diff --git a/Cronet/tests/cts/src/org/chromium/net/test/util/TestUrlRequestCallback.java b/Cronet/tests/cts/src/org/chromium/net/test/util/TestUrlRequestCallback.java
new file mode 100644
index 0000000..3c7c001
--- /dev/null
+++ b/Cronet/tests/cts/src/org/chromium/net/test/util/TestUrlRequestCallback.java
@@ -0,0 +1,459 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * 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 org.chromium.net.test.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import android.os.ConditionVariable;
+import android.os.StrictMode;
+
+import org.chromium.net.CallbackException;
+import org.chromium.net.CronetException;
+import org.chromium.net.InlineExecutionProhibitedException;
+import org.chromium.net.UrlRequest;
+import org.chromium.net.UrlResponseInfo;
+
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Callback that tracks information from different callbacks and has a
+ * method to block thread until the request completes on another thread.
+ * Allows us to cancel, block request or throw an exception from an arbitrary step.
+ */
+public class TestUrlRequestCallback extends UrlRequest.Callback {
+    private static final int TIMEOUT_MS = 12_000;
+    public ArrayList<UrlResponseInfo> mRedirectResponseInfoList = new ArrayList<>();
+    public ArrayList<String> mRedirectUrlList = new ArrayList<>();
+    public UrlResponseInfo mResponseInfo;
+    public CronetException mError;
+
+    public ResponseStep mResponseStep = ResponseStep.NOTHING;
+
+    public int mRedirectCount;
+    public boolean mOnErrorCalled;
+    public boolean mOnCanceledCalled;
+
+    public int mHttpResponseDataLength;
+    public String mResponseAsString = "";
+
+    public int mReadBufferSize = 32 * 1024;
+
+    // When false, the consumer is responsible for all calls into the request
+    // that advance it.
+    private boolean mAutoAdvance = true;
+    // Whether an exception is thrown by maybeThrowCancelOrPause().
+    private boolean mCallbackExceptionThrown;
+
+    // Whether to permit calls on the network thread.
+    private boolean mAllowDirectExecutor;
+
+    // Whether to stop the executor thread after reaching a terminal method.
+    // Terminal methods are (onSucceeded, onFailed or onCancelled)
+    private boolean mBlockOnTerminalState;
+
+    // Conditionally fail on certain steps.
+    private FailureType mFailureType = FailureType.NONE;
+    private ResponseStep mFailureStep = ResponseStep.NOTHING;
+
+    // Signals when request is done either successfully or not.
+    private final ConditionVariable mDone = new ConditionVariable();
+
+    // Hangs the calling thread until a terminal method has started executing.
+    private final ConditionVariable mWaitForTerminalToStart = new ConditionVariable();
+
+    // Signaled on each step when mAutoAdvance is false.
+    private final ConditionVariable mStepBlock = new ConditionVariable();
+
+    // Executor Service for Cronet callbacks.
+    private final ExecutorService mExecutorService;
+    private Thread mExecutorThread;
+
+    // position() of ByteBuffer prior to read() call.
+    private int mBufferPositionBeforeRead;
+
+    private static class ExecutorThreadFactory implements ThreadFactory {
+        @Override
+        public Thread newThread(final Runnable r) {
+            return new Thread(new Runnable() {
+                @Override
+                public void run() {
+                    StrictMode.ThreadPolicy threadPolicy = StrictMode.getThreadPolicy();
+                    try {
+                        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
+                                .detectNetwork()
+                                .penaltyLog()
+                                .penaltyDeath()
+                                .build());
+                        r.run();
+                    } finally {
+                        StrictMode.setThreadPolicy(threadPolicy);
+                    }
+                }
+            });
+        }
+    }
+
+    public enum ResponseStep {
+        NOTHING,
+        ON_RECEIVED_REDIRECT,
+        ON_RESPONSE_STARTED,
+        ON_READ_COMPLETED,
+        ON_SUCCEEDED,
+        ON_FAILED,
+        ON_CANCELED,
+    }
+
+    public enum FailureType {
+        NONE,
+        CANCEL_SYNC,
+        CANCEL_ASYNC,
+        // Same as above, but continues to advance the request after posting
+        // the cancellation task.
