Raise a useful error when reconnecting with a circuit breaker (#145)

* Raise a useful error when reconnecting with a circuit breaker

If you have reconnects enabled, and a circuit breaker configured,
it's useful to raise the actual underlying error when we actually
attempted the connection instead of simply the circuit breaker
error. The circuit breaker error will still be raised if no
attempts were tried.

* Use descriptive name for error.

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

* Tweak preferred_error assignment

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

---------

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

lib/redis_client.rb

@@ -669,6 +669,7 @@ def ensure_connected(retryable: true)
     elsif retryable
       tries = 0
       connection = nil
+      preferred_error = nil
       begin
         connection = raw_connection
         if block_given?
@@ -677,13 +678,15 @@ def ensure_connected(retryable: true)
           connection
         end
       rescue ConnectionError, ProtocolError => error
+        preferred_error ||= error
+        preferred_error = error unless error.is_a?(CircuitBreaker::OpenCircuitError)
         close
 
         if !@disable_reconnection && config.retry_connecting?(tries, error)
           tries += 1
           retry
         else
-          raise
+          raise preferred_error
         end
       end
     else

test/redis_client/connection_test.rb

@@ -227,6 +227,18 @@ def test_circuit_breaker
       end
     end
 
+    def test_circuit_breaker_initial_connection_exception
+      circuit_breaker = CircuitBreaker.new(error_threshold: 1, success_threshold: 1, error_timeout: 1)
+      @redis = new_client(circuit_breaker: circuit_breaker, reconnect_attempts: 2)
+
+      Toxiproxy[/redis/].down do
+        error = assert_raises CannotConnectError do
+          @redis.call("PING")
+        end
+        refute_instance_of CircuitBreaker::OpenCircuitError, error
+      end
+    end
+
     def test_killed_connection
       client = new_client(reconnect_attempts: 1, id: "background")