Difference between revisions of "Protocol FAQ"

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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.
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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 [irc://irc.freenode.net/mcdevs #mcdevs on irc.freenode.net].
  
===Is the protocol documentation complete?===
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== Is the protocol documentation complete? ==
<blockquote>
+
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.
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 [[MC-Ver|have a script]] that monitors for new versions of the client and notifies us, allowing us to quickly document new packets.
 
</blockquote>
 
  
=== What's the normal login sequence for a client? ===
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== What's the normal login sequence for a client? ==
 +
See [[Authentication]] for communication with Mojang's servers.
 +
 
 +
The recommended login sequence looks like this, where '''C''' is the client and '''S''' is the server:
 +
# Client connects to server
 +
# '''C'''→'''S''': [[Protocol#Handshake|Handshake]] State=2
 +
# '''C'''→'''S''': [[Protocol#Login Start|Login Start]]
 +
# '''S'''→'''C''': [[Protocol#Encryption Request|Encryption Request]]
 +
# Client auth
 +
# '''C'''→'''S''': [[Protocol#Encryption Response|Encryption Response]]
 +
# Server auth, both enable encryption
 +
# '''S'''→'''C''': [[Protocol#Set Compression|Set Compression]] (Optional, enables compression)
 +
# '''S'''→'''C''': [[Protocol#Login Success|Login Success]]
 +
# '''S'''→'''C''': [[Protocol#Join Game|Join Game]]
 +
# '''S'''→'''C''': [[Protocol#Plugin Message (clientbound) |Plugin Message]]: [[Plugin channel#minecraft%3Abrand|<code>minecraft:brand</code>]] with the server's brand (Optional)
 +
# '''S'''→'''C''': [[Protocol#Server Difficulty|Server Difficulty]] (Optional)
 +
# '''S'''→'''C''': [[Protocol#Player Abilities (clientbound)|Player Abilities]] (Optional)
 +
# '''C'''→'''S''': [[Protocol#Plugin Message (serverbound)|Plugin Message]]: [[Plugin channel#minecraft%3Abrand|<code>minecraft:brand</code>]] with the client's brand (Optional)
 +
# '''C'''→'''S''': [[Protocol#Client Settings|Client Settings]]
 +
# '''S'''→'''C''': [[Protocol#Held Item Change (clientbound)|Held Item Change]]
 +
# '''S'''→'''C''': [[Protocol#Declare Recipes|Declare Recipes]]
 +
# '''S'''→'''C''': [[Protocol#Tags|Tags]]
 +
# '''S'''→'''C''': [[Protocol#Entity Status|Entity Status]]
 +
# '''S'''→'''C''': [[Protocol#Declare Commands|Declare Commands]]
 +
# '''S'''→'''C''': [[Protocol#Unlock Recipes|Unlock Recipes]]
 +
# '''S'''→'''C''': [[Protocol#Player Position And Look (clientbound)|Player Position And Look]]
 +
# '''S'''→'''C''': [[Protocol#Player Info|Player Info]] (Add Player action)
 +
# '''S'''→'''C''': [[Protocol#Player Info|Player Info]] (Update latency action)
 +
# '''S'''→'''C''': [[Protocol#Update View Position|Update View Position]]
 +
# '''S'''→'''C''': [[Protocol#Update Light|Update Light]] (One sent for each chunk in a square centered on the player's position)
 +
# '''S'''→'''C''': [[Protocol#Chunk Data|Chunk Data]] (One sent for each chunk in a square centered on the player's position)
 +
# '''S'''→'''C''': [[Protocol#World Border|World Border]] (Once the world is finished loading)
 +
# '''S'''→'''C''': [[Protocol#Spawn Position|Spawn Position]] (“home” spawn, not where the client will spawn on login)
 +
# '''S'''→'''C''': [[Protocol#Player Position And Look (clientbound)|Player Position And Look]] (Required, tells the client they're ready to spawn)
 +
# '''C'''→'''S''': [[Protocol#Teleport Confirm|Teleport Confirm]]
 +
# '''C'''→'''S''': [[Protocol#Player Position And Look (serverbound)|Player Position And Look]] (to confirm the spawn position)
 +
# '''C'''→'''S''': [[Protocol#Client Status|Client Status]] (sent either before or while receiving chunks, further testing needed, server handles correctly if not sent)
 +
# '''S'''→'''C''': inventory, entities, etc
 +
 
 +
== Offline mode ==
 +
If the server is in offline mode, it will not send the [[Protocol#Encryption Request|Encryption Request]] packet, and likewise, the client should not send [[Protocol#Encryption Response|Encryption Response]]. In this case, encryption is never enabled, and no authentication is performed.
  
