smack-a-brother/src/protocol.h

#pragma once

// What the game and the server agree on. The server hands out lobby codes, keeps each lobby's members and passes
// WebRTC signaling between them; matches themselves run peer to peer. Messages are JSON objects with a "type":
//
// Game to server:
//   create  {name, version}         make a lobby and join it as host
//   join    {code, name, version}   join a lobby by its code
//   leave   {}                      leave the lobby
//   kick    {id, reason}            (the host) put someone out of the lobby
//   signal  {to, payload}           pass a WebRTC description or candidate to another member
//   ping    {}                      keeps the connection alive through proxies (answered with pong)
//
// Server to game:
//   welcome      {id, code, host, members: [{id, name}]}   in a lobby (members includes this one)
//   member_join  {id, name}
//   member_leave {id, host, kicked?, reason?}              host is who hosts now; kicked says they were kicked
//   kicked       {reason}                                  this member was kicked out of the lobby
//   signal       {from, payload}
//   error        {message}                                 the request failed; the connection stays open
//   pong         {}
//
// A signal's payload is either a description {sdp, kind} or a candidate {candidate, mid}.

#include <cstring>
#include <string>
#include <string_view>
#include <type_traits>

constexpr int PROTOCOL_VERSION = 4;
constexpr int LOBBY_MEMBERS_MAX = 16;
constexpr int LOBBY_CODE_LENGTH = 4;
// Letters only, without I and O, so codes are easy to read out and type.
constexpr const char LOBBY_CODE_LETTERS[] = "ABCDEFGHJKLMNPQRSTUVWXYZ";
constexpr int PLAYER_NAME_MAX = 24;
constexpr int CHAT_MESSAGE_MAX = 100;
constexpr int KICK_REASON_MAX = 60;
constexpr const char SERVER_URL_DEFAULT[] = "wss://shweetz.net/smack-a-brother/ws";
constexpr int SERVER_URL_LENGTH = 128;

// Binary messages between a game and the server once it's in a lobby, each starting with its type. A room is one
// online game (a lobby's sandbox, or a game queued in it), numbered by the server.
//
// Game to server:
//   PACKET_PROFILE   Profile                                    the fighter this player brings into the lobby
//   PACKET_INPUTS    room, ack, first, Uint16 count, Controls*  this player's controls from a tick on, and the last
//                                                               tick it has confirmed
//   PACKET_QUEUE     Uint8 isOpen, Rules                        queue a game in the sandbox, or stop queueing it
//   PACKET_CHAT      Uint16 length, text
//   PACKET_TYPING    Uint8 isTyping
//   PACKET_RENAME    Uint16 length, text
//   PACKET_PING      Uint16 milliseconds                        this player's round trip to the server
//
// Server to game:
//   PACKET_STATE     room, tick, state                          the game this player is in now, as a tick starts
//   PACKET_EVENT     room, serial, RoomEvent                    the room's events, numbered from 0, in order
//   PACKET_FRAMES    room, lead, first, Uint16 count, then for each tick: Uint16 events, Uint8 fighters, Controls*
//                                                               every fighter's controls as the server played them,
//                                                               once the events before them are in, and how early
//                                                               (in ticks) this player's last controls came
//   PACKET_CHECKSUM  room, tick, Uint32                         the room's state as that tick starts
//   PACKET_CHAT      from, Uint16 length, text                  and the same for typing, renames and pings
enum PacketType : unsigned char
{
    PACKET_PROFILE = 1,
    PACKET_INPUTS,
    PACKET_QUEUE,
    PACKET_CHAT,
    PACKET_TYPING,
    PACKET_RENAME,
    PACKET_STATE,
    PACKET_EVENT,
    PACKET_FRAMES,
    PACKET_CHECKSUM,
    PACKET_PING
};

// Packets are plain values one after another, as they sit in memory (every platform agrees on these layouts).
struct PacketWriter
{
    std::string bytes;

    template <class T> PacketWriter& put(const T& value)
    {
        static_assert(std::is_trivially_copyable_v<T>);
        bytes.append(reinterpret_cast<const char*>(&value), sizeof(T));
        return *this;
    }
};

struct PacketReader
{
    const std::string& bytes;
    size_t at = 0;

    template <class T> bool get(T& value)
    {
        static_assert(std::is_trivially_copyable_v<T>);
        if (at + sizeof(T) > bytes.size())
            return false;
        std::memcpy(static_cast<void*>(&value), bytes.data() + at, sizeof(T));
        at += sizeof(T);
        return true;
    }
};

// Text from elsewhere (another player, or the server) made safe to show: only printable ASCII (what the game's font
// has; anything else, emoji included, is dropped), cut to max characters, with spaces at its ends trimmed.
inline std::string text_clean(std::string_view raw, size_t max)
{
    std::string text;
    for (char c : raw)
        if (c >= ' ' && c <= '~' && text.size() < max)
            text += c;
    size_t first = text.find_first_not_of(' ');
    size_t last = text.find_last_not_of(' ');
    return first == std::string::npos ? "" : text.substr(first, last - first + 1);
}

// A count of seconds in words: "1 second", "29 seconds".
inline std::string seconds_say(int seconds)
{
    return std::to_string(seconds) + (seconds == 1 ? " second" : " seconds");
}

// A string as a JSON string literal, quotes included.
inline std::string json_quote(const std::string& text)
{
    std::string quoted = "\"";
    for (unsigned char c : text)
        if (c == '"' || c == '\\')
            quoted += '\\', quoted += (char)c;
        else if (c == '\n')
            quoted += "\\n";
        else if (c == '\r')
            quoted += "\\r";
        else if (c == '\t')
            quoted += "\\t";
        else if (c < 0x20)
        {
            constexpr char HEX[] = "0123456789abcdef";
            quoted += "\\u00";
            quoted += HEX[c >> 4];
            quoted += HEX[c & 15];
        }
        else
            quoted += (char)c;
    return quoted + "\"";
}