[PATCH v2] emulate sd_listen_fds for systemd support

[Eric Wong <e@80x24.org>]

systemd socket emulation shares FDs across execve, just like
the built-in SIGUSR2 upgrade process in unicorn.  Thus it is
easy to support inheriting sockets from systemd.

Tested-by: Christos Trochalakis <yatiohi@ideopolis.gr>
---
  Christos Trochalakis <yatiohi@ideopolis.gr> wrote:
  > On Sat, Jun 27, 2015 at 04:01:36AM +0000, Eric Wong wrote:
  > >Unfortunately, testing this is tricky because FD=3
  > >(SD_LISTEN_FDS_START) tends to be grabbed by (MRI) Ruby 1.9.3
  > >and onwards for the internal self-pipe.

  OK, that was a bogus note.
  I forgot exec() in Ruby 1.9+ supports redirects natively.
  Test included in updated patch.

  > I have also tested it and works as expected. Also, hardcoding
  > SD_LISTEN_FDS_START seems like the best option. I 'd like to see that
  > applied to master.

  Thanks.  This will be in 5.0.0.pre2

 lib/unicorn/http_server.rb | 16 +++++++++++++---
 test/exec/test_exec.rb     | 24 ++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 297b9f9..0f97516 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -766,12 +766,22 @@ class Unicorn::HttpServer
   def inherit_listeners!
     # inherit sockets from parents, they need to be plain Socket objects
     # before they become Kgio::UNIXServer or Kgio::TCPServer
-    inherited = ENV['UNICORN_FD'].to_s.split(',').map do |fd|
-      io = Socket.for_fd(fd.to_i)
+    inherited = ENV['UNICORN_FD'].to_s.split(',')
+
+    # emulate sd_listen_fds() for systemd
+    sd_pid, sd_fds = ENV.values_at('LISTEN_PID', 'LISTEN_FDS')
+    if sd_pid && sd_pid.to_i == $$
+      # 3 = SD_LISTEN_FDS_START
+      inherited.concat((3...(3 + sd_fds.to_i)).map { |fd| Socket.for_fd(fd) })
+    end
+    # to ease debugging, we will not unset LISTEN_PID and LISTEN_FDS
+
+    inherited.map! do |fd|
+      io = String === fd ? Socket.for_fd(fd.to_i) : fd
       io.autoclose = false
       io = server_cast(io)
       set_server_sockopt(io, listener_opts[sock_name(io)])
-      logger.info "inherited addr=#{sock_name(io)} fd=#{fd}"
+      logger.info "inherited addr=#{sock_name(io)} fd=#{io.fileno}"
       io
     end
 
diff --git a/test/exec/test_exec.rb b/test/exec/test_exec.rb
index 6deb96b..af8de26 100644
--- a/test/exec/test_exec.rb
+++ b/test/exec/test_exec.rb
@@ -96,6 +96,30 @@ run lambda { |env|
     end
   end
 
+  def test_sd_listen_fds_emulation
+    File.open("config.ru", "wb") { |fp| fp.write(HI) }
+    sock = TCPServer.new(@addr, @port)
+    sock.setsockopt(:SOL_SOCKET, :SO_KEEPALIVE, 0)
+
+    pid = xfork do
+      redirect_test_io do
+        # pretend to be systemd
+        ENV['LISTEN_PID'] = "#$$"
+        ENV['LISTEN_FDS'] = '1'
+
+        # 3 = SD_LISTEN_FDS_START
+        exec($unicorn_bin, "-l", "#@addr:#@port", 3 => sock)
+      end
+    end
+    res = hit(["http://#{@addr}:#{@port}/"])
+    assert_equal [ "HI\n"], res
+    assert_shutdown(pid)
+    assert_equal 1, sock.getsockopt(:SOL_SOCKET, :SO_KEEPALIVE).int,
+                 "unicorn should always set SO_KEEPALIVE on inherited sockets"
+  ensure
+    sock.close if sock
+  end
+
   def test_working_directory_rel_path_config_file
     other = Tempfile.new('unicorn.wd')
     File.unlink(other.path)
-- 
EW