nodemcu-firmware/docs/en/modules/net.md

net Module

Since	Origin / Contributor	Maintainer	Source
2014-12-22	PhoeniX	Johny Mattsson, Arnim Läuger	net.c

Constants

Constants to be used in other functions: net.TCP, net.UDP

net.createConnection()

Creates a client.

Syntax

net.createConnection([type[, secure]])

Parameters

• type net.TCP (default) or net.UDP
• secure 0 for plain (default)

!!! attention Secure connections are not supported, and the secure parameter is ignored.

There's no such thing as a UDP _connection_ because UDP is connection*less*. Thus no connection `type` parameter should be required. For UDP use [net.createUDPSocket()](#netcreateudpsocket) instead.

Returns

• for net.TCP - net.socket sub module
• for net.UDP - net.udpsocket sub module

Example

net.createConnection(net.TCP)

See also

net.createServer(), net.createUDPSocket()

net.createServer()

Creates a server.

Syntax

net.createServer([type[, timeout]])

Parameters

• type net.TCP (default) or net.UDP
• timeout for a TCP server timeout is 1~28'800 seconds, 30 sec by default (for an inactive client to be disconnected)

!!! attention The type parameter will be removed in upcoming releases so that net.createServer will always create a TCP-based server. For UDP use net.createUDPSocket() instead.

Returns

• for net.TCP - net.server sub module
• for net.UDP - net.udpsocket sub module

Example

net.createServer(net.TCP, 30) -- 30s timeout

See also

net.createConnection(), net.createUDPSocket()

net.createUDPSocket()

Creates an UDP socket.

Syntax

net.createUDPSocket()

Parameters

none

Returns

net.udpsocket sub module

See also

net.createConnection()

net.multicastJoin()

Join multicast group.

Syntax

net.multicastJoin(if_ip, multicast_ip)

Parameters

• if_ip string containing the interface ip to join the multicast group. "any" or "" affects all interfaces.
• multicast_ip of the group to join

Returns

nil

net.multicastLeave()

Leave multicast group.

Syntax

net.multicastLeave(if_ip, multicast_ip)

Parameters

• if_ip string containing the interface ip to leave the multicast group. "any" or "" affects all interfaces.
• multicast_ip of the group to leave

Returns

nil

net.server Module

net.server:close()

Closes the server.

Syntax

net.server.close()

Parameters

none

Returns

nil

Example

-- creates a server
sv = net.createServer(net.TCP, 30)
-- closes the server
sv:close()

See also

net.createServer()

net.server:listen()

Listen on port from IP address.

Syntax

net.server.listen([port],[ip],function(net.socket))

Parameters

• port port number, can be omitted (random port will be chosen)
• ip IP address string, can be omitted
• function(net.socket) callback function, pass to caller function as param if a connection is created successfully

Returns

nil

Example

-- server listens on 80, if data received, print data to console and send "hello world" back to caller
-- 30s time out for a inactive client
sv = net.createServer(net.TCP, 30)

function receiver(sck, data)
  print(data)
  sck:close()
end

if sv then
  sv:listen(80, function(conn)
    conn:on("receive", receiver)
    conn:send("hello world")
  end)
end

See also

net.createServer()

net.server:getaddr()

Returns server local address/port.

Syntax

net.server.getaddr()

Parameters

none

Returns

port, ip (or nil, nil if not listening)

See also

net.server:listen()

net.socket Module

net.socket:close()

Closes socket.

Syntax

close()

Parameters

none

Returns

nil

See also

net.createServer()

net.socket:connect()

Connect to a remote server.

Syntax

connect(port, ip|domain)

Parameters

• port port number
• ip IP address or domain name string

Returns

nil

See also

net.socket:on()

net.socket:dns()

Provides DNS resolution for a hostname.

Syntax

dns(domain, function(net.socket, ip))

Parameters

• domain domain name
• function(net.socket, ip) callback function. The first parameter is the socket, the second parameter is the IP address as a string.

