Improve user-agent configuration

- Support setting the user-agent in CronetDataSource
- Support setting the default user-agent in CronetEngineWrapper
- Use the underlying network stack's default user-agent by
  default. Many applications will configure the underlying
  CronetEngine or OkHttpClient with a user-agent that they
  expect to be used throughout their app, so always overriding
  this with our own default, on reflection, is not the best
  thing to do!

Issue: #8395
PiperOrigin-RevId: 350921963

RELEASENOTES.md

@@ -99,6 +99,8 @@
         ([#1807](https://github.com/google/ExoPlayer/issues/1807)).
 *   Metadata retriever:
     *   Parse Google Photos HEIC motion photos metadata.
+*   Data sources:
+    *   Use the user agent of the underlying network stack by default.
 *   IMA extension:
     *   Add support for playback of ads in playlists
         ([#3750](https://github.com/google/ExoPlayer/issues/3750)).
@@ -116,6 +118,8 @@
     *   Add `OkHttpDataSource.Factory` and deprecate `OkHttpDataSourceFactory`.
 *   Cronet extension:
     *   Add `CronetDataSource.Factory` and deprecate `CronetDataSourceFactory`.
+    *   Support setting the user agent on `CronetDataSource.Factory` and
+        `CronetEngineWrapper`.
 *   Media2 extension
     *   Make media2-extension depend on AndroidX media2:media2-session:1.1.0 to
         fix a deadlock while creating PlaybackStateCompat internally.

demos/main/src/main/java/com/google/android/exoplayer2/demo/DemoUtil.java

@@ -16,7 +16,9 @@
 package com.google.android.exoplayer2.demo;
 
 import android.content.Context;
+import android.os.Build;
 import com.google.android.exoplayer2.DefaultRenderersFactory;
+import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.RenderersFactory;
 import com.google.android.exoplayer2.database.DatabaseProvider;
 import com.google.android.exoplayer2.database.ExoDatabaseProvider;
@@ -44,6 +46,13 @@ public final class DemoUtil {
 
   public static final String DOWNLOAD_NOTIFICATION_CHANNEL_ID = "download_channel";
 
+  private static final String USER_AGENT =
+      "ExoPlayerDemo/"
+          + ExoPlayerLibraryInfo.VERSION
+          + " (Linux; Android "
+          + Build.VERSION.RELEASE
+          + ") "
+          + ExoPlayerLibraryInfo.VERSION_SLASHY;
   private static final String TAG = "DemoUtil";
   private static final String DOWNLOAD_ACTION_FILE = "actions";
   private static final String DOWNLOAD_TRACKER_ACTION_FILE = "tracked_actions";
@@ -79,7 +88,8 @@ public final class DemoUtil {
   public static synchronized HttpDataSource.Factory getHttpDataSourceFactory(Context context) {
     if (httpDataSourceFactory == null) {
       context = context.getApplicationContext();
-      CronetEngineWrapper cronetEngineWrapper = new CronetEngineWrapper(context);
+      CronetEngineWrapper cronetEngineWrapper =
+          new CronetEngineWrapper(context, USER_AGENT, /* preferGMSCoreCronet= */ false);
       httpDataSourceFactory =
           new CronetDataSource.Factory(cronetEngineWrapper, Executors.newSingleThreadExecutor());
     }

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetDataSource.java

@@ -83,6 +83,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
     @Nullable private HttpDataSource.Factory fallbackFactory;
     @Nullable private Predicate<String> contentTypePredicate;
     @Nullable private TransferListener transferListener;
+    @Nullable private String userAgent;
     private int connectTimeoutMs;
     private int readTimeoutMs;
     private boolean resetTimeoutOnRedirects;
@@ -121,6 +122,22 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
       return this;
     }
 
