in_tcp: Add message_length_limit

Add the same feature to `in_tcp` as `message_length_limit` in
`in_udp`, to drop too large incoming data.

If there is subsequent data, that part may fail to parse and
warning log is output, but this fix considers it a specification.

Signed-off-by: Daijiro Fukuda <[email protected]>

lib/fluent/plugin/in_tcp.rb

@@ -36,6 +36,10 @@ class TcpInput < Input
     desc "The field name of the client's address."
     config_param :source_address_key, :string, default: nil
 
+    # Setting default to nil for backward compatibility
+    desc "The max bytes of message."
+    config_param :message_length_limit, :size, default: nil
+
     config_param :blocking_timeout, :time, default: 0.5
 
     desc 'The payload is read up to this character.'
@@ -111,6 +115,11 @@ def start
 
           conn.buffer << data
           buf = conn.buffer
+          if !@message_length_limit.nil? && @message_length_limit < buf.bytesize
+            log.info "The receiving data is larger than 'message_length_limit', dropped:", limit: @message_length_limit, size: buf.bytesize, head: buf[...32]
+            buf.clear
+            next
+          end
           pos = 0
           while i = buf.index(@delimiter, pos)
             msg = buf[pos...i]
@@ -141,6 +150,11 @@ def start
 
           conn.buffer << data
           buf = conn.buffer
+          if !@message_length_limit.nil? && @message_length_limit < buf.bytesize
+            log.info "The receiving data is larger than 'message_length_limit', dropped:", limit: @message_length_limit, size: buf.bytesize, head: buf[...32]
+            buf.clear
+            next
+          end
           pos = 0
           es = Fluent::MultiEventStream.new
           while i = buf.index(@delimiter, pos)