Returns

nil

Example

sk = net.createConnection(net.TCP, 0)
sk:dns("www.nodemcu.com", function(conn, ip) print(ip) end)
sk = nil

See also

net.createServer()

net.socket:getpeer()

Retrieve port and ip of remote peer.

Syntax

getpeer()

Parameters

none

Returns

port, ip (or nil, nil if not connected)

net.socket:getaddr()

Retrieve local port and ip of socket.

Syntax

getaddr()

Parameters

none

Returns

port, ip (or nil, nil if not connected)

net.socket:hold()

Throttle data reception by placing a request to block the TCP receive function. This request is not effective immediately, Espressif recommends to call it while reserving 5*1460 bytes of memory.

Syntax

hold()

Parameters

none

Returns

nil

See also

net.socket:unhold()

net.socket:on()

Register callback functions for specific events.

Syntax

on(event, function())

Parameters

• event string, which can be "connection", "reconnection", "disconnection", "receive" or "sent"
• function(net.socket[, string]) callback function. Can be nil to remove callback.

The first parameter of callback is the socket.

• If event is "receive", the second parameter is the received data as string.
• If event is "disconnection" or "reconnection", the second parameter is error code.

If reconnection event is specified, disconnection receives only "normal close" events.

Otherwise, all connection errors (with normal close) passed to disconnection event.

Returns

nil

Example

srv = net.createConnection(net.TCP, 0)
srv:on("receive", function(sck, c) print(c) end)
-- Wait for connection before sending.
srv:on("connection", function(sck, c)
  -- 'Connection: close' rather than 'Connection: keep-alive' to have server 
  -- initiate a close of the connection after final response (frees memory 
  -- earlier here), https://tools.ietf.org/html/rfc7230#section-6.6 
  sck:send("GET /get HTTP/1.1\r\nHost: httpbin.org\r\nConnection: close\r\nAccept: */*\r\n\r\n")
end)
srv:connect(80,"httpbin.org")

!!! note The receive event is fired for every network frame! Hence, if the data sent to the device exceeds 1460 bytes (derived from Ethernet frame size) it will fire more than once. There may be other situations where incoming data is split across multiple frames (e.g. HTTP POST with multipart/form-data). You need to manually buffer the data and find means to determine if all data was received.

local buffer = nil

srv:on("receive", function(sck, c)
  if buffer == nil then
    buffer = c
  else
    buffer = buffer .. c
  end
end)
-- throttling could be implemented using socket:hold()
-- example: https://github.com/nodemcu/nodemcu-firmware/blob/master/lua_examples/pcm/play_network.lua#L83

See also

• net.createServer()
• net.socket:hold()

net.socket:send()

Sends data to remote peer.

Syntax

send(string[, function(sent)])

sck:send(data, fnA) is functionally equivalent to sck:send(data) sck:on("sent", fnA).

Parameters

• string data in string which will be sent to server
• function(sent) callback function for sending string

Returns

nil

Note

Multiple consecutive send() calls aren't guaranteed to work (and often don't) as network requests are treated as separate tasks by the SDK. Instead, subscribe to the "sent" event on the socket and send additional data (or close) in that callback. See #730 for details.

Example

srv = net.createServer(net.TCP)

function receiver(sck, data)
  local response = {}

  -- if you're sending back HTML over HTTP you'll want something like this instead
  -- local response = {"HTTP/1.0 200 OK\r\nServer: NodeMCU on ESP8266\r\nContent-Type: text/html\r\n\r\n"}

  response[#response + 1] = "lots of data"
  response[#response + 1] = "even more data"
  response[#response + 1] = "e.g. content read from a file"

  -- sends and removes the first element from the 'response' table
  local function send(localSocket)
    if #response > 0 then
      localSocket:send(table.remove(response, 1))
    else
      localSocket:close()
      response = nil
    end
  end

  -- triggers the send() function again once the first chunk of data was sent
  sck:on("sent", send)

  send(sck)
end

srv:listen(80, function(conn)
  conn:on("receive", receiver)
end)

If you do not or can not keep all the data you send back in memory at one time (remember that response is an aggregation) you may use explicit callbacks instead of building up a table like so:

sck:send(header, function() 
  local data1 = "some large chunk of dynamically loaded data"
  sck:send(data1, function()
    local data2 = "even more dynamically loaded data"
    sck:send(data2, function(sk) 
      sk:close()
    end)
  end)
end)

See also

net.socket:on()

net.socket:unhold()

Unblock TCP receiving data by revocation of a preceding hold().