+    /**
+     * Sets the user agent that will be used.
+     *
+     * <p>The default is {@code null}, which causes the default user agent of the underlying {@link
+     * CronetEngine} to be used.
+     *
+     * @param userAgent The user agent that will be used, or {@code null} to use the default user
+     *     agent of the underlying {@link CronetEngine}.
+     * @return This factory.
+     */
+    public Factory setUserAgent(@Nullable String userAgent) {
+      this.userAgent = userAgent;
+      internalFallbackFactory.setUserAgent(userAgent);
+      return this;
+    }
+
     /**
      * Sets the connect timeout, in milliseconds.
      *
@@ -239,6 +256,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
               readTimeoutMs,
               resetTimeoutOnRedirects,
               handleSetCookieRequests,
+              userAgent,
               defaultRequestProperties,
               contentTypePredicate);
       if (transferListener != null) {
@@ -293,6 +311,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
   private final int readTimeoutMs;
   private final boolean resetTimeoutOnRedirects;
   private final boolean handleSetCookieRequests;
+  @Nullable private final String userAgent;
   @Nullable private final RequestProperties defaultRequestProperties;
   private final RequestProperties requestProperties;
   private final ConditionVariable operation;
@@ -352,6 +371,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
         readTimeoutMs,
         resetTimeoutOnRedirects,
         /* handleSetCookieRequests= */ false,
+        /* userAgent= */ null,
         defaultRequestProperties,
         /* contentTypePredicate= */ null);
   }
@@ -373,6 +393,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
         readTimeoutMs,
         resetTimeoutOnRedirects,
         handleSetCookieRequests,
+        /* userAgent= */ null,
         defaultRequestProperties,
         /* contentTypePredicate= */ null);
   }
@@ -434,6 +455,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
         readTimeoutMs,
         resetTimeoutOnRedirects,
         handleSetCookieRequests,
+        /* userAgent= */ null,
         defaultRequestProperties,
         contentTypePredicate);
   }
@@ -445,6 +467,7 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
       int readTimeoutMs,
       boolean resetTimeoutOnRedirects,
       boolean handleSetCookieRequests,
+      @Nullable String userAgent,
       @Nullable RequestProperties defaultRequestProperties,
       @Nullable Predicate<String> contentTypePredicate) {
     super(/* isNetwork= */ true);
@@ -453,8 +476,9 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
     this.connectTimeoutMs = connectTimeoutMs;
     this.readTimeoutMs = readTimeoutMs;
     this.resetTimeoutOnRedirects = resetTimeoutOnRedirects;
-    this.defaultRequestProperties = defaultRequestProperties;
     this.handleSetCookieRequests = handleSetCookieRequests;
+    this.userAgent = userAgent;
+    this.defaultRequestProperties = defaultRequestProperties;
     this.contentTypePredicate = contentTypePredicate;
     clock = Clock.DEFAULT;
     urlRequestCallback = new UrlRequestCallback();
@@ -820,6 +844,9 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
       }
       requestBuilder.addHeader("Range", rangeValue.toString());
     }
+    if (userAgent != null) {
+      requestBuilder.addHeader("User-Agent", userAgent);
+    }
     // TODO: Uncomment when https://bugs.chromium.org/p/chromium/issues/detail?id=711810 is fixed
     // (adjusting the code as necessary).
     // Force identity encoding unless gzip is allowed.

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetDataSourceFactory.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.ext.cronet;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.upstream.DefaultHttpDataSourceFactory;
@@ -92,7 +91,7 @@ public final class CronetDataSourceFactory extends BaseFactory {
    * @param executor The {@link java.util.concurrent.Executor} that will perform the requests.
    */
   public CronetDataSourceFactory(CronetEngineWrapper cronetEngineWrapper, Executor executor) {
-    this(cronetEngineWrapper, executor, DEFAULT_USER_AGENT);
+    this(cronetEngineWrapper, executor, /* userAgent= */ (String) null);
   }
 
