NodeMCU: code responsible for creating server stops working after building new firmware

Question

Since I have updated the firmware (using https://nodemcu-build.com/ and pyflasher) from the 0.9.6-dev_20150704 release to a one newer, as follows:

NodeMCU custom build by frightanic.com  
branch: master  
commit: c8ac5cfb912ff206b03dd7c60ffbb2dafb83fe5e  
SSL: false  
modules: file,gpio,net,node,rtcmem,rtctime,tmr,uart,wifi  
build   built on: 2017-05-27 13:10  
powered by Lua 5.1.4 on SDK 2.1.0(116b762)  

the following code (example from http://nodemcu.com/index_en.html) stopped working:

print(wifi.sta.getip())
--nil
wifi.setmode(wifi.STATION)
wifi.sta.config("SSID","password")
print(wifi.sta.getip())
--192.168.18.110

-- a simple http server
srv=net.createServer(net.TCP) 
srv:listen(80,function(conn) 
    conn:on("receive",function(conn,payload) 
    print(payload) 
    conn:send("<h1> Hello, NodeMcu.</h1>")
    end) 
end)

To be clear, it seems that the connection works (because I see MCU on the list on my router), but when I type the corresponding address of MCU in the browser, it could not connect to the server. Do you have any ideas how to fix it?

Answer 1

the following code (example from http://nodemcu.com/index_en.html) stopped working:

Your code example is NOT listed as such on that page. You stitched together two individual examples from there into a single program and that fails. That's in part because one of those examples isn't really helpful anymore.

The problem is right here:

wifi.sta.config("SSID","password")
print(wifi.sta.getip())
--192.168.18.110

It suggests that wifi.sta.config be a synchronous operation that blocks until the device got an IP address from the access point. That's not the case and, hence, it's close to impossible that by the time the next line is execute the device got an IP. If you check your serial console you probably see nil there.

What's worse, by the time net.createServer runs there's still no IP. Thus, the server socket isn't bound to anything and you created a zombie server.

The main message here: wait until the device got an IP and continue only then. We used to have a pretty simple template in our documentation, but for the sake of completeness it was recently updated: https://nodemcu.readthedocs.io/en/latest/en/upload/#initlua. For starters it may be stripped down to this:

-- load credentials, 'SSID' and 'PASSWORD' declared and initialize in there
dofile("credentials.lua")

function startup()
  if file.open("init.lua") == nil then
    print("init.lua deleted or renamed")
  else
    print("Running")
    file.close("init.lua")
    -- the actual application is stored in 'application.lua'
    -- dofile("application.lua")
  end
end

-- Define WiFi station event callbacks
wifi_got_ip_event = function(T)
  -- Note: Having an IP address does not mean there is internet access!
  -- Internet connectivity can be determined with net.dns.resolve().
  print("Wifi connection is ready! IP address is: " .. T.IP)
  print("Startup will resume momentarily, you have 3 seconds to abort.")
  print("Waiting...")
  tmr.create():alarm(3000, tmr.ALARM_SINGLE, startup)
end



-- Register WiFi Station event callbacks
wifi.eventmon.register(wifi.eventmon.STA_GOT_IP, wifi_got_ip_event)

print("Connecting to WiFi access point...")
wifi.setmode(wifi.STATION)
wifi.sta.config({ ssid = SSID, pwd = PASSWORD, save = true })
-- wifi.sta.connect() not necessary because config() uses auto-connect=true by default

Furthermore, your server should send proper HTTP headers if you're testing from a browser. Something like this:

local content = "<h1>Hello, world!</h1>"
conn:send("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\nConnection: close\r\n\r\n" .. content)