# UDP Server Example Explanation

## Environment Preparation

To ensure a smooth demonstration of UDP communication, we need to confirm that the following environment is correctly configured:

### Hardware Connection

- Ensure that your CanMV development board and computer are connected to the same router or switch via Ethernet cable, forming a local area network (LAN).
- Ensure that the router or switch is functioning properly to maintain a stable network connection.

### Disable Firewall

- To prevent the firewall from blocking UDP communication, it is recommended to temporarily disable the firewall on your computer.

```{image} ../../../zh/example/images/network/image-20240722145319713.png
:scale: 50 %
```

### Tool Preparation

- Download and install [NetAssist Network Debug Assistant](https://www.bing.com/search?q=netassist+cmsoft) as a network communication testing tool to help with sending and receiving network data.

### Obtain IP Address

- Open the command prompt (CMD), enter `ipconfig`, and query and record the IP address of the computer's network card for subsequent configuration and testing.

```{image} ../../../zh/example/images/network/image-20240722145500693.png
:scale: 50 %
```

## Server Example Analysis

This example demonstrates how to create a simple UDP server, including configuring the network interface, creating a socket, binding the address and port, receiving and sending data, and closing the socket. Through this example, you can learn how to build a basic network communication application.

### Import Necessary Libraries

```python
import socket
import network
import time
```

- `socket`: Used to create sockets, which are the basis of network communication.
- `network`: Used to configure network interfaces, such as LAN or WLAN.
- `time`: Used for delay processing, which may be used for timeout control in network requests.

### Configure Network Interface

```python
def network_use_wlan(is_wlan=True):
    if is_wlan:
        sta = network.WLAN(0)
        sta.connect("TEST", "12345678")
        print(sta.status())
        while sta.ifconfig()[0] == '0.0.0.0':
            os.exitpoint()
        print(sta.ifconfig())
        ip = sta.ifconfig()[0]
        return ip
    else:
        a = network.LAN()
        if not a.active():
            raise RuntimeError("LAN interface is not active.")
        a.ifconfig("dhcp")
        print(a.ifconfig())
        ip = a.ifconfig()[0]
        return ip
```

This code configures the network interface based on the input parameters, following these steps:

1. **WLAN Mode**:
   - If `is_wlan=True`, configure the wireless network interface (WLAN) and connect to the specified Wi-Fi network (SSID "TEST", password "12345678").
   - Output the WLAN connection status and wait for a valid IP address to be assigned.
   - After a successful connection, print the network configuration and return the IP address.

1. **LAN Mode**:
   - If `is_wlan=False`, configure the wired network interface (LAN).
   - Activate the LAN interface and check its status. If not activated, raise an exception.
   - Use DHCP to obtain an IP address, print the network configuration, and return the IP address.

### Create UDP Socket

```python
# Create UDP socket
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
# Set socket options to allow address reuse
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# Get address and port number and bind socket
ai = socket.getaddrinfo(ip, 8080)
addr = ai[0][-1]
s.bind(addr)
```

We created a UDP-type socket and set the `SO_REUSEADDR` option to allow address reuse. Then, we used `getaddrinfo` to get the address and port number information and bound the socket to that address and port.

### Receive and Send Data

```python
# Delay 1 second to ensure socket binding is complete
time.sleep(1)

# Receive data and reply
for j in range(10):
    try:
        data, addr = s.recvfrom(800)  # Receive data, up to 800 bytes
        print("Received:", data, "from", addr)
        # Reply with a message containing the received data and receive count
        response = b"%s have recv count=%d " % (data, j)
        s.sendto(response, addr)
    except Exception as e:
        print("Error:", e)  # Print exception information for debugging

# Close socket
s.close()
print("UDP Server exited!!")
```

The program receives up to 800 bytes of data using the `recvfrom` method and prints the received data and client address. Then, it constructs a reply message and sends it using `sendto`. The program includes exception handling to capture and debug errors.

### Complete Example

```python
# Configure TCP/UDP socket debugging tool
import socket
import time, os
import network

def network_use_wlan(is_wlan=True):
    if is_wlan:
        sta = network.WLAN(0)
        sta.connect("TEST", "12345678")
        print(sta.status())
        while sta.ifconfig()[0] == '0.0.0.0':
            os.exitpoint()
        print(sta.ifconfig())
        ip = sta.ifconfig()[0]
        return ip
    else:
        a = network.LAN()
        if not a.active():
            raise RuntimeError("LAN interface is not active.")
        a.ifconfig("dhcp")
        print(a.ifconfig())
        ip = a.ifconfig()[0]
        return ip

def udpserver():
    # Get LAN interface IP address
    ip = network_use_wlan(True)

    # Get address and port number corresponding address
    ai = socket.getaddrinfo(ip, 8080)
    print("Address infos:", ai)
    addr = ai[0][-1]

    print("udp server %s port:%d\n" % (ip, 8080))
    # Establish socket
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind(addr)
    time.sleep(1)  # Delay 1 second to ensure socket is ready

    counter = 0
    while True:
        os.exitpoint()
        data, addr = s.recvfrom(800)
        if data == b"":
            continue
        print("recv %d" % counter, data, addr)
        s.sendto(b"%s have recv count=%d " % (data, counter), addr)
        counter += 1
        if counter > 10:
            break
    s.close()
    print("udp server exit!!")


#main()
udpserver()
```

For specific interface definitions, please refer to [socket](../../api/extmod/K230_CanMV_socket_API_Manual.md) and [network](../../api/extmod/K230_CanMV_network_API_Manual.md).

## Example Phenomenon and Operation Instructions

After running the code, the serial terminal will output the server's IP address and port number information:

![image-20240722165929097](https://www.kendryte.com/api/imagecdn/zh/sdk/canmv_k230_sdk/example/images/network/image-20240722165929097.png)

In the network debugging assistant, select UDP and configure the connection parameters:

```{image} ../../../zh/example/images/network/image-20240722170233348.png
:scale: 50 %
```

Send data and observe the server's response:

```{image} ../../../zh/example/images/network/image-20240722170412175.png
:scale:  50 %
```