See [[Authentication]] for communication with Mojang's servers.
+
Clients can tell that a server is in offline mode if the server sends a [[Protocol#Login Success|Login Success]] without sending [[Protocol#Encryption Request|Encryption Request]].
 +
 
 +
== I think I've done everything right, but… ==
 +
=== …my player isn't spawning! ===
 +
After sending the common-sense packets ([[Protocol#Handshake|Handshake]], [[Protocol#Login Start|Login Start]], [[Protocol#Window Items|inventory]], [[Protocol#Spawn Position|compass]], and [[Protocol#Chunk Data|chunks]]), you need to finally send the player their [[Protocol#Player Position And Look|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 [[Protocol#Spawn Position|Spawn Position]] packet
 +
# Send [[Protocol#Player Position And Look|Player Position And Look]] packet
  
{{Warning|Information might not be totally up to date}}
+
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.
  
<blockquote>
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=== …my client isn't receiving complete map chunks! ===
The recommended login sequence looks like this, where C is the client and S is the server:<br /><br />
+
''Main article: [[How to Write a Client]]''
  
# Client connects to server
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The standard Minecraft server sends full chunks only when your client is sending player status update packets (any of [[Protocol#Player|Player (0x03)]] through [[Protocol#Player Position And Look|Player Position And Look (0x06)]]).
# '''C→S''': [[Protocol#Handshake|Handshake]] State=2
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# '''C→S''': [[Protocol#Login Start|Login Start]]
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=== …all connecting clients spasm and jerk uncontrollably! ===
# '''S→C''': [[Protocol#Encryption Request|Encryption Request]]
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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.
# (Client Auth)
 
# '''C→S''': [[Protocol#Encryption Response|Encryption Response]]
 
# (Server Auth, Both enable encryption)
 
# '''S→C''': [[Protocol#Login Success|Login Success]]
 
# '''S→C''': [[Protocol#Join Game|Join Game]]
 
# '''S→C''': [[Protocol#Spawn Position|Spawn Position]] (“home” spawn, not where the client will spawn on login)
 
# '''S→C''': [[Protocol#Player Abilities|Player Abilities]]
 
# '''S→C''': [[Protocol#Player Position And Look|Player Position And Look]] (tells the client they're ready to spawn)
 
# '''C→S''': [[Protocol#Player Position And Look 2|Player Position And Look]] (to confirm the spawn position)
 
# '''S→C''': inventory, [[Protocol#Map Chunk Bulk|Map Chunk Bulk]], entities, etc
 
</blockquote>
 
  
===I think I've done everything right, but…===
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=== …the client is trying to send an invalid packet that begins with 0xFE01 ===
 +
The client is attempting a [[Server_List_Ping#1.6|legacy ping]], this happens if your server did not respond to the [[Server List Ping]] properly, including if it sent malformed JSON.
  
====…my player isn't spawning!====
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=== …the client disconnects after some time with a "Timed out" error ===
<blockquote>
+
The server is expected to send a [[Protocol#Keep Alive (clientbound)|Keep Alive]] packet every second, and the client should respond with the serverbound version of that packet. If either party does not receive keep alives for some period of time, they will disconnect.
After sending the common-sense packets ([[protocol#handshake_0x02|Handshake]], [[protocol#login_request_0x01|Login]], [[protocol#player_inventory_0x05|Inventory]], [[protocol#spawn_position_0x06|Compass]] and [[protocol#map_chunk_0x33|Chunks]]) you need to finally send the player their [[protocol#player_position_look_0x0d|initial position]] for them to leave the "Loading Map" screen.
 
</blockquote>
 
  
'''Note that if the following steps are taken, a Minecraft client will spawn the player:'''
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== How do I open/save a command block? ==
 +
The process to actually open the command block window clientside is somewhat complex; the client actually uses the [[Protocol#Update Block Entity|Update Block Entity (0x09)]] packet to open it.
  