+        CANCEL_ASYNC_WITHOUT_PAUSE,
+        THROW_SYNC
+    }
+
+    private static void assertContains(String expectedSubstring, String actualString) {
+        assertNotNull(actualString);
+        assertTrue("String [" + actualString + "] doesn't contain substring [" + expectedSubstring
+                + "]", actualString.contains(expectedSubstring));
+
+    }
+
+    /**
+     * Set {@code mExecutorThread}.
+     */
+    private void fillInExecutorThread() {
+        mExecutorService.execute(new Runnable() {
+            @Override
+            public void run() {
+                mExecutorThread = Thread.currentThread();
+            }
+        });
+    }
+
+    private boolean isTerminalCallback(ResponseStep step) {
+        switch (step) {
+            case ON_SUCCEEDED:
+            case ON_CANCELED:
+            case ON_FAILED:
+                return true;
+            default:
+                return false;
+        }
+    }
+
+    /**
+     * Create a {@link TestUrlRequestCallback} with a new single-threaded executor.
+     */
+    public TestUrlRequestCallback() {
+        this(Executors.newSingleThreadExecutor(new ExecutorThreadFactory()));
+    }
+
+    /**
+     * Create a {@link TestUrlRequestCallback} using a custom single-threaded executor.
+     */
+    public TestUrlRequestCallback(ExecutorService executorService) {
+        mExecutorService = executorService;
+        fillInExecutorThread();
+    }
+
+    /**
+     * This blocks the callback executor thread once it has reached a final state callback.
+     * In order to continue execution, this method must be called again and providing {@code false}
+     * to continue execution.
+     *
+     * @param blockOnTerminalState the state to set for the executor thread
+     */
+    public void setBlockOnTerminalState(boolean blockOnTerminalState) {
+        mBlockOnTerminalState = blockOnTerminalState;
+        if (!blockOnTerminalState) {
+            mDone.open();
+        }
+    }
+
+    public void setAutoAdvance(boolean autoAdvance) {
+        mAutoAdvance = autoAdvance;
+    }
+
+    public void setAllowDirectExecutor(boolean allowed) {
+        mAllowDirectExecutor = allowed;
+    }
+
+    public void setFailure(FailureType failureType, ResponseStep failureStep) {
+        mFailureStep = failureStep;
+        mFailureType = failureType;
+    }
+
+    /**
+     * Blocks the calling thread till callback execution is done
+     *
+     * @return true if the condition was opened, false if the call returns because of the timeout.
+     */
+    public boolean blockForDone() {
+        return mDone.block(TIMEOUT_MS);
+    }
+
+    /**
+     * Waits for a terminal callback to complete execution before failing if the callback
+     * is not the expected one
+     *
+     * @param expectedStep the expected callback step
+     */
+    public void expectCallback(ResponseStep expectedStep) {
+        if (isTerminalCallback(expectedStep)) {
+            assertTrue("Did not receive terminal callback before timeout", blockForDone());
+        }
+        assertSame(expectedStep, mResponseStep);
+    }
+
+    /**
+     * Blocks the calling thread until one of the final states has been called.
+     * This is called before the callback has finished executed.
+     */
+    public void waitForTerminalToStart() {
+        mWaitForTerminalToStart.block();
+    }
+
+    public void waitForNextStep() {
+        mStepBlock.block();
+        mStepBlock.close();
+    }
+
+    public ExecutorService getExecutor() {
+        return mExecutorService;
+    }
+
+    public void shutdownExecutor() {
+        mExecutorService.shutdown();
+    }
+
+    /**
+     * Shuts down the ExecutorService and waits until it executes all posted
+     * tasks.
+     */
+    public void shutdownExecutorAndWait() {
+        mExecutorService.shutdown();
+        try {
+            // Termination shouldn't take long. Use 1 min which should be more than enough.
