# Pub/Sub Realtime Telemetry Protocol (PSRT) Specifications
## Common
Default port: 2873
All numbers are processed as little-endian.
PROTOCOL VERSION: 1
LEN = data 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 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.
Any other control frame can be used as keep-alive signal as well. So ff the
client sends many control frames, ping frames can be delayed or omitted.
### 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
The 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
