Add Rename filter to rename event fields

lib/rackstash/filters/rename.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+#
+# Copyright 2017 Holger Just
+#
+# This software may be modified and distributed under the terms
+# of the MIT license. See the LICENSE.txt file for details.
+
+module Rackstash
+  module Filters
+    # Rename one or more fields in the given event.
+    #
+    # @example
+    #   Rackstash::Flow.new(STDOUT) do
+    #     # Renames the "HOST_OR_IP" field to "client_ip"
+    #     filter :rename, "HOST_OR_IP" => "client_ip"
+    #   end
+    class Rename
+      # @param spec [Hash<#to_s => #to_s>] a `Hash` specifying how fields should
+      #   be renamed, with the existing field name as a hash key and the new
+      #   field name as the respective value.
+      def initialize(spec)
+        @rename = {}
+        Hash(spec).each_pair do |key, value|
+          @rename[key.to_s] = value.to_s
+        end
+      end
+
+      # Rename fields in the event to a new name. If a field was not found,
+      # it will be ignored.
+      #
+      # @param event [Hash] an event hash
+      # return [Hash] the given `event` with the fields renamed
+      def call(event)
+        @rename.each_pair do |old_key, new_key|
+          next unless event.key?(old_key)
+          event[new_key] = event.delete(old_key)
+        end
+        event
+      end
+    end
+  end
+end

spec/rackstash/filters/rename_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+#
+# Copyright 2017 Holger Just
+#
+# This software may be modified and distributed under the terms
+# of the MIT license. See the LICENSE.txt file for details.
+
+require 'spec_helper'
+
+require 'rackstash/filters/rename'
+
+describe Rackstash::Filters::Rename do
+  let(:event) {
+    {
+      'foo' => 'foo value',
+      'bar' => 'bar value'
+    }
+  }
+
+  def filter!(spec)
+    described_class.new(spec).call(event)
+  end
+
+  it 'renames existing fields' do
+    filter!('foo' => 'awesome')
+    expect(event).to eql 'awesome' => 'foo value', 'bar' => 'bar value'
+  end
+
+  it 'it ignores missing fields' do
+    filter!('unknown' => 'ohnoes')
+    expect(event).to eql 'foo' => 'foo value', 'bar' => 'bar value'
+  end
+
+  it 'stringifies spec values' do
+    filter!(foo: :bam)
+    expect(event).to eql 'bam' => 'foo value', 'bar' => 'bar value'
+  end
+
+  it 'overwrites conflicting keys' do
+    filter!('foo' => 'bar')
+    expect(event).to eql 'bar' => 'foo value'
+  end
+
+  it 'returns the given event object' do
+    expect(filter!('bar' => 'baz')).to equal event
+  end
+end