+            mExecutorService.awaitTermination(1, TimeUnit.MINUTES);
+        } catch (InterruptedException e) {
+            fail("ExecutorService is interrupted while waiting for termination");
+        }
+        assertTrue(mExecutorService.isTerminated());
+    }
+
+    @Override
+    public void onRedirectReceived(
+            UrlRequest request, UrlResponseInfo info, String newLocationUrl) {
+        checkExecutorThread();
+        assertFalse(request.isDone());
+        assertTrue(mResponseStep == ResponseStep.NOTHING
+                || mResponseStep == ResponseStep.ON_RECEIVED_REDIRECT);
+        assertNull(mError);
+
+        mResponseStep = ResponseStep.ON_RECEIVED_REDIRECT;
+        mRedirectUrlList.add(newLocationUrl);
+        mRedirectResponseInfoList.add(info);
+        ++mRedirectCount;
+        if (maybeThrowCancelOrPause(request)) {
+            return;
+        }
+        request.followRedirect();
+    }
+
+    @Override
+    public void onResponseStarted(UrlRequest request, UrlResponseInfo info) {
+        checkExecutorThread();
+        assertFalse(request.isDone());
+        assertTrue(mResponseStep == ResponseStep.NOTHING
+                || mResponseStep == ResponseStep.ON_RECEIVED_REDIRECT);
+        assertNull(mError);
+
+        mResponseStep = ResponseStep.ON_RESPONSE_STARTED;
+        mResponseInfo = info;
+        if (maybeThrowCancelOrPause(request)) {
+            return;
+        }
+        startNextRead(request);
+    }
+
+    @Override
+    public void onReadCompleted(UrlRequest request, UrlResponseInfo info, ByteBuffer byteBuffer) {
+        checkExecutorThread();
+        assertFalse(request.isDone());
+        assertTrue(mResponseStep == ResponseStep.ON_RESPONSE_STARTED
+                || mResponseStep == ResponseStep.ON_READ_COMPLETED);
+        assertNull(mError);
+
+        mResponseStep = ResponseStep.ON_READ_COMPLETED;
+
+        final byte[] lastDataReceivedAsBytes;
+        final int bytesRead = byteBuffer.position() - mBufferPositionBeforeRead;
+        mHttpResponseDataLength += bytesRead;
+        lastDataReceivedAsBytes = new byte[bytesRead];
+        // Rewind |byteBuffer.position()| to pre-read() position.
+        byteBuffer.position(mBufferPositionBeforeRead);
+        // This restores |byteBuffer.position()| to its value on entrance to
+        // this function.
+        byteBuffer.get(lastDataReceivedAsBytes);
+        mResponseAsString += new String(lastDataReceivedAsBytes);
+
+        if (maybeThrowCancelOrPause(request)) {
+            return;
+        }
+        startNextRead(request);
+    }
+
+    @Override
+    public void onSucceeded(UrlRequest request, UrlResponseInfo info) {
+        checkExecutorThread();
+        assertTrue(request.isDone());
+        assertTrue(mResponseStep == ResponseStep.ON_RESPONSE_STARTED
+                || mResponseStep == ResponseStep.ON_READ_COMPLETED);
+        assertFalse(mOnErrorCalled);
+        assertFalse(mOnCanceledCalled);
+        assertNull(mError);
+
+        mResponseStep = ResponseStep.ON_SUCCEEDED;
+        mResponseInfo = info;
+        mWaitForTerminalToStart.open();
+        if (mBlockOnTerminalState) mDone.block();
+        openDone();
+        maybeThrowCancelOrPause(request);
+    }
+
+    @Override
+    public void onFailed(UrlRequest request, UrlResponseInfo info, CronetException error) {
+        // If the failure is because of prohibited direct execution, the test shouldn't fail
+        // since the request already did.
+        if (error.getCause() instanceof InlineExecutionProhibitedException) {
+            mAllowDirectExecutor = true;
+        }
+        checkExecutorThread();
+        assertTrue(request.isDone());
+        // Shouldn't happen after success.
+        assertTrue(mResponseStep != ResponseStep.ON_SUCCEEDED);
+        // Should happen at most once for a single request.
