeenBrowserViewState = viewState
@@ -6131,6 +6153,8 @@ class BrowserTabFragment :
                             showHome()
                         }
                     }
+                } else if (redirectSuggestionChanged) {
+                    renderRedirectSuggestion(viewState.redirectSuggestion)
                 }
 
                 omnibar.renderBrowserViewState(viewState)

app/src/main/java/com/duckduckgo/app/browser/BrowserTabViewModel.kt

@@ -63,6 +63,7 @@ import com.duckduckgo.app.browser.SpecialUrlDetector.UrlType.AppLink
 import com.duckduckgo.app.browser.SpecialUrlDetector.UrlType.NonHttpAppLink
 import com.duckduckgo.app.browser.SpecialUrlDetector.UrlType.ShouldLaunchDuckChatLink
 import com.duckduckgo.app.browser.SpecialUrlDetector.UrlType.ShouldLaunchSubscriptionLink
+import com.duckduckgo.app.browser.WebViewErrorResponse.BAD_URL
 import com.duckduckgo.app.browser.WebViewErrorResponse.LOADING
 import com.duckduckgo.app.browser.WebViewErrorResponse.OMITTED
 import com.duckduckgo.app.browser.addtohome.AddToHomeCapabilityDetector
@@ -222,6 +223,8 @@ import com.duckduckgo.app.browser.progressbar.ProgressBarUpgradeFeature
 import com.duckduckgo.app.browser.refreshpixels.RefreshPixelSender
 import com.duckduckgo.app.browser.santize.NonHttpAppLinkChecker
 import com.duckduckgo.app.browser.session.WebViewSessionStorage
+import com.duckduckgo.app.browser.suggestredirect.SuggestRedirectEvaluator
+import com.duckduckgo.app.browser.suggestredirect.SuggestRedirectOnUnresolvedErrorFeature
 import com.duckduckgo.app.browser.tabs.TabManager
 import com.duckduckgo.app.browser.uilock.BROWSER_UI_LOCK_FEATURE_NAME
 import com.duckduckgo.app.browser.uilock.BrowserUiLockFeature
@@ -591,6 +594,8 @@ class BrowserTabViewModel @Inject constructor(
     private val adBlockingOmnibarAnimationProvider: AdBlockingOmnibarAnimationProvider,
     private val newTabPageModalPresenterRegistry: NewTabPageModalPresenterRegistry,
     private val newTabPageModalTrigger: NewTabPageModalTrigger,
+    private val suggestRedirectOnUnresolvedErrorFeature: SuggestRedirectOnUnresolvedErrorFeature,
+    private val suggestRedirectEvaluator: SuggestRedirectEvaluator,
 ) : ViewModel(),
     WebViewClientListener,
     EditSavedSiteListener,
@@ -742,6 +747,7 @@ class BrowserTabViewModel @Inject constructor(
     private var autoCompleteJob = ConflatedJob()
     private var serpLogoJob = ConflatedJob()
     private var pdfDownloadJob = ConflatedJob()
+    private var suggestRedirectJob = ConflatedJob()
 
     private var site: Site? = null
         set(value) {
@@ -1588,10 +1594,12 @@ class BrowserTabViewModel @Inject constructor(
                 queryOrFullUrl = if (isDuckChatUrl) "" else trimmedInput,
                 forceExpand = true,
             )
+        suggestRedirectJob.cancel()
         browserViewState.value =
             currentBrowserViewState().copy(
                 browserShowing = true,
                 browserError = OMITTED,
+                redirectSuggestion = null,
                 sslError = NONE,
                 maliciousSiteBlocked = false,
                 maliciousSiteStatus = null,
@@ -1943,6 +1951,7 @@ class BrowserTabViewModel @Inject constructor(
             duckChat.endVoiceChatSession(tabId)
         }
         pdfDownloadJob.cancel()
+        suggestRedirectJob.cancel()
         site = null
         onSiteChanged()
         webNavigationState = null
@@ -4451,14 +4460,16 @@ class BrowserTabViewModel @Inject constructor(
     }
 
