[PATCH 2/2] inheriting sockets from UNICORN_FD does not close them

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

For some reason, I thought invalid descriptors passed to UNICORN_FD
would be automatically closed by the master process; but apparently
this hasn't been the case.  On the other hand, this bug has been
around for over 6 years now and nobody noticed or cared enough to
tell us, so fixing it might break existing setups.

Since there may be users relying on this behavior, we cannot change
the behavior anymore; so update the documentation and write at test
to ensure we can never "fix" this bug at the expense of breaking
any working setups which may be out there.

Keep in mind that a before_exec hook may always be used to modify
the UNICORN_FD environment by setting the close_on_exec flag and
removing the appropriate descriptor from the environment.

I originally intended to add the ability to inherit new listeners
without a config file specification so systemd users can avoid
repeating themselves in the systemd and unicorn config files,
but apparently there is nothing to change in our code.
---
 Documentation/unicorn.1.txt |  4 +---
 test/exec/test_exec.rb      | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Documentation/unicorn.1.txt b/Documentation/unicorn.1.txt
index 193860f..5b82ad5 100644
--- a/Documentation/unicorn.1.txt
+++ b/Documentation/unicorn.1.txt
@@ -166,9 +166,7 @@ variable internally when doing transparent upgrades.
 UNICORN_FD is a comma-delimited list of one or more file descriptors
 used to implement USR2 upgrades.  Init systems may bind listen sockets
 itself and spawn unicorn with UNICORN_FD set to the file descriptor
-numbers of the listen socket(s).  The unicorn CONFIG_FILE must still
-have the inherited listen socket parameters defined as in a normal
-startup, otherwise the socket will be closed.
+numbers of the listen socket(s).
 
 # SEE ALSO
 
diff --git a/test/exec/test_exec.rb b/test/exec/test_exec.rb
index af6f151..ca0b7bc 100644
--- a/test/exec/test_exec.rb
+++ b/test/exec/test_exec.rb
@@ -128,6 +128,26 @@ def test_sd_listen_fds_emulation
     # [ruby-core:69895] [Bug #11336] fixed by r51576
   end if RUBY_VERSION.to_f >= 2.3
 
+  def test_inherit_listener_unspecified
+    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
+        ENV['UNICORN_FD'] = sock.fileno.to_s
+        exec($unicorn_bin, sock.fileno => sock.fileno)
+      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