Pocket Edition Protocol Documentation
This is the (unofficial) protocol documentation for Minecraft Pocket Edition. The protocol currently uses UDP for communication, different from PC (which uses TCP). The usual UDP issues are still here (lost packets, wrong order, etc.), but the protocol solves a few of those problems using special packet encapsulation, based on TCP. The Minecraft: PE client uses RakNet as its networking library. Even though it uses RakNet, you can still write software without the library.
Currently, the game's default port is 19132. It is recommended to use this when possible because processes such as server discovering will not work otherwise.
Contents
- 1 Data Types
- 2 Packet format
- 3 RakNet protocol
- 3.1 Connected Ping
- 3.2 Unconnected Ping
- 3.3 Connected Pong
- 3.4 Offline Connection Request 1
- 3.5 Offline Connection Response 1
- 3.6 Offline Connection Request 2
- 3.7 Offline Connection Response 2
- 3.8 Online Connection Request
- 3.9 Online Connection Request Accepted
- 3.10 Unconnected Pong
- 3.11 Frame Set Packet
- 3.12 Game Packet
- 3.13 NACK
- 3.14 ACK
- 4 RakNet Reliability
- 5 References
Data Types
Minecraft packets use different data types to communicate with each other. The documented ones are listed below:
Size | Range | Notes | |
---|---|---|---|
byte | 1 | -128 to 127 |
|
short | 2 | -32768 to 32767 |
|
uint24le | 3 | 0 to 16777216 | Little-Endian 24-bit unsigned integer. Commonly used by RakNet for counters. |
int | 4 | -2147483648 to 2147483647 |
|
long | 8 |
| |
MAGIC | 16 | 0x00ffff00fefefefefdfdfdfd12345678
|
always those hex bytes, corresponding to RakNet's default OFFLINE_MESSAGE_DATA_ID |
string | unsigned short + string | N/A | Prefixed by a short containing the length of the string in characters. It appears that only the following ASCII characters can be displayed: !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ |
address | 7 | N/A | IP Address and port. First byte is the version (0x04), then come the address bytes and finally an unsigned short for the port. |
NBT | N/A | N/A | NBT data in PE is always little-endian. This includes short, int, long, float, double tags and the length headers for arrays, strings and lists. |
Item Stack | N/A | N/A | First short is the item ID. If this is not 0, then follows the item count ubyte. If this is also not 0, then follows the item data short and a little-endian short denoting the length of the following NBT data, or 0 for no NBT. Then follows an NBT tag described above of that length. |
UUID | 16 | 00000000-0000-0000-0000-000000000000
to ffffffff-ffff-ffff-ffff-ffffffffffff |
|
Position | 12 | N/A | Three consecutive floats for x, y and z respectively. |
Block Position | 12 | N/A | Three consecutive ints for x, y and z respectively. |
Packet format
All packets in Minecraft: Pocket Edition start with their ID, which is an unsigned byte. If you are using a language which does not support unsigned types such as Java, you can do (byte & 0xFF) to get the unsigned version.
RakNet protocol
Connected Ping
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x00 | Time | long |
Unconnected Ping
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x01, 0x02 | Time | long | |
GUID | long |
0x02
is only replied to if there are open connections to the server.
Connected Pong
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x03 | Ping Time | long | |
Pong Time | long |
Offline Connection Request 1
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x05 | Magic | MAGIC | |
Protocol version | byte | Currently 7 | |
MTU | mtu-46 zero bytes | The MTU sent in the response appears to be somewhere around the size of this padding + 46 (28 udp overhead, 1 packet id, 16 magic, 1 protocol version) |
The client sends these to the target server with ever decreasing MTU until the server responds. This is used to discover the MTU size for the connection.
Offline Connection Response 1
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x06 | Magic | MAGIC | |
Server GUID | long | ||
MTU | short | see Offline Connection Request 1 |
Offline Connection Request 2
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x07 | Magic | MAGIC | |
Server Address | address | ||
MTU | short | ||
Client GUID | long |
Offline Connection Response 2
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x08 | Magic | MAGIC | |
Server GUID | long | ||
Client Address | address | ||
MTU | short | ||
Encryption enabled? | byte | 0 for disabled. |
Online Connection Request
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x09 | GUID | long | |
Time | long |
Online Connection Request Accepted
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x10 | Client address | address | |
System index | short | Unknown what this does. 0 works as a value. | |
Internal IDs | 10x address | Unknown what these do. 255.255.255.255:19132 for all of them seems to work, any other address will probably work as well. | |
Request time | long | ||
Time | long |
Unconnected Pong
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x1c | Time | long | |
Server GUID | long | ||
Magic | MAGIC | ||
Server info | string | MCPE;##Name##;##Protocol Version##;##Client Version##;##Online player count##;##Max player count##;##Server GUID##; . Protocol version is currently (0.14.1) 46. Client version can be left empty or be something like '0.14.1'. Server GUID is a 64-bit unsigned integer, 0 works as a value. Example: MCPE;kitty;46;0.14.1;1;5;18446744071609048444;
|
Frame Set Packet
Packet ID | Field Name | Field Type | Notes | ||
---|---|---|---|---|---|
0x80..0x8d | Frame Set index | uint24le | |||
Frames | Flags | byte | Top 3 bits are reliability type, fourth bit is 1 when the frame is fragmented and part of a compound. | ||
Length IN BITS | short | Length of the body in bits. | |||
Reliable frame index | uint24le | only if reliable | |||
Sequenced frame index | uint24le | only if sequenced | |||
Order | Ordered frame index | uint24le | only if ordered | ||
Order channel | byte | ||||
Fragment | Compound size | int | only if fragmented | ||
Compound ID | short | ||||
Index | int | ||||
Body | ceil(length/8) bytes |
The reliability types are as follows:
ID | Name | Reliable | Ordered | Sequenced |
---|---|---|---|---|
0 | unreliable | |||
1 | unreliable sequenced | x | x | |
2 | reliable | x | ||
3 | reliable ordered | x | x | |
4 | reliable sequenced | x | x | x |
5 | unreliable (+ ACK receipt) | |||
6 | reliable (+ ACK receipt) | x | ||
7 | reliable ordered (+ ACK receipt) | x | x |
Sequenced implies ordered.
