Using Genie in an interactive environment (Jupyter/IJulia, REPL, etc)

Genie can be used for ad-hoc exploratory programming, to quickly whip up a web server and expose your Julia functions.

Once you have Genie into scope, you can define a new route. A route maps a URL to a function.

julia> using Genie

julia> route("/") do
         "Hi there!"
       end

You can now start the web server using

julia> up()

Finally, now navigate to http://localhost:8000 – you should see the message "Hi there!".

We can define more complex URIs which can also map to previously defined functions:

julia> function hello_world()
         "Hello World!"
       end
julia> route("/hello/world", hello_world)

The route handler functions can be defined anywhere (in any other file or module) as long as they are accessible in the current scope.

You can now visit http://localhost:8000/hello/world in the browser.

We can access route params that are defined as part of the URL, like :message in the following example:

julia> route("/echo/:message") do
         params(:message)
       end

Accessing http://localhost:8000/echo/ciao should echo "ciao".

And we can even match route params by types (and automatically convert them to the correct type):

julia> route("/sum/:x::Int/:y::Int") do
         params(:x) + params(:y)
       end

By default, route params are extracted as SubString (more exactly, SubString{String}). If type constraints are added, Genie will attempt to convert the SubString to the indicated type.

For the above to work, we also need to tell Genie how to perform the conversion:

julia> Base.convert(::Type{Int}, s::AbstractString) = parse(Int, s)

Now if we access http://localhost:8000/sum/2/3 we should see 5

Handling query params

Query params, which look like ...?foo=bar&baz=2 are automatically unpacked by Genie and placed into the params collection. For example:

julia> route("/sum/:x::Int/:y::Int") do
         params(:x) + params(:y) + parse(Int, get(params, :initial_value, "0"))
       end

Accessing http://localhost:8000/sum/2/3?initial_value=10 will now output 15.