add setting class that coerces value to array

Fixes #6630

logstash-core/lib/logstash/settings.rb

@@ -489,6 +489,32 @@ module LogStash
         Util::TimeValue.from_value(value).to_nanos
       end
     end
+
+    class ArrayCoercible < Coercible
+      def initialize(name, klass, default, strict=true, &validator_proc)
+        @element_class = klass
+        super(name, ::Array, default, strict, &validator_proc)
+      end
+
+      def coerce(value)
+        Array(value)
+      end
+
+      protected
+      def validate(input)
+        if !input.is_a?(@klass)
+          raise ArgumentError.new("Setting \"#{@name}\" must be a #{@klass}. Received: #{input} (#{input.class})")
+        end
+
+        unless input.all? {|el| el.kind_of?(@element_class) }
+          raise ArgumentError.new("Values of setting \"#{@name}\" must be #{@element_class}. Received: #{input.map(&:class)}")
+        end
+
+        if @validator_proc && !@validator_proc.call(input)
+          raise ArgumentError.new("Failed to validate setting \"#{@name}\" with value: #{input}")
+        end
+      end
+    end
   end
 
 

logstash-core/spec/logstash/settings/array_coercible_spec.rb

@@ -0,0 +1,46 @@
+# encoding: utf-8
+require "spec_helper"
+require "logstash/settings"
+
+describe LogStash::Setting::ArrayCoercible do
+  subject { described_class.new("option", element_class, value) }
+  let(:value) { [ ] }
+  let(:element_class) { Object }
+
+  context "when given a non array value" do
+    let(:value) { "test" }
+    describe "the value" do
+      it "is converted to an array with that single element" do
+        expect(subject.value).to eq(["test"])
+      end
+    end
+  end
+
+  context "when given an array value" do
+    let(:value) { ["test"] }
+    describe "the value" do
+      it "is not modified" do
+        expect(subject.value).to eq(value)
+      end
+    end
+  end
+
+  describe "initialization" do
+    subject { described_class }
+    let(:element_class) { Fixnum }
+    context "when given values of incorrect element class" do
+      let(:value) { "test" }
+
+      it "will raise an exception" do
+        expect { described_class.new("option", element_class, value) }.to raise_error(ArgumentError)
+      end
+    end
+    context "when given values of correct element class" do
+      let(:value) { 1 }
+
+      it "will not raise an exception" do
+        expect { described_class.new("option", element_class, value) }.not_to raise_error
+      end
+    end
+  end
+end