Why JsonRpcRemote

Robot Framework runs the keywords of a library in its own process. Often they have to run somewhere else:

• on the machine or device with the system under test, while the tests run on a CI agent;
• in an environment with dependencies, a Python version or an operating system that the test environment does not have;
• in a container next to the tests, for example as a sidecar in Kubernetes;
• in a program written in another language, such as Java, .NET or Rust.

Robot Framework’s Remote library exists for this: it calls the keywords of a remote server over XML-RPC. JsonRpcRemote serves the same purpose on a modern foundation, JSON-RPC 2.0, and goes further where the Remote library stops.

What JsonRpcRemote does better

A standard that every language speaks

JSON-RPC 2.0 is a simple, standardized protocol; the Language Server Protocol uses it, and every common programming language has libraries for it. A server that offers keywords can therefore be written in any language, often in a few lines of code. Values are JSON: null stays null, and integers keep their size, where the Remote library turns None into an empty string and XML-RPC stops at 32-bit integers. Between Python peers, Python objects travel unchanged.

Any library, without code

For the Remote library, every library needs a server that wraps it, for Python a script with robotremoteserver. robot-jsonrpcremote-server MyLibrary makes almost any Robot Framework library remote without code: Robot Framework itself imports and runs it, so argument conversion with type hints and custom converters works as for a local library, and the suite passes the library’s arguments. One server serves several libraries.

Logs while the keyword runs

The Remote library gets the output of a keyword with its result, after the keyword has finished. JsonRpcRemote keeps a connection that carries messages both ways, so the log messages of a remote keyword appear in the Robot Framework log while the keyword runs, which matters for keywords that take long.

The server starts with the tests

Over stdio, the client starts the server for a session and stops it again: there is no server to set up beforehand and no port to manage. Over TCP, named pipes, Unix domain sockets, WebSockets or Streamable HTTP, with TLS, it reaches a server on another machine or in a container.

A fresh library for each test or suite

With the Remote library, there is one instance of the library for as long as the server runs, shared by every suite. JsonRpcRemote imports the library for each session, for a test, a suite or the whole run, so tests start from a known state.

Made for containers and networks

JsonRpcRemote detects a lost connection and reports its cause, waits for a server that is still starting, and reconnects with a check that the library has not changed. Failures arrive as in Robot Framework, continuable, fatal or skipped, with the type and the traceback of the error, and keyword timeouts, including the test and keyword timeouts of Robot Framework, end a keyword that hangs.

At a glance

	Remote and robotremoteserver	JsonRpcRemote
Protocol	XML-RPC over HTTP or HTTPS	JSON-RPC 2.0 over a stream, framed as in the Language Server Protocol
Connection	a new HTTP connection for each call	one connection per session, with a handshake and an orderly end
Direction	the client calls the server	both ways: the server sends log messages while a keyword runs
Log messages	the output of a keyword arrives with its result	log messages arrive while the keyword runs
Transports	HTTP and HTTPS	TCP; stdio, where the client starts and stops the server; named pipes, Unix domain sockets, WebSockets and Streamable HTTP
Libraries per server	one	several, which the client chooses by name
Making a library remote	a script that creates the library and starts the server with it	robot-jsonrpcremote-server MyLibrary: Robot Framework itself imports and runs the library
Arguments of the library	fixed in the server script	given in the suite and converted on the server
Life of the library instance	as long as the server runs	as long as the session: a test, a suite or the run
Argument conversion	on the client, by the types that the server reports; robotremoteserver reports none	on the server, by Robot Framework, with custom converters
Values	XML-RPC types: integers up to 32 bits, None becomes an empty string, other types become strings	JSON values; between Python peers, also Python objects, which travel unchanged
Lost connections	the call fails with Connection to remote server broken	detected with their cause; connect retry, and a reconnect that checks the library definition
Failures	continuable and fatal failures, with the traceback	continuable, fatal and skipped failures, with the type and the traceback of the error
Timeouts	a socket timeout, which also ends a keyword call	for connecting and for each session, and keyword timeouts with cancellation, including the test and keyword timeouts of Robot Framework
Encryption	HTTPS	TLS
Servers in other languages	ready-made servers for Java, .NET, Ruby and others	any language: with a JSON-RPC library, a server takes only a few lines of code; see the protocol