Clean up some DataSource implementations

- Make read return 0 if readLength==0
- Return RESULT_END_OF_INPUT properly in the case that
  bytesRemaining is unset (this was broken previously,
  but only applies for assets > 2^31 bytes, so it's
  unlikely anyone ever hit this issue)

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135136541

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

@@ -338,17 +338,21 @@ public class OkHttpDataSource implements HttpDataSource {
    * @throws IOException If an error occurs reading from the source.
    */
   private int readInternal(byte[] buffer, int offset, int readLength) throws IOException {
-    readLength = bytesToRead == C.LENGTH_UNSET ? readLength
-        : (int) Math.min(readLength, bytesToRead - bytesRead);
     if (readLength == 0) {
-      // We've read all of the requested data.
+      return 0;
+    }
+    if (bytesToRead != C.LENGTH_UNSET) {
+      long bytesRemaining = bytesToRead - bytesRead;
+      if (bytesRemaining == 0) {
         return C.RESULT_END_OF_INPUT;
       }
+      readLength = (int) Math.min(readLength, bytesRemaining);
+    }
 
     int read = responseByteStream.read(buffer, offset, readLength);
     if (read == -1) {
-      if (bytesToRead != C.LENGTH_UNSET && bytesToRead != bytesRead) {
+      if (bytesToRead != C.LENGTH_UNSET) {
-        // The server closed the connection having not sent sufficient data.
+        // End of stream reached having not read sufficient data.
         throw new EOFException();
       }
       return C.RESULT_END_OF_INPUT;

library/src/main/java/com/google/android/exoplayer2/upstream/AssetDataSource.java

@@ -104,9 +104,12 @@ public final class AssetDataSource implements DataSource {
 
   @Override
   public int read(byte[] buffer, int offset, int readLength) throws AssetDataSourceException {
-    if (bytesRemaining == 0) {
+    if (readLength == 0) {
+      return 0;
+    } else if (bytesRemaining == 0) {
       return C.RESULT_END_OF_INPUT;
-    } else {
+    }
+
     int bytesRead;
     try {
       int bytesToRead = bytesRemaining == C.LENGTH_UNSET ? readLength
@@ -116,18 +119,21 @@ public final class AssetDataSource implements DataSource {
       throw new AssetDataSourceException(e);
     }
 
-      if (bytesRead > 0) {
+    if (bytesRead == -1) {
+      if (bytesRemaining != C.LENGTH_UNSET) {
+        // End of stream reached having not read sufficient data.
+        throw new AssetDataSourceException(new EOFException());
+      }
+      return C.RESULT_END_OF_INPUT;
+    }
     if (bytesRemaining != C.LENGTH_UNSET) {
       bytesRemaining -= bytesRead;
     }
     if (listener != null) {
       listener.onBytesTransferred(this, bytesRead);
     }
-      }
-
     return bytesRead;
   }
-  }
 
   @Override
   public Uri getUri() {

library/src/main/java/com/google/android/exoplayer2/upstream/ByteArrayDataSource.java

@@ -54,15 +54,18 @@ public final class ByteArrayDataSource implements DataSource {
   }
 
   @Override
-  public int read(byte[] buffer, int offset, int length) throws IOException {
+  public int read(byte[] buffer, int offset, int readLength) throws IOException {
-    if (bytesRemaining == 0) {
+    if (readLength == 0) {
+      return 0;
+    } else if (bytesRemaining == 0) {
       return C.RESULT_END_OF_INPUT;
     }
-    length = Math.min(length, bytesRemaining);
+
-    System.arraycopy(data, readPosition, buffer, offset, length);
+    readLength = Math.min(readLength, bytesRemaining);
-    readPosition += length;
+    System.arraycopy(data, readPosition, buffer, offset, readLength);
-    bytesRemaining -= length;
+    readPosition += readLength;
-    return length;
+    bytesRemaining -= readLength;
+    return readLength;
   }
 
   @Override

library/src/main/java/com/google/android/exoplayer2/upstream/ContentDataSource.java

@@ -103,9 +103,12 @@ public final class ContentDataSource implements DataSource {
 
   @Override
   public int read(byte[] buffer, int offset, int readLength) throws ContentDataSourceException {
-    if (bytesRemaining == 0) {
+    if (readLength == 0) {
+      return 0;
+    } else if (bytesRemaining == 0) {
       return C.RESULT_END_OF_INPUT;
-    } else {
+    }
+
     int bytesRead;
     try {
       int bytesToRead = bytesRemaining == C.LENGTH_UNSET ? readLength
@@ -115,18 +118,21 @@ public final class ContentDataSource implements DataSource {
       throw new ContentDataSourceException(e);
     }
 
