Add Crystal services intro

docker/crystal/Dockerfile

@@ -1,4 +1,4 @@
-FROM crystallang/crystal:1.6.2-alpine AS build
+FROM crystallang/crystal:1.20.0-alpine AS build
 
 WORKDIR /opt/app
 

docker/crystal/shard.lock

@@ -6,5 +6,9 @@ shards:
 
   nats:
     git: https://github.com/jgaskins/nats.git
-    version: 1.2.2
+    version: 1.6.0
+
+  openssl_ext:
+    git: https://github.com/spider-gazelle/openssl_ext.git
+    version: 2.8.5
 

examples/services/intro/crystal/main.cr

@@ -0,0 +1,73 @@
+require "nats"
+require "nats/services"
+
+# Get the `NATS_URL` from the environment or fallback to the default. This can
+# be a comma-separated string. We convert it to an `Array(URI)` to pass to the
+# NATS client.
+servers = ENV.fetch("NATS_URL", "nats://localhost:4222")
+  .split(',')
+  .map { |url| URI.parse(url) }
+
+# Create a client connection to an available NATS server.
+nats = NATS::Client.new(servers)
+
+# When the program exits, we close the NATS client which waits for any pending
+# messages (published or in a subscription) to be flushed.
+at_exit { nats.close }
+
+# ### Defining a service
+#
+# This will create a service definition. Service definitions are made up of
+# the service name (which can't have things like whitespace in it), a version,
+# and a description. Even with no running endpoints, this service is discoverable
+# via the service protocol and by service discovery tools like `nats service`.
+# All of the default background handlers for discovery, PING, and stats are
+# started at this point.
+service = nats.services.add "minmax",
+  version: "0.0.1",
+  description: "Returns the min/max number in a request"
+
+puts "Created service: #{service.name} (#{service.id})"
+
+# ### Adding endpoints
+#
+# Groups serve as namespaces and are used as a subject prefix when endpoints
+# don't supply fixed subjects. In this case, all endpoints will be listening
+# on a subject that starts with `minmax.`
+service.add_group "minmax" do |root|
+  # Each endpoint represents a subscription. The supplied handlers will respond
+  # to `minmax.min` and `minmax.max`, respectively.
+
+  # Add a `min` endpoint to the service, which returns the minimum
+  # value from a JSON-serialized list of integer values.
+  root.add_endpoint "min" do |request|
+    min = Array(Int64).from_json(request.data_string).min
+
+    nats.reply request, min.to_json
+  end
+
+  # Add a `max` endpoint to the service, which returns the maximum
+  # value from a JSON-serialized list of integer values.
+  root.add_endpoint "max" do |request|
+    max = Array(Int64).from_json(request.data_string).max
+
+    nats.reply request, max.to_json
+  end
+end
+
+# ### Sending a request
+#
+# Now we create a list of integer values to send to our `minmax.min` and
+# `minmax.max` endpoints.
+request_data = [-1, 2, 100, -2000]
+
+# Send a request to the `minmax.min` endpoint containing the array above. Note
+# that this is just a regular NATS request.
+if response = nats.request("minmax.min", request_data.to_json, timeout: 2.seconds)
+  puts "Requested min value, got #{response.data_string.to_i}"
+end
+
+# Now we do the same thing with our `minmax.max` endpoint.
+if response = nats.request("minmax.max", request_data.to_json, timeout: 2.seconds)
+  puts "Requested max value, got #{response.data_string.to_i}"
+end