setoption failing in 3.0.0 (works with the old RC)

[Tieske]

Downstream issue: Kong/kong#8590

To reproduce run this docker command:

docker run -it --rm ubuntu /bin/bash

Once in the shell create a Lua file called test.lua;

local socket = require "socket"
local server = assert(socket.tcp())
server:settimeout(60)
assert(server:setoption("reuseaddr", true))
assert(server:bind("*", 14123))

Execute the following commands:

apt update
apt install luarocks
luarocks install luasocket
lua test.lua

Output:

root@3c61aa79bab9:/# lua test.lua
lua: test.lua:4: setsockopt failed
stack traceback:
	[C]: in function 'assert'
	test.lua:4: in main chunk
	[C]: ?
root@3c61aa79bab9:/#

[Tieske]

This seems to work:

local socket = require "socket"
local server = assert(socket.tcp())
server:settimeout(60)
assert(server:bind("*", 14123))	-- switch position between 'bind' and 'setoption'
assert(server:setoption("reuseaddr", true))

[alerque]

This seems to bisect to 77bba62.

[Tieske]

adding to my previous comment: using setoption after bind doesn't make sense, because bind would already have failed if it was in use.

[Tieske]

This looks nasty on a first glance, as per the docs:

• internal socket is invalid until ipv4 or ipv6 is selected, setoption fails while in this state
• ip-family is selected upon calling bind
• SO_REUSEADDR option should be set before calling bind

So there's a catch 22 it seems.

Any ideas @diegonehab @Florob (pinging because the referenced commit above mentions you)

[Florob]

I've been out of the loop for most things Lua for a few years, so not sure how much I can help here.

Judging by the discussion in #147 and looking at inet_trybind() the problem is probably yet worse. inet_trybind() will create multiple new sockets while attempting to bind to addresses resolved by getaddrinfo. So even if we could set the option before calling bind() it would potentially get lost. This is part of why we deemed starting out with an invalid socket acceptable.

A pragmatic approach might be to add an optional reuseaddr parameter to bind(). When true the implementation would set SO_REUSEADDR on the sockets it creates.