   /**
@@ -106,10 +105,12 @@ public final class CronetDataSourceFactory extends BaseFactory {
    *
    * @param cronetEngineWrapper A {@link CronetEngineWrapper}.
    * @param executor The {@link java.util.concurrent.Executor} that will perform the requests.
-   * @param userAgent A user agent used to create a fallback HttpDataSource if needed.
+   * @param userAgent The user agent that will be used by the fallback {@link HttpDataSource} if
+   *     needed, or {@code null} for the fallback to use the default user agent of the underlying
+   *     platform.
    */
   public CronetDataSourceFactory(
-      CronetEngineWrapper cronetEngineWrapper, Executor executor, String userAgent) {
+      CronetEngineWrapper cronetEngineWrapper, Executor executor, @Nullable String userAgent) {
     this(
         cronetEngineWrapper,
         executor,
@@ -136,7 +137,9 @@ public final class CronetDataSourceFactory extends BaseFactory {
    * @param connectTimeoutMs The connection timeout, in milliseconds.
    * @param readTimeoutMs The read timeout, in milliseconds.
    * @param resetTimeoutOnRedirects Whether the connect timeout is reset when a redirect occurs.
-   * @param userAgent A user agent used to create a fallback HttpDataSource if needed.
+   * @param userAgent The user agent that will be used by the fallback {@link HttpDataSource} if
+   *     needed, or {@code null} for the fallback to use the default user agent of the underlying
+   *     platform.
    */
   public CronetDataSourceFactory(
       CronetEngineWrapper cronetEngineWrapper,
@@ -144,7 +147,7 @@ public final class CronetDataSourceFactory extends BaseFactory {
       int connectTimeoutMs,
       int readTimeoutMs,
       boolean resetTimeoutOnRedirects,
-      String userAgent) {
+      @Nullable String userAgent) {
     this(
         cronetEngineWrapper,
         executor,
@@ -238,7 +241,7 @@ public final class CronetDataSourceFactory extends BaseFactory {
       CronetEngineWrapper cronetEngineWrapper,
       Executor executor,
       @Nullable TransferListener transferListener) {
-    this(cronetEngineWrapper, executor, transferListener, DEFAULT_USER_AGENT);
+    this(cronetEngineWrapper, executor, transferListener, /* userAgent= */ (String) null);
   }
 
   /**
@@ -253,13 +256,15 @@ public final class CronetDataSourceFactory extends BaseFactory {
    * @param cronetEngineWrapper A {@link CronetEngineWrapper}.
    * @param executor The {@link java.util.concurrent.Executor} that will perform the requests.
    * @param transferListener An optional listener.
-   * @param userAgent A user agent used to create a fallback HttpDataSource if needed.
+   * @param userAgent The user agent that will be used by the fallback {@link HttpDataSource} if
+   *     needed, or {@code null} for the fallback to use the default user agent of the underlying
+   *     platform.
    */
   public CronetDataSourceFactory(
       CronetEngineWrapper cronetEngineWrapper,
       Executor executor,
       @Nullable TransferListener transferListener,
-      String userAgent) {
+      @Nullable String userAgent) {
     this(
         cronetEngineWrapper,
         executor,
@@ -287,7 +292,9 @@ public final class CronetDataSourceFactory extends BaseFactory {
    * @param connectTimeoutMs The connection timeout, in milliseconds.
    * @param readTimeoutMs The read timeout, in milliseconds.
    * @param resetTimeoutOnRedirects Whether the connect timeout is reset when a redirect occurs.
-   * @param userAgent A user agent used to create a fallback HttpDataSource if needed.
+   * @param userAgent The user agent that will be used by the fallback {@link HttpDataSource} if
+   *     needed, or {@code null} for the fallback to use the default user agent of the underlying
+   *     platform.
    */
   public CronetDataSourceFactory(
       CronetEngineWrapper cronetEngineWrapper,
@@ -296,7 +303,7 @@ public final class CronetDataSourceFactory extends BaseFactory {
       int connectTimeoutMs,
       int readTimeoutMs,
       boolean resetTimeoutOnRedirects,
-      String userAgent) {
+      @Nullable String userAgent) {
     this(
         cronetEngineWrapper,
         executor,

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetEngineWrapper.java

@@ -73,25 +73,29 @@ public final class CronetEngineWrapper {
   public static final int SOURCE_UNAVAILABLE = 4;
 
   /**
-   * Creates a wrapper for a {@link CronetEngine} which automatically selects the most suitable
+   * Creates a wrapper for a {@link CronetEngine} built using the most suitable {@link
-   * {@link CronetProvider}. Sets wrapper to prefer natively bundled Cronet over GMSCore Cronet
+   * CronetProvider}. When natively bundled Cronet and GMSCore Cronet are both available, the
-   * if both are available.
+   * natively bundled provider is preferred.
    *
    * @param context A context.
    */
   public CronetEngineWrapper(Context context) {
-    this(context, false);
+    this(context, /* userAgent= */ null, /* preferGMSCoreCronet= */ false);
   }
 
