feat: answer and hang up blocked calls so spam can't leave voicemail (#26)

An "Answer & hang up blocked calls" switch in Settings, off by default. A
call CallShield would reject is answered audio-only and ended after a delay
the user sets (1 to 10 seconds, default 1), so spam can't leave a voicemail.

- Applies only where the screening service would reject outright. Silent
  voicemail, low-confidence auto-mute and category voicemail actions keep
  their silence; with the switch off nothing changes.
- The screening response is sent first. A process-wide
  AnswerHangUpController arms for that number only, and a manifest
  PHONE_STATE receiver answers the matching ring and ends the call once it's
  off-hook, backed by a 250 ms call-state poll.
- Plain rejection is the fallback for a missing permission, an active call,
  audio in call or communication mode, a call already mid-answer, or any
  error. An outgoing call cancels a pending hang-up.
- ANSWER_PHONE_CALLS is requested by the switch, not at setup.
- Answered-caller trust and the repeated-urgent allow ignore incoming
  call-log rows under 15 seconds while the switch is on, so the short
  answered calls can't earn a spammer trust.
- Backup and restore carry both settings, with the delay clamped.

Tested by the contributor on an Android 15 emulator (adb emu gsm call) and a
Galaxy S23 Ultra on Android 14.

Refs #22.

Co-authored-by: Aows <nulledsender@gmail.com>

Author: tikkamasalla

app/src/main/AndroidManifest.xml

@@ -155,6 +155,14 @@
             android:taskAffinity=""
             android:theme="@android:style/Theme.NoDisplay" />
 
+        <receiver
+            android:name=".service.AnswerHangUpReceiver"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.PHONE_STATE" />
+            </intent-filter>
+        </receiver>
+
         <receiver
             android:name=".service.SmsReceiver"
             android:permission="android.permission.BROADCAST_SMS"

app/src/main/java/com/sysadmindoc/callshield/data/BackupRestore.kt

@@ -16,6 +16,7 @@ import com.sysadmindoc.callshield.data.model.RestoreJournal
 import com.sysadmindoc.callshield.data.model.SmsKeywordRule
 import com.sysadmindoc.callshield.data.model.WildcardRule
 import com.sysadmindoc.callshield.domain.model.BlockReasonCode
+import com.sysadmindoc.callshield.service.AnswerHangUpController
 import com.sysadmindoc.callshield.util.filterAsciiDigits
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.first
@@ -181,6 +182,8 @@ object BackupRestore {
         val rcsFilterEnabled: Boolean = true,
         val postCallScreenEnabled: Boolean = false,
         val silentVoicemailEnabled: Boolean = false,
+        val answerHangUpEnabled: Boolean = false,
+        val hangUpDelaySeconds: Int = AnswerHangUpController.DEFAULT_DELAY_SECONDS,
         val pushAlertEnabled: Boolean = true,
         val pushAlertDisabledPackages: List<String> = emptyList(),
         val regionBlockEnabled: Boolean = false,

app/src/main/java/com/sysadmindoc/callshield/data/BackupSettingsPreferences.kt

@@ -3,12 +3,19 @@ package com.sysadmindoc.callshield.data
 import androidx.datastore.preferences.core.MutablePreferences
 import androidx.datastore.preferences.core.Preferences
 import com.sysadmindoc.callshield.data.BackupRestore.BackupSettings
+import com.sysadmindoc.callshield.service.AnswerHangUpController
 
 // Settings half of a backup: reading the DataStore snapshot into a
 // BackupSettings, bounding what a (possibly hostile) backup carries, and
 // writing it back. Pure functions over Preferences, kept out of BackupRestore
 // so each file stays readable.
 
