Mupen64Plus v2.0 Core Netplay

Mupen64Plus Netplay API

The Mupen64Plus netplay API is based on a client/server architecture. It supports syncing core settings and save files. It also supports raw input (tested with Raphnet input plugin). TCP is used to deal with player registration, and syncing settings and saves. UDP is used to transfer key input data. Data is sent in Network Byte Order (Big Endian).

The server is responsible for maintaining healthy buffers and also for detecting desyncs. The server is the source of truth for input data (for instance, when player 1 pushes "A", it sends that information to the server via UDP. That "A" is not registered as input for player 1 until the client receives a packet from the server indicating what input frame to register that "A" in)

UDP Packet formats

• Request input for a player (sent by client):
  • 12 bytes
  • byte[0] = 2
  • byte[1] = player number (this is the player we need key inputs for)
  • byte[2-5] = client registration ID
  • byte[6-9] = current event count
  • byte[10] = whether client is a spectator
  • byte[11] = local buffer size of the client

• Key input data (sent by server):
  • Variable length, payload cannot be larger than 512 bytes
  • byte[0] = 1
  • byte[1] = player number the key inputs pertain to
  • byte[2] = current status. Bit 0 indicates whether the game has desynced (1 means desync). Bits 1-4 indicate whether a player has disconnected (for instance, if bit 2 is set, that means player 2 has disconnected). Bits 5-7 are currently unused.
  • byte[3] = how far we lag behind the lead player
  • byte[4] = number of events in this packet
  • The following items will repeat/loop for the number of events in the packet
    • byte[5-8] = event count
    • byte[9-12] = key input data
    • byte[13] = current plugin

• Key input data (sent by client):
  • 11 bytes
  • byte[0] = 0
  • byte[1] = player number
  • byte[2-5] = current event count
  • byte[6-9] = key input data
  • byte[10] = current plugin

• Client sync data (sent by client):
  • 133 bytes
  • byte[0] = 4
  • byte[1-4] = current VI count
  • byte[5-132] = CP0 registers

TCP Packet formats

• Player disconnection notice (sent by client):
  • 5 bytes
  • byte[0] = 7
  • byte[1-4] = client registration ID

• Player registration request (sent by client):
  • 8 bytes
  • byte[0] = 5
  • byte[1] = player the client is trying to register
  • byte[2] = plugin for this player
  • byte[3] = whether to use a raw input plugin
  • byte[4-7] = client registration ID

• Player registration response (sent by server):
  • 2 bytes
  • byte[0] = response (1 if registration was successful, 0 otherwise)
  • byte[1] = local buffer target for the client

• Send save file data (sent by client):
  • Variable length
  • byte[0] = 1
  • byte[1 - next '\0'] = file name
  • byte[4 bytes] = size of save file in bytes
  • byte[size of file] = save file data

• Request save file data (sent by client):
  • Variable length
  • byte[0] = 2
  • byte[1 - next '\0'] = file name

• Receive save file data (sent by server):
  • Server responds with this data right after the above request
  • Variable length
  • byte[file size] = save file data

• Send settings (sent by client):
  • 21 bytes
  • byte[0] = 3
  • byte[1-4] = count_per_op
  • byte[5-8] = disable_extra_mem
  • byte[9-12] = si_dma_duration
  • byte[13-16] = emumode
  • byte[17-20] = no_compiled_jump

• Request settings (sent by client):
  • 1 byte
  • byte[0] = 4

• Send settings (sent by server):
  • Server responds with this data right after the above request
  • 20 bytes
  • byte[0-3] = count_per_op
  • byte[4-7] = disable_extra_mem
  • byte[8-11] = si_dma_duration
  • byte[12-15] = emumode
  • byte[16-19] = no_compiled_jump

• Request player registration data (sent by client):
  • 1 byte
  • byte[0] = 6

• Send player registration data (sent by server):
  • 24 bytes
  • The following bytes loop 4 times (once for each player)
    • byte[0-3] = player registration ID
    • byte[4] = player plugin
    • byte[5] = whether the player is using raw data input