From e933ccb59c7f032d2ffc5c5f7046317a06e85e14 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Tue, 17 Oct 2023 02:30:52 +0200
Subject: codec,codec-minecraft: Adding basic foundations needed for the
 minecraft protocol

---
 c++/codec-minecraft/minecraft.h | 116 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 c++/codec-minecraft/minecraft.h

(limited to 'c++/codec-minecraft/minecraft.h')

diff --git a/c++/codec-minecraft/minecraft.h b/c++/codec-minecraft/minecraft.h
new file mode 100644
index 0000000..670b019
--- /dev/null
+++ b/c++/codec-minecraft/minecraft.h
@@ -0,0 +1,116 @@
+#pragma once
+
+#include <forstio/core/error.h>
+#include <forstio/codec/data.h>
+#include <forstio/codec/stream_value.h>
+
+namespace saw {
+namespace encode {
+struct Minecraft {};
+struct VarIntTransport {};
+}
+
+template<typename T>
+class data<T, encode::Minecraft> {
+private:
+	ring_buffer buffer_;
+public:
+	data() = default;
+	data(std::size_t size):
+		buffer_{size}
+	{}
+
+	buffer& get_buffer(){
+		return buffer_;
+	}
+};
+
+namespace mc {
+namespace impl {
+union minecraft_signed_four_conversion {
+		int32_t s;
+		uint32_t u;
+};
+
+union minecraft_signed_eight_conversion {
+		int64_t s;
+		uint64_t u;
+};
+
+template<typename Schema, typename FromEnc>
+class minecraft_encode {
+	static_assert(always_false<Schema, FromEnc>, "This schema type is not being handled by the Minecraft encoding.");
+};
+
+template<typename FromEnc>
+class minecraft_encode<schema::VarInt, FromEnc>{
+	static error_or<void> encode(const data<schema::VarInt, FromEnc>& from, buffer& to){
+		uint8_t encode_index = 0;
+		minecraft_signed_four_conversion value;
+		value.s = from.get();
+
+		/**
+		 * VarInt max length is 5 bytes
+		 */
+		std::array<uint8_t, 5> encode_data;
+
+		do {
+				uint8_t step = static_cast<uint8_t>(value.u & 0x7F);
+				value.u = value.u >> 7;
+				if(value.u != 0){
+						step |= 0x80;
+				}
+				encode_data[encode_index] = step;
+				++encode_index;
+		}while(value.u != 0);
+		
+		auto err = buffer.push(encode_data[0], encode_index);
+		if (!err.template is_type<err::no_error>()) {
+				return err;
+		}
+
+		return no_error();
+	}
+};
+
+template<typename Schema, typename FromEnc>
+class minecraft_decode {
+	static_assert(always_false<Schema, FromEnc>, "This schema type is not being handled by the Minecraft encoding.");
+};
+
+template<typename FromEnc>
+class minecraft_decode<schema::VarInt, FromEnc>{
+		static error_or<void> decode(buffer& from, data<schema::VarInt, FromEnc>& to){
+				uint8_t num_reads = 0;
+
+				minecraft_signed_four_conversion value;
+				value.u = 0;
+				
+				uint8_t read{};
+				do {
+						auto err = from.pop(read);
+						if( !err.template is_type<err::no_error>() ){
+								return err;
+						}
+						value.u |= ((read & 0x7F) << (7*num_reads));
+						++num_reads;
+						if(num_reads > 5){
+								return make_error<err::>();
+						}
+				} while( (read & 0x80) != 0);
+
+				to.set(value.s);
+
+				return no_error();
+		}
+};
+
+}
+}
+
+
+
+namespace mc {
+
+}
+}
-- 
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