Treat ReadOnlyError as a ConnectionError

Fix: #1168

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- Treat ReadOnlyError as ConnectionError. See #1168.
+
 # 5.0.5
 
 - Fix automatic disconnection when the process was forked. See #1157.

lib/redis/errors.rb

@@ -26,9 +26,6 @@ class PermissionError < CommandError
   class WrongTypeError < CommandError
   end
 
-  class ReadOnlyError < CommandError
-  end
-
   class OutOfMemoryError < CommandError
   end
 
@@ -52,6 +49,10 @@ class TimeoutError < BaseConnectionError
   class InheritedError < BaseConnectionError
   end
 
+  # Generally raised during Redis failover scenarios
+  class ReadOnlyError < BaseConnectionError
+  end
+
   # Raised when client options are invalid.
   class InvalidClientOptionError < BaseError
   end

test/redis/internals_test.rb

@@ -291,4 +291,38 @@ def test_can_be_duped_to_create_a_new_connection
 
     assert_equal clients + 1, r.info["connected_clients"].to_i
   end
+
+  def test_reconnect_on_readonly_errors
+    tcp_server = TCPServer.new("127.0.0.1", 0)
+    tcp_server.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEADDR, true)
+    port = tcp_server.addr[1]
+
+    server_thread = Thread.new do
+      session = tcp_server.accept
+      io = RedisClient::RubyConnection::BufferedIO.new(session, read_timeout: 1, write_timeout: 1)
+      2.times do
+        command = RedisClient::RESP3.load(io)
+        case command.first.upcase
+        when "PING"
+          session.write("+PONG\r\n")
+        when "SET"
+          session.write("-READONLY You can't write against a read only replica.\r\n")
+        else
+          session.write("-ERR Unknown command #{command.first}\r\n")
+        end
+      end
+      session.close
+    end
+
+    redis = Redis.new(host: "127.0.0.1", port: port, timeout: 2, reconnect_attempts: 0)
+    assert_equal "PONG", redis.ping
+
+    assert_raises Redis::ReadOnlyError do
+      redis.set("foo", "bar")
+    end
+
+    refute_predicate redis, :connected?
+  ensure
+    server_thread&.kill
+  end
 end