How Are Codes Used To Relay Messages

Relay message protocol

If you're using the Unity engine for your project, the Relay bulletin protocol is already supported. However, if you want to utilise an alternative engine, you lot'll need to implement the Relay bulletin protocol before using it. Utilize the Relay message protocol specifications to implement the Relay message protocol manually.

The Relay message protocol expects yous to express messages in big-endian order, also known as the "network order," where the most significant byte occurs get-go. The Relay message protocol uses this ordering to avoid the overhead of reversing the order on encode or decode.

Letters are not authenticated with the exception of the Bind message, which uses an HMAC An HMAC, or hash-based message authentication code, is a blazon of message authentication code that uses a cryptographic hash function and keys to authenticate messages. signature.

Players can only connect and relay messages with other players from the same Unity projection and surround. Any attempts to communicate across Unity environments will exist rejected.

All letters have a standard header and a message-specific message trunk. Encounter Standard header and Message bodies.

Message types

Code	Name	Description
`0`	`BIND bulletin`	A `Demark` bulletin indicates a bind request sent from a client to a Relay server.
`1`	`BIND_RECEIVED message`	A `BIND_RECEIVED` bulletin indicates a successful response from the Relay server to a client subsequently receiving a `Demark request`.
`2`	`PING bulletin`	A `PING` message indicates a ping bulletin sent between a client and a Relay server (both directions) to continue the connection alive.
`iii`	`CONNECT_REQUEST bulletin`	A `CONNECT_REQUEST` bulletin indicates a asking from a player (the requesting client) to connect to some other player (the target client).
`iv`	Reserved.
`five`	Reserved.
`half dozen`	`Accustomed message`	An `Accustomed` message indicates a confirmation message sent from a Relay server to a requesting customer later a successful connection to a target client.
`seven`	Reserved.
`8`	Reserved.
`ix`	`DISCONNECT bulletin`	A `DISCONNECT` message indicates a request to disconnect two connected players.
`ten`	`RELAY message`	A `RELAY` message indicates a request to ship a message between 2 players (clients).
`11`	`CLOSE message`	A `Close` message indicates a request from a client to unbind from a Relay server.
`12`	`ERROR message`	An `ERROR` message indicates an error that has occurred.

Accept manner types

The have fashion defines how a Relay server should handle requests from clients trying to connect.

Relay only supports the AUTO have mode. A connection mode of AUTO means the Relay server automatically accepts that connection if the capacity allows (the number of connections must be less than the maximum number of immune connections An integer that indicates the maximum number of peer connections a client allows to communicate with them. This parameter must be less than or equal to 100.).

In later releases, the have way will let for more command over the way in which players establish communication with each other.

Code	Proper name	Clarification
`0`	`AcceptModeAuto`	`AcceptModeAuto` indicates that connections to clients will be automatically accustomed by the Relay server.
`1`		Reserved.

Standard header

All message types share a standard header that contains a signature, the Relay bulletin protocol version, and the blazon of message contained in the torso of the package.

Bytes	i .. 2	iii	4
Purpose	`Signature`	`Version`	`Type`

The post-obit table describes each field found in the standard header.

Field	Type	Description
`Signature`	[]byte	The `Signature` is always `0xDA72`.
`Version`	uint8	The `Version` is the Relay message protocol version. The value should be 0 for the initial release.
`Type`	uint8	The `Type` is an integer representing the message type contained in the body. Meet Message types.

Bulletin bodies

BIND message

Demark messages are sent from a client to a Relay server to create a mapping from a client's IP accost and port for a specific allotment. This bulletin is authenticated to verify the identity of the client.

The response received from the Allocations service contains the information necessary for the client to cosign its BIND messages. The response from the Allocations service to the Demark bulletin shows the binding status.

Clients can transport identical Demark messages as long as the customer's IP accost and port have not inverse. For case, if a customer sends a Bind bulletin on a subsequent connexion after changing its IP address or port, the Nonce value must exist greater than the previously supplied value.

Bytes	1 .. 4	5	6 .. 7	viii	9 .. North	North+1 .. 33
Purpose	Header (Type 0)	`AcceptMode`	`Nonce`	`ConnectionDataLength`	`ConnectionData`	`HMAC`

The following table describes each field found in a BIND message.

