From e8842b939ccb4dc246e30b9a8aa1676f03a65539 Mon Sep 17 00:00:00 2001
From: ibaker <ibaker@google.com>
Date: Mon, 10 Mar 2025 10:01:36 -0700
Subject: [PATCH] Prevent `ParsableByteArray.bytesLeft()` returning a negative
 value

PiperOrigin-RevId: 735417945
---
 .../media3/common/util/ParsableByteArray.java |  4 ++--
 .../androidx/media3/common/util/Util.java     |  2 +-
 .../common/util/ParsableByteArrayTest.java    | 20 +++++++++++++++++++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/libraries/common/src/main/java/androidx/media3/common/util/ParsableByteArray.java b/libraries/common/src/main/java/androidx/media3/common/util/ParsableByteArray.java
index 7fcc0fa4eb..d1b2cf00c2 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/ParsableByteArray.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/ParsableByteArray.java
@@ -142,7 +142,7 @@ public final class ParsableByteArray {
 
   /** Returns the number of bytes yet to be read. */
   public int bytesLeft() {
-    return limit - position;
+    return Math.max(limit - position, 0);
   }
 
   /** Returns the limit. */
@@ -261,7 +261,7 @@ public final class ParsableByteArray {
   public char peekChar(Charset charset) {
     Assertions.checkArgument(
         SUPPORTED_CHARSETS_FOR_READLINE.contains(charset), "Unsupported charset: " + charset);
-    if (bytesLeft() < 1) {
+    if (bytesLeft() == 0) {
       return 0;
     }
     if (charset.equals(StandardCharsets.US_ASCII)) {
diff --git a/libraries/common/src/main/java/androidx/media3/common/util/Util.java b/libraries/common/src/main/java/androidx/media3/common/util/Util.java
index 6626cff721..eca114ec3e 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/Util.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/Util.java
@@ -3061,7 +3061,7 @@ public final class Util {
   @UnstableApi
   public static boolean inflate(
       ParsableByteArray input, ParsableByteArray output, @Nullable Inflater inflater) {
-    if (input.bytesLeft() <= 0) {
+    if (input.bytesLeft() == 0) {
       return false;
     }
     if (output.capacity() < input.bytesLeft()) {
diff --git a/libraries/common/src/test/java/androidx/media3/common/util/ParsableByteArrayTest.java b/libraries/common/src/test/java/androidx/media3/common/util/ParsableByteArrayTest.java
index 4b8674a422..22bea475ee 100644
--- a/libraries/common/src/test/java/androidx/media3/common/util/ParsableByteArrayTest.java
+++ b/libraries/common/src/test/java/androidx/media3/common/util/ParsableByteArrayTest.java
@@ -77,6 +77,26 @@ public final class ParsableByteArrayTest {
     assertThat(array.limit()).isEqualTo(4);
   }
 
+  @Test
+  public void bytesLeft() {
+    ParsableByteArray array = getTestDataArray();
+    assertThat(array.bytesLeft()).isEqualTo(TEST_DATA.length);
+
+    array.setPosition(1);
+    array.setLimit(2);
+    assertThat(array.bytesLeft()).isEqualTo(1);
+  }
+
+  @Test
+  public void bytesLeft_positionExceedsLimit_returnsZero() {
+    ParsableByteArray array = getTestDataArray();
+    array.setLimit(1);
+    // readInt advances position without checking limit (see b/147657250)
+    int unused = array.readInt();
+
+    assertThat(array.bytesLeft()).isEqualTo(0);
+  }
+
   @Test
   public void readShort() {
     testReadShort((short) -1);