luasocket invalidates its internal state by closing the socket when setsockname() fails

[Sam Roberts <vieuxtech@...>]

This is purely a luasocket behaviour. The system calls allow bind() to
fail, leaving the socket valid.

This behaviour of luasocket is particularly anti-social when
attempting to repeatedly bind to local ports, to search for one that
is free.


Code:

require"socket"

print(socket._VERSION)

s = assert(socket.udp())

print("setname", s:setsockname("*", 9876))
print("getname", s:getsockname())

c = assert(socket.udp())

print("setname", c:setsockname("*", 9876))
print("setname", c:setsockname("*", 9875))


Output:

lua udpe.lua
LuaSocket 2.0.1
setname 1
getname 0.0.0.0 9876
setname nil     address already in use
setname nil     Bad file descriptor


Strace:


bind(3, {sa_family=AF_INET, sin_port=htons(9876),
sin_addr=inet_addr("0.0.0.0")}, 16) = 0

socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 4
bind(4, {sa_family=AF_INET, sin_port=htons(9876),
sin_addr=inet_addr("0.0.0.0")}, 16) = -1 EADDRINUSE (Address already
in use)

bind of descriptor 4 fails, this should be a no-op, but instead
luasocket closes the fd!

close(4)                                = 0

write(1, "setname\tnil\taddress already in u"..., 35setname     nil
 address already in use
) = 35


It doesn't remember that it closed it, though, and keeps trying to use it...

fcntl(-1, F_GETFL)                      = -1 EBADF (Bad file descriptor)
fcntl(-1, F_SETFL,
O_ACCMODE|O_CREAT|O_EXCL|O_NOCTTY|O_TRUNC|O_APPEND|O_SYNC|O_ASYNC|O_DIRECT|O_LARGEFILE|O_DIRECTORY|O_NOFOLLOW|O_NOATIME|0xfff8003c)
= -1 EBADF (Bad file descriptor)
bind(4294967295, {sa_family=AF_INET, sin_port=htons(9875),
sin_addr=inet_addr("0.0.0.0")}, 16) = -1 EBADF (Bad file descriptor)