Handle size==0 in MP4 atoms

Issue: #3191

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=165925148

library/core/src/androidTest/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4ExtractorTest.java

@@ -16,7 +16,6 @@
 package com.google.android.exoplayer2.extractor.mp4;
 
 import android.test.InstrumentationTestCase;
-import com.google.android.exoplayer2.ParserException;
 import com.google.android.exoplayer2.extractor.Extractor;
 import com.google.android.exoplayer2.testutil.ExtractorAsserts;
 import com.google.android.exoplayer2.testutil.ExtractorAsserts.ExtractorFactory;
@@ -38,11 +37,6 @@ public final class FragmentedMp4ExtractorTest extends InstrumentationTestCase {
         "mp4/sample_fragmented_sei.mp4", getInstrumentation());
   }
 
-  public void testAtomWithZeroSize() throws Exception {
-    ExtractorAsserts.assertThrows(getExtractorFactory(), "mp4/sample_fragmented_zero_size_atom.mp4",
-        getInstrumentation(), ParserException.class);
-  }
-
   private static ExtractorFactory getExtractorFactory() {
     return getExtractorFactory(0);
   }

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Atom.java

@@ -39,9 +39,14 @@ import java.util.List;
   public static final int LONG_HEADER_SIZE = 16;
 
   /**
-   * Value for the first 32 bits of atomSize when the atom size is actually a long value.
+   * Value for the size field in an atom that defines its size in the largesize field.
    */
-  public static final int LONG_SIZE_PREFIX = 1;
+  public static final int DEFINES_LARGE_SIZE = 1;
+
+  /**
+   * Value for the size field in an atom that extends to the end of the file.
+   */
+  public static final int EXTENDS_TO_END_SIZE = 0;
 
   public static final int TYPE_ftyp = Util.getIntegerCodeForString("ftyp");
   public static final int TYPE_avc1 = Util.getIntegerCodeForString("avc1");

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java

@@ -283,12 +283,22 @@ public final class FragmentedMp4Extractor implements Extractor {
       atomType = atomHeader.readInt();
     }
 
-    if (atomSize == Atom.LONG_SIZE_PREFIX) {
-      // Read the extended atom size.
+    if (atomSize == Atom.DEFINES_LARGE_SIZE) {
+      // Read the large size.
       int headerBytesRemaining = Atom.LONG_HEADER_SIZE - Atom.HEADER_SIZE;
       input.readFully(atomHeader.data, Atom.HEADER_SIZE, headerBytesRemaining);
       atomHeaderBytesRead += headerBytesRemaining;
       atomSize = atomHeader.readUnsignedLongToLong();
+    } else if (atomSize == Atom.EXTENDS_TO_END_SIZE) {
+      // The atom extends to the end of the file. Note that if the atom is within a container we can
+      // work out its size even if the input length is unknown.
+      long endPosition = input.getLength();
+      if (endPosition == C.LENGTH_UNSET && !containerAtoms.isEmpty()) {
+        endPosition = containerAtoms.peek().endPosition;
+      }
+      if (endPosition != C.LENGTH_UNSET) {
+        atomSize = endPosition - input.getPosition() + atomHeaderBytesRead;
+      }
     }
 
     if (atomSize < atomHeaderBytesRead) {

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Mp4Extractor.java

@@ -205,12 +205,26 @@ public final class Mp4Extractor implements Extractor, SeekMap {
       atomType = atomHeader.readInt();
     }
 
-    if (atomSize == Atom.LONG_SIZE_PREFIX) {
-      // Read the extended atom size.
+    if (atomSize == Atom.DEFINES_LARGE_SIZE) {
+      // Read the large size.
       int headerBytesRemaining = Atom.LONG_HEADER_SIZE - Atom.HEADER_SIZE;
       input.readFully(atomHeader.data, Atom.HEADER_SIZE, headerBytesRemaining);
       atomHeaderBytesRead += headerBytesRemaining;
       atomSize = atomHeader.readUnsignedLongToLong();
+    } else if (atomSize == Atom.EXTENDS_TO_END_SIZE) {
+      // The atom extends to the end of the file. Note that if the atom is within a container we can
+      // work out its size even if the input length is unknown.
+      long endPosition = input.getLength();
+      if (endPosition == C.LENGTH_UNSET && !containerAtoms.isEmpty()) {
+        endPosition = containerAtoms.peek().endPosition;
+      }
+      if (endPosition != C.LENGTH_UNSET) {
+        atomSize = endPosition - input.getPosition() + atomHeaderBytesRead;
+      }
+    }
+
+    if (atomSize < atomHeaderBytesRead) {
+      throw new ParserException("Atom size less than header length (unsupported).");
     }
 
     if (shouldParseContainerAtom(atomType)) {

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Sniffer.java

@@ -104,11 +104,18 @@ import java.io.IOException;
       input.peekFully(buffer.data, 0, headerSize);
       long atomSize = buffer.readUnsignedInt();
       int atomType = buffer.readInt();
-      if (atomSize == Atom.LONG_SIZE_PREFIX) {
+      if (atomSize == Atom.DEFINES_LARGE_SIZE) {
+        // Read the large atom size.
         headerSize = Atom.LONG_HEADER_SIZE;
         input.peekFully(buffer.data, Atom.HEADER_SIZE, Atom.LONG_HEADER_SIZE - Atom.HEADER_SIZE);
         buffer.setLimit(Atom.LONG_HEADER_SIZE);
         atomSize = buffer.readUnsignedLongToLong();
+      } else if (atomSize == Atom.EXTENDS_TO_END_SIZE) {
+        // The atom extends to the end of the file.
+        long endPosition = input.getLength();
+        if (endPosition != C.LENGTH_UNSET) {
+          atomSize = endPosition - input.getPosition() + headerSize;
+        }
       }
 
       if (atomSize < headerSize) {