Support Linux's abstract sockets

Closes puma#2526

lib/puma.rb

@@ -39,6 +39,20 @@ def self.ssl?
     HAS_SSL
   end
 
+  def self.abstract_unix_socket?
+    @abstract_unix ||=
+      if HAS_UNIX_SOCKET
+        begin
+          ::UNIXServer.new("\0puma.temp.unix").close
+          true
+        rescue ArgumentError  # darwin
+          false
+        end
+      else
+        false
+      end
+  end
+
   # @!attribute [rw] stats_object=
   def self.stats_object=(val)
     @get_stats = val

lib/puma/binder.rb

@@ -177,11 +177,19 @@ def parse(binds, logger, log_msg = 'Listening')
           @listeners << [str, io] if io
         when "unix"
           path = "#{uri.host}#{uri.path}".gsub("%20", " ")
+          abstract = false
+          if str.start_with? 'unix://@'
+            raise "OS does not support abstract UNIXSockets" unless Puma.abstract_unix_socket?
+            abstract = true
+            path = "@#{path}"
+          end
 
           if fd = @inherited_fds.delete(str)
+            @unix_paths << path unless abstract
             io = inherit_unix_listener path, fd
             logger.log "* Inherited #{str}"
           elsif sock = @activated_sockets.delete([ :unix, path ])
+            @unix_paths << path unless abstract || File.exist?(path)
             io = inherit_unix_listener path, sock
             logger.log "* Activated #{str}"
           else
@@ -205,6 +213,7 @@ def parse(binds, logger, log_msg = 'Listening')
               end
             end
 
+            @unix_paths << path unless abstract || File.exist?(path)
             io = add_unix_listener path, umask, mode, backlog
             logger.log "* #{log_msg} on #{str}"
           end
@@ -355,8 +364,6 @@ def inherit_ssl_listener(fd, ctx)
     # Tell the server to listen on +path+ as a UNIX domain socket.
     #
     def add_unix_listener(path, umask=nil, mode=nil, backlog=1024)
-      @unix_paths << path unless File.exist? path
-
       # Let anyone connect by default
       umask ||= 0
 
@@ -374,7 +381,7 @@ def add_unix_listener(path, umask=nil, mode=nil, backlog=1024)
           end
         end
 
-        s = UNIXServer.new(path)
+        s = UNIXServer.new path.sub(/\A@/, "\0")
         s.listen backlog
         @ios << s
       ensure
@@ -393,8 +400,6 @@ def add_unix_listener(path, umask=nil, mode=nil, backlog=1024)
     end
 
     def inherit_unix_listener(path, fd)
-      @unix_paths << path unless File.exist? path
-
       s = fd.kind_of?(::TCPServer) ? fd : ::UNIXServer.for_fd(fd)
 
       @ios << s
@@ -407,24 +412,24 @@ def inherit_unix_listener(path, fd)
     end
 
     def close_listeners
-      listeners.each do |l, io|
-        io.close unless io.closed? # Ruby 2.2 issue
-        uri = URI.parse(l)
+      @listeners.each do |l, io|
+        io.close unless io.closed?
+        uri = URI.parse l
         next unless uri.scheme == 'unix'
         unix_path = "#{uri.host}#{uri.path}"
-        File.unlink unix_path if unix_paths.include? unix_path
+        File.unlink unix_path if @unix_paths.include?(unix_path) && File.exist?(unix_path)
       end
     end
 
     def redirects_for_restart
-      redirects = listeners.map { |a| [a[1].to_i, a[1].to_i] }.to_h
+      redirects = @listeners.map { |a| [a[1].to_i, a[1].to_i] }.to_h
       redirects[:close_others] = true
       redirects
     end
 
     # @version 5.0.0
     def redirects_for_restart_env
-      listeners.each_with_object({}).with_index do |(listen, memo), i|
+      @listeners.each_with_object({}).with_index do |(listen, memo), i|
         memo["PUMA_INHERIT_#{i}"] = "#{listen[1].to_i}:#{listen[0]}"
       end
     end

lib/puma/control_cli.rb

@@ -176,7 +176,8 @@ def send_request
         when 'tcp'
           TCPSocket.new uri.host, uri.port
         when 'unix'
-          UNIXSocket.new "#{uri.host}#{uri.path}"
+          UNIXSocket.new(@control_url.start_with?('unix://@') ?
+            "\0#{uri.host}#{uri.path}" : "#{uri.host}#{uri.path}")
         else
           raise "Invalid scheme: #{uri.scheme}"
         end