Add readVarInt and writeVarInt extension methods

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

buffer/src/main/kotlin/org/openrs2/buffer/ByteBufExtensions.kt

@@ -128,6 +128,40 @@ public fun ByteBuf.writeVersionedString(s: CharSequence): ByteBuf {
     return this
 }
 
+public fun ByteBuf.readVarInt(): Int {
+    var value = 0
+
+    var byte: Int
+    do {
+        byte = readUnsignedByte().toInt()
+        value = (value shl 7) or (byte and 0x7F)
+    } while ((byte and 0x80) != 0)
+
+    return value
+}
+
+public fun ByteBuf.writeVarInt(v: Int): ByteBuf {
+    if ((v and 0x7F.inv()) != 0) {
+        if ((v and 0x3FFF.inv()) != 0) {
+            if ((v and 0x1FFFFF.inv()) != 0) {
+                if ((v and 0xFFFFFFF.inv()) != 0) {
+                    writeByte(((v ushr 28) and 0x7F) or 0x80)
+                }
+
+                writeByte(((v ushr 21) and 0x7F) or 0x80)
+            }
+
+            writeByte(((v ushr 14) and 0x7F) or 0x80)
+        }
+
+        writeByte(((v ushr 7) and 0x7F) or 0x80)
+    }
+
+    writeByte(v and 0x7F)
+
+    return this
+}
+
 public fun ByteBuf.crc32(): Int {
     return crc32(readerIndex(), readableBytes())
 }

buffer/src/test/kotlin/org/openrs2/buffer/ByteBufExtensionsTest.kt

@@ -586,6 +586,108 @@ class ByteBufExtensionsTest {
         }
     }
 
+    @Test
+    fun testReadVarInt() {
+        wrappedBuffer(0x7F).use { buf ->
+            assertEquals(0x7F, buf.readVarInt())
+        }
+
+        wrappedBuffer(0x81.toByte(), 0x00).use { buf ->
+            assertEquals(0x80, buf.readVarInt())
+        }
+
+        wrappedBuffer(0xFF.toByte(), 0x7F).use { buf ->
+            assertEquals(0x3FFF, buf.readVarInt())
+        }
+
+        wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x00).use { buf ->
+            assertEquals(0x4000, buf.readVarInt())
+        }
+
+        wrappedBuffer(0xFF.toByte(), 0xFF.toByte(), 0x7F.toByte()).use { buf ->
+            assertEquals(0x1FFFFF, buf.readVarInt())
+        }
+
+        wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x80.toByte(), 0x00).use { buf ->
+            assertEquals(0x200000, buf.readVarInt())
+        }
+
+        wrappedBuffer(0xFF.toByte(), 0xFF.toByte(), 0xFF.toByte(), 0x7F).use { buf ->
+            assertEquals(0xFFFFFFF, buf.readVarInt())
+        }
+
+        wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x80.toByte(), 0x80.toByte(), 0x00).use { buf ->
+            assertEquals(0x10000000, buf.readVarInt())
+        }
+    }
+
+    @Test
+    fun testWriteVarInt() {
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x7F)
+
+            wrappedBuffer(0x7F).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x80)
+
+            wrappedBuffer(0x81.toByte(), 0x00).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x3FFF)
+
+            wrappedBuffer(0xFF.toByte(), 0x7F).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x4000)
+
+            wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x00).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x1FFFFF)
+
+            wrappedBuffer(0xFF.toByte(), 0xFF.toByte(), 0x7F).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x200000)
+
+            wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x80.toByte(), 0x00).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0xFFFFFFF)
+
+            wrappedBuffer(0xFF.toByte(), 0xFF.toByte(), 0xFF.toByte(), 0x7F).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+
+        ByteBufAllocator.DEFAULT.buffer().use { actual ->
+            actual.writeVarInt(0x10000000)
+
+            wrappedBuffer(0x81.toByte(), 0x80.toByte(), 0x80.toByte(), 0x80.toByte(), 0x00).use { expected ->
+                assertEquals(expected, actual)
+            }
+        }
+    }
+
     @Test
     fun testCrc32() {
         val s = "AAThe quick brown fox jumps over the lazy dogA"