Julia Gateway

Introduction

Fjage.jl provides a Julia interface to fjåge. Like the other gateways, it lets a Julia application connect to a fjåge master container, exchange messages with agents, and look up services. Fjage.jl goes further than the other gateways, however — it is a full Julia port of fjåge, so you can also develop agents, behaviors and containers natively in Julia. Fjage.jl is maintained in its own repository and has its own documentation; this chapter introduces the gateway functionality and defers to that documentation for the full API reference and for Julia-side agent development.

Fjage.jl is registered in the Julia package registry. To install it, press ] at the Julia REPL to enter the package manager, and:

pkg> add Fjage

Connecting to fjåge

Just as with the Python gateway, we assume a fjåge master container is running with a TCP port open (see Distributed Agents). Open a gateway to it, look up an agent providing the service you want, and interact with it. For example, to interact with the shell agent:

julia> using Fjage
julia> gw = Gateway("localhost", 1100);
julia> shell = agentforservice(gw, "org.arl.fjage.shell.Services.SHELL")
shell
julia> shell.language        # read a parameter of the shell agent
"Groovy"
julia> request(gw, ShellExecReq(recipient=shell, command="ps"))
AGREE
julia> shell << ShellExecReq(command="ps")   # shorthand for the same request
AGREE
julia> close(gw)

The gateway supports the same messaging primitives as the other gateways — send, receive, request, subscribe/unsubscribe, agentforservice/agentsforservice — with Julia-idiomatic lowercase names. They are documented in the Gateway section of the Fjage.jl manual.

Working with message classes

Message types corresponding to fjåge message classes are declared with the @message macro, which plays the role that MessageClass plays in the Python and JavaScript gateways. The declaration specifies the fully qualified Java class name and the message fields:

@message "org.arl.fjage.demo.WeatherForecastReqMsg" struct WeatherForecastReqMsg
  city::Union{String,Nothing} = nothing
  country::Union{String,Nothing} = nothing
end

All messages automatically carry the standard fjåge fields (performative, messageID, inReplyTo, sender, recipient, sentAt), and the performative is guessed from the class name (...Req becomes a REQUEST). For one-off or dynamic interactions, a GenericMessage can be used without declaring a message type, much like generic messages on the Java side. See the Messages section of the Fjage.jl manual for details, including performative overrides and message inheritance.