Boost ASIO - How to perpend header in front of TCP Message - c++

Question

Here is my code minimized for the purpose of readability.
I was following this guide: https://www.boost.org/doc/libs/1_63_0/doc/html/boost_asio/example/cpp11/chat/chat_server.cpp
Packet.h:
#ifndef VIBRANIUM_CORE_PACKET_H
#define VIBRANIUM_CORE_PACKET_H
#include <cstdio>
#include <cstdlib>
#include <cstring>
class Packet {
public:
Packet() : body_length_(0)
{
}
enum { max_body_length = 1024 };
enum { header_length = 8 };
char header_[header_length];
const char* data() const;
char* data();
size_t length() const;
const char* body() const;
char* body();
size_t body_length() const;
void body_length(std::size_t new_length);
bool decode_header();
void encode_header();
private:
char data_[header_length + max_body_length];
size_t body_length_;
};
#endif //VIBRANIUM_CORE_PACKET_H
Packet.cpp:
#include "Packet.h"
const char *Packet::data() const {
return data_;
}
char *Packet::data() {
return data_;
}
size_t Packet::length() const {
return header_length + body_length_;
}
const char *Packet::body() const {
return data_ + header_length;
}
char *Packet::body() {
return data_ + header_length;
}
size_t Packet::body_length() const {
return body_length_;
}
void Packet::body_length(std::size_t new_length) {
body_length_ = new_length;
if (body_length_ > max_body_length)
body_length_ = max_body_length;
}
bool Packet::decode_header() {
char header[header_length + 1] = "";
std::strncat(header, data_, header_length);
body_length_ = std::atoi(header);
if (body_length_ > max_body_length)
{
body_length_ = 0;
return false;
}
return true;
}
void Packet::encode_header() {
char header[header_length + 1] = "";
std::sprintf(header, "%4d", static_cast<int>(body_length_));
std::memcpy(data_, header, header_length);
}
ServerOpcode.h:
#ifndef VIBRANIUM_CORE_SERVEROPCODE_H
#define VIBRANIUM_CORE_SERVEROPCODE_H
#include <cstdint>
enum ServerOpcode : uint16_t{
SMSG_AUTH_CONNECTION_RESPONSE = 0x001,
SMSG_LOGIN_REQUEST_RESPONSE = 0x002,
};
#endif //VIBRANIUM_CORE_SERVEROPCODE_H
So I would like to modify encode_header() to set a ServerOpcode as a packet header. I was trying this but it's not working:
void Packet::encode_header(ServerOpcode serverOpcode) {
char header[header_length + 1] = "";
std::strcat(header, static_cast<char>(serverOpcode));
std::memcpy(data_, header, header_length);
}
I have two questions:
How can I make encode header prepend the ServerOpcode? Where is my mistake how can I fix it?
How can I decode an incoming message header than with decode_header()?