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

# TLS Module
| Since  | Origin / Contributor  | Maintainer  | Source  |
| :----- | :-------------------- | :---------- | :------ |
| 2016-12-15 | [PhoeniX](https://github.com/djphoenix) | [PhoeniX](https://github.com/djphoenix) | [tls.c](../../../app/modules/tls.c)|

**SSL/TLS support**

!!! important
    TLS module requires [net](net.md) module.

NodeMCU includes [mbed TLS library](https://tls.mbed.org/). With default config it supports **TLS** 1.0 / 1.1 / 1.2 and most common cipher suites, including DH/ECDH key exchange methods.

Full list of features you may get on [mbed TLS page](https://tls.mbed.org/core-features).

This controls certificate verification when SSL is in use.

## tls.createConnection()

Creates TLS connection.

#### Syntax
`tls.createConnection()`

#### Parameters
none

#### Returns
tls.socket sub module

#### Example

```lua
tls.createConnection()
```

# tls.socket Module

## tls.socket:close()

Closes socket.

#### Syntax
`close()`

#### Parameters
none

#### Returns
`nil`

#### See also
[`tls.createConnection()`](#tlscreateconnection)

## tls.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
[`tls.socket:on()`](#tlssocketon)

## tls.socket:dns()

Provides DNS resolution for a hostname.

#### Syntax
`dns(domain, function(tls.socket, ip))`

#### Parameters
- `domain` domain name
- `function(tls.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 = tls.createConnection()
sk:dns("google.com", function(conn, ip) print(ip) end)
sk = nil
```

## tls.socket:getpeer()

Retrieve port and ip of peer.

#### Syntax
`getpeer()`

#### Parameters
none

#### Returns
- `ip` of peer
- `port` of peer

## tls.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
[`tls.socket:unhold()`](#tlssocketunhold)

## tls.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(tls.socket[, string])` callback function. The first parameter is the socket.
If event is "receive", the second parameter is the received data as string.
If event is "reconnection", the second parameter is the reason of connection error (string).

#### Returns
`nil`

#### Example
```lua
srv = tls.createConnection()
srv:on("receive", function(sck, c) print(c) end)
srv:on("connection", function(sck, c)
  -- Wait for connection before sending.
  sck:send("GET / HTTP/1.1\r\nHost: google.com\r\nConnection: keep-alive\r\nAccept: */*\r\n\r\n")
end)
srv:connect(443,"google.com")
```

#### See also
- [`tls.createConnection()`](#tlscreateconnection)
- [`tls.socket:hold()`](#tlssockethold)

## tls.socket:send()

Sends data to remote peer.

#### Syntax
`send(string)`

#### Parameters
- `string` data in string which will be sent to server

#### 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 details.

#### See also
[`tls.socket:on()`](#tlssocketon)

## tls.socket:unhold()

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

#### Syntax
`unhold()`

#### Parameters
none

#### Returns
`nil`

#### See also
[`tls.socket:hold()`](#tlssockethold)








# tls.cert Module

## tls.cert.verify()

Controls the vertificate verification process when the Nodemcu makes a secure connection.

#### Syntax
`tls.cert.verify(enable)`

`tls.cert.verify(pemdata)`

#### Parameters
- `enable` A boolean which indicates whether verification should be enabled or not. The default at boot is `false`.
- `pemdata` A string containing the CA certificate to use for verification.

#### Returns
`true` if it worked. 

Can throw a number of errors if invalid data is supplied.

#### Example
Make a secure https connection and verify that the certificate chain is valid.
```
tls.cert.verify(true)
http.get("https://example.com/info", nil, function (code, resp) print(code, resp) end)
```

Load a certificate into the flash chip and make a request. This is the [startssl](https://startssl.com) root certificate. They provide free
certificates.

```
tls.cert.verify([[
-----BEGIN CERTIFICATE-----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Av+Z6+hsTXBbKWWc3apdzK8BMewM69KN6Oqce+Zu9ydmDBpI125C4z/eIT574Q1w
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26Nu/yYwl/WL3YlXtq09s68rxbd2AvCl1iuahhQqcvbjM4xdCUsT37uMdBNSSwID
AQABo4ICUjCCAk4wDAYDVR0TBAUwAwEB/zALBgNVHQ8EBAMCAa4wHQYDVR0OBBYE
FE4L7xqkQFulF2mHMMo0aEPQQa7yMGQGA1UdHwRdMFswLKAqoCiGJmh0dHA6Ly9j
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cnQgQ29tbWVyY2lhbCAoU3RhcnRDb20pIEx0ZC4wAwIBARqBl0xpbWl0ZWQgTGlh
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bGFibGUgYXQgaHR0cDovL2NlcnQuc3RhcnRjb20ub3JnL3BvbGljeS5wZGYwEQYJ
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ewT4F+irsfMuXGRuczE6Eri8sxHkfY+BUZo7jYn0TZNmezwD7dOaHZrzZVD1oNB1
ny+v8OqCQ5j4aZyJecRDjkZy42Q2Eq/3JR44iZB3fsNrarnDy0RLrHiQi+fHLB5L
EUTINFInzQpdn4XBidUaePKVEFMy3YCEZnXZtWgo+2EuvoSoOMCZEoalHmdkrQYu
L6lwhceWD3yJZfWOQ1QOq92lgDmUYMA0yZZwLKMS9R9Ie70cfmu3nZD0Ijuu+Pwq
yvqCUqDvr0tVk+vBtfAii6w0TiYiBKGHLHVKt+V9E9e4DGTANtLJL4YSjCMJwRuC
O3NJo2pXh5Tl1njFmUNj403gdy3hZZlyaQQaRwnmDwFWJPsfvw55qVguucQJAX6V
um0ABj6y6koQOdjQK/W/7HW/lwLFCRsI3FU34oH7N4RDYiDK51ZLZer+bMEkkySh
NOsF/5oirpt9P/FlUQqmMGqz9IgcgA38corog14=
-----END CERTIFICATE-----
]])

http.get("https://pskreporter.info/gen404", nil, function (code, resp) print(code, resp) end)
```

#### Notes
The certificate needed for verification is stored in the flash chip. The `tls.cert.verify` call with `true`
enables verification against the value stored in the flash. 

The certificate can be loaded into the flash chip in two ways -- one at firmware build time, and the other at initial boot
of the firmware. In order to load the certificate at build time, just place a file containing the CA certificate (in PEM format) 
at `server-ca.crt` in the root of the nodemcu-firmware build tree. The build scripts will incorporate this into the resulting
firmware image.

The alternative approach is easier for development, and that is to supply the PEM data as a string value to `tls.cert.verify`. This
will store the certificate into the flash chip and turn on verification for that certificate. Subsequent boots of the nodemcu can then
use `tls.cert.verify(true)` and use the stored certificate.