package com.example.embeddedproxy.network.util; import io.netty.buffer.ByteBuf; /** * Utilities for reading and writing Minecraft's variable-length integer encoding. * * VarInt encoding: each byte contributes 7 bits of value. The MSB (bit 7) is a * continuation flag — if set, more bytes follow. Maximum 5 bytes for a 32-bit int. */ public final class VarIntUtil { private VarIntUtil() {} /** * Read a VarInt from the buffer. Advances the reader index. * Throws {@link IllegalStateException} if the buffer contains an invalid VarInt. */ public static int readVarInt(ByteBuf buf) { int value = 0; int shift = 0; byte b; do { if (!buf.isReadable()) { throw new IllegalStateException("Buffer ended before VarInt was complete"); } b = buf.readByte(); value |= (b & 0x7F) << shift; shift += 7; if (shift > 35) { throw new IllegalStateException("VarInt too large (> 5 bytes)"); } } while ((b & 0x80) != 0); return value; } /** * Peek at a VarInt without advancing the reader index. * Returns the decoded value, or -1 if not enough bytes are available. */ public static int peekVarInt(ByteBuf buf) { int savedIndex = buf.readerIndex(); try { return readVarInt(buf); } catch (Exception e) { return -1; } finally { buf.readerIndex(savedIndex); } } /** * Write a VarInt into the buffer. */ public static void writeVarInt(ByteBuf buf, int value) { while (true) { if ((value & ~0x7F) == 0) { buf.writeByte(value); return; } buf.writeByte((value & 0x7F) | 0x80); value >>>= 7; } } /** * Returns the number of bytes required to encode the given value as a VarInt. */ public static int varIntSize(int value) { if ((value & (0xFFFFFFFF << 7)) == 0) return 1; if ((value & (0xFFFFFFFF << 14)) == 0) return 2; if ((value & (0xFFFFFFFF << 21)) == 0) return 3; if ((value & (0xFFFFFFFF << 28)) == 0) return 4; return 5; } /** * Returns the number of bytes the next VarInt in the buffer occupies, * without consuming any bytes. Returns -1 if not enough data is available. */ public static int varIntByteLength(ByteBuf buf) { int count = 0; for (int i = buf.readerIndex(); i < buf.writerIndex(); i++) { count++; byte b = buf.getByte(i); if ((b & 0x80) == 0) return count; if (count == 5) return -1; // malformed } return -1; // incomplete } }