Race between socket accept and receive

Question

I am using nodemcu with an esp-32 and recently came across an annoying problem. I refer to this sample from the NodeMCU Github page:

-- a simple HTTP server
srv = net.createServer(net.TCP)
srv:listen(80, function(conn)
    conn:on("receive", function(sck, payload)
        print(payload)
        sck:send("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n<h1> Hello, NodeMCU.</h1>")
    end)
    conn:on("sent", function(sck) sck:close() end)
end)

This doesn't seem to work in every case. If I try it with telnet, there is no issue:

$ telnet 172.17.10.59 80
Trying 172.17.10.59...
Connected to 172.17.10.59.
Escape character is '^]'.
GET / HTTP/1.1
HTTP/1.0 200 OK
Content-Type: text/html

<h1> Hello, NodeMCU.</h1>
Connection closed by foreign host.

But when using wget, it hangs most of the time:

$ wget http://172.17.10.59/
--2017-05-12 15:00:09--  http://172.17.10.59/
Connecting to 172.17.10.59:80... connected.
HTTP request sent, awaiting response...

After some research, the root cause seems to be, that the receive callback is registered after the first data was received from the client. This doesn't happen when testing manually with telnet, but with a client like wget or a browser, the delay between connecting and receiving the first data seems to be too small to register the receive handler first.

I have looked into the nodemcu code and there doesn't seem to be an easy way to work around this problem. Or do I miss something here?

Does the problem persist when using the [`httpserver`](https://nodemcu.readthedocs.io/en/master/lua-modules/httpserver/#httpservercreateserver) Lua module? — ant, Feb 26 '20 at 11:31

score 0 · Answer 1 · answered Nov 05 '21 at 08:55

In HTTP/1.0, you need the "Content-Length" in the HTTP header when there is a message-body.

For example:

"HTTP/1.0 200 OK\r\nContent-Type: text/html\r\nContent-Length: 25 \r\n\r\n<h1> Hello, NodeMCU.</h1>"

ref: https://www.w3.org/Protocols/HTTP/1.0/spec.html#Content-Length

Race between socket accept and receive

1 Answers1