Note

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HTTP Client Routine Explanation

Routine Location

• Development board firmware path: /sdcard/examples/14-Socket/http_client.py

• SDK source code path: src/canmv/resources/examples/14-Socket/http_client.py

This routine first establishes a network connection, then accesses http://www.baidu.com/index.html, and demonstrates both the Socket file stream interface and the regular send/receive interface.

Preparation Before Running

Modify the network configuration at the top of the script:

NETWORK_TYPE = "wifi_sta"  # "default", "lan", "wifi_sta" or "wifi_ap"
WLAN_DEVICE = "auto"       # "auto", "usb", "sdio" or "spi"
WIFI_SSID = "TEST"
WIFI_PASSWORD = "12345678"
NETWORK_TIMEOUT = 20

The HTTP client requires internet access and proper DNS resolution. When using a wired network, change NETWORK_TYPE to "lan"; use "default" to reuse the already-connected default interface.

Code Flow

Connect to the Network

netif, _ = connect_network(
    NETWORK_TYPE,
    ssid=WIFI_SSID,
    password=WIFI_PASSWORD,
    wlan_device=WLAN_DEVICE,
    timeout=NETWORK_TIMEOUT,
)

connect_network() waits for the interface to obtain a valid IP and sets it as the default uplink interface. An exception is thrown if the network is not ready within NETWORK_TIMEOUT seconds, and the HTTP request will not proceed.

Resolve the Server Address

ai = socket.getaddrinfo("www.baidu.com", 80)
addr = ai[0][-1]

The routine retries DNS resolution up to 3 times. The Address infos in the serial console is the resolution result, and Connect address is the actual address used by this connection.

Establish a TCP Connection

s = socket.socket()
s.connect(addr)

HTTP/1.0 runs on TCP, so you must first connect to the server’s port 80.

Send and Receive Using the File Stream Interface

s = s.makefile("rwb", 0)
s.write(b"GET /index.html HTTP/1.0\r\n\r\n")
print(s.read())

makefile() wraps the Socket into a stream that can call read() and write(). After the HTTP/1.0 request is complete, the server closes the connection, so read() can read until the response ends.

Send and Receive Using the Regular Socket Interface

s.send(b"GET /index.html HTTP/1.0\r\n\r\n")
print(s.recv(4096))

The regular interface uses send() and recv(). A single recv(4096) reads at most 4096 bytes and does not guarantee obtaining the complete response; practical applications should read in a loop until the server closes the connection or the protocol provides a complete length.

At the end of the script, main(use_stream=True) and main(use_stream=False) are called in sequence, so two independent requests are initiated.

Running and Troubleshooting

1. Open the script under the development board firmware path in CanMV IDE and run it.

2. Confirm that the serial console first outputs network connection information, then outputs the DNS address and HTTP response.

3. If getaddrinfo again keeps appearing, check DNS, gateway, and internet connection.

4. If the domain name resolves but the connection fails, check the target service, default uplink, and network firewall.

For related interfaces, see network module and socket module.