Add CRC-32 extension method to the ByteBuf class

Signed-off-by: Graham <gpe@openrs2.dev>

buffer/src/main/java/dev/openrs2/buffer/ByteBufExtensions.kt

@@ -1,6 +1,8 @@
 package dev.openrs2.buffer
 
 import io.netty.buffer.ByteBuf
+import io.netty.buffer.ByteBufUtil
+import java.util.zip.CRC32
 
 public fun ByteBuf.readShortSmart(): Int {
     val peek = getUnsignedByte(readerIndex()).toInt()
@@ -77,3 +79,29 @@ public fun ByteBuf.writeUnsignedIntSmart(v: Int): ByteBuf {
 
     return this
 }
+
+public fun ByteBuf.crc32(): Int {
+    return crc32(readerIndex(), readableBytes())
+}
+
+public fun ByteBuf.crc32(index: Int, len: Int): Int {
+    if (index < 0 || index >= capacity() || len < 0 || (index + len) >= capacity()) {
+        throw IndexOutOfBoundsException()
+    }
+
+    val crc = CRC32()
+    val count = nioBufferCount()
+
+    when {
+        hasArray() -> crc.update(array(), arrayOffset() + index, len)
+        count > 1 -> {
+            for (b in nioBuffers(index, len)) {
+                crc.update(b)
+            }
+        }
+        count == 1 -> crc.update(nioBuffer(index, len))
+        else -> crc.update(ByteBufUtil.getBytes(this, index, len))
+    }
+
+    return crc.value.toInt()
+}

buffer/src/test/java/dev/openrs2/buffer/ByteBufExtensionsTest.kt

@@ -391,4 +391,64 @@ object ByteBufExtensionsTest {
             }
         }
     }
+
+    @Test
+    fun testCrc32() {
+        val s = "AAThe quick brown fox jumps over the lazy dogA"
+
+        /*
+         * Tests the hasArray() case. The slicedBuf trickery is to allow us
+         * to test a non-zero arrayOffset().
+         */
+        Unpooled.wrappedBuffer(s.toByteArray()).use { buf ->
+            val slicedBuf = buf.slice(1, buf.readableBytes() - 1)
+            assertEquals(0x414FA339, slicedBuf.crc32(1, slicedBuf.writerIndex() - 2))
+        }
+
+        // Tests the nioBufferCount() == 1 case.
+        Unpooled.wrappedBuffer(s.toByteArray()).use { buf ->
+            ByteBufAllocator.DEFAULT.directBuffer().use { directBuf ->
+                directBuf.writeBytes(buf, 0, buf.capacity())
+
+                assertEquals(0x414FA339, directBuf.crc32(2, directBuf.writerIndex() - 3))
+            }
+        }
+
+        // Tests the nioBufferCount() > 1 case.
+        Unpooled.wrappedBuffer(
+            Unpooled.wrappedBuffer("AAThe quick brown fox ".toByteArray()),
+            Unpooled.wrappedBuffer("jumps over the lazy dogA".toByteArray())
+        ).use { buf ->
+            assertEquals(0x414FA339, buf.crc32(2, buf.writerIndex() - 3))
+        }
+
+        /*
+         * Check the crc32() method (with no arguments) sets the index/length
+         * correctly.
+         */
+        Unpooled.wrappedBuffer(s.toByteArray()).use { buf ->
+            buf.readerIndex(2)
+            buf.writerIndex(buf.writerIndex() - 1)
+            assertEquals(0x414FA339, buf.crc32())
+        }
+    }
+
+    @Test
+    fun testCrc32Bounds() {
+        assertThrows<IndexOutOfBoundsException> {
+            Unpooled.EMPTY_BUFFER.crc32(-1, 0)
+        }
+
+        assertThrows<IndexOutOfBoundsException> {
+            Unpooled.EMPTY_BUFFER.crc32(0, -1)
+        }
+
+        assertThrows<IndexOutOfBoundsException> {
+            Unpooled.EMPTY_BUFFER.crc32(1, 0)
+        }
+
+        assertThrows<IndexOutOfBoundsException> {
+            Unpooled.EMPTY_BUFFER.crc32(0, 1)
+        }
+    }
 }