implement haproxy socket type from configuration

[mecampbellsoup]

Resolves #114.

When the Lua HAProxy core object is detected, the socket class will
automatically use its (non-blocking) socket type. The pattern is similar
to existing auto-detection of whether pgmoon is running inside an NGINX
context or not and choosing that socket type if so.

http://www.arpalert.org/src/haproxy-lua-api/1.7/index.html#core.get_info

[mecampbellsoup]

@leafo using your create_luasocket interface now instead, just using the raw core.tcp wasn't playing well with the expected socket API.

[cesarmesones]

we are also using haproxy in lua and would love to be able to use this api!

[pyreta]

we are also using haproxy in lua and would love to be able to use this api!

plus one!

[JsmithCoreWeave]

we are also using haproxy in lua and would love to be able to use this api!

Would be helpful for us as well.

[leafo]

Just adding comment in case it's helpful to anyone: if it's API compatible with LuaSocket then you can run package.loaded.socket = core before creating your connection object.

Be warned, I have no idea how this will play with ssl. (This change in this patch too is unknown)

[mecampbellsoup]

Just adding comment in case it's helpful to anyone: if it's API compatible with LuaSocket then you can run package.loaded.socket = core before creating your connection object.

I tried using pgmoon:master without our HAProxy-specific changes and putting package.loaded.socket = core in our connect DB function as follows:

function connect_db(pg_settings)
    -- Returns a pgmoon postgres object or nil on failure.

    package.loaded.socket = core

    local pg = pgmoon.new(pg_settings)
    -- Set the timeout value (in milliseconds) for all socket operations
    -- (connect, write, receive)
    pg:settimeout(5000)
    pg.convert_null = true -- https://github.com/leafo/pgmoon#converting-nulls
    local success, err = pg:connect()

However this does not seem to work.

[mecampbellsoup]

if it's API compatible with LuaSocket then you can run package.loaded.socket = core before creating your connection object.

Surprising it didn't work since the HAProxy Lua API docs specify the same constraint:

This class must be compatible with the Lua Socket class. Only the ‘client’ functions are available.

https://www.arpalert.org/src/haproxy-lua-api/2.6/index.html#Socket