Varlink is a kernel interface and protocol that is readable by both humans and machines.
Interface Varlink combines classic UNIX command line options, STDIN/OUT/ERROR text formats, man pages, service metadata, and is equivalent to an FD3 file descriptor. Varlink available from any programming environment.
Varlink interface determineswhat methods will be implemented and how. Each of the methods has a name and specified input and output parameters.
It is possible to document by adding comments before the documented piece of code.
Π protocol Varlink all messages are encoded as JSON objects and terminated by a NUL byte.
The service responds to requests in the same order in which they were received - messages are never multiplexed. However, multiple requests can be queued on a connection to enable pipelining.
A common case is a simple method call with a single response. In some other cases, the server may not respond at all, or it may respond multiple times to the same call. More detailed description here.
Source: linux.org.ru