Check #EXTM3U header is present in HLS playlists

Issue:#2301

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=144334062

library/src/androidTest/java/com/google/android/exoplayer2/source/hls/playlist/HlsMasterPlaylistParserTest.java

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.source.hls.playlist;
 import android.net.Uri;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.ParserException;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.nio.charset.Charset;
@@ -29,9 +30,9 @@ import junit.framework.TestCase;
  */
 public class HlsMasterPlaylistParserTest extends TestCase {
 
-  public void testParseMasterPlaylist() {
-    Uri playlistUri = Uri.parse("https://example.com/test.m3u8");
-    String playlistString = "#EXTM3U\n"
+  private static final String PLAYLIST_URI = "https://example.com/test.m3u8";
+
+  private static final String MASTER_PLAYLIST = " #EXTM3U \n"
       + "\n"
       + "#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS=\"mp4a.40.2,avc1.66.30\",RESOLUTION=304x128\n"
       + "http://example.com/low.m3u8\n"
@@ -47,10 +48,13 @@ public class HlsMasterPlaylistParserTest extends TestCase {
       + "\n"
       + "#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS=\"mp4a.40.5\"\n"
       + "http://example.com/audio-only.m3u8";
-    ByteArrayInputStream inputStream = new ByteArrayInputStream(
-        playlistString.getBytes(Charset.forName(C.UTF8_NAME)));
-    try {
-      HlsPlaylist playlist = new HlsPlaylistParser().parse(playlistUri, inputStream);
+
+  private static final String PLAYLIST_WITH_INVALID_HEADER = "#EXTMU3\n"
+      + "#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS=\"mp4a.40.2,avc1.66.30\",RESOLUTION=304x128\n"
+      + "http://example.com/low.m3u8\n";
+
+  public void testParseMasterPlaylist() throws IOException{
+    HlsPlaylist playlist = parsePlaylist(PLAYLIST_URI, MASTER_PLAYLIST);
     assertNotNull(playlist);
     assertEquals(HlsPlaylist.TYPE_MASTER, playlist.type);
 
@@ -90,9 +94,22 @@ public class HlsMasterPlaylistParserTest extends TestCase {
     assertEquals(Format.NO_VALUE, variants.get(4).format.width);
     assertEquals(Format.NO_VALUE, variants.get(4).format.height);
     assertEquals("http://example.com/audio-only.m3u8", variants.get(4).url);
-    } catch (IOException exception) {
-      fail(exception.getMessage());
+  }
+
+  public void testPlaylistWithInvalidHeader() throws IOException {
+    try {
+      parsePlaylist(PLAYLIST_URI, PLAYLIST_WITH_INVALID_HEADER);
+      fail("Expected exception not thrown.");
+    } catch (ParserException e) {
+      // Expected due to invalid header.
     }
   }
 
+  private static HlsPlaylist parsePlaylist(String uri, String playlistString) throws IOException {
+    Uri playlistUri = Uri.parse(uri);
+    ByteArrayInputStream inputStream = new ByteArrayInputStream(
+        playlistString.getBytes(Charset.forName(C.UTF8_NAME)));
+    return new HlsPlaylistParser().parse(playlistUri, inputStream);
+  }
+
 }

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

@@ -39,6 +39,22 @@ import java.util.regex.Pattern;
  */
 public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlaylist> {
 
+  /**
+   * Thrown if the input does not start with an HLS playlist header.
+   */
+  public static final class UnrecognizedInputFormatException extends ParserException {
+
+    public final Uri inputUri;
+
+    public UnrecognizedInputFormatException(Uri inputUri) {
+      super("Input does not start with the #EXTM3U header. Uri: " + inputUri);
+      this.inputUri = inputUri;
+    }
+
+  }
+
+  private static final String PLAYLIST_HEADER = "#EXTM3U";
+
   private static final String TAG_VERSION = "#EXT-X-VERSION";
   private static final String TAG_STREAM_INF = "#EXT-X-STREAM-INF";
   private static final String TAG_MEDIA = "#EXT-X-MEDIA";
@@ -97,6 +113,9 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     Queue<String> extraLines = new LinkedList<>();
     String line;
     try {
+      if (!checkPlaylistHeader(reader)) {
+        throw new UnrecognizedInputFormatException(uri);
+      }
       while ((line = reader.readLine()) != null) {
         line = line.trim();
         if (line.isEmpty()) {
@@ -124,6 +143,35 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     throw new ParserException("Failed to parse the playlist, could not identify any tags.");
   }
 
+  private static boolean checkPlaylistHeader(BufferedReader reader) throws IOException {
+    int last = reader.read();
+    if (last == 0xEF) {
+      if (reader.read() != 0xBB || reader.read() != 0xBF) {
+        return false;
+      }
+      // The playlist contains a Byte Order Mark, which gets discarded.
+      last = reader.read();
+    }
+    last = skipIgnorableWhitespace(reader, true, last);
+    int playlistHeaderLength = PLAYLIST_HEADER.length();
+    for (int i = 0; i < playlistHeaderLength; i++) {
+      if (last != PLAYLIST_HEADER.charAt(i)) {
+        return false;
+      }
+      last = reader.read();
+    }
+    last = skipIgnorableWhitespace(reader, false, last);
+    return Util.isLinebreak(last);
+  }
+
+  private static int skipIgnorableWhitespace(BufferedReader reader, boolean skipLinebreaks, int c)
+      throws IOException {
+    while (c != -1 && Character.isWhitespace(c) && (skipLinebreaks || !Util.isLinebreak(c))) {
+      c = reader.read();
+    }
+    return c;
+  }
+
   private static HlsMasterPlaylist parseMasterPlaylist(LineIterator iterator, String baseUri)
       throws IOException {
     ArrayList<HlsMasterPlaylist.HlsUrl> variants = new ArrayList<>();

library/src/main/java/com/google/android/exoplayer2/util/ParsableByteArray.java

@@ -494,7 +494,7 @@ public final class ParsableByteArray {
       return null;
     }
     int lineLimit = position;
-    while (lineLimit < limit && data[lineLimit] != '\n' && data[lineLimit] != '\r') {
+    while (lineLimit < limit && !Util.isLinebreak(data[lineLimit])) {
       lineLimit++;
     }
     if (lineLimit - position >= 3 && data[position] == (byte) 0xEF

library/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -254,6 +254,16 @@ public final class Util {
     return value.getBytes(Charset.defaultCharset()); // UTF-8 is the default on Android.
   }
 
+  /**
+   * Returns whether the given character is a carriage return ('\r') or a line feed ('\n').
+   *
+   * @param c The character.
+   * @return Whether the given character is a linebreak.
+   */
+  public static boolean isLinebreak(int c) {
+    return c == '\n' || c == '\r';
+  }
+
   /**
    * Converts text to lower case using {@link Locale#US}.
    *