Remove BOM check in Webvtt header checks

Reverts the BOM check changes in []

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211826731

library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java

@@ -28,8 +28,6 @@ public final class WebvttParserUtil {
 
   private static final Pattern COMMENT = Pattern.compile("^NOTE((\u0020|\u0009).*)?$");
   private static final String WEBVTT_HEADER = "WEBVTT";
-  private static final int WEBVTT_BOM_BE = 0xfeff;
-  private static final int WEBVTT_BOM_LE = 0xfffe;
 
   private WebvttParserUtil() {}
 
@@ -53,15 +51,6 @@ public final class WebvttParserUtil {
    * @param input The input from which the line should be read.
    */
   public static boolean isWebvttHeaderLine(ParsableByteArray input) {
-    if (input.bytesLeft() < 2) {
-      return false;
-    }
-    int startPosition = input.getPosition();
-    int firstTwoBytes = input.readUnsignedShort();
-    if (firstTwoBytes != WEBVTT_BOM_BE && firstTwoBytes != WEBVTT_BOM_LE) {
-      // Not the BOM, should not be discarded.
-      input.setPosition(startPosition);
-    }
     String line = input.readLine();
     return line != null && line.startsWith(WEBVTT_HEADER);
   }

library/core/src/test/assets/webvtt/with_bom

@@ -1,4 +1,4 @@
-坅䉖呔‣⁔桩猠捯浭敮琠楳⁡汬潷敤
+WEBVTT # This comment is allowed
 
 00:00.000 --> 00:01.234
 This is the first subtitle.

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/WebvttExtractor.java

@@ -46,7 +46,8 @@ public final class WebvttExtractor implements Extractor {
 
   private static final Pattern LOCAL_TIMESTAMP = Pattern.compile("LOCAL:([^,]+)");
   private static final Pattern MEDIA_TIMESTAMP = Pattern.compile("MPEGTS:(\\d+)");
-  private static final int HEADER_MAX_LENGTH = 2 /* optional Byte Order Mark */ + 6 /* "WEBVTT" */;
+  private static final int HEADER_MIN_LENGTH = 6 /* "WEBVTT" */;
+  private static final int HEADER_MAX_LENGTH = 3 /* optional Byte Order Mark */ + HEADER_MIN_LENGTH;
 
   private final String language;
   private final TimestampAdjuster timestampAdjuster;
@@ -68,8 +69,19 @@ public final class WebvttExtractor implements Extractor {
 
   @Override
   public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
+    // Check whether there is a header without BOM.
     input.peekFully(
-        sampleData, /* offset= */ 0, /* length= */ HEADER_MAX_LENGTH, /* allowEndOfInput= */ false);
+        sampleData, /* offset= */ 0, /* length= */ HEADER_MIN_LENGTH, /* allowEndOfInput= */ false);
+    sampleDataWrapper.reset(sampleData, HEADER_MIN_LENGTH);
+    if (WebvttParserUtil.isWebvttHeaderLine(sampleDataWrapper)) {
+      return true;
+    }
+    // The header did not match, try including the BOM.
+    input.peekFully(
+        sampleData,
+        /* offset= */ HEADER_MIN_LENGTH,
+        HEADER_MAX_LENGTH - HEADER_MIN_LENGTH,
+        /* allowEndOfInput= */ false);
     sampleDataWrapper.reset(sampleData, HEADER_MAX_LENGTH);
     return WebvttParserUtil.isWebvttHeaderLine(sampleDataWrapper);
   }

library/hls/src/test/java/com/google/android/exoplayer2/source/hls/WebvttExtractorTest.java

@@ -20,6 +20,7 @@ import static com.google.common.truth.Truth.assertThat;
 import com.google.android.exoplayer2.extractor.ExtractorInput;
 import com.google.android.exoplayer2.testutil.FakeExtractorInput;
 import com.google.android.exoplayer2.util.TimestampAdjuster;
+import java.io.EOFException;
 import java.io.IOException;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -37,30 +38,37 @@ public class WebvttExtractorTest {
 
   @Test
   public void sniff_discardsByteOrderMark() throws IOException, InterruptedException {
-    byte[] data = new byte[] {(byte) 0xFE, (byte) 0xFF, 'W', 'E', 'B', 'V', 'T', 'T', '\n', ' '};
+    byte[] data =
+        new byte[] {(byte) 0xEF, (byte) 0xBB, (byte) 0xBF, 'W', 'E', 'B', 'V', 'T', 'T', '\n', ' '};
     assertThat(sniffData(data)).isTrue();
   }
 
   @Test
   public void sniff_failsForIncorrectBom() throws IOException, InterruptedException {
-    byte[] data = new byte[] {(byte) 0xFE, (byte) 0xFE, 'W', 'E', 'B', 'V', 'T', 'T', '\n'};
+    byte[] data =
+        new byte[] {(byte) 0xEF, (byte) 0xBB, (byte) 0xBB, 'W', 'E', 'B', 'V', 'T', 'T', '\n'};
     assertThat(sniffData(data)).isFalse();
   }
 
   @Test
   public void sniff_failsForIncompleteHeader() throws IOException, InterruptedException {
-    byte[] data = new byte[] {(byte) 0xFE, (byte) 0xFE, 'W', 'E', 'B', 'V', 'T', '\n'};
+    byte[] data = new byte[] {'W', 'E', 'B', 'V', 'T', '\n'};
     assertThat(sniffData(data)).isFalse();
   }
 
   @Test
   public void sniff_failsForIncorrectHeader() throws IOException, InterruptedException {
-    byte[] data = new byte[] {(byte) 0xFE, (byte) 0xFE, 'W', 'e', 'B', 'V', 'T', 'T', '\n'};
+    byte[] data =
+        new byte[] {(byte) 0xEF, (byte) 0xBB, (byte) 0xBF, 'W', 'e', 'B', 'V', 'T', 'T', '\n'};
     assertThat(sniffData(data)).isFalse();
   }
 
   private static boolean sniffData(byte[] data) throws IOException, InterruptedException {
     ExtractorInput input = new FakeExtractorInput.Builder().setData(data).build();
-    return new WebvttExtractor(/* language= */ null, new TimestampAdjuster(0)).sniff(input);
+    try {
+      return new WebvttExtractor(/* language= */ null, new TimestampAdjuster(0)).sniff(input);
+    } catch (EOFException e) {
+      return false;
+    }
   }
 }