# PSRT protocol specifications
## Common
Default port: 2883
All numbers are processed as little-endian.
PROTOCOL VERSION: 1
LEN = packet length (4 bytes = u32)
Response codes:
* 0x00 - NOP (pings, should be sent every N < timeout seconds to make sure the
socket is alive)
* 0x01 - OK
* 0x02 - OK\_WAITING (waiting for data, used in replication only)
* 0xE0 - NOT\_REQUIRED (used in replication only)
* 0xFE - ERR\_ACCESS (pub/sub access denied)
* 0xFF - ERROR (all other errors)
Data sockets usually use the same port as control ones.
Priority byte is not used at the moment (reserved for the future) and should be
always 0x7F.
## Control socket
### Greetings
Client: EE AA <00 / 01 for STARTTLS>
Server: sets mode or disconnects
Server (4 byte): EE AA 01 00 (01 00 - protocol version)
Client: LEN LOGIN 00 PASSWORD (for anonymous login send = 01 00 00 00 00)
Server: 32 bytes (*client token) or closes the socket
### Keep-alive pings
The client MUST ping the server by sending OP\_NOP with frequency higher than
the server timeout, otherwise the socket is automatically closed by the server.
### Subscribe
OP\_SUBCRIBE = 0x02
Client:
0x02 LEN TOPIC (or multiple topics splitted by 0x00)
Server:
OK/ERROR
### Unsubscribe
OP\_UNSUBCRIBE = 0x02
Client:
0x03 LEN TOPIC (or multiple topics splitted by 0x00)
Server:
OK/ERROR
### Publish
OP\_PUBLISH = 0x01
Client:
0x01 PRI(u8=7F) LEN TOPIC \x0 MESSAGE
Server:
OK/ERROR
### Publish if subscribed (replicate)
OP\_PUBLISH\_REPL = 0x11
Client:
0x11 LEN TOPIC
Server:
OK\_WAIT/ERROR/NOT\_REQIRED
Client (if required)
PRIO(u8=7F) TIMESTAMP(u64, nanoseconds) LEN MESSAGE
### Bye
OP\_BYE = 0xFF
Client:
0xFF
Server: closes the socket
The client may keep or close a data socket if opened.
## Data socket
Note: A data socket is forcibly disconnected by the server when the client is
disconnected from the control socket.
### Greetings
Client: 0xEE 0xAB <0x00 / 0x01 for STARTTLS>
Server: sets mode or disconnects
Server (4 byte): EE AB 01 00 (01 00 - protocol version)
Client: 32 bytes (client token) TIMEOUT\_SEC (u8)
Server: OK or closes the socket
The client can have only one data socket with the same token. The client may
close the data socket and then reuse the token to open a new one.
### Keep-alive pings
The server pings the client by sending OP\_NOP with frequency TIMEOUT\_SEC / 2,
where TIMEOUT\_SEC is the value reported by the client during greetings.
### Message push
Server:
x01 PRI(u8=7F) LEN TOPIC 00 MESSAGE
Server also sends beacon OP\_NOP messages with TIMEOUT/2 interval
### Bye
Not required. The client can close the data socket at any time.
## UDP
* 0x01 - OP\_PUBLISH
* 0x21 - OP\_PUBLISH\_NO\_ACK
Client:
EE AA 01 00 LOGIN 00 PASSWORD 00 OP PRIO(u8=7F) TOPIC 00 DATA
Server (if ack required):
CONTROL\_HEADER (2 bytes) PROTOCOL\_VER (2 bytes) OK
