Add method for peeking at the version trailer

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

cache/src/main/kotlin/org/openrs2/cache/VersionTrailer.kt

@@ -3,6 +3,14 @@ package org.openrs2.cache
 import io.netty.buffer.ByteBuf
 
 public object VersionTrailer {
+    public fun peek(buf: ByteBuf): Int? {
+        return if (buf.readableBytes() >= 2) {
+            buf.getUnsignedShort(buf.writerIndex() - 2)
+        } else {
+            null
+        }
+    }
+
     public fun strip(buf: ByteBuf): Int? {
         return if (buf.readableBytes() >= 2) {
             val index = buf.writerIndex() - 2

cache/src/test/kotlin/org/openrs2/cache/VersionTrailerTest.kt

@@ -8,6 +8,23 @@ import kotlin.test.assertEquals
 import kotlin.test.assertNull
 
 class VersionTrailerTest {
+    @Test
+    fun testPeek() {
+        assertNull(VersionTrailer.peek(Unpooled.EMPTY_BUFFER))
+
+        wrappedBuffer(0).use { buf ->
+            assertNull(VersionTrailer.peek(buf))
+        }
+
+        wrappedBuffer(0x12, 0x34).use { buf ->
+            assertEquals(0x1234, VersionTrailer.peek(buf))
+        }
+
+        wrappedBuffer(0x12, 0x34, 0x56).use { buf ->
+            assertEquals(0x3456, VersionTrailer.peek(buf))
+        }
+    }
+
     @Test
     fun testStrip() {
         assertNull(VersionTrailer.strip(Unpooled.EMPTY_BUFFER))