[Ortega]: # "Jose Manuel Ortega, et al. Learning Python Networking."

:point_right: [Sockets tutorial](https://youtu.be/Lbfe3-v7yE0)

The socket module is Python's standard interface for the transport layer.
Sockets can be classified by **`family`**
- **`AF_INET`** Internet
- `AF_UNIX` for UNIX sockets

and **`type`**:
  - **`SOCK_STREAM`** TCP
  - `SOCK_DGRAM` UDP

These enum values are required upon initialization of a socket object: <sup>[Ortega][Ortega]: 25</sup>
```py
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
```
#### Simple implementation
Websocket server
```py
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((socket.gethostname(),1234))
s.listen(5)

while True:
  clientsocket, address = s.accept()
  print(f'Connection from {address} has been established')
  clientsocket.send(bytes('Welcome to the server', 'utf-8'))
```

Websocket client
```py
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((socket.gethostname(), 1234))
msg = s.recv(1024)
print(msg.decode('utf-8'))
```

### API
- [socket.bind](#socketbind)
- [socket.connect](#socketconnect)
- [socket.gethostname](#socketgethostname)
- [socket.listen](#socketlisten)
- [socket.recv](#socketrecv)

#### socket.bind
Define port on which to listen for connections.
```py
serversocket.bind(('localhost',80))
```

#### socket.connect
Connect to a remote socket in one direction
```py
client_socket.connect(('www.packtpub.com',80))
```

#### socket.gethostbyname
Convert a domain name into IPv4 address

```py
socket.gethostbyname('packtpub.com') # '83.166.169.231'
```

#### socket.gethostname
Defaults to **localhost** with no arguments

```py
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((socket.gethostname(),1234))
```

#### socket.getservbyport
Get protocol name from port number
```py
socket.getservbyport(80) # 'http'
```

#### socket.listen
Listen to a maximum of 10 connections
```py
serversocket.listen(10)
```

#### socket.recv
Receive bytestream from server
```py
msg = s.recv(1024)
print(msg.decode('utf-8'))
```