   /**
-   * Creates a wrapper for a {@link CronetEngine} which automatically selects the most suitable
+   * Creates a wrapper for a {@link CronetEngine} built using the most suitable {@link
-   * {@link CronetProvider} based on user preference.
+   * CronetProvider}. When natively bundled Cronet and GMSCore Cronet are both available, {@code
+   * preferGMSCoreCronet} determines which is preferred.
    *
    * @param context A context.
+   * @param userAgent A default user agent, or {@code null} to use a default user agent of the
+   *     {@link CronetEngine}.
    * @param preferGMSCoreCronet Whether Cronet from GMSCore should be preferred over natively
    *     bundled Cronet if both are available.
    */
-  public CronetEngineWrapper(Context context, boolean preferGMSCoreCronet) {
+  public CronetEngineWrapper(
+      Context context, @Nullable String userAgent, boolean preferGMSCoreCronet) {
     CronetEngine cronetEngine = null;
     @CronetEngineSource int cronetEngineSource = SOURCE_UNAVAILABLE;
     List<CronetProvider> cronetProviders = new ArrayList<>(CronetProvider.getAllProviders(context));
@@ -108,7 +112,11 @@ public final class CronetEngineWrapper {
     for (int i = 0; i < cronetProviders.size() && cronetEngine == null; i++) {
       String providerName = cronetProviders.get(i).getName();
       try {
-        cronetEngine = cronetProviders.get(i).createBuilder().build();
+        CronetEngine.Builder cronetEngineBuilder = cronetProviders.get(i).createBuilder();
+        if (userAgent != null) {
+          cronetEngineBuilder.setUserAgent(userAgent);
+        }
+        cronetEngine = cronetEngineBuilder.build();
         if (providerComparator.isNativeProvider(providerName)) {
           cronetEngineSource = SOURCE_NATIVE;
         } else if (providerComparator.isGMSCoreProvider(providerName)) {
@@ -133,9 +141,9 @@ public final class CronetEngineWrapper {
   }
 
   /**
-   * Creates a wrapper for an existing CronetEngine.
+   * Creates a wrapper for an existing {@link CronetEngine}.
    *
-   * @param cronetEngine An existing CronetEngine.
+   * @param cronetEngine The CronetEngine to wrap.
    */
   public CronetEngineWrapper(CronetEngine cronetEngine) {
     this.cronetEngine = cronetEngine;

extensions/cronet/src/test/java/com/google/android/exoplayer2/ext/cronet/CronetDataSourceTest.java

@@ -36,7 +36,6 @@ import android.os.SystemClock;
 import androidx.test.core.app.ApplicationProvider;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.android.exoplayer2.C;
-import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.DefaultHttpDataSource;
 import com.google.android.exoplayer2.upstream.HttpDataSource;
@@ -1412,8 +1411,6 @@ public final class CronetDataSourceTest {
 
     dataSourceUnderTest.open(dataSpec);
 
-    Headers headers = mockWebServer.takeRequest(10, SECONDS).getHeaders();
-    assertThat(headers.get("user-agent")).isEqualTo(ExoPlayerLibraryInfo.DEFAULT_USER_AGENT);
     verify(mockTransferListener)
         .onTransferInitializing(eq(dataSourceUnderTest), eq(dataSpec), /* isNetwork= */ eq(true));
     verify(mockTransferListener)

extensions/okhttp/src/main/java/com/google/android/exoplayer2/ext/okhttp/OkHttpDataSource.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.ext.okhttp;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 import static com.google.android.exoplayer2.util.Util.castNonNull;
 import static java.lang.Math.min;
 
@@ -83,7 +82,6 @@ public class OkHttpDataSource extends BaseDataSource implements HttpDataSource {
     public Factory(Call.Factory callFactory) {
       this.callFactory = callFactory;
       defaultRequestProperties = new RequestProperties();
-      userAgent = DEFAULT_USER_AGENT;
     }
 
