For simple_server.py, inherit listening socket if present.

This adds support for getting the listening socket from
systemd.

quixote/server/simple_server.py

@@ -2,11 +2,48 @@
 """A simple, single threaded, synchronous HTTP server.
 """
 import sys
+import socket
 from http.server import BaseHTTPRequestHandler, HTTPServer
+from socketserver import BaseServer
 import urllib.request, urllib.parse, urllib.error
 import quixote
 from quixote import get_publisher
 from quixote.util import import_object
+from scgi.systemd_socket import get_systemd_socket
+
+
+class SockInheritHTTPServer(HTTPServer):
+    def __init__(self, address_info, handler, bind_and_activate=True):
+        # This is ugly.  We have to re-implement HTTPServer.__init__
+        # and server_bind().  We want to get the inherited socket if
+        # available.  If we inherit then we need to skip the bind() call.
+        BaseServer.__init__(self, address_info, handler)
+        sock = get_systemd_socket()
+        if sock is not None:
+            print('Using inherited socket %s' % (sock.getsockname(),))
+            self._skip_bind = True
+        else:
+            sock = socket.socket(self.address_family, self.socket_type)
+            self._skip_bind = False
+        self.socket = sock
+        if bind_and_activate:
+            try:
+                self.server_bind()
+                self.server_activate()
+            except:
+                self.server_close()
+                raise
+
+    def server_bind(self):
+        if not self._skip_bind:
+            HTTPServer.server_bind(self)
+        else:
+            self.server_address = self.socket.getsockname()
+            host, port = self.socket.getsockname()[:2]
+            self.server_name = socket.getfqdn(host)
+            self.server_port = port
+
+
 
 class HTTPRequestHandler(BaseHTTPRequestHandler):
 
@@ -83,7 +120,7 @@ def run(create_publisher, host='', port=80, https=False):
     """
     if https:
         HTTPRequestHandler.required_cgi_environment['HTTPS'] = 'on'
-    httpd = HTTPServer((host, port), HTTPRequestHandler)
+    httpd = SockInheritHTTPServer((host, port), HTTPRequestHandler)
     def handle_error(request, client_address):
         HTTPServer.handle_error(httpd, request, client_address)
         if sys.exc_info()[0] is SystemExit:

quixote/server/systemd_socket.py

@@ -0,0 +1,66 @@
+# Inherit activation sockets from systemd, see systemd man page for
+# sd_listen_fds().
+import os
+import socket
+
+SD_LISTEN_FDS_START = 3
+
+def _set_close_on_exec(fds):
+    try:
+        import fcntl
+    except ImportError:
+        return
+    if not hasattr(fcntl, 'FD_CLOEXEC'):
+        return
+    for fd in range(SD_LISTEN_FDS_START, SD_LISTEN_FDS_START + fds):
+        fcntl.fcntl(fd, fcntl.F_SETFD, fcntl.FD_CLOEXEC)
+
+
+def sd_listen_fds():
+    """Return the number of inherited sockets.  Return zero if there are
+    none.
+    """
+    try:
+        pid = int(os.environ['LISTEN_PID'])
+    except (ValueError, KeyError):
+        return 0
+    if os.getpid() != pid:
+        return 0
+    try:
+        fds = int(os.environ['LISTEN_FDS'])
+    except (ValueError, KeyError):
+        raise OSError('invalid LISTEN_FDS value')
+    _set_close_on_exec(fds)
+    return fds
+
+
+def _socket_from_fd(fd):
+    # This is ugly; Python doesn't provide a nice way to use
+    # getsockopt() and getsockname() to determine the type of
+    # socket.  Using AF_UNIX is a kludge to avoid messing up the
+    # getsockname() return value.
+    s = socket.fromfd(fd, socket.AF_UNIX, socket.SOCK_STREAM)
+    name = s.getsockname()
+    s.close() # fromfd() calls dup, close the new fd
+    if isinstance(name, (str, bytes)):
+        family = socket.AF_UNIX
+    elif ':' in name[0]:
+        family = socket.AF_INET6
+    else:
+        family = socket.AF_INET
+    # we assume we are getting a SOCK_STREAM socket
+    s = socket.fromfd(fd, family, socket.SOCK_STREAM)
+    os.close(fd) # fromfd() calls dup, close old fd
+    return s
+
+
+def get_systemd_socket():
+    """Return the inherited socket, if there is one.  If not, return None.
+    """
+    num = sd_listen_fds()
+    if not num:
+        return None
+    if num > 1:
+        raise OSError('only one inherited socket supported')
+    sock = _socket_from_fd(SD_LISTEN_FDS_START)
+    return sock