Field	Type	Description
`AcceptMode`	uint8	`AcceptMode` defines how a Relay server should handle requests from clients trying to connect to the owner of this allocation. Only the `AUTO` accept mode is supported. See Take mode types.
`Nonce`	uint16	`Nonce` is a single-use cryptographic nonce. Each subsequent `Demark` message must accept an incremented nonce value.
`ConnectionDataLength`	uint8	`ConnectionDataLength` describes the byte length of `ConnectionData`. The maximum allowed value is 255.
`ConnectionData`	[]byte	`ConnectionData` is the encrypted connectedness data of the connecting client A connecting histrion (or joining player) is a role player that wants to join a host player for a game session on a Relay server.. This field'south length is variable. The maximum length is 255 bytes.
`HMAC`	[32]byte	`HMAC` is a hash-based message authentication code generated using a known key and the preceding bytes in the message, including the header. See Authentication.

Security

Y'all should sign the HMAC with the secret central returned from the Allocations service. If the HMAC is invalid, the Relay server silently rejects the BIND message.

The Relay server likewise validates the nonce A nonce, or cryptographic nonce, is an incrementing number that is used in cryptographic communication to ensure previous letters cannot be resent arbitrarily. Each subsequent bulletin should increment the nonce. This way, if a bad actor tries to use a previous message in a replay assault, the service can reject the bulletin. In the Relay service, you use nonces as part of the HMAC cosmos process. value to mitigate message replay attacks by bad actors. If the Relay server determines that a nonce is invalid, it silently rejects information technology. If it's the first time the client is bounden to a Relay server with a Demark message, the nonce value tin be 0.

BIND_RECEIVED message

Relay servers send BIND_RECEIVED messages to requesting clients to ostend they have successfully bound to the Relay server through a Demark request. Later on receiving the confirmation, the requesting client A requesting client is the game client of a connecting role player—the requesting customer requests to join a target customer on a Relay server for a game session. tin initiate communication with a target client A host player is a actor that initiates a game session on a Relay server and generates a join code to share with other players. There is just one host role player per game lucifer. using a CONNECT_REQUEST message.

Note: The Relay server sends a BIND_RECEIVED bulletin to the client for each successfully candy BIND request.

Bytes	1 .. 4
Purpose	Header (Type one)

PING message

PING messages are uncomplicated messages that keep the binding between a client and a Relay server alive by resetting the x 2nd timeout. Relay servers automatically deallocates clients later on x seconds of inactivity. Any message received by the Relay server involving this client, either equally a sender or receiver, resets this timeout. For games with a lower message frequency, the PING message allows clients to reset the disconnection timer. See Customer timeouts.

Note: Clients should send PING letters every 2d or two in add-on to the other letters to ensure the connection doesn't timeout.

Each PING message contains the customer's allotment ID and an arbitrary number that identifies the message.

When a Relay server receives a PING message from a client, it sends the packet dorsum to the client without altering it. This allows you lot to use PING messages to check connectivity and mensurate round trip fourth dimension.

Warning: Clients must bind with the Relay server through a Demark bulletin prior to sending a PING message. The following scenarios volition result in the Relay server returning a ErrClientPlayerMismatch ERROR message:

The client sends a PING message before binding to the Relay server through a Bind message.
The client sends a PING message subsequently its IP address has changed and before rebinding to the Relay server with the new IP address.

Bytes	ane .. iv	5 .. 20	21 .. 22
Purpose	Header (Type two)	`AllocationID`	`Number`

The post-obit table describes each field constitute in a PING bulletin.

Field	Type	Description
`AllocationID`	[16]byte	`AllocationID` is a xvi-byte UUID identifying the allocated client sending the ping.
`Number`	uint16	`Number` is an arbitrary unsigned integer the Relay server echoes back to the client.

CONNECT_REQUEST message

CONNECT_REQUEST messages are sent from a requesting customer A requesting client is the game client of a connecting player—the requesting customer requests to bring together a target client on a Relay server for a game session. to a Relay server to found a connection to a target client A target client is the game client of a host actor—the target client is the target of a request from a requesting client to join a game session on a Relay server.. The histrion the client wants to connect to (or the target client) is represented by ToConnectionData, which the Relay server decrypts to make up one's mind which thespian to connect with.