+internal fun clampHangUpDelaySeconds(value: Int?): Int =
+    value?.coerceIn(
+        AnswerHangUpController.MIN_DELAY_SECONDS,
+        AnswerHangUpController.MAX_DELAY_SECONDS,
+    ) ?: AnswerHangUpController.DEFAULT_DELAY_SECONDS
+
 @Suppress("LongMethod")
 internal fun Preferences.toBackupSettings(): BackupSettings =
     BackupSettings(
@@ -51,6 +58,8 @@ internal fun Preferences.toBackupSettings(): BackupSettings =
         rcsFilterEnabled = this[SpamRepository.KEY_RCS_FILTER] ?: true,
         postCallScreenEnabled = this[SpamRepository.KEY_POST_CALL_SCREEN] ?: false,
         silentVoicemailEnabled = this[SpamRepository.KEY_SILENT_VOICEMAIL] ?: false,
+        answerHangUpEnabled = this[SpamRepository.KEY_ANSWER_HANG_UP] ?: false,
+        hangUpDelaySeconds = clampHangUpDelaySeconds(this[SpamRepository.KEY_HANG_UP_DELAY_SECONDS]),
         pushAlertEnabled = this[SpamRepository.KEY_PUSH_ALERT] ?: true,
         pushAlertDisabledPackages = (this[SpamRepository.KEY_PUSH_ALERT_DISABLED] ?: emptySet()).sorted(),
         regionBlockEnabled = this[SpamRepository.KEY_REGION_BLOCK] ?: false,
@@ -94,6 +103,7 @@ internal fun BackupSettings.sanitized(): BackupSettings =
         timeBlockEndHour = BackupRestore.sanitizeScheduleHour(timeBlockEndHour),
         frequencyThreshold = frequencyThreshold.coerceIn(1, 25),
         cleanupDays = cleanupDays.coerceIn(1, 365),
+        hangUpDelaySeconds = clampHangUpDelaySeconds(hangUpDelaySeconds),
         pushAlertDisabledPackages =
             pushAlertDisabledPackages
                 .map { it.trim() }
@@ -162,6 +172,8 @@ internal fun BackupSettings.writeTo(preferences: MutablePreferences) {
     preferences[SpamRepository.KEY_RCS_FILTER] = rcsFilterEnabled
     preferences[SpamRepository.KEY_POST_CALL_SCREEN] = postCallScreenEnabled
     preferences[SpamRepository.KEY_SILENT_VOICEMAIL] = silentVoicemailEnabled
+    preferences[SpamRepository.KEY_ANSWER_HANG_UP] = answerHangUpEnabled
+    preferences[SpamRepository.KEY_HANG_UP_DELAY_SECONDS] = hangUpDelaySeconds
     preferences[SpamRepository.KEY_PUSH_ALERT] = pushAlertEnabled
     if (pushAlertDisabledPackages.isEmpty()) {
         preferences.remove(SpamRepository.KEY_PUSH_ALERT_DISABLED)

app/src/main/java/com/sysadmindoc/callshield/data/CallbackDetector.kt

@@ -83,14 +83,21 @@ class CallbackDetector
             windowMinutes: Int = 5,
             threshold: Int = 2,
             minRetryIntervalMillis: Long = MIN_URGENT_RETRY_INTERVAL_MILLIS,
+            minIncomingDurationSeconds: Int = 0,
         ): Boolean =
             withContext(Dispatchers.IO) {
                 val digits = filterAsciiDigitsLast(number, 10)
                 if (digits.length < 7) return@withContext false
                 val last7 = digits.takeLast(7)
 
                 try {
-                    val query = buildRepeatedUrgentCallQuery(System.currentTimeMillis(), windowMinutes, last7)
+                    val query =
+                        buildRepeatedUrgentCallQuery(
+                            nowMillis = System.currentTimeMillis(),
+                            windowMinutes = windowMinutes,
+                            last7Digits = last7,
+                            minIncomingDurationSeconds = minIncomingDurationSeconds,
+                        )
                     val cursor =
                         context.contentResolver.query(
                             CallLog.Calls.CONTENT_URI,
@@ -251,15 +258,32 @@ class CallbackDetector
             nowMillis: Long,
             windowMinutes: Int,
             last7Digits: String,
+            minIncomingDurationSeconds: Int = 0,
         ): CallLogQuery {
             val safeWindowMinutes = windowMinutes.coerceAtLeast(1)
             val cutoff = (nowMillis - safeWindowMinutes * 60_000L).toString()
+            if (minIncomingDurationSeconds <= 0) {
+                return CallLogQuery(
+                    selection = "${CallLog.Calls.TYPE} IN (?, ?) AND ${CallLog.Calls.DATE} > ? AND ${CallLog.Calls.NUMBER} LIKE ?",
+                    selectionArgs =
+                        arrayOf(
+                            CallLog.Calls.INCOMING_TYPE.toString(),
+                            CallLog.Calls.MISSED_TYPE.toString(),
+                            cutoff,
+                            "%$last7Digits",
+                        ),
+                )
+            }
             return CallLogQuery(
-                selection = "${CallLog.Calls.TYPE} IN (?, ?) AND ${CallLog.Calls.DATE} > ? AND ${CallLog.Calls.NUMBER} LIKE ?",
+                selection =
+                    "(${CallLog.Calls.TYPE} = ? OR (${CallLog.Calls.TYPE} = ? AND " +
+                        "${CallLog.Calls.DURATION} >= ?)) AND ${CallLog.Calls.DATE} > ? " +
+                        "AND ${CallLog.Calls.NUMBER} LIKE ?",
                 selectionArgs =
                     arrayOf(
-                        CallLog.Calls.INCOMING_TYPE.toString(),
                         CallLog.Calls.MISSED_TYPE.toString(),
+                        CallLog.Calls.INCOMING_TYPE.toString(),
+                        minIncomingDurationSeconds.toString(),
                         cutoff,
                         "%$last7Digits",
                     ),
@@ -320,6 +344,9 @@ class CallbackDetector
             const val DEFAULT_ANSWERED_CALLER_THRESHOLD = 2
             const val DEFAULT_EMERGENCY_CALLBACK_WINDOW_MINUTES = 240
             const val MIN_ANSWERED_CALL_DURATION_SECONDS = 1
+
+            // Answer-and-hang-up creates 1-11 second incoming rows; SpamBlocker's trust rule uses this 15-second floor.
+            const val AUTO_ANSWER_MIN_TRUSTED_SECONDS = 15
             const val MIN_URGENT_RETRY_INTERVAL_MILLIS = 15_000L
             private const val MILLIS_PER_DAY = 86_400_000L
             private const val MILLIS_PER_MINUTE = 60_000L
@@ -341,13 +368,15 @@ class CallbackDetector
                 windowMinutes: Int = 5,
                 threshold: Int = 2,
                 minRetryIntervalMillis: Long = MIN_URGENT_RETRY_INTERVAL_MILLIS,
+                minIncomingDurationSeconds: Int = 0,
             ): Boolean =
                 shared.isRepeatedUrgentCall(
                     context,
                     number,
                     windowMinutes,
                     threshold,
                     minRetryIntervalMillis,
+                    minIncomingDurationSeconds,
                 )
 
