Add Packer/Unpacker, add serialization to LuaSnap

luprex/core/cpp/packer.hpp

@@ -0,0 +1,72 @@
+#ifndef PACKER_HPP
+#define PACKER_HPP
+
+#include "luastack.hpp"
+#include <cstdint>
+#include <string>
+#include <sstream>
+#include <cassert>
+
+class Packer {
+private:
+    std::ostringstream *oss_;
+
+    // Packer is not copyable.
+    Packer(const Packer &other) { assert(false); }
+public:
+    using fixhandle = size_t;
+    Packer(std::ostringstream *s) : oss_(s) {}
+
+    // Get the current file position.
+    size_t tellp() { return oss_->tellp(); }
+    
+    void write_int8(int8_t v);
+    void write_int16(int16_t v);
+    void write_int32(int32_t v);
+    void write_int64(int64_t v);
+
+    // Sometimes, you want to write a length followed by a block of data.
+    // Sometimes, you don't know the length until after you've written the block
+    // of data.  To help with this situation, we provide the overwrite_int
+    // functions.  Here's what you do:
+    //
+    // 1. write a dummy length into the stream.
+    // 2. use 'tellp' to fetch the stream position *after* the dummy length.
+    // 3. write the block of data.
+    // 4. use an overwrite function below to overwrite the dummy length.
+    //
+    void overwrite_int8(size_t tell_after, int8_t value);
+    void overwrite_int16(size_t tell_after, int16_t value);
+    void overwrite_int32(size_t tell_after, int32_t value);
+    void overwrite_int64(size_t tell_after, int64_t value);
+
+    // The packer can be used as a lua_Writer.
+    static int lua_writer(lua_State *L, const void *p, size_t sz, void *ud);
+    void *lua_writer_ud() { return this; }
+};
+
+class Unpacker {
+private:
+    const char *data_;
+    size_t size_;
+
+public:
+    Unpacker(const char *d, size_t s);
+    const char *data() { return data_; }
+    size_t size() { return size_; }
+    
+    int8_t  read_int8();
+    int16_t read_int16();
+    int32_t read_int32();
+    int64_t read_int64();
+    void skip(size_t n);
+    Unpacker read_section(size_t n);
+
+    // The unpacker can be used as a lua_Reader
+    static const char *lua_reader(lua_State *L, void *ud, size_t *size);
+    void *lua_reader_ud() { return this; }
+};
+
+
+
+#endif // PACKER_HPP