     /** @deprecated Use {@link #setDefaultRequestProperties(Map)} instead. */
@@ -102,12 +100,14 @@ public class OkHttpDataSource extends BaseDataSource implements HttpDataSource {
     /**
      * Sets the user agent that will be used.
      *
-     * <p>The default is {@link ExoPlayerLibraryInfo#DEFAULT_USER_AGENT}.
+     * <p>The default is {@code null}, which causes the default user agent of the underlying {@link
+     * OkHttpClient} to be used.
      *
-     * @param userAgent The user agent that will be used.
+     * @param userAgent The user agent that will be used, or {@code null} to use the default user
+     *     agent of the underlying {@link OkHttpClient}.
      * @return This factory.
      */
-    public Factory setUserAgent(String userAgent) {
+    public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       return this;
     }
@@ -193,7 +193,7 @@ public class OkHttpDataSource extends BaseDataSource implements HttpDataSource {
   @SuppressWarnings("deprecation")
   @Deprecated
   public OkHttpDataSource(Call.Factory callFactory) {
-    this(callFactory, DEFAULT_USER_AGENT);
+    this(callFactory, /* userAgent= */ null);
   }
 
   /** @deprecated Use {@link OkHttpDataSource.Factory} instead. */

extensions/okhttp/src/main/java/com/google/android/exoplayer2/ext/okhttp/OkHttpDataSourceFactory.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.ext.okhttp;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.upstream.HttpDataSource;
@@ -40,7 +39,7 @@ public final class OkHttpDataSourceFactory extends BaseFactory {
    *     by the sources created by the factory.
    */
   public OkHttpDataSourceFactory(Call.Factory callFactory) {
-    this(callFactory, DEFAULT_USER_AGENT, /* listener= */ null, /* cacheControl= */ null);
+    this(callFactory, /* userAgent= */ null, /* listener= */ null, /* cacheControl= */ null);
   }
 
   /**

library/common/src/main/java/com/google/android/exoplayer2/ExoPlayerLibraryInfo.java

@@ -46,9 +46,14 @@ public final class ExoPlayerLibraryInfo {
   // Intentionally hardcoded. Do not derive from other constants (e.g. VERSION) or vice versa.
   public static final int VERSION_INT = 2012002;
 
-  /** The default user agent for requests made by the library. */
+  /**
+   * The default user agent for requests made by the library.
+   *
+   * @deprecated ExoPlayer now uses the user agent of the underlying network stack by default.
+   */
+  @Deprecated
   public static final String DEFAULT_USER_AGENT =
-      VERSION_SLASHY + " (Linux;Android " + Build.VERSION.RELEASE + ") " + VERSION_SLASHY;
+      VERSION_SLASHY + " (Linux; Android " + Build.VERSION.RELEASE + ") " + VERSION_SLASHY;
 
   /**
    * Whether the library was compiled with {@link com.google.android.exoplayer2.util.Assertions}

library/core/src/main/java/com/google/android/exoplayer2/source/MediaSourceDrmHelper.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.source;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 import static com.google.android.exoplayer2.drm.DefaultDrmSessionManager.MODE_PLAYBACK;
 
 import androidx.annotation.Nullable;
@@ -24,6 +23,7 @@ import com.google.android.exoplayer2.drm.DefaultDrmSessionManager;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.FrameworkMediaDrm;
 import com.google.android.exoplayer2.drm.HttpMediaDrmCallback;
+import com.google.android.exoplayer2.upstream.DefaultHttpDataSource;
 import com.google.android.exoplayer2.upstream.DefaultHttpDataSourceFactory;
 import com.google.android.exoplayer2.upstream.HttpDataSource;
 import com.google.android.exoplayer2.util.Assertions;
@@ -73,7 +73,7 @@ public final class MediaSourceDrmHelper {
     HttpDataSource.Factory dataSourceFactory =
         drmHttpDataSourceFactory != null
             ? drmHttpDataSourceFactory
-            : new DefaultHttpDataSourceFactory(userAgent != null ? userAgent : DEFAULT_USER_AGENT);
+            : new DefaultHttpDataSource.Factory().setUserAgent(userAgent);
     HttpMediaDrmCallback httpDrmCallback =
         new HttpMediaDrmCallback(
             drmConfiguration.licenseUri == null ? null : drmConfiguration.licenseUri.toString(),