     fun resetBrowserError() {
-        browserViewState.value = currentBrowserViewState().copy(browserError = OMITTED)
+        suggestRedirectJob.cancel()
+        browserViewState.value = currentBrowserViewState().copy(browserError = OMITTED, redirectSuggestion = null)
         // Catches the race where pageFinished fired while browserError was still LOADING.
         onDuckAiOnboardingPageFinishedIfApplicable()
     }
 
     fun refreshBrowserError() {
+        suggestRedirectJob.cancel()
         if (currentBrowserViewState().browserError != OMITTED && currentBrowserViewState().browserError != LOADING) {
-            browserViewState.value = currentBrowserViewState().copy(browserError = LOADING)
+            browserViewState.value = currentBrowserViewState().copy(browserError = LOADING, redirectSuggestion = null)
         }
         if (currentBrowserViewState().sslError != NONE) {
             browserViewState.value = currentBrowserViewState().copy(browserShowing = true, sslError = NONE)
@@ -4548,12 +4559,21 @@ class BrowserTabViewModel @Inject constructor(
             browserViewState.value =
                 currentBrowserViewState().copy(
                     browserError = errorType,
+                    redirectSuggestion = null,
                     showPrivacyShield = HighlightableButton.Visible(enabled = false),
                 )
             if (androidBrowserConfig.errorPagePixel().isEnabled()) {
                 pixel.enqueueFire(AppPixelName.ERROR_PAGE_SHOWN)
             }
             command.value = WebViewError(errorType, url)
+            suggestRedirectJob.cancel() // Cancel previous in-flight job as the new errorType might not be BAD_URL
+        }
+        if (errorType == BAD_URL && suggestRedirectOnUnresolvedErrorFeature.suggestRedirect().isEnabled()) {
+            suggestRedirectJob += viewModelScope.launch {
+                suggestRedirectEvaluator.suggestRedirect(url)?.let { suggestion ->
+                    browserViewState.value = currentBrowserViewState().copy(redirectSuggestion = suggestion)
+                }
+            }
         }
         if (androidBrowserConfig.errorCodePixel().isEnabled()) {
             pixel.enqueueFire(AppPixelName.ERROR_CODE_PIXEL, mapOf("error_code" to errorCode))
@@ -5797,6 +5817,11 @@ class BrowserTabViewModel @Inject constructor(
         }
     }
 
+    fun onRedirectSuggestionClicked(url: String) {
+        resetBrowserError()
+        command.value = NavigationCommand.Navigate(url, getUrlHeaders(url))
+    }
+
     private fun trackersCount(): String =
         siteLiveData.value?.trackerCount?.takeIf { it > 0 }?.toString() ?: ""
 

app/src/main/java/com/duckduckgo/app/browser/suggestredirect/SuggestRedirectEvaluator.kt

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2026 DuckDuckGo
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.duckduckgo.app.browser.suggestredirect
+
+import android.net.Uri
+import androidx.core.net.toUri
+import com.duckduckgo.common.utils.DispatcherProvider
+import com.duckduckgo.common.utils.extensions.toTldPlusOne
+import com.duckduckgo.di.scopes.AppScope
+import com.squareup.anvil.annotations.ContributesBinding
+import kotlinx.coroutines.withContext
+import javax.inject.Inject
+
+data class RedirectSuggestion(
+    val domain: String,
+    val url: String,
+)
+
+interface SuggestRedirectEvaluator {
+    /**
+     * Decides whether the error page for a failed [url] due to unresolved host should suggest
+     * redirecting to the "www." prefixed variant of its host.
+     *
+     * @return the suggestion to offer when [url] points at a bare domain (no "www." prefix)
+     * whose "www." variant resolves; `null` otherwise.
+     */
+    suspend fun suggestRedirect(url: String): RedirectSuggestion?
+}
+
+@ContributesBinding(AppScope::class)
+class RealSuggestRedirectEvaluator @Inject constructor(
+    private val hostnameResolver: HostnameResolver,
+    private val dispatcherProvider: DispatcherProvider,
+) : SuggestRedirectEvaluator {
+    override suspend fun suggestRedirect(url: String): RedirectSuggestion? = withContext(dispatcherProvider.io()) {
+        val uri = url.toUri()
+        val hostname = uri.host ?: return@withContext null
+
+        if (hostname.startsWith(WWW_PREFIX)) {
+            return@withContext null
+        }
+
+        if (hostname != hostname.toTldPlusOne()) {
+            // Non-registrable (eTLD+1) domains are rejected (e.g. localhost, a.b.domain.com)
+            return@withContext null
+        }
+
+        val suggestedDomain = "${WWW_PREFIX}$hostname"
+        if (!hostnameResolver.resolves(suggestedDomain)) {
+            return@withContext null
+        }
+
+        return@withContext RedirectSuggestion(
+            domain = suggestedDomain,
+            url = uri.replaceHost(suggestedDomain).toString(),
+        )
+    }
+
+    private fun Uri.replaceHost(host: String): Uri {
+        val authority = if (this.port != -1) "$host:${this.port}" else host
+        return this.buildUpon().encodedAuthority(authority).build()
+    }
+
+    companion object {
+        private const val WWW_PREFIX = "www."
+    }
+}

