lua curl multi api work with libuv.

curl_multi_work_with_libuv.lua

local uv = require_uv()

-- run uv event loop in engine loop.
return RunLoop.schedule(function()
    uv.run('nowait')
end, 0.02, 0.02)

local multi = curl.multi()

local function check_info()
    while true do
        local easy, done = multi:info_read(true)
        if easy and done then
            print('finish', easy:getinfo(curl.INFO_RESPONSE_CODE))
        else
            break
        end
    end
end

local fdmap = {}
multi:setopt_socketfunction(function(handler, fd, action)
    local poll = fdmap[fd]
    if not poll then
        poll = uv.new_socket_poll(fd)
        fdmap[fd] = poll
    end

    if action == curl.POLL_REMOVE then
        if poll then
            fdmap[fd] = nil
            poll:stop()
        end
    else
        local events = ''
        if action ~= curl.POLL_IN or action == curl.POLL_INOUT then
            events = 'r'
        end
        if action == curl.POLL_OUT or action == curl.POLL_INOUT then
            events = events .. 'w'
        end
        if events ~= '' then
            poll:start(events, function(status, evt)
                local flags = 0
                if evt == 'r' then
                    flags = curl.CSELECT_IN
                elseif evt == 'w' then
                    flags = curl.CSELECT_OUT
                elseif evt == 'rw' then
                    flags = bit.bor(curl.CSELECT_IN, curl.CSELECT_OUT)
                end
                multi:socket_action(fd, flags)
                check_info()
            end)
        end
    end

    return 0
end)
local timer = uv.new_timer()
multi:setopt_timerfunction(function(timeout)
    if timeout < 0 then
        timer:stop()
    else
        timer:start(timeout, 0, function()
            multi:socket_action(curl.SOCKET_TIMEOUT)
            check_info()
        end)
    end
end)

local easy = curl.easy()
easy:setopt_url('http://www.baidu.com')
easy:setopt_writefunction(function(buf)
    print('recv', #buf)
end)
multi:add_handle(easy)