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultDataSource.java

@@ -19,7 +19,6 @@ import android.content.ContentResolver;
 import android.content.Context;
 import android.net.Uri;
 import androidx.annotation.Nullable;
-import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.Util;
@@ -89,7 +88,7 @@ public final class DefaultDataSource implements DataSource {
   public DefaultDataSource(Context context, boolean allowCrossProtocolRedirects) {
     this(
         context,
-        ExoPlayerLibraryInfo.DEFAULT_USER_AGENT,
+        /* userAgent= */ null,
         DefaultHttpDataSource.DEFAULT_CONNECT_TIMEOUT_MILLIS,
         DefaultHttpDataSource.DEFAULT_READ_TIMEOUT_MILLIS,
         allowCrossProtocolRedirects);
@@ -99,11 +98,13 @@ public final class DefaultDataSource implements DataSource {
    * Constructs a new instance, optionally configured to follow cross-protocol redirects.
    *
    * @param context A context.
-   * @param userAgent The User-Agent to use when requesting remote data.
+   * @param userAgent The user agent that will be used when requesting remote data, or {@code null}
+   *     to use the default user agent of the underlying platform.
    * @param allowCrossProtocolRedirects Whether cross-protocol redirects (i.e. redirects from HTTP
    *     to HTTPS and vice versa) are enabled when fetching remote data.
    */
-  public DefaultDataSource(Context context, String userAgent, boolean allowCrossProtocolRedirects) {
+  public DefaultDataSource(
+      Context context, @Nullable String userAgent, boolean allowCrossProtocolRedirects) {
     this(
         context,
         userAgent,
@@ -116,7 +117,8 @@ public final class DefaultDataSource implements DataSource {
    * Constructs a new instance, optionally configured to follow cross-protocol redirects.
    *
    * @param context A context.
-   * @param userAgent The User-Agent to use when requesting remote data.
+   * @param userAgent The user agent that will be used when requesting remote data, or {@code null}
+   *     to use the default user agent of the underlying platform.
    * @param connectTimeoutMillis The connection timeout that should be used when requesting remote
    *     data, in milliseconds. A timeout of zero is interpreted as an infinite timeout.
    * @param readTimeoutMillis The read timeout that should be used when requesting remote data, in
@@ -126,7 +128,7 @@ public final class DefaultDataSource implements DataSource {
    */
   public DefaultDataSource(
       Context context,
-      String userAgent,
+      @Nullable String userAgent,
       int connectTimeoutMillis,
       int readTimeoutMillis,
       boolean allowCrossProtocolRedirects) {

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultDataSourceFactory.java

@@ -15,8 +15,6 @@
  */
 package com.google.android.exoplayer2.upstream;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
-
 import android.content.Context;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.upstream.DataSource.Factory;
@@ -37,16 +35,17 @@ public final class DefaultDataSourceFactory implements Factory {
    * @param context A context.
    */
   public DefaultDataSourceFactory(Context context) {
-    this(context, DEFAULT_USER_AGENT, /* listener= */ null);
+    this(context, /* userAgent= */ (String) null, /* listener= */ null);
   }
 
   /**
    * Creates an instance.
    *
    * @param context A context.
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used when requesting remote data, or {@code null}
+   *     to use the default user agent of the underlying platform.
    */
-  public DefaultDataSourceFactory(Context context, String userAgent) {
+  public DefaultDataSourceFactory(Context context, @Nullable String userAgent) {
     this(context, userAgent, /* listener= */ null);
   }
 
@@ -54,11 +53,12 @@ public final class DefaultDataSourceFactory implements Factory {
    * Creates an instance.
    *
    * @param context A context.
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used when requesting remote data, or {@code null}
+   *     to use the default user agent of the underlying platform.
    * @param listener An optional listener.
    */
   public DefaultDataSourceFactory(
-      Context context, String userAgent, @Nullable TransferListener listener) {
+      Context context, @Nullable String userAgent, @Nullable TransferListener listener) {
     this(context, listener, new DefaultHttpDataSource.Factory().setUserAgent(userAgent));
   }
 

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultHttpDataSource.java

@@ -15,7 +15,6 @@
  */
 package com.google.android.exoplayer2.upstream;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 import static java.lang.Math.max;
 import static java.lang.Math.min;
 
@@ -24,7 +23,6 @@ import android.text.TextUtils;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 import com.google.android.exoplayer2.C;
-import com.google.android.exoplayer2.ExoPlayerLibraryInfo;
 import com.google.android.exoplayer2.upstream.DataSpec.HttpMethod;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Log;
@@ -69,7 +67,7 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
 
