feat: [#39] Introduce retry pattern for establishing connection to (#40)

RabbitMQ

* Implement retry for Harmoniser::Connection#start
* Prevent Harmoniser::Connection#close to raise exception. Prefer log to
  error the exception and terminate gracefully

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [0.8.0] - 2024-03-31
+
+### Added
+- Implement retry mechanism to establish connection to RabbitMQ. More details at [issue](https://github.com/jollopre/harmoniser/issues/39).
+- Strengthen at_exit hook to not break when connection cannot be closed.
+
 ## [0.7.0] - 2024-01-03
 
 ### Added

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    harmoniser (0.7.0)
+    harmoniser (0.8.0)
       bunny (~> 2.22)
 
 GEM

lib/harmoniser/cli.rb

@@ -22,7 +22,6 @@ def initialize
 
     def call
       parse_options
-      define_signals
       run
     end
 
@@ -50,6 +49,8 @@ def run
         .new(configuration: configuration, logger: logger)
         .start
 
+      define_signals
+
       while @read_io.wait_readable
         signal = @read_io.gets.strip
         handle_signal(signal)

lib/harmoniser/connectable.rb

@@ -37,11 +37,10 @@ def at_exit_handler
       logger = Harmoniser.logger
 
       logger.info("Shutting down!")
-      if connection? && connection.open?
-        stringified_connection = connection.to_s
-        logger.info("Connection will be closed: connection = `#{stringified_connection}`")
-        connection.close
-        logger.info("Connection closed: connection = `#{stringified_connection}`")
+      if connection? && @connection.open?
+        logger.info("Connection will be closed: connection = `#{@connection}`")
+        @connection.close
+        logger.info("Connection closed: connection = `#{@connection}`")
       end
       logger.info("Bye!")
     end

lib/harmoniser/connection.rb

@@ -27,7 +27,7 @@ class Connection
       write_timeout: 5
     }
 
-    def_delegators :@bunny, :close, :create_channel, :open?, :recovering_from_network_failure?, :start
+    def_delegators :@bunny, :create_channel, :open?, :recovering_from_network_failure?
 
     def initialize(opts)
       @bunny = Bunny.new(opts)
@@ -37,6 +37,26 @@ def to_s
       "<#{self.class.name}>: #{user}@#{host}:#{port}, connection_name = `#{connection_name}`, vhost = `#{vhost}`"
     end
 
+    def start
+      retries = 0
+      begin
+        with_signal_handler { @bunny.start }
+      rescue => e
+        Harmoniser.logger.error("Connection attempt failed: retries = `#{retries}`, error_class = `#{e.class}`, error_message = `#{e.message}`")
+        with_signal_handler { sleep(1) }
+        retries += 1
+        retry
+      end
+    end
+
+    def close
+      @bunny.close
+      true
+    rescue => e
+      Harmoniser.logger.error("Connection#close failed: error_class = `#{e.class}`, error_message = `#{e.message}`")
+      false
+    end
+
     private
 
     def connection_name
@@ -58,5 +78,12 @@ def user
     def vhost
       @bunny.vhost
     end
+
+    def with_signal_handler
+      yield if block_given?
+    rescue SignalException => e
+      Harmoniser.logger.info("Signal received: signal = `#{Signal.signame(e.signo)}`")
+      exit(0)
+    end
   end
 end

lib/harmoniser/version.rb

@@ -1,3 +1,3 @@
 module Harmoniser
-  VERSION = "0.7.0"
+  VERSION = "0.8.0"
 end

spec/harmoniser/connection_spec.rb

@@ -20,13 +20,60 @@
     expect(subject).to respond_to(:recovering_from_network_failure?)
   end
 
-  it "responds to start" do
-    expect(subject).to respond_to(:start)
-  end
-
   describe "#to_s" do
     it "returns a string representation of the connection" do
       expect(subject.to_s).to eq("<Harmoniser::Connection>: [email protected]:5672, connection_name = `wadus`, vhost = `/`")
     end
   end
+
+  describe "#start" do
+    let(:bunny) { subject.instance_variable_get(:@bunny) }
+
+    it "retries establishing connection until succeeding" do
+      allow(Harmoniser.logger).to receive(:error)
+      allow(subject).to receive(:sleep)
+      allow(bunny).to receive(:start) do
+        @retries ||= 0
+        if @retries < 2
+          @retries += 1
+          raise "Error"
+        end
+      end
+
+      subject.start
+
+      expect(Harmoniser.logger).to have_received(:error).with(/Connection attempt failed: retries = `.*`, error_class = `RuntimeError`, error_message = `Error`/).twice
+    end
+  end
+
+  describe "#close" do
+    let(:bunny) { subject.instance_variable_get(:@bunny) }
+
+    it "returns true" do
+      allow(bunny).to receive(:close)
+
+      result = subject.close
+
+      expect(result).to eq(true)
+    end
+
+    context "when closing connection fails" do
+      it "returns false" do
+        allow(bunny).to receive(:close).and_raise("Error")
+
+        result = subject.close
+
+        expect(result).to eq(false)
+      end
+
+      it "log with error severity is output" do
+        allow(bunny).to receive(:close).and_raise("Error")
+        allow(Harmoniser.logger).to receive(:error)
+
+        subject.close
+
+        expect(Harmoniser.logger).to have_received(:error).with(/Connection#close failed: error_class = `RuntimeError`, error_message = `Error`/)
+      end
+    end
+  end
 end

spec/shared_context/configurable.rb

@@ -1,6 +1,5 @@
 RSpec.shared_context "configurable" do
   let(:host) { ENV.fetch("RABBITMQ_HOST") }
-  let(:bunny) { Bunny.new(host: host, logger: Logger.new(IO::NULL)).start }
 
   before do
     Harmoniser.configure do |config|
@@ -18,4 +17,17 @@ def declare_queue(name, exchange_name)
     channel = bunny.create_channel
     Bunny::Queue.new(channel, name, {auto_delete: true}).bind(exchange_name)
   end
+
+  def bunny
+    @bunny ||= Bunny.new(host: host, logger: Logger.new(IO::NULL))
+    return @bunny if @bunny.open?
+
+    begin
+      @bunny.start
+    rescue => e
+      puts "start connection attempt failed: error_class = `#{e.class}`, error_message = `#{e.message}`"
+      sleep(1)
+      retry
+    end
+  end
 end