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

# net Module
| Since  | Origin / Contributor  | Maintainer  | Source  |
| :----- | :-------------------- | :---------- | :------ |
| 2014-12-22 | [Zeroday](https://github.com/funshine) | [Zeroday](https://github.com/funshine) | [net.c](../../../app/modules/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` or `net.UDP`
- `secure` 1 for encrypted, 0 for plain

#### Returns
net.socket sub module

#### Example

```lua
net.createConnection(net.UDP, 0)
```

#### See also
[`net.createServer()`](#netcreateserver)

## net.createServer()

Creates a server.

#### Syntax
`net.createServer(type, timeout)`

#### Parameters
- `type` `net.TCP` or `net.UDP`
- `timeout` for a TCP server timeout is 1~28'800 seconds (for an inactive client to be disconnected)

#### Returns
net.server sub module

#### Example

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

#### See also
[`net.createConnection()`](#netcreateconnection)

# net.server Module

## net.server:close()

Closes the server.

#### Syntax
`net.server.close()`

#### Parameters
none

#### Returns
`nil`

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

#### See also
[`net.createServer()`](#netcreateserver)

## net.server:listen()

Listen on port from IP address.

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

#### Parameters
- `port` port number
- `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
```lua
 -- 30s time out for a inactive client
sv = net.createServer(net.TCP, 30)
-- server listens on 80, if data received, print data to console and send "hello world" back to caller
sv:listen(80, function(c)
	c:on("receive", function(c, pl) 
		print(pl)
	end)
	c:send("hello world")
end)
```

#### See also
[`net.createServer()`](#netcreateserver)

# net.socket Module
## net.socket:close()

Closes socket.

#### Syntax
`close()`

#### Parameters
none

#### Returns
`nil`

#### See also
[`net.createServer()`](#netcreateserver)

## 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()`](#netsocketon)

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

#### See also
[`net.createServer()`](#netcreateserver)

## 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. The first parameter is the socket. If event is "receive", the second parameter is the received data as string.

#### Returns
`nil`

#### Example
```lua
sk = net.createConnection(net.TCP, 0)
sk:on("receive", function(sck, c) print(c) end )
sk:connect(80,"192.168.0.66")
sk:on("connection", function(sck,c)
    -- Wait for connection before sending.
    sk:send("GET / HTTP/1.1\r\nHost: 192.168.0.66\r\nConnection: keep-alive\r\nAccept: */*\r\n\r\n")
end)
```

#### See also
[`net.createServer()`](#netcreateserver)

## net.socket:send()

Sends data to server.

#### Syntax
`send(string, function(sent))`

#### 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](https://github.com/nodemcu/nodemcu-firmware/issues/730#issuecomment-154241161) for an example and explanation.

#### See also
[`net.socket:on()`](#netsocketon)

# 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
```lua
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()`](#netdnssetdnsserver)

## net.dns.resolve()

Resolve a hostname to an IP address. Doesn't require a socket like [`net.socket.dns()`](#netsocketdns).

#### Syntax
`net.dns.resolve(host, function(ip))`

#### Parameters
- `host` hostname to resolve
- `function(sk, ip)` callback called when the name was resolved. Don't use `sk`, it's a socket used internally to resolve the hostname.

#### Returns
`nil`

#### Example
```lua
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()`](#netsocketdns)

## 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()`](#netdnsgetdnsserver)