BPO-17561: set create_server backlog default to None (GH-12735)

giampaolo · web-flow · commit 8702b67dad62 · 2019-04-09T04:42:06.000+02:00
It turns out doing socket.listen(0) does not equal to "choose a reasonable default". It actually means "set backlog to 0". As such set backlog=None as the default for socket.create_server. Fixes the following BB failures: #11784 (comment) Ref. BPO-1756, GH-11784.
diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst
@@ -595,7 +595,7 @@ The following functions all create :ref:`socket objects <socket-objects>`.
    .. versionchanged:: 3.2
       *source_address* was added.
 
-.. function:: create_server(address, *, family=AF_INET, backlog=0, reuse_port=False, dualstack_ipv6=False)
+.. function:: create_server(address, *, family=AF_INET, backlog=None, reuse_port=False, dualstack_ipv6=False)
 
    Convenience function which creates a TCP socket bound to *address* (a 2-tuple
    ``(host, port)``) and return the socket object.
diff --git a/Lib/socket.py b/Lib/socket.py
@@ -745,7 +745,7 @@ def has_dualstack_ipv6():
         return False
 
 
-def create_server(address, *, family=AF_INET, backlog=0, reuse_port=False,
+def create_server(address, *, family=AF_INET, backlog=None, reuse_port=False,
                   dualstack_ipv6=False):
     """Convenience function which creates a SOCK_STREAM type socket
     bound to *address* (a 2-tuple (host, port)) and return the socket
@@ -804,7 +804,10 @@ def create_server(address, *, family=AF_INET, backlog=0, reuse_port=False,
             msg = '%s (while attempting to bind on address %r)' % \
                 (err.strerror, address)
             raise error(err.errno, msg) from None
-        sock.listen(backlog)
+        if backlog is None:
+            sock.listen()
+        else:
+            sock.listen(backlog)
         return sock
     except error:
         sock.close()
diff --git a/Misc/NEWS.d/next/Library/2019-04-09-04-08-46.bpo-17561.hOhVnh.rst b/Misc/NEWS.d/next/Library/2019-04-09-04-08-46.bpo-17561.hOhVnh.rst
@@ -0,0 +1 @@
+Set backlog=None as the default for socket.create_server.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Set backlog=None as the default for socket.create_server.`