Limit log message length

lib/contextual_logging/logstash_message_formatter.rb

@@ -1,11 +1,46 @@
 module ContextualLogging
   class LogstashMessageFormatter
+    MAX_MESSAGE_LENGTH = 2000
+
     def format(severity, message, extra_context)
-      msg_hash = HashWithIndifferentAccess.new('message' => message, 'log_level' => severity)
-      logstash_data = extra_context.merge(msg_hash)
+      if severity == 'INFO'
+        truncated_message = truncate(message)
+        limited_extra_context = truncate_log_extra_context(extra_context)
+      else
+        truncated_message = message
+        limited_extra_context = extra_context
+      end
+
+      logstash_data = HashWithIndifferentAccess.new(
+        'message' => truncated_message,
+        'log_level' => severity
+      ).merge(limited_extra_context)
+
       logstash_event = LogStash::Event.new(logstash_data)
       logstash_event.to_json
     end
+
+    private
+
+    def truncate(message)
+      message[0...MAX_MESSAGE_LENGTH]
+    end
+
+    def truncate_log_extra_context(extra_context)
+      extra_context.each_with_object(HashWithIndifferentAccess.new) do |(key, value), limited_extra_context|
+        if value.is_a?(Hash)
+          limited_extra_context[key] = HashWithIndifferentAccess.new
+          value.each do |k, v|
+            if v.is_a?(String)
+              limited_extra_context[key][k] = truncate(v)
+            else
+              limited_extra_context[key][k] = truncate(v.inspect)
+            end
+          end
+        else
+          limited_extra_context[key] = value
+        end
+      end
+    end
   end
 end
-

spec/contextual_logging_spec.rb

@@ -1,4 +1,22 @@
 require 'spec_helper'
 
-describe ContextualLogging do
+describe ContextualLogging::LogstashMessageFormatter do
+  message_formatter = ContextualLogging::LogstashMessageFormatter.new
+    it 'should limit message size to 2000 characters when severity level is INFO' do
+      message = (0...3000).map { ('a'..'z').to_a[rand(26)] }.join
+      log_message = message_formatter.format('INFO', message, {})
+      expect(JSON[log_message]['message'].length).to equal 2000
+    end
+
+    it 'should limit extra context values that are two levels deep to 2000 characters when severity level is INFO' do
+      message = (0...3000).map { ('a'..'z').to_a[rand(26)] }.join
+      extra_context = HashWithIndifferentAccess.new
+      extra_context['params'] = HashWithIndifferentAccess.new(nodes: {})
+      extra_context['text'] = (0...3000).map { ('a'..'z').to_a[rand(26)] }.join
+      extra_context['params']['nodes']['a'] = (0...3000).map { ('a'..'z').to_a[rand(26)] }.join
+
+      log_message = message_formatter.format('INFO', message, extra_context)
+      expect(JSON[log_message]['params']['nodes'].length).to equal 2000
+      expect(JSON[log_message]['text'].length).to equal 3000
+    end
 end