Open source AccessibilityForwarder.

This change publishes the source code for `AccessibilityForwarder`, our app
that receives accessibility events and trees and sends them externally via
gRPC. This resolves issue #224.

At the moment we do not have build files, this may come later. We are still
deciding the build system (we'd like to use Bazel since it aligns with our
internal build system), but for the moment this provides valuable information
trying to use this, especially with
[AndroidWorld](https://github.com/google-research/android_world).

PiperOrigin-RevId: 686494976

android_env/apps/java/com/google/androidenv/accessibilityforwarder/AccessibilityForwarder.kt

@@ -0,0 +1,280 @@
+// Copyright 2024 DeepMind Technologies Limited.
+//
+// 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.google.androidenv.accessibilityforwarder
+
+import android.accessibilityservice.AccessibilityService
+import android.util.Log
+import android.view.accessibility.AccessibilityEvent
+import android.view.accessibility.AccessibilityNodeInfo
+import android.view.accessibility.AccessibilityWindowInfo
+import com.google.androidenv.accessibilityforwarder.A11yServiceGrpcKt.A11yServiceCoroutineStub
+import io.grpc.ManagedChannel
+import io.grpc.ManagedChannelBuilder
+import io.grpc.ProxyDetector
+import io.grpc.StatusException
+import kotlinx.coroutines.TimeoutCancellationException
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeout
+
+/**
+ * An Android service that listens to accessibility events and forwards them via gRPC.
+ *
+ * This service also logs the accessibility tree if [LogFlags.logAccessibilityTree] is set and if
+ * [LogFlags.grpcPort] is positive.
+ *
+ * Please see
+ * https://developer.android.com/reference/android/view/accessibility/AccessibilityEvent#getEventType()
+ * for a comprehensive list of events emitted by Android.
+ */
+class AccessibilityForwarder(
+  private val channelFactory: (host: String, port: Int) -> ManagedChannel = { host, port ->
+    ManagedChannelBuilder.forAddress(host, port)
+      .proxyDetector(ProxyDetector { _ -> null })
+      .usePlaintext()
+      .build()
+  }
+) : AccessibilityService() {
+
+  init {
+    // Spawn long-running thread for periodically logging the tree.
+    Thread(
+        Runnable {
+          while (LogFlags.a11yTreePeriodMs > 0) {
+            try {
+              val windows = this.windows
+              logAccessibilityTree(windows)
+            } catch (e: ConcurrentModificationException) {
+              continue
+            }
+
+            Thread.sleep(/* millis= */ LogFlags.a11yTreePeriodMs)
+          }
+        }
+      )
+      .start()
+  }
+
+  // grpcStub has a backing property that can be reset to null.
+  private var _grpcStub: A11yServiceCoroutineStub? = null
+  val grpcStub: A11yServiceCoroutineStub
+    get() {
+      if (_grpcStub == null) {
+        Log.i(TAG, "Building channel on ${LogFlags.grpcHost}:${LogFlags.grpcPort}.")
+        _grpcStub = A11yServiceCoroutineStub(channelFactory(LogFlags.grpcHost, LogFlags.grpcPort))
+      }
+      return _grpcStub!!
+    }
+
+  private fun resetGrpcStub() {
+    _grpcStub = null
+  }
+
+  override fun onInterrupt() {
+    LogFlags.a11yTreePeriodMs = 0 // Turn off periodic tree forwarding.
+  }
+
+  override fun onAccessibilityEvent(event: AccessibilityEvent?) {
+    if (event == null) {
+      Log.i(TAG, "`event` is null.")
+      return
+    }
+
+    logExtrasForEvent(event)
+    val eventType = event.eventType
+    val eventTypeStr: String = AccessibilityEvent.eventTypeToString(eventType)
+    if (eventTypeStr.isNotEmpty()) {
+      Log.i(TAG, eventTypeStr)
+    }
+  }
+
+  private fun logAccessibilityTree(windows: List<AccessibilityWindowInfo>) {
+    if (!LogFlags.logAccessibilityTree) {
+      Log.i(TAG, "Not logging accessibility tree")
+      return
+    }
+
+    // Check gRPC port before actually building the forest.
+    if (LogFlags.grpcPort <= 0) {
+      Log.w(TAG, "Can't log accessibility tree because gRPC port has not been set.")
+      return
+    }
+
+    val forest = creator.buildForest(windows)
+    try {
+      val grpcTimeoutMillis = 1000L
+      val response: ForestResponse =
+        with(grpcStub) {
+          Log.i(TAG, "sending (blocking) gRPC request for tree.")
+          runBlocking { withTimeout(grpcTimeoutMillis) { sendForest(forest) } }
+        }
+      if (response.error.isNotEmpty()) {
+        Log.w(TAG, "gRPC response.error: ${response.error}")
+      } else {
+        Log.i(TAG, "gRPC request for tree succeeded.")
+      }
+    } catch (e: StatusException) {
+      Log.w(TAG, "gRPC StatusException; are you sure networking is turned on?")
+      Log.i(TAG, "extra: exception ['$e']")
+      resetGrpcStub()
+    } catch (e: TimeoutCancellationException) {
+      Log.w(TAG, "gRPC TimeoutCancellationException; are you sure networking is turned on?")