app/src/main/java/com/duckduckgo/app/browser/viewstate/BrowserViewState.kt

@@ -21,6 +21,7 @@ import com.duckduckgo.app.browser.SSLErrorType
 import com.duckduckgo.app.browser.SpecialUrlDetector
 import com.duckduckgo.app.browser.WebViewErrorResponse
 import com.duckduckgo.app.browser.omnibar.QueryOrigin
+import com.duckduckgo.app.browser.suggestredirect.RedirectSuggestion
 import com.duckduckgo.app.global.model.MaliciousSiteStatus
 import com.duckduckgo.browser.ui.browsermenu.VpnMenuState
 import com.duckduckgo.savedsites.api.models.SavedSite
@@ -55,6 +56,7 @@ data class BrowserViewState(
     val isPrinting: Boolean = false,
     val showAutofill: Boolean = false,
     val browserError: WebViewErrorResponse = WebViewErrorResponse.OMITTED,
+    val redirectSuggestion: RedirectSuggestion? = null,
     val sslError: SSLErrorType = SSLErrorType.NONE,
     val maliciousSiteBlocked: Boolean = false,
     val maliciousSiteStatus: MaliciousSiteStatus? = null,

app/src/main/res/layout/include_error_view.xml

@@ -71,5 +71,22 @@
             app:textType="secondary"
             tools:text="@string/webViewErrorBadUrl" />
 
+        <com.duckduckgo.common.ui.view.text.DaxTextView
+            android:id="@+id/redirect_suggestion_message"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="40dp"
+            android:layout_marginEnd="40dp"
+            android:gravity="center"
+            android:paddingBottom="@dimen/keyline_5"
+            android:visibility="gone"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@+id/error_message"
+            app:typography="body1"
+            app:textType="secondary"
+            tools:text="@string/webViewErrorRedirectSuggestionMessage"
+            tools:visibility="visible" />
+
     </androidx.constraintlayout.widget.ConstraintLayout>
 </ScrollView>

app/src/main/res/values/donottranslate.xml

@@ -24,6 +24,7 @@
     <string name="webViewErrorNoConnection">The internet connection appears to be offline.</string>
     <string name="webViewErrorBadUrl">A server with the specified hostname could not be found.</string>
     <string name="webViewErrorSslProtocol"><![CDATA[The certificate for this server is invalid. You might be connecting to a server that is pretending to be <b>%1$s</b> which could put your confidential information at risk.]]></string>
+    <string name="webViewErrorRedirectSuggestionMessage" instruction="Shown when a domain fails to load, offering a link to the www. version of the address. ^1 is the suggested address and is displayed as a tappable link.">Did you mean <annotation type="redirect_link">^1</annotation>?</string>
 
     <!-- Broken Sites-->
     <string name="brokenSitesLoginHint">What site are you signing in to? (required)</string>