Load JSON at runtime

Closes puma#2206

lib/puma.rb

@@ -20,6 +20,7 @@ def self.stats_object=(val)
   end
 
   def self.stats
+    require 'json'
     @get_stats.stats.to_json
   end
 

lib/puma/app/status.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'json'
-
 module Puma
   module App
     # Check out {#call}'s source code to see what actions this web application
@@ -19,6 +17,10 @@ def call(env)
           return rack_response(403, 'Invalid auth token', 'text/plain')
         end
 
+        if env['PATH_INFO'] =~ /\/(gc-stats|stats|thread-backtraces)$/
+          require 'json'
+        end
+
         case env['PATH_INFO']
         when /\/stop$/
           @cli.stop

lib/puma/cluster.rb

@@ -5,7 +5,6 @@
 require 'puma/plugin'
 
 require 'time'
-require 'json'
 
 module Puma
   # This class is instantiated by the `Puma::Launcher` and used
@@ -95,6 +94,7 @@ def term?
 
       def ping!(status)
         @last_checkin = Time.now
+        require 'json'
         @last_status = JSON.parse(status, symbolize_names: true)
       end
 
@@ -330,6 +330,7 @@ def worker(index, master)
         while true
           sleep Const::WORKER_CHECK_INTERVAL
           begin
+            require 'json'
             io << "p#{Process.pid}#{server.stats.to_json}\n"
           rescue IOError
             Thread.current.purge_interrupt_queue if Thread.current.respond_to? :purge_interrupt_queue