+      Log.i(TAG, "extra: exception ['$e']")
+      resetGrpcStub()
+    }
+  }
+
+  /** Logs extras for all event types. */
+  private fun logExtrasForEvent(event: AccessibilityEvent) {
+
+    val events: MutableMap<String, String> = mutableMapOf()
+
+    val sourceDescription = event.source?.contentDescription()
+    if (!sourceDescription.isNullOrEmpty()) {
+      events.put("source_content_description", sourceDescription)
+    }
+
+    // Output the event text.
+    val eventText = event.text.joinToString(", ")
+    if (eventText.isNotEmpty()) {
+      events.put("event_text", eventText)
+    }
+
+    // Output the source text.
+    val sourceText = event.source?.text?.toString()
+    if (!sourceText.isNullOrEmpty()) {
+      events.put("source_text", sourceText)
+    }
+
+    val eventTypeStr: String = AccessibilityEvent.eventTypeToString(event.eventType)
+    if (eventTypeStr.isNotEmpty()) {
+      events.put("event_type", eventTypeStr)
+    }
+
+    val className = event.source?.className?.toString()
+    if (!className.isNullOrEmpty()) {
+      events.put("source_class_name", className)
+    }
+
+    val packageName = event.packageName?.toString()
+    if (!packageName.isNullOrEmpty()) {
+      events.put("event_package_name", packageName)
+    }
+
+    // Text editing properties.
+    val beforeText = event.beforeText?.toString()
+    if (!beforeText.isNullOrEmpty()) {
+      events.put("before_text", beforeText)
+    }
+
+    val fromIndex = event.fromIndex
+    if (fromIndex != -1) {
+      events.put("from_index", fromIndex.toString())
+    }
+
+    val toIndex = event.toIndex
+    if (toIndex != -1) {
+      events.put("to_index", toIndex.toString())
+    }
+
+    val addedCount = event.addedCount
+    if (addedCount != -1) {
+      events.put("added_count", addedCount.toString())
+    }
+
+    val removedCount = event.removedCount
+    if (removedCount != -1) {
+      events.put("removed_count", removedCount.toString())
+    }
+
+    //  Text traversal properties
+    val movementGranularity = event.movementGranularity
+    if (movementGranularity != 0) {
+      events.put("movement_granularity", movementGranularity.toString())
+    }
+
+    val action = event.action
+    if (action != 0) {
+      events.put("action", action.toString())
+    }
+
+    // Scrolling properties.
+    if (eventTypeStr == "TYPE_VIEW_SCROLLED") {
+      events.put("scroll_delta_x", event.scrollDeltaX.toString())
+      events.put("scroll_delta_y", event.scrollDeltaY.toString())
+    }
+
+    // Report viewID so we know exactly where the event came from.
+    val viewId = event.source?.viewIdResourceName?.toString()
+    if (!viewId.isNullOrEmpty()) {
+      events.put("view_id", viewId)
+    }
+
+    // Format [events] as a Python dict.
+    if (events.isNotEmpty()) {
+      events.put("event_timestamp_ms", event.eventTime.toString(10))
+      // Check if we want to use gRPC.
+      if (LogFlags.grpcPort > 0) {
+        try {
+          val grpcTimeoutMillis = 1000L
+          val request = eventRequest { this.event.putAll(events) }
+          val response: EventResponse =
+            with(grpcStub) {
+              Log.i(TAG, "sending (blocking) gRPC request for event.")
+              runBlocking { withTimeout(grpcTimeoutMillis) { sendEvent(request) } }
+            }
+          if (response.error.isNotEmpty()) {
+            Log.w(TAG, "gRPC response.error: ${response.error}")
+          } else {
+            Log.i(TAG, "gRPC request for event succeeded.")
+          }
+        } catch (e: StatusException) {
+          Log.w(TAG, "gRPC StatusException; are you sure networking is turned on?")
+          Log.i(TAG, "extra: exception ['$e']")
+          resetGrpcStub()
+        } catch (e: TimeoutCancellationException) {
+          Log.w(TAG, "gRPC TimeoutCancellationException; are you sure networking is turned on?")
+          Log.i(TAG, "extra: exception ['$e']")
+          resetGrpcStub()
+        }
+      } else {
+        Log.w(TAG, "Can't log accessibility event because gRPC port has not been set.")
+      }
+    }
+  }
+
+  /** Recursively climbs the accessibility tree until the root, collecting descriptions. */
+  private fun AccessibilityNodeInfo?.contentDescription(): String {
+    if (this == null) {
+      return ""
+    }
+
+    val descriptions = mutableListOf<String>()
+    var current: AccessibilityNodeInfo? = this
+    while (current != null) {
+      val description = current.contentDescription
+      if (description != null) {
+        descriptions.add(description.toString())
+      }
+
+      current = current.parent
+    }
+    return descriptions.joinToString(", ")
+  }
+
+  companion object {
+    private const val TAG = "AndroidRLTask"
+    private val creator = AccessibilityTreeCreator()
+  }
+}