-      if (bytesRead > 0) {
+    if (bytesRead == -1) {
+      if (bytesRemaining != C.LENGTH_UNSET) {
+        // End of stream reached having not read sufficient data.
+        throw new ContentDataSourceException(new EOFException());
+      }
+      return C.RESULT_END_OF_INPUT;
+    }
     if (bytesRemaining != C.LENGTH_UNSET) {
       bytesRemaining -= bytesRead;
     }
     if (listener != null) {
       listener.onBytesTransferred(this, bytesRead);
     }
-      }
-
     return bytesRead;
   }
-  }
 
   @Override
   public Uri getUri() {

library/src/main/java/com/google/android/exoplayer2/upstream/DataSource.java

@@ -55,14 +55,18 @@ public interface DataSource {
 
   /**
    * Reads up to {@code length} bytes of data and stores them into {@code buffer}, starting at
-   * index {@code offset}. Blocks until at least one byte of data can be read, the end of the opened
+   * index {@code offset}.
-   * range is detected, or an exception is thrown.
+   * <p>
+   * If {@code length} is zero then 0 is returned. Otherwise, if no data is available because the
+   * end of the opened range has been reached, then {@link C#RESULT_END_OF_INPUT} is returned.
+   * Otherwise, the call will block until at least one byte of data has been read and the number of
+   * bytes read is returned.
    *
    * @param buffer The buffer into which the read data should be stored.
    * @param offset The start offset into {@code buffer} at which data should be written.
    * @param readLength The maximum number of bytes to read.
-   * @return The number of bytes read, or {@link C#RESULT_END_OF_INPUT} if the end of the opened
+   * @return The number of bytes read, or {@link C#RESULT_END_OF_INPUT} if no data is avaliable
-   *     range is reached.
+   *     because the end of the opened range has been reached.
    * @throws IOException If an error occurs reading from the source.
    */
   int read(byte[] buffer, int offset, int readLength) throws IOException;

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

@@ -550,11 +550,18 @@ public class DefaultHttpDataSource implements HttpDataSource {
     if (readLength == 0) {
       return 0;
     }
+    if (bytesToRead != C.LENGTH_UNSET) {
+      long bytesRemaining = bytesToRead - bytesRead;
+      if (bytesRemaining == 0) {
+        return C.RESULT_END_OF_INPUT;
+      }
+      readLength = (int) Math.min(readLength, bytesRemaining);
+    }
 
     int read = inputStream.read(buffer, offset, readLength);
     if (read == -1) {
-      if (bytesToRead != C.LENGTH_UNSET && bytesToRead != bytesRead) {
+      if (bytesToRead != C.LENGTH_UNSET) {
-        // The server closed the connection having not sent sufficient data.
+        // End of stream reached having not read sufficient data.
         throw new EOFException();
       }
       return C.RESULT_END_OF_INPUT;

library/src/main/java/com/google/android/exoplayer2/upstream/RawResourceDataSource.java

@@ -132,9 +132,12 @@ public final class RawResourceDataSource implements DataSource {
 
   @Override
   public int read(byte[] buffer, int offset, int readLength) throws RawResourceDataSourceException {
-    if (bytesRemaining == 0) {
+    if (readLength == 0) {
+      return 0;
+    } else if (bytesRemaining == 0) {
       return C.RESULT_END_OF_INPUT;
-    } else {
+    }
+
     int bytesRead;
     try {
       int bytesToRead = bytesRemaining == C.LENGTH_UNSET ? readLength
@@ -144,18 +147,21 @@ public final class RawResourceDataSource implements DataSource {
       throw new RawResourceDataSourceException(e);
     }
 
-      if (bytesRead > 0) {
+    if (bytesRead == -1) {
+      if (bytesRemaining != C.LENGTH_UNSET) {
+        // End of stream reached having not read sufficient data.
+        throw new RawResourceDataSourceException(new EOFException());
+      }
+      return C.RESULT_END_OF_INPUT;
+    }
     if (bytesRemaining != C.LENGTH_UNSET) {
       bytesRemaining -= bytesRead;
     }
     if (listener != null) {
       listener.onBytesTransferred(this, bytesRead);
     }
-      }
-
     return bytesRead;
   }
-  }
 
   @Override
   public Uri getUri() {