1) Do Handshake (See [[Protocol_Encryption|Protocol Encryption]])<br />
+
First, the client must have at least an {{Minecraft Wiki|Server.properties#op-permission-level|OP permission level}} of 2, or else the client will refuse to open the command block.  (The op permission level is set with the [[Protocol#Entity Status|Entity Status]] packet)
2) Send [[protocol#spawn_position_0x06|Spawn Position]] PDU<br />
 
3) Send [[protocol#player_position_look_0x0d|Player Position and Look]] PDU<br />
 
  
While the above steps are sufficient for Minecraft 1.4.5, it is good form to send PDUs that inform the client about the world around the player before allowing the player to spawn.
+
To actually open the command block:
  
====…my client isn't receiving complete map chunks!====
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# '''C'''→'''S''': [[Protocol#Player Block Placement|Player Block Placement (0x1C)]], with the position being the command block that was right-clicked.
''Main article: [[How to Write a Client]]''
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# '''S'''→'''C''': [[Protocol#Update Block Entity|Update Block Entity (0x09)]], with the NBT of the command block.
<blockquote>
 
The standard Minecraft server sends full chunks only when your client is sending player status update packets (any of [[protocol#Player (0x0A)|Player (0x0A)]] through [[protocol#Player Position & Look (0x0D)|Player Position & Look (0x0D)]]).
 
</blockquote>
 
  
====…all connecting clients spasm and jerk uncontrollably!====
+
And to save it, use the [[Plugin channels#MC.7CAutoCmd|<code>MC|AutoCmd</code> plugin channel]].
<blockquote>
 
For newer clients, your server needs to send 49 chunks ahead of time, not just one. Send a 7x7 square of chunks, centered on the connecting client's position, '''before''' spawning them.
 
</blockquote>
 
  
 
[[Category:Protocol Details]]
 
[[Category:Protocol Details]]
 
[[Category:Minecraft Modern]]
 
[[Category:Minecraft Modern]]

Latest revision as of 03:39, 11 January 2020

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.

The recommended login sequence looks like this, where C is the client and S is the server:

  1. Client connects to server
  2. CS: Handshake State=2
  3. CS: Login Start
  4. SC: Encryption Request
  5. Client auth
  6. CS: Encryption Response
  7. Server auth, both enable encryption
  8. SC: Set Compression (Optional, enables compression)
  9. SC: Login Success
  10. SC: Join Game
  11. SC: Plugin Message: minecraft:brand with the server's brand (Optional)
  12. SC: Server Difficulty (Optional)
  13. SC: Player Abilities (Optional)
  14. CS: Plugin Message: minecraft:brand with the client's brand (Optional)
  15. CS: Client Settings
  16. SC: Held Item Change
  17. SC: Declare Recipes
  18. SC: Tags
  19. SC: Entity Status
  20. SC: Declare Commands
  21. SC: Unlock Recipes
  22. SC: Player Position And Look
  23. SC: Player Info (Add Player action)
  24. SC: Player Info (Update latency action)
  25. SC: Update View Position
  26. SC: Update Light (One sent for each chunk in a square centered on the player's position)
  27. SC: Chunk Data (One sent for each chunk in a square centered on the player's position)
  28. SC: World Border (Once the world is finished loading)
  29. SC: Spawn Position (“home” spawn, not where the client will spawn on login)
  30. SC: Player Position And Look (Required, tells the client they're ready to spawn)
  31. CS: Teleport Confirm
  32. CS: Player Position And Look (to confirm the spawn position)
  33. CS: Client Status (sent either before or while receiving chunks, further testing needed, server handles correctly if not sent)
  34. SC: inventory, entities, etc

Offline mode

If the server is in offline mode, it will not send the Encryption Request packet, and likewise, the client should not send Encryption Response. In this case, encryption is never enabled, and no authentication is performed.

Clients can tell that a server is in offline mode if the server sends a Login Success without sending Encryption Request.

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:

  1. Do Handshake (see Protocol Encryption)
  2. Send Spawn Position packet
  3. 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.

…the client is trying to send an invalid packet that begins with 0xFE01

The client is attempting a legacy ping, this happens if your server did not respond to the Server List Ping properly, including if it sent malformed JSON.

…the client disconnects after some time with a "Timed out" error

The server is expected to send a Keep Alive packet every second, and the client should respond with the serverbound version of that packet. If either party does not receive keep alives for some period of time, they will disconnect.

How do I open/save a command block?

The process to actually open the command block window clientside is somewhat complex; the client actually uses the Update Block Entity (0x09) packet to open it.

First, the client must have at least an OP permission level of 2, or else the client will refuse to open the command block. (The op permission level is set with the Entity Status packet)

To actually open the command block:

  1. CS: Player Block Placement (0x1C), with the position being the command block that was right-clicked.
  2. SC: Update Block Entity (0x09), with the NBT of the command block.

And to save it, use the MC|AutoCmd plugin channel.