[IMAGING-389] Fix searchQuad byte matching

src/changes/changes.xml

@@ -48,6 +48,7 @@ The <action> type attribute can be add,update,fix,remove.
   <body>
     <release version="1.0.0-alpha7" date="YYYY-MM-DD" description="This release requires Java 8.">
       <!-- FIX -->
+      <action type="fix" due-to="Aryan Ganjoo" issue="IMAGING-389">Fix BinaryFunctions.searchQuad matching for high-bit bytes and overlapping prefixes.</action>
       <action type="fix" dev="ggregory" due-to="Gary Gregory">Fix Apache RAT plugin console warnings.</action>
       <action type="fix" dev="ggregory" due-to="Gary Gregory">Fix Javadoc warnings.</action>
       <action type="fix" dev="ggregory" due-to="alhuda, Gary Gregory">Fix int overflow in PCX image buffer sizing, now throws AllocationRequestException (#552).</action>

src/main/java/org/apache/commons/imaging/common/BinaryFunctions.java

@@ -426,17 +426,16 @@ public static byte[] remainingBytes(final String name, final byte[] bytes, final
      * @throws IOException Thrown if it fails to read from the given input stream.
      */
     public static boolean searchQuad(final int quad, final InputStream in) throws IOException {
-        final byte[] needle = quadsToByteArray(quad);
-        int b = -1;
-        int position = 0;
+        // Slide a 4-byte window over the stream, so that bytes >= 0x80 and overlapping partial matches are handled.
+        int window = 0;
+        int count = 0;
+        int b;
         while ((b = in.read()) != -1) {
-            if (needle[position] == b) {
-                position++;
-                if (position == needle.length) {
-                    return true;
-                }
-            } else {
-                position = 0;
+            window = window << 8 | b;
+            if (count < 3) {
+                count++;
+            } else if (window == quad) {
+                return true;
             }
         }
         return false;

src/test/java/org/apache/commons/imaging/common/BinaryFunctionsTest.java

@@ -64,6 +64,35 @@ public void testReadBytes() throws IOException {
         assertArrayEquals(new byte[] { 1, 2, 3 }, read);
     }
 
+    @Test
+    public void testSearchQuad() throws IOException {
+        final int quad = BinaryFunctions.charsToQuad('8', 'B', 'I', 'M');
+        assertTrue(BinaryFunctions.searchQuad(quad, new ByteArrayInputStream(new byte[] { 0, '8', 'B', 'I', 'M', 1 })));
+        assertFalse(BinaryFunctions.searchQuad(quad, new ByteArrayInputStream(new byte[] { '8', 'B', 'I', 'X' })));
+        assertFalse(BinaryFunctions.searchQuad(quad, new ByteArrayInputStream(new byte[] { '8', 'B', 'I' })));
+    }
+
+    @Test
+    public void testSearchQuadAfterPartialMatch() throws IOException {
+        // The byte that breaks a partial match may itself start the quad.
+        final int quad = BinaryFunctions.charsToQuad('8', 'B', 'I', 'M');
+        final InputStream is = new ByteArrayInputStream(new byte[] { '8', '8', 'B', 'I', 'M', 1 });
+        assertTrue(BinaryFunctions.searchQuad(quad, is));
+        // The stream is left positioned right after the quad.
+        assertEquals(1, is.read());
+        // Overlapping prefix: "AAAB" inside "AAAAB".
+        final int aaab = BinaryFunctions.charsToQuad('A', 'A', 'A', 'B');
+        assertTrue(BinaryFunctions.searchQuad(aaab, new ByteArrayInputStream(new byte[] { 'A', 'A', 'A', 'A', 'B' })));
+    }
+
+    @Test
+    public void testSearchQuadWithHighBitBytes() throws IOException {
+        // Bytes >= 0x80 must match, for example a JPEG SOI + APP0 marker.
+        final InputStream is = new ByteArrayInputStream(new byte[] { 0, (byte) 0xFF, (byte) 0xD8, (byte) 0xFF, (byte) 0xE0, 7 });
+        assertTrue(BinaryFunctions.searchQuad(0xFFD8FFE0, is));
+        assertEquals(7, is.read());
+    }
+
     @Test
     public void testStartsWith() {
         final byte[] haystack = { 1, 2, 3, 4, 5 };