Warning: The target client and the requesting client must be on the same Unity projection and environment.

Note: Relay servers have no formal concept of histrion groups (often referred to every bit sessions). All players within a logical game session are bound to the same Relay server. By extension of this, Relay doesn't make any assumptions near the length of a histrion's bindings and connections in relation to the game session. Information technology's up to the game client to determine whether players unbind from the Relays server at the cease of a session or use the same binding for multiple sessions.

Bytes	1 .. four	5 .. xx	21	22 ..
Purpose	Header (Type three)	`AllocationID`	`ToConnectionData Length`	`ToConnectionData`

The following table describes each field establish in a CONNECT_REQUEST bulletin.

Field	Type	Description
`AllocationID`	[16]byte	`AllocationID` is a 16-byte UUID that identifies the allocated client that is requesting the connexion.
`ToConnectionDataLength`	uint8	`ToConnectionDataLength` is the byte length of `ConnectionData`. The maximum immune value is 255.
`ToConnectionData`	[]byte	`ToConnectionData` is an encrypted data blob that describes the client to connect to. Meet connexion data. This field has a variable length. The maximum byte length is 255.

Accustomed message

A Relay server sends an Accustomed message to a requesting client after a successful connection to a target client.

Bytes	1 .. four	v .. twenty	21 .. 36
Purpose	Header (Type half dozen)	`FromAllocationID`	`ToAllocationID`

The post-obit tabular array describes each field plant in an ACCEPTED message.

Field	Blazon	Description
`FromAllocationID`	[sixteen]byte	`FromAllocationID` is a 16-byte UUID that identifies the target customer.
`ToAllocationID`	[16]byte	`ToAllocationID` is a 16-byte UUID that identifies the allocated client that requested the connection (the requesting client).

DISCONNECT message

The DISCONNECT bulletin is the inverse of the CONNECT_REQUEST handshake and allows a client to disconnect from some other client. A client tin can disconnect from any other customer it has connected with by sending a DISCONNECT bulletin to the Relay server.

When the Relay server receives the bulletin, it removes the specified allocation ID from the requesting client's list of connected players. The Relay server too frontward the DISCONNECT request to the host client so the client tin update its map.

The Relay server and so sends the DISCONNECT message back to the client as a confirmation. If either of the allocation IDs in the message body is invalid, the Relay server sends an ERROR message instead.

Once a customer has disconnected, the Relay server rejects all RELAY letters sent to that client'due south allocation ID. A client tin re-establish a connection with a CONNECT_REQUEST message.

Note: The host and connecting clients can send a DISCONNECT message. However, if a host client sends a DISCONNECT message, the client must migrate the joining players to a new host or disconnect them. Relay does not handle host migration.

Bytes	1 .. 4	five .. 20	21 .. 36
Purpose	Header (Type ix)	`FromAllocationID`	`ToAllocationID`

The post-obit table describes each field plant in a DISCONNECT message.

Field	Type	Description
`FromAllocationID`	[sixteen]byte	`FromAllocationID` is a 16-byte UUID that identifies the allocated client that requested to close the connection (the requesting customer).
`ToAllocationID`	[16]byte	`ToAllocationID` is a xvi-byte UUID that identifies the allocated customer whose connectedness is being airtight (the target client).

RELAY message

RELAY letters allow clients to transport messages containing whatsoever arbitrary payload of bytes between each other without awareness of each other's IP addresses and ports.

Before sending a RELAY message between clients, the Relay server ensures the client sending the parcel has previously been authenticated as the FromAllocationID through a Bind message. If the client has not previously leap, the Relay server returns an ErrClientPlayerMismatch Fault message.

The Relay server also ensures the two clients have an established connection through a previous CONNECT_REQUEST exchange. The Relay server returns an ErrNotConnected Mistake message if the clients are non connected.

If all validations laissez passer, the Relay server sends the unabridged message to the ToAllocationID as-is. The Relay server does not ship any confirmation message to the FromAllocationID.