     @Nullable private TransferListener transferListener;
     @Nullable private Predicate<String> contentTypePredicate;
-    private String userAgent;
+    @Nullable private String userAgent;
     private int connectTimeoutMs;
     private int readTimeoutMs;
     private boolean allowCrossProtocolRedirects;
@@ -77,7 +75,6 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
     /** Creates an instance. */
     public Factory() {
       defaultRequestProperties = new RequestProperties();
-      userAgent = DEFAULT_USER_AGENT;
       connectTimeoutMs = DEFAULT_CONNECT_TIMEOUT_MILLIS;
       readTimeoutMs = DEFAULT_READ_TIMEOUT_MILLIS;
     }
@@ -98,12 +95,14 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
     /**
      * Sets the user agent that will be used.
      *
-     * <p>The default is {@link ExoPlayerLibraryInfo#DEFAULT_USER_AGENT}.
+     * <p>The default is {@code null}, which causes the default user agent of the underlying
+     * platform to be used.
      *
-     * @param userAgent The user agent that will be used.
+     * @param userAgent The user agent that will be used, or {@code null} to use the default user
+     *     agent of the underlying platform.
      * @return This factory.
      */
-    public Factory setUserAgent(String userAgent) {
+    public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       return this;
     }
@@ -214,7 +213,7 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
   private final boolean allowCrossProtocolRedirects;
   private final int connectTimeoutMillis;
   private final int readTimeoutMillis;
-  private final String userAgent;
+  @Nullable private final String userAgent;
   @Nullable private final RequestProperties defaultRequestProperties;
   private final RequestProperties requestProperties;
 
@@ -235,23 +234,21 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
   @SuppressWarnings("deprecation")
   @Deprecated
   public DefaultHttpDataSource() {
-    this(
+    this(/* userAgent= */ null, DEFAULT_CONNECT_TIMEOUT_MILLIS, DEFAULT_READ_TIMEOUT_MILLIS);
-        ExoPlayerLibraryInfo.DEFAULT_USER_AGENT,
-        DEFAULT_CONNECT_TIMEOUT_MILLIS,
-        DEFAULT_READ_TIMEOUT_MILLIS);
   }
 
   /** @deprecated Use {@link DefaultHttpDataSource.Factory} instead. */
   @SuppressWarnings("deprecation")
   @Deprecated
-  public DefaultHttpDataSource(String userAgent) {
+  public DefaultHttpDataSource(@Nullable String userAgent) {
     this(userAgent, DEFAULT_CONNECT_TIMEOUT_MILLIS, DEFAULT_READ_TIMEOUT_MILLIS);
   }
 
   /** @deprecated Use {@link DefaultHttpDataSource.Factory} instead. */
   @SuppressWarnings("deprecation")
   @Deprecated
-  public DefaultHttpDataSource(String userAgent, int connectTimeoutMillis, int readTimeoutMillis) {
+  public DefaultHttpDataSource(
+      @Nullable String userAgent, int connectTimeoutMillis, int readTimeoutMillis) {
     this(
         userAgent,
         connectTimeoutMillis,
@@ -263,7 +260,7 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
   /** @deprecated Use {@link DefaultHttpDataSource.Factory} instead. */
   @Deprecated
   public DefaultHttpDataSource(
-      String userAgent,
+      @Nullable String userAgent,
       int connectTimeoutMillis,
       int readTimeoutMillis,
       boolean allowCrossProtocolRedirects,
@@ -278,14 +275,14 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
   }
 
   private DefaultHttpDataSource(
-      String userAgent,
+      @Nullable String userAgent,
       int connectTimeoutMillis,
       int readTimeoutMillis,
       boolean allowCrossProtocolRedirects,
       @Nullable RequestProperties defaultRequestProperties,
       @Nullable Predicate<String> contentTypePredicate) {
     super(/* isNetwork= */ true);
-    this.userAgent = Assertions.checkNotEmpty(userAgent);
+    this.userAgent = userAgent;
     this.connectTimeoutMillis = connectTimeoutMillis;
     this.readTimeoutMillis = readTimeoutMillis;
     this.allowCrossProtocolRedirects = allowCrossProtocolRedirects;
@@ -620,7 +617,9 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
       }
       connection.setRequestProperty("Range", rangeRequest);
     }
+    if (userAgent != null) {
       connection.setRequestProperty("User-Agent", userAgent);
+    }
     connection.setRequestProperty("Accept-Encoding", allowGzip ? "gzip" : "identity");
     connection.setInstanceFollowRedirects(followRedirects);
     connection.setDoOutput(httpBody != null);

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultHttpDataSourceFactory.java

@@ -15,17 +15,15 @@
  */
 package com.google.android.exoplayer2.upstream;
 
-import static com.google.android.exoplayer2.ExoPlayerLibraryInfo.DEFAULT_USER_AGENT;
 
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.upstream.HttpDataSource.BaseFactory;
-import com.google.android.exoplayer2.util.Assertions;
 
 /** @deprecated Use {@link DefaultHttpDataSource.Factory} instead. */
 @Deprecated
 public final class DefaultHttpDataSourceFactory extends BaseFactory {
 
-  private final String userAgent;
+  @Nullable private final String userAgent;
   @Nullable private final TransferListener listener;
   private final int connectTimeoutMillis;
   private final int readTimeoutMillis;
@@ -37,7 +35,7 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
    * timeout and disables cross-protocol redirects.
    */
   public DefaultHttpDataSourceFactory() {
-    this(DEFAULT_USER_AGENT);
+    this(/* userAgent= */ null);
   }
 
   /**
@@ -45,9 +43,10 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
    * connection timeout, {@link DefaultHttpDataSource#DEFAULT_READ_TIMEOUT_MILLIS} as the read
    * timeout and disables cross-protocol redirects.
    *
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used, or {@code null} to use the default user
+   *     agent of the underlying platform.
    */
-  public DefaultHttpDataSourceFactory(String userAgent) {
+  public DefaultHttpDataSourceFactory(@Nullable String userAgent) {
     this(userAgent, null);
   }
 
@@ -56,17 +55,20 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
    * connection timeout, {@link DefaultHttpDataSource#DEFAULT_READ_TIMEOUT_MILLIS} as the read
    * timeout and disables cross-protocol redirects.
    *
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used, or {@code null} to use the default user
+   *     agent of the underlying platform.
    * @param listener An optional listener.
    * @see #DefaultHttpDataSourceFactory(String, TransferListener, int, int, boolean)
    */
-  public DefaultHttpDataSourceFactory(String userAgent, @Nullable TransferListener listener) {
+  public DefaultHttpDataSourceFactory(
+      @Nullable String userAgent, @Nullable TransferListener listener) {
     this(userAgent, listener, DefaultHttpDataSource.DEFAULT_CONNECT_TIMEOUT_MILLIS,
         DefaultHttpDataSource.DEFAULT_READ_TIMEOUT_MILLIS, false);
   }
 
   /**
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used, or {@code null} to use the default user
+   *     agent of the underlying platform.
    * @param connectTimeoutMillis The connection timeout that should be used when requesting remote
    *     data, in milliseconds. A timeout of zero is interpreted as an infinite timeout.
    * @param readTimeoutMillis The read timeout that should be used when requesting remote data, in
@@ -75,7 +77,7 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
    *     to HTTPS and vice versa) are enabled.
    */
   public DefaultHttpDataSourceFactory(
-      String userAgent,
+      @Nullable String userAgent,
       int connectTimeoutMillis,
       int readTimeoutMillis,
       boolean allowCrossProtocolRedirects) {
@@ -88,7 +90,8 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
   }
 
   /**
-   * @param userAgent The User-Agent string that should be used.
+   * @param userAgent The user agent that will be used, or {@code null} to use the default user
+   *     agent of the underlying platform.
    * @param listener An optional listener.
    * @param connectTimeoutMillis The connection timeout that should be used when requesting remote
    *     data, in milliseconds. A timeout of zero is interpreted as an infinite timeout.
@@ -98,12 +101,12 @@ public final class DefaultHttpDataSourceFactory extends BaseFactory {
    *     to HTTPS and vice versa) are enabled.
    */
   public DefaultHttpDataSourceFactory(
-      String userAgent,
+      @Nullable String userAgent,
       @Nullable TransferListener listener,
       int connectTimeoutMillis,
       int readTimeoutMillis,
       boolean allowCrossProtocolRedirects) {
-    this.userAgent = Assertions.checkNotEmpty(userAgent);
+    this.userAgent = userAgent;
     this.listener = listener;
     this.connectTimeoutMillis = connectTimeoutMillis;
     this.readTimeoutMillis = readTimeoutMillis;