             suspend fun wasAnsweredRepeatedly(
@@ -373,7 +402,14 @@ class CallbackDetector
                 nowMillis: Long,
                 windowMinutes: Int,
                 last7Digits: String,
-            ): CallLogQuery = shared.buildRepeatedUrgentCallQuery(nowMillis, windowMinutes, last7Digits)
+                minIncomingDurationSeconds: Int = 0,
+            ): CallLogQuery =
+                shared.buildRepeatedUrgentCallQuery(
+                    nowMillis,
+                    windowMinutes,
+                    last7Digits,
+                    minIncomingDurationSeconds,
+                )
 
             internal fun hasUrgentRetrySpacing(
                 timestamps: List<Long>,

app/src/main/java/com/sysadmindoc/callshield/data/SpamRepository.kt

@@ -255,6 +255,8 @@ class SpamRepository(
         // reaches voicemail, user can review later without the interruption
         // or the missed-call entry from a rejection.
         val KEY_SILENT_VOICEMAIL = booleanPreferencesKey("silent_voicemail_mode")
+        val KEY_ANSWER_HANG_UP = booleanPreferencesKey("answer_hang_up_mode")
+        val KEY_HANG_UP_DELAY_SECONDS = intPreferencesKey("hang_up_delay_seconds")
 
         // A3 push-alert bridge — master toggle. When off, the registry is
         // not fed by RcsNotificationListener and PushAlertChecker returns
@@ -429,6 +431,8 @@ class SpamRepository(
     val postCallScreenEnabled: Flow<Boolean> = settingsRepository.postCallScreenEnabled
     val notificationScreeningPackages: Flow<Set<String>> = settingsRepository.notificationScreeningPackages
     val silentVoicemailEnabled: Flow<Boolean> = settingsRepository.silentVoicemailEnabled
+    val answerHangUpEnabled: Flow<Boolean> = settingsRepository.answerHangUpEnabled
+    val hangUpDelaySeconds: Flow<Int> = settingsRepository.hangUpDelaySeconds
     val pushAlertEnabled: Flow<Boolean> = settingsRepository.pushAlertEnabled
     val pushAlertDisabledPackages: Flow<Set<String>> = settingsRepository.pushAlertDisabledPackages
     internal val smsMessageCapabilityStatus: Flow<MessageCapabilityStatus> = settingsRepository.smsMessageCapabilityStatus
@@ -526,6 +530,10 @@ class SpamRepository(
 
     suspend fun setSilentVoicemail(enabled: Boolean) = settingsRepository.setSilentVoicemail(enabled)
 
+    suspend fun setAnswerHangUpEnabled(enabled: Boolean) = settingsRepository.setAnswerHangUpEnabled(enabled)
+
+    suspend fun setHangUpDelaySeconds(seconds: Int) = settingsRepository.setHangUpDelaySeconds(seconds)
+
     suspend fun setPushAlert(enabled: Boolean) = settingsRepository.setPushAlert(enabled)
 
     suspend fun togglePushAlertPackage(

app/src/main/java/com/sysadmindoc/callshield/data/checker/Checkers.kt

@@ -584,7 +584,23 @@ internal class AnsweredCallerChecker(
                     ?: CallbackDetector.DEFAULT_ANSWERED_CALLER_WINDOW_DAYS
             ).coerceAtLeast(1)
 
