Adding elixir sample for request-reply (#172)

Co-authored-by: Byron Ruth <[email protected]>

examples/messaging/request-reply/elixir/main.exs

@@ -0,0 +1,84 @@
+# Set up the dependencies for this script. Ordinarily you would have this set of dependencies
+# declared in your `mix.exs` file.
+Mix.install([
+  # For documentation on the Gnat library, see https://hexdocs.pm/gnat/readme.html
+  {:gnat, "~> 1.7.1"},
+  {:jason, "~> 1.0"}
+])
+
+url = System.get_env("NATS_URL", "nats://0.0.0.0:4222")
+uri = URI.parse(url)
+
+# Call `start_link` on `Gnat` to start the Gnat application supervisor
+{:ok, gnat} = Gnat.start_link(%{host: uri.host, port: uri.port})
+
+# The `Gnat.ConnectionSupervisor` is a process that monitors your NATS connection. If connection
+# is lost, this process will retry according to its backoff settings to re-establish a connection.
+# You can communicate with NATS without this, but we recommend using supervised connections
+# and consumers
+gnat_supervisor_settings = %{
+  name: :gnat,
+  backoff_period: 4_000,
+  connection_settings: [
+    %{host: uri.host, port: uri.port}
+  ]
+}
+
+{:ok, _conn} = Gnat.ConnectionSupervisor.start_link(gnat_supervisor_settings)
+
+# Give the connection time to establish (this is only needed for these examples and not in production)
+if Process.whereis(:gnat) == nil do
+  Process.sleep(300)
+end
+
+
+# Now let's set up a consumer supervisor. We use the `subscription_topics` field in the configuration
+# map to set up a list of subscriptions which can optionally have queue names.
+consumer_supervisor_settings = %{
+  connection_name: :gnat,
+  # This is the name of a module defined below
+  module: ExampleService,
+  subscription_topics: [
+    %{topic: "request.demo"},
+  ]
+
+}
+
+# Starting the consumer supervisor will create the subscription and will monitor
+# the connection to re-establish subscriptions in case of failure
+{:ok , _pid} = Gnat.ConsumerSupervisor.start_link(consumer_supervisor_settings)
+
+
+# This is a module that conforms to the `Gnat.Server` behavior. The name of this module
+# matches the `module` field in the consumer supervisor settings.
+defmodule ExampleService do
+  use Gnat.Server
+
+  # This handler will simulate an error
+  def request(%{topic: "request.demo", body: body}) when body == "failure" do
+    {:error, "something went wrong!"}
+  end
+
+  # This handler is matching just on the subject
+  def request(%{topic: "request.demo", body: body}) do
+    IO.puts "Demo request received message: #{inspect(body)}"
+    {:reply, "This is a demo"}
+  end
+
+   # Defining an error handler is optional, the default one will just call Logger.error for you
+   def error(%{gnat: gnat, reply_to: reply_to}, error) do
+    Gnat.pub(gnat, reply_to, "An error occurred: #{inspect(error)}")
+  end
+end
+
+# Now that we know there's an active subscription on the `request.demo` subject, we can
+# make a request and process the reply using `Gnat.request`
+{:ok, %{body: res}} = Gnat.request(:gnat, "request.demo", "input data")
+IO.puts("First result: #{res}")
+
+{:ok, %{body: res}} = Gnat.request(:gnat, "request.demo", "more data")
+IO.puts("Second result: #{res}")
+
+# Now cause a failure so we can see error responses
+{:ok, %{body: res}} = Gnat.request(:gnat, "request.demo", "failure")
+IO.puts("Failure result: #{res}")

examples/messaging/request-reply/meta.yaml

@@ -7,7 +7,7 @@ description: |-
   information.
 
   Unlike request-reply constrained protocols like HTTP, NATS is not limited
-  to a strict point-to-point interfaction between a client and server. The
+  to a strict point-to-point interaction between a client and server. The
   request-reply pattern is built on top of the core [publish-subscribe][pubsub]
   model.