People very, very often have questions regarding the Minecraft Modern Protocol, so we'll try to address some of the most common ones on this document. If you're still having trouble, join us on IRC, channel #mcdevs on irc.freenode.net.
Is the protocol documentation complete?
Depending on your definition, yes! All packet types are known and their layout documented. Some finer details are missing, but everything you need to make functional programs is present. We also collect information on the pre-release protocol changes, allowing us to quickly document new releases.
What's the normal login sequence for a client?
See Authentication for communication with Mojang's servers.
Information might not be totally up to date
The recommended login sequence looks like this, where C is the client and S is the server:
- Client connects to server
- C→S: Handshake State=2
- C→S: Login Start
- S→C: Encryption Request
- Client auth
- C→S: Encryption Response
- Server auth, both enable encryption
- S→C: Login Success
- S→C: Join Game
- S→C: Spawn Position (“home” spawn, not where the client will spawn on login)
- S→C: Player Abilities
- S→C: Player Position And Look (tells the client they're ready to spawn)
- C→S: Player Position And Look (to confirm the spawn position)
- C→S: Client Status (sent either before or while receiving chunks, further testing needed)
- S→C: inventory, Map Chunk Bulk, entities, etc
I think I've done everything right, but…
…my player isn't spawning!
After sending the common-sense packets (Handshake, Login Start, inventory, compass, and chunks), you need to finally send the player their initial position for them to leave the “Loading Map” screen.
Note that if the following steps are taken, a Minecraft client will spawn the player:
- Do Handshake (see Protocol Encryption)
- Send Spawn Position packet
- Send Player Position And Look packet
While the above steps are sufficient for Minecraft 1.4.5, it is good form to send packets that inform the client about the world around the player before allowing the player to spawn.
…my client isn't receiving complete map chunks!
Main article: How to Write a Client
The standard Minecraft server sends full chunks only when your client is sending player status update packets (any of Player (0x03) through Player Position And Look (0x06)).
…all connecting clients spasm and jerk uncontrollably!
For newer clients, your server needs to send 49 chunks ahead of time, not just one. Send a 7×7 square of chunks, centered on the connecting client's position, before spawning them.