Syntax

unhold()

Parameters

none

Returns

nil

See also

net.socket:hold()

net.udpsocket Module

Remember that in contrast to TCP UDP is connectionless. Therefore, there is a minor but natural mismatch as for TCP/UDP functions in this module. While you would call net.createConnection() for TCP it is net.createUDPSocket() for UDP.

Other points worth noting:

• UDP sockets do not have a connection callback for the listen function.
• UDP sockets do not have a connect function. Remote IP and port thus need to be defined in send().
• UDP socket's receive callback receives port/ip after the data argument.

net.udpsocket:close()

Closes UDP socket.

The syntax and functional identical to net.socket:close().

net.udpsocket:listen()

Listen on port from IP address.

The syntax and functional similar to net.server:listen(), but callback parameter is not provided.

net.udpsocket:on()

Register callback functions for specific events.

The syntax and functional similar to net.socket:on(). However, only "receive", "sent" and "dns" are supported events.

!!! note The receive callback receives port and ip after the data argument.

net.udpsocket:send()

Sends data to specific remote peer.

Syntax

send(port, ip, data)

Parameters

• port remote socket port
• ip remote socket IP
• data the payload to send

Returns

nil

Example

udpSocket = net.createUDPSocket()
udpSocket:listen(5000)
udpSocket:on("receive", function(s, data, port, ip)
    print(string.format("received '%s' from %s:%d", data, ip, port))
    s:send(port, ip, "echo: " .. data)
end)
port, ip = udpSocket:getaddr()
print(string.format("local UDP socket address / port: %s:%d", ip, port))

On *nix systems that can then be tested by issuing

echo -n "foo" | nc -w1 -u <device-IP-address> 5000

net.udpsocket:dns()

Provides DNS resolution for a hostname.

The syntax and functional identical to net.socket:dns().

net.udpsocket:getaddr()

Retrieve local port and ip of socket.

The syntax and functional identical to net.socket:getaddr().

net.dns Module

net.dns.getdnsserver()

Gets the IP address of the DNS server used to resolve hostnames.

Syntax

net.dns.getdnsserver(dns_index)

Parameters

dns_index which DNS server to get (range 0~1)

Returns

IP address (string) of DNS server

Example

print(net.dns.getdnsserver(0)) -- 208.67.222.222
print(net.dns.getdnsserver(1)) -- nil

net.dns.setdnsserver("8.8.8.8", 0)
net.dns.setdnsserver("192.168.1.252", 1)

print(net.dns.getdnsserver(0)) -- 8.8.8.8
print(net.dns.getdnsserver(1)) -- 192.168.1.252

See also

net.dns:setdnsserver()

net.dns.resolve()

Resolve a hostname to an IP address. Doesn't require a socket like net.socket.dns().

Syntax

net.dns.resolve(host, function(sk, ip))

Parameters

• host hostname to resolve
• function(sk, ip) callback called when the name was resolved. sk is always nil

Returns

nil

Example

net.dns.resolve("www.google.com", function(sk, ip)
    if (ip == nil) then print("DNS fail!") else print(ip) end
end)

See also

net.socket:dns()

net.dns.setdnsserver()

Sets the IP of the DNS server used to resolve hostnames. Default: resolver1.opendns.com (208.67.222.222). You can specify up to 2 DNS servers.

Syntax

net.dns.setdnsserver(dns_ip_addr, dns_index)

Parameters

• dns_ip_addr IP address of a DNS server
• dns_index which DNS server to set (range 0~1). Hence, it supports max. 2 servers.

Returns

nil

See also

net.dns:getdnsserver()