-        return if (callbackDetector.wasAnsweredRepeatedly(appContext, ctx.number, windowDays, threshold)) {
+        val wasAnsweredRepeatedly =
+            if (ctx.prefs[SpamRepository.KEY_ANSWER_HANG_UP] == true) {
+                callbackDetector.wasAnsweredRepeatedly(
+                    appContext,
+                    ctx.number,
+                    windowDays,
+                    threshold,
+                    maxOf(
+                        CallbackDetector.MIN_ANSWERED_CALL_DURATION_SECONDS,
+                        CallbackDetector.AUTO_ANSWER_MIN_TRUSTED_SECONDS,
+                    ),
+                )
+            } else {
+                callbackDetector.wasAnsweredRepeatedly(appContext, ctx.number, windowDays, threshold)
+            }
+
+        return if (wasAnsweredRepeatedly) {
             BlockResult.allow("answered_caller")
         } else {
             null
@@ -624,7 +640,18 @@ internal class RepeatedUrgentChecker(
     override val name = "repeated_urgent"
 
     override suspend fun check(ctx: CheckContext): BlockResult? =
-        if (callbackDetector.isRepeatedUrgentCall(appContext, ctx.number)) {
+        if (
+            callbackDetector.isRepeatedUrgentCall(
+                appContext,
+                ctx.number,
+                minIncomingDurationSeconds =
+                    if (ctx.prefs[SpamRepository.KEY_ANSWER_HANG_UP] == true) {
+                        CallbackDetector.AUTO_ANSWER_MIN_TRUSTED_SECONDS
+                    } else {
+                        0
+                    },
+            )
+        ) {
             BlockResult.allow("repeated_urgent")
         } else {
             null

app/src/main/java/com/sysadmindoc/callshield/data/repository/SettingsRepository.kt

@@ -29,6 +29,7 @@ import com.sysadmindoc.callshield.data.model.ExternalBlocklistSubscription
 import com.sysadmindoc.callshield.data.model.HotDataHealth
 import com.sysadmindoc.callshield.data.model.HotDataHealthUpdate
 import com.sysadmindoc.callshield.data.remote.FeedMirror
+import com.sysadmindoc.callshield.service.AnswerHangUpController
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.first
@@ -193,6 +194,12 @@ class SettingsRepository(
         }
     val silentVoicemailEnabled: Flow<Boolean> =
         dataStore.data.map { it[SpamRepository.KEY_SILENT_VOICEMAIL] ?: false }
+    val answerHangUpEnabled: Flow<Boolean> =
+        dataStore.data.map { it[SpamRepository.KEY_ANSWER_HANG_UP] ?: false }
+    val hangUpDelaySeconds: Flow<Int> =
+        dataStore.data.map {
+            AnswerHangUpController.clampDelaySeconds(it[SpamRepository.KEY_HANG_UP_DELAY_SECONDS])
+        }
     val pushAlertEnabled: Flow<Boolean> = dataStore.data.map { it[SpamRepository.KEY_PUSH_ALERT] ?: true }
     val pushAlertDisabledPackages: Flow<Set<String>> =
         dataStore.data.map { it[SpamRepository.KEY_PUSH_ALERT_DISABLED] ?: emptySet() }
@@ -363,6 +370,13 @@ class SettingsRepository(
 
     suspend fun setSilentVoicemail(enabled: Boolean) = dataStore.edit { it[SpamRepository.KEY_SILENT_VOICEMAIL] = enabled }
 
+    suspend fun setAnswerHangUpEnabled(enabled: Boolean) = dataStore.edit { it[SpamRepository.KEY_ANSWER_HANG_UP] = enabled }
+
+    suspend fun setHangUpDelaySeconds(seconds: Int) =
+        dataStore.edit {
+            it[SpamRepository.KEY_HANG_UP_DELAY_SECONDS] = AnswerHangUpController.clampDelaySeconds(seconds)
+        }
+
     suspend fun setPushAlert(enabled: Boolean) = dataStore.edit { it[SpamRepository.KEY_PUSH_ALERT] = enabled }
 
     internal suspend fun recordMessageCapability(status: MessageCapabilityStatus) =

app/src/main/java/com/sysadmindoc/callshield/permissions/CallShieldPermissions.kt

@@ -104,8 +104,14 @@ object CallShieldPermissions {
      * Runtime grants requested during first-run setup. Keeping this list next
      * to the capability contract prevents onboarding from silently omitting a
      * permission that the live call path expects on some Android builds.
+     *
+     * ANSWER_PHONE_CALLS is deliberately NOT requested here: it is asked for
+     * only when the user enables "Answer & hang up blocked calls" in
+     * Settings, so users who never enable that feature are never prompted
+     * for it.
      */
-    val onboardingRuntimePermissions = (corePermissions + compatibilityPermissions).distinct()
+    val onboardingRuntimePermissions =
+        (corePermissions + listOf(Manifest.permission.READ_PHONE_STATE)).distinct()
 
     val permissionCapabilityContracts =
         listOf(