7. HTTP-Client Example Explanation#

1. Environment Setup#

First, ensure that the CanMV development board is connected to a router or switch via an Ethernet port, and that the router is functioning properly with internet access. This is the basic setup for making HTTP requests.

2. Detailed Example#

The following Python example demonstrates how to implement an HTTP client on the CanMV development board. This client sends an HTTP GET request to a specified server (in this case, Baidu) and receives the response content.

2.1 Import Necessary Modules#

import network  
import socket

The network module is used to manage network interfaces.
The socket module provides the underlying interface for network communication.

2.2 Define the Main Function#

def main(use_stream=True):  
    # ... (subsequent code)

The main function defines a parameter use_stream which determines whether to use a stream interface to read the response data. The default value is True, which controls the data reception method.

2.3 Configure Network Interface#

def network_use_wlan(is_wlan=True):
    if is_wlan:
        sta = network.WLAN(0)
        sta.connect("Canaan", "Canaan314")
        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 function configures the network interface based on the input:

WLAN Mode: Connects to a specified Wi-Fi network (SSID is “Canaan”) using the wireless network interface (WLAN).
LAN Mode: Automatically obtains an IP address using the wired network interface (LAN).

2.4 Create and Configure Socket#

# Create socket object  
s = socket.socket()   
# Get target address and port number  
ai = []  
for attempt in range(0, 3):  
    try:  
        ai = socket.getaddrinfo("www.baidu.com", 80)  
        break  
    except:  
        print("getaddrinfo again")  
  
if ai == []:  
    print("Connection error")  
    s.close()  
    return  
  
addr = ai[0][-1]  
print("Connection address:", addr)

This code creates a socket object and uses the getaddrinfo function to obtain the server’s (Baidu) address and port information. It employs a retry mechanism to enhance robustness.

2.5 Send HTTP Request and Receive Response#

# Connect to the server  
s.connect(addr)  
  
if use_stream:  
    # Use stream interface to read response  
    s = s.makefile("rwb", 0)  
    s.write(b"GET /index.html HTTP/1.0\r\n\r\n")  
    print(s.read())  
else:  
    # Directly use socket interface to send and receive data  
    s.send(b"GET /index.html HTTP/1.0\r\n\r\n")  
    print(s.recv(4096))  
   
# Close socket  
s.close()

The code selects whether to use the stream interface or directly use the socket interface to send an HTTP request and read the response data based on the use_stream parameter.

2.6 Function Invocation#

# Test both stream and non-stream interfaces  
main(use_stream=True)  
main(use_stream=False)

The main function is called with different use_stream parameters to test the effects of reading the HTTP response using stream and non-stream methods. If use_stream is True, it uses the stream interface to send the request and read the entire response; if False, it directly sends the request and receives a fixed length of response data (4096 bytes in this example). Finally, the socket connection is closed to release resources.

2.7 Complete Example#

import network
import socket
import os, time

def network_use_wlan(is_wlan=True):
    if is_wlan:
        sta = network.WLAN(0)
        sta.connect("Canaan", "Canaan314")
        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 main(use_stream=True):
    # Get LAN interface
    network_use_wlan(True)
    # Create socket
    s = socket.socket()
    # Get address and port number
    ai = []
    for attempt in range(0, 3):
        try:
            ai = socket.getaddrinfo("www.baidu.com", 80)
            break
        except:
            print("getaddrinfo again")
    
    if ai == []:
        print("Connection error")
        s.close()
        return

    addr = ai[0][-1]
    print("Connection address:", addr)
    # Connect
    s.connect(addr)

    if use_stream:
        s = s.makefile("rwb", 0)
        s.write(b"GET /index.html HTTP/1.0\r\n\r\n")
        print(s.read())
    else:
        s.send(b"GET /index.html HTTP/1.0\r\n\r\n")
        print(s.recv(4096))

    s.close()
 
# main()
main(use_stream=True)
main(use_stream=False)

For specific interface definitions, please refer to socket and network.

7. HTTP-Client Example Explanation

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