+        assertFalse(mOnErrorCalled);
+        assertFalse(mOnCanceledCalled);
+        assertNull(mError);
+        if (mCallbackExceptionThrown) {
+            assertTrue(error instanceof CallbackException);
+            assertContains("Exception received from UrlRequest.Callback", error.getMessage());
+            assertNotNull(error.getCause());
+            assertTrue(error.getCause() instanceof IllegalStateException);
+            assertContains("Listener Exception.", error.getCause().getMessage());
+        }
+
+        mResponseStep = ResponseStep.ON_FAILED;
+        mOnErrorCalled = true;
+        mError = error;
+        mWaitForTerminalToStart.open();
+        if (mBlockOnTerminalState) mDone.block();
+        openDone();
+        maybeThrowCancelOrPause(request);
+    }
+
+    @Override
+    public void onCanceled(UrlRequest request, UrlResponseInfo info) {
+        checkExecutorThread();
+        assertTrue(request.isDone());
+        // Should happen at most once for a single request.
+        assertFalse(mOnCanceledCalled);
+        assertFalse(mOnErrorCalled);
+        assertNull(mError);
+
+        mResponseStep = ResponseStep.ON_CANCELED;
+        mOnCanceledCalled = true;
+        mWaitForTerminalToStart.open();
+        if (mBlockOnTerminalState) mDone.block();
+        openDone();
+        maybeThrowCancelOrPause(request);
+    }
+
+    public void startNextRead(UrlRequest request) {
+        startNextRead(request, ByteBuffer.allocateDirect(mReadBufferSize));
+    }
+
+    public void startNextRead(UrlRequest request, ByteBuffer buffer) {
+        mBufferPositionBeforeRead = buffer.position();
+        request.read(buffer);
+    }
+
+    public boolean isDone() {
+        // It's not mentioned by the Android docs, but block(0) seems to block
+        // indefinitely, so have to block for one millisecond to get state
+        // without blocking.
+        return mDone.block(1);
+    }
+
+    protected void openDone() {
+        mDone.open();
+    }
+
+    private void checkExecutorThread() {
+        if (!mAllowDirectExecutor) {
+            assertEquals(mExecutorThread, Thread.currentThread());
+        }
+    }
+
+    /**
+     * Returns {@code false} if the listener should continue to advance the
+     * request.
+     */
+    private boolean maybeThrowCancelOrPause(final UrlRequest request) {
+        checkExecutorThread();
+        if (mResponseStep != mFailureStep || mFailureType == FailureType.NONE) {
+            if (!mAutoAdvance) {
+                mStepBlock.open();
+                return true;
+            }
+            return false;
+        }
+
+        if (mFailureType == FailureType.THROW_SYNC) {
+            assertFalse(mCallbackExceptionThrown);
+            mCallbackExceptionThrown = true;
+            throw new IllegalStateException("Listener Exception.");
+        }
+        Runnable task = new Runnable() {
+            @Override
+            public void run() {
+                request.cancel();
+            }
+        };
+        if (mFailureType == FailureType.CANCEL_ASYNC
+                || mFailureType == FailureType.CANCEL_ASYNC_WITHOUT_PAUSE) {
+            getExecutor().execute(task);
+        } else {
+            task.run();
+        }
+        return mFailureType != FailureType.CANCEL_ASYNC_WITHOUT_PAUSE;
+    }
+}
diff --git a/framework/src/android/net/TestNetworkInterface.java b/framework/src/android/net/TestNetworkInterface.java
index 26200e1..4c4e2d9 100644
--- a/framework/src/android/net/TestNetworkInterface.java
+++ b/framework/src/android/net/TestNetworkInterface.java
@@ -29,6 +29,9 @@
 /**
  * This class is used to return the interface name, fd, MAC, and MTU of the test interface
  *
+ * TestNetworkInterfaces are created by TestNetworkService and provide a
+ * wrapper around a tun/tap interface that can be used in integration tests.
+ *
  * @hide
  */
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
@@ -97,11 +100,25 @@
         return mInterfaceName;
     }
 
+    /**
+     * Returns the tap interface MacAddress.
+     *
+     * When TestNetworkInterface wraps a tun interface, the MAC address is null.
+     *
+     * @return the tap interface MAC address or null.
+     */
     @Nullable
     public MacAddress getMacAddress() {
         return mMacAddress;
     }
 
+    /**
+     * Returns the interface MTU.
+     *
+     * MTU defaults to 1500 if an error occurs.
+     *
+     * @return MTU in bytes.
+     */
     public int getMtu() {
         return mMtu;
     }