Game Packet
Packet ID | Field Name | Field Type | Notes |
---|---|---|---|
0x8e | Body | bytes | Single packet of the GAME protocol. |
NACK
Packet ID | Field Name | Field Type | Notes | ||
---|---|---|---|---|---|
0xa0 | Record count | short | |||
Record | Is Range? | byte | 0 for range, 1 for no range | ||
No Range | Index | uint24le | |||
Range | Start Index | uint24le | |||
End Index | uint24le |
ACK
Packet ID | Field Name | Field Type | Notes | ||
---|---|---|---|---|---|
0xc0 | Record count | short | |||
Record | Is Range? | byte | 0 for range, 1 for no range | ||
No Range | Index | uint24le | |||
Range | Start Index | uint24le | |||
End Index | uint24le |
RakNet Reliability
RakNet reliability and ordering is handled on multiple levels.
Frame set reliability
FrameSetPackets carry a unique index. This index may only appear once in a connection (per direction). Getting the same index twice means you have received a duplicate datagram - ignore one.
Upon receiving a frame set, an ACK packet for that frame set is sent back. Since the frame set index is a sequential counter, you can deduce which frame sets are missing, for which a NACK packet is sent. For every received frame set, RakNet sends at most one NACK and one ACK.
Frame sets consist of frames. Internally, raknet uses a "resend queue" (priority heap / priority queue) of frames it needs to send. This queue is ordered by targeted send time. Whenever possible, raknet takes the top few sendable frames from this resend queue and combines them into a frame set smaller than the MTU. It then moves the reliable frames further down the queue by setting their resend time to a bunch of milliseconds in the future. unreliable frames are discarded after being first sent.
When an ACK is received, all frames of the container indices in that ACK packet are removed from the resend queue because they arrived safely on the client and don't need a resend.
When a NACK is received, all frames of the container indices in that NACK packet are moved to the top of the resend queue by setting their targeted resend time to the present or past.
To send a frame, raknet simply adds it to the resend queue with the present as the targeted send time. It is then intermixed with normal resends and other frames for the next frame set packet.
Fragmentation
Some packets (notably chunks) are larger than the MTU. These are split up into a compound. You need to consider the frame and frame set overhead when fragmenting frames. A fragmented frame contains the compound ID (reusable when compound is complete), compound size (in fragments) and index (0 up to compound size exclusive). All fragments of a compound share the same order and sequencing information, if any. All fragmented frames are also reliable.
Order and Sequencing
Some frames are ordered or sequenced. For order and sequencing, there exist order channels. These act independently. Since all sequenced reliability types are also ordered, an order channel is present for every ordered or sequenced frame.
Ordered means that frames with higher order indices are always handled after frames with lower order indices. Higher order index frames are withheld until their lower peers arrive and it's their turn.
Sequenced means that frames with lower sequence indices are never handled after frames with higher sequence indices. Lower sequence index frames are discarded if their higher index frames have already been handled.
Sequenced frames also include an order index. It is unknown how the order index influences handling, and this should be researched at some point.
References
RakNet datagram and message header information: http://jenkinssoftware.com/raknet/manual/systemoverview.html
The latest version of the protocol is not fully documented yet, but all of the packets can be found in the Dragonet server code https://github.com/DragonetMC/Dragonet/tree/master/src/main/java/org/dragonet/net/packet Protocol Version: 23 (MCPE 0.11.0b6)
The older protocol specification(ver <= 0.10.x): There is also an automatically generated specification of many of the packages can be found in the MiNET server code https://github.com/NiclasOlofsson/MiNET/blob/master/src/MiNET/MiNET/Net/MCPE%20Protocol%20Documentation.md
The MiNET wiki also contain development notes around some functionality https://github.com/NiclasOlofsson/MiNET/wiki These will be migrated to this wiki in due time.