Server helper: Suppress error of UDPServer over max_bytes on Windows

lib/fluent/plugin_helper/server.rb

@@ -545,6 +545,10 @@ def on_readable_without_sock
               data = @sock.recv(@max_bytes, @flags)
             rescue Errno::EAGAIN, Errno::EWOULDBLOCK, Errno::EINTR, Errno::ECONNRESET, IOError, Errno::EBADF
               return
+            rescue Errno::EMSGSIZE
+              # Windows ONLY: This happens when the data size is larger than `@max_bytes`.
+              @log.info "A received data was ignored since it was too large."
+              return
             end
             @callback.call(data)
           rescue => e
@@ -558,6 +562,10 @@ def on_readable_with_sock
               data, addr = @sock.recvfrom(@max_bytes)
             rescue Errno::EAGAIN, Errno::EWOULDBLOCK, Errno::EINTR, Errno::ECONNRESET, IOError, Errno::EBADF
               return
+            rescue Errno::EMSGSIZE
+              # Windows ONLY: This happens when the data size is larger than `@max_bytes`.
+              @log.info "A received data was ignored since it was too large."
+              return
             end
             @callback.call(data, UDPCallbackSocket.new(@sock, addr, close_socket: @close_socket))
           rescue => e

test/plugin_helper/test_server.rb

@@ -29,6 +29,7 @@ class Dummy < Fluent::Plugin::TestBase
     ENV['SERVERENGINE_SOCKETMANAGER_PATH'] = @socket_manager_path.to_s
 
     @d = Dummy.new
+    @d.under_plugin_development = true
     @d.start
     @d.after_start
   end
@@ -794,6 +795,50 @@ class Dummy < Fluent::Plugin::TestBase
         end
       end
     end
+
+    sub_test_case 'over max_bytes' do
+      data("cut off on Non-Windows", { max_bytes: 32, records: ["a" * 40], expected: ["a" * 32] }, keep: true) unless Fluent.windows?
+      data("drop on Windows", { max_bytes: 32, records: ["a" * 40], expected: [] }, keep: true) if Fluent.windows?
+      test 'with sock' do |data|
+        max_bytes, records, expected = data.values
+
+        actual_records = []
+        @d.server_create_udp(:myserver, @port, max_bytes: max_bytes) do |data, sock|
+          actual_records << data
+        end
+
+        open_client(:udp, "127.0.0.1", @port) do |sock|
+          records.each do |record|
+            sock.send(record, 0)
+          end
+        end
+
+        waiting(10) { sleep 0.1 until actual_records.size >= expected.size }
+        sleep 1 if expected.size == 0 # To confirm no record recieved.
+
+        assert_equal expected, actual_records
+      end
+
+      test 'without sock' do |data|
+        max_bytes, records, expected = data.values
+
+        actual_records = []
+        @d.server_create_udp(:myserver, @port, max_bytes: max_bytes) do |data|
+          actual_records << data
+        end
+
+        open_client(:udp, "127.0.0.1", @port) do |sock|
+          records.each do |record|
+            sock.send(record, 0)
+          end
+        end
+
+        waiting(10) { sleep 0.1 until actual_records.size >= expected.size }
+        sleep 1 if expected.size == 0 # To confirm no record recieved.
+
+        assert_equal expected, actual_records
+      end
+    end
   end
 
   module CertUtil
@@ -1575,6 +1620,10 @@ def assert_certificate(cert, expected_extensions)
 
   def open_client(proto, addr, port)
     client = case proto
+             when :udp
+               c = UDPSocket.open
+               c.connect(addr, port)
+               c
              when :tcp
                TCPSocket.open(addr, port)
              when :tls