Follow 307/308 POST redirects for license requests

I was considering putting this directly in DefaultHttpDataSource, however:

- We'd need to modify at least OkHttpDataSource as well. I'm not sure whether
  Cronet follows this type of redirect automatically or not.
- HttpDataSource instances don't know how they're going to be used, so it's
  probably correct that they behave like the underlying network stack.

Issue: #4108

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192745408

RELEASENOTES.md

@@ -51,13 +51,15 @@
   * Add release method to Cache interface.
   * Prevent multiple instances of SimpleCache in the same folder.
     Previous instance must be released.
-  * Store redirected URI
-  ([#2360](https://github.com/google/ExoPlayer/issues/2360)).
+  * Cache redirect URLs
+    ([#2360](https://github.com/google/ExoPlayer/issues/2360)).
 * DRM:
   * Allow multiple listeners for `DefaultDrmSessionManager`.
   * Pass `DrmSessionManager` to `ExoPlayerFactory` instead of `RendererFactory`.
   * Change minimum API requirement for CBC and pattern encryption from 24 to 25
     ([#4022][https://github.com/google/ExoPlayer/issues/4022]).
+  * Fix handling of 307/308 redirects when making license requests
+    ([#4108](https://github.com/google/ExoPlayer/issues/4108)).
 * Removed default renderer time offset of 60000000 from internal player. The
   actual renderer timestamp offset can be obtained by listening to
   `BaseRenderer.onStreamChanged`.

library/core/src/main/java/com/google/android/exoplayer2/drm/HttpMediaDrmCallback.java

@@ -24,10 +24,12 @@
 import com.google.android.exoplayer2.upstream.DataSourceInputStream;
 import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.HttpDataSource;
+import com.google.android.exoplayer2.upstream.HttpDataSource.InvalidResponseCodeException;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Util;
 import java.io.IOException;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
@@ -37,6 +39,8 @@
 @TargetApi(18)
 public final class HttpMediaDrmCallback implements MediaDrmCallback {
 
+  private static final int MAX_MANUAL_REDIRECTS = 5;
+
   private final HttpDataSource.Factory dataSourceFactory;
   private final String defaultLicenseUrl;
   private final boolean forceDefaultLicenseUrl;
@@ -138,14 +142,46 @@ private static byte[] executePost(HttpDataSource.Factory dataSourceFactory, Stri
         dataSource.setRequestProperty(requestProperty.getKey(), requestProperty.getValue());
       }
     }
-    DataSpec dataSpec = new DataSpec(Uri.parse(url), data, 0, 0, C.LENGTH_UNSET, null,
-        DataSpec.FLAG_ALLOW_GZIP);
-    DataSourceInputStream inputStream = new DataSourceInputStream(dataSource, dataSpec);
-    try {
-      return Util.toByteArray(inputStream);
-    } finally {
-      Util.closeQuietly(inputStream);
+
+    int manualRedirectCount = 0;
+    while (true) {
+      DataSpec dataSpec =
+          new DataSpec(
+              Uri.parse(url),
+              data,
+              /* absoluteStreamPosition= */ 0,
+              /* position= */ 0,
+              /* length= */ C.LENGTH_UNSET,
+              /* key= */ null,
+              DataSpec.FLAG_ALLOW_GZIP);
+      DataSourceInputStream inputStream = new DataSourceInputStream(dataSource, dataSpec);
+      try {
+        return Util.toByteArray(inputStream);
+      } catch (InvalidResponseCodeException e) {
+        // For POST requests, the underlying network stack will not normally follow 307 or 308
+        // redirects automatically. Do so manually here.
+        boolean manuallyRedirect =
+            (e.responseCode == 307 || e.responseCode == 308)
+                && manualRedirectCount++ < MAX_MANUAL_REDIRECTS;
+        url = manuallyRedirect ? getRedirectUrl(e) : null;
+        if (url == null) {
+          throw e;
+        }
+      } finally {
+        Util.closeQuietly(inputStream);
+      }
+    }
+  }
+
+  private static String getRedirectUrl(InvalidResponseCodeException exception) {
+    Map<String, List<String>> headerFields = exception.headerFields;
+    if (headerFields != null) {
+      List<String> locationHeaders = headerFields.get("Location");
+      if (locationHeaders != null && !locationHeaders.isEmpty()) {
+        return locationHeaders.get(0);
+      }
     }
+    return null;
   }
 
 }