Unix sockets

Spacebar is capable of using Unix sockets for message passing. This is quite efficient, as it does not have the overhead of using TCP/IP sockets, like RabbitMQ would.

This however relies on all parts of the server being on the same machine, as unix sockets are solely authenticated via filesystem permissions.

Configuration

You can configure the spacebar server to use Unix sockets by setting these environment variables:

EVENT_TRANSMISSION=unix
EVENT_SOCKET_PATH=/path/to/socket/directory #eg. /var/run/spacebar

Any socket in this directory will receive all traffic.

Developer note: message format

Unix socket replication in Spacebar uses a very simple message format:

---------------------------------------------
| length (4 bytes) | JSON data (n bytes...) |
---------------------------------------------

Length is sent as a 32-bit network order (big endian) number, while JSON data is encoded as UTF-8.

One read operation from the socket connection may not contain a complete payload, it is up to the recipient to buffer data as necessary, in order to have a full payload to decode.

Message sending is also relatively simple: connect to all sockets in the directory, copy the message to each of them. It is up to the sender to handle errors when connecting or writing data.