Bytes	one .. iv	5 .. twenty	21 .. 36	37 .. 38	39 ..
Purpose	Header (Blazon x)	`FromAllocationID`	`ToAllocationID`	`Length`	`Content`

Note: The maximum length of a RELAY message is not guaranteed at the protocol level. It is defined past the configuration of the Relay server itself, which has a default maximum content length of 1400 bytes and results in a RELAY maximum size of 1438 bytes.

The following table describes each field found in a RELAY bulletin.

Field	Type	Clarification
`FromAllocationID`	[16]byte	`FromAllocationID` is a sixteen-byte UUID that identifies the allocated client sending the message (the requesting customer).
`ToAllocationID`	[sixteen]byte	`ToAllocateID` is a 16-byte UUID that identifies the allocated client receiving the message (the target client).
`Length`	uint16	`Length` specifies the length of the message content in bytes. The maximum value is 1400.
`Content`	[]byte	`Content` contains the content of the message.

Close message

Close messages are idempotent messages that allow a client to unbind and deallocate from a Relay server. Clients should send a Shut message to the Relay server when leaving their game session or when closing the game client. Clients can simply close their own bindings to the Relay server; they cannot close another client'due south binding.

Clients should send CLOSE messages multiple times to increase the hazard of successful delivery. Since Close messages are idempotent, at that place'due south no risk of the Relay server sending an ERROR message if the client has already been disconnected.

The Close message is a all-time endeavor to gracefully terminate an allocation, and in that location is no guarantee it volition succeed. Because Relay servers can deallocate clients with a timeout, Relay servers do not rely on a CLOSE message to remove a customer resource allotment.

The client sending the Shut message must be bound to the Relay server through a previous BIND request. If the client is not leap to the Relay server (or the client's IP address has changed), the Relay server will silently reject the bulletin. Use PING messages to forbid unintended allocation timeouts.

Note: Unbound clients withal expire through timeout. Meet Client timeouts.

Bytes	ane .. 4	5 .. 20
Purpose	Header (Type 11)	`AllocationID`

The following table describes each field found in a Close message.

Field	Blazon	Description
`AllocationID`	[16]byte	`AllocationID` is a 16-byte UUID that identifies the client's allocation.

Mistake message

Relay servers utilise Error messages strictly to inform the client that an mistake has occurred.

Bytes	1 .. 4	5 .. 20	21
Purpose	Header (Blazon 12)	`AllocationID`	`ErrorCode`

The following table describes each field constitute in an Mistake message.

Field	Type	Description
`AllocationID`	[16]byte	`AllocationID` is a 16-byte UUID that identifies the client's resource allotment.
`ErrorCode`	uint8	`ErrorCode` represents an error code. Come across Mistake codes.

Error codes

The following tabular array describes each of the possible error messages a Relay server tin can send to a client.

Code	Proper noun	Description
`0`	Invalid protocol version (`ErrInvalidProtocolVersion`)	`ErrInvalidProtocolVersion` is returned when a parsed message has an unexpected protocol version.
`ane`	Thespian timed out due to inactivity (`ErrTimeout`)	`ErrTimeout` is returned when a client'south bounden to a Relay server has timed out. See Client timeouts. Clients should use `PING messages` to prevent this type of error.
`2`	Unauthorized (`ErrUnauthorized`)	`ErrUnauthorized` is returned when a client attempts to perform an operation that it is not authorized to perform.
`3`	Allocation ID customer mismatch (`ErrClientPlayerMismatch`)	`ErrClientPlayerMismatch` is returned when a client has sent a `RELAY` message to the server using an unknown network connection. It is intended to inform the customer that the IP accost they are using has changed from the 1 the Relay server is aware of. This mistake message indicates the client should re-demark with a new `BIND bulletin`.
`4`	Allocation ID not found (`ErrAllocationNotFound`)	`ErrAllocationNotFound` is returned when the Relay server cannot find an allotment for the given allocation ID.
`5`	Not connected (`ErrNotConnected`)	`ErrNotConnected` is returned when a customer attempts to communicate with a client to whom it'due south not continued.
`6`	Cocky-connect not immune (`ErrSelfConnectNotAllowed`)	`ErrSelfConnectNotAllowed` is returned when a client sends a `CONNECT_REQUEST